Increasing phosphorus fertilizer value of recycled iron phosphates in strong P-fixing soils by prolonged flooding and organic matter addition

Increasing phosphorus fertilizer value of recycled iron phosphates in strong P-fixing soils by prolonged flooding and organic matter addition | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Increasing phosphorus fertilizer value of recycled iron phosphates in strong P-fixing soils by prolonged flooding and organic matter addition Rochelle Joie Saracanlao, Hannah Ryckel, Maarten Everaert, Mieke Verbeeck, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-2138400/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Iron (Fe) minerals are commonly used to remove phosphorus (P) from waste streams, producing P-loaded Fe(III) oxides or Fe(II)P minerals (e.g. vivianite). These minerals may be used as fertilizers to enhance P circularity if solubilized in soil. Here, we tested the P fertilizer value of recycled iron phosphates (FePs) in a pot trial and in an incubation experiment, hypothesizing that P release from FePs is possible under Fe(III) reducing conditions. First, a pot trial was set up with rice (Oryza sativa) in all combinations of soil flooding or not, three P-deficient soils (acid, neutral, calcareous) and six FePs (three Fe(III) and three Fe(II)phosphates) referenced to triple superphosphate (TSP) or zero amendments. Shoot P uptake responded to TSP applications in all treatments but only marginally to FePs. The redox potential did not decrease below 200 mV by flooding for a brief period during the pot trial. A longer incubation experiment (60 days) was performed which included a treatment of glutamate addition to stimulate reductive conditions and P availability was assessed with CaCl 2 extraction of soils. Glutamate addition and/or longer incubation lowered soil redox potential to <-100 mV. On the longer term, Fe(III) minerals released P and adequate P was reached in the calcareous soil and in the neutral soil amended with Fe(III)P-sludge. It can be concluded that prolonged soil flooding and organic matter (OM) addition can enhance the P fertilizer efficiency of FePs. Additional treatments showed that application of FeP in powder form may enhance P availability. Phosphorus fertilizer efficiency P recycled products P-loaded Fe(III) oxides vivianite Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction The global use of phosphorus (P) fertilizers has increased, driven primarily by the growing demand for food and feed (Vance et al. 2003 ). This large consumption threatens the stock of phosphate rock and, at the same time, leads to local environmental issues where excess fertilizer has been used. To target both issues, P can be removed from P-rich waste streams and potentially be recycled into an effective fertilizer, thereby closing the P cycle in agriculture (Melia et al. 2017 ). Currently, most approaches to recover P from wastewater in wastewater treatment plants (WWTPs) focus on crystallization of struvite, direct application of sewage sludge to agricultural fields, or techniques relying on sludge incineration. Each of these has disadvantages regarding recovery efficiencies and applicability. In contrast, the recovery of P as vivianite (Fe(II) 3 [PO 4 ] 2 ⋅8H 2 O), a mineral that is formed when ferrous iron (Fe) is added to wastewaters to remove P, is promising for several reasons. First, it is naturally ubiquitous in sewage sludge, accounting for 70–90% of all phosphates (Wilfert et al. 2016 ). Second, it has higher P content (Fe:P molar ratio of 1.5) compared to other ferric precipitates in WWTPs. Third, vivianite, owing to its paramagnetic properties, can be separated from sewage sludge, and be collected in relatively pure phase using magnetic separators (Wilfert et al. 2018 ). For the removal of P from diffuse agricultural sources, P removal via adsorption processes using low-cost P-sorbing materials (PSMs) has garnered attention due to the fast immobilization of P (Liu et al. 2018 ). These PSMs contain metal cations, typically aluminum (Al), calcium (Ca), magnesium (Mg), and Fe, that form an insoluble compound with dissolved P. Specifically, Fe-coated sands and Fe sludges are Fe(III) based minerals that are very effective at removing P (Lambert et al., 2021 ). These materials are by-products from drinking water production, that are formed during Fe removal to prevent colored and bad-tasting water. Aeration of the groundwater leads to the oxidation of Fe(II) to Fe(OH) 3 , which coats the sand and gravel filter beds, yielding Fe-coated sand. Alternatively, the Fe-coated sand can be washed for reuse of the sand, producing Fe-sludges (Liu et al. 2018 ). The FeP minerals, obtained by trapping P from waste streams using Fe minerals, have the potential to be reused as fertilizers. From the perspective of P recovery, the strong interaction between Fe and P is a clear advantage, however, the poor solubility P from the FeP materials could strongly limit the plant availability of the recovered P (Samie and Romer al., 2001; Kahiluoto et al. 2015 ), particularly in aerobic conditions. The Fe(II) based ones such as vivianites have been used as P fertilizer but are mostly limited to those of geologic origin (Yaya et al., 2015 ) or of peat origin in various crop experiments in Russia (Bodrova and Ozolina, 1968; Gamzikov and Marmulev, 2007 ). Next to their potential as P source, vivianites can also be valorized as Fe fertilizers to mitigate Fe chlorosis in various crops growing in calcareous soils in the Mediterranean region (Díaz et al. 2009 ; Rosado et al. 2002 ). In contrast, Fe(III) based P fertilizers rarely exhibit positive P fertilizer effects, even when added as nanoparticles to soil (Bollyn et al. 2019 ). However, in some conditions, positive fertilizer values have been found. For example, P sorbed on Fe minerals was used to prepare a P-mineral complex for growing rice in a glasshouse of which 15–31% of sorbed P was recovered by rice within 3 months (He et al. 1994 ). Similarly, ochre (hydrous ferrous oxides) from coal mines that were subsequently loaded with P performed well as slow-release P fertilizer in cereals and trees (Dobbie et al. 2005 ). Synthetic iron phosphates showed a slightly higher biomass yield but lower P uptake in comparison with monocalcium phosphates in ryegrass (Johnston and Richards 2003 ), yet no explanation was provided for the relatively good performance of the material. Iron phosphates as by-products of fertilizer reactions in the soil (e.g., hydrogen ammonium iron phosphates and colloidal ferric phosphates) and as impurities of commercial P fertilizers (reported as citrate-insoluble P) were reported to have residual P availability (Lindsay and Demnet 1961; Sikora and Mullins 1995 ) suggesting the release of P in the long term. This could be beneficial for plants requiring frequent P fertilization like tree stands in peatland forests (Nieminen et al. 2011 ). Here, we hypothesized that Fe-based P recycling products can be suitable P fertilizers in flooded soils, e.g. in soils used in growing paddy rice. It is well established that soil P availability increases upon soil flooding following reductive dissolution of soil Fe(III) minerals (Rakotoson et al. 2016 ), and the addition of an organic carbon (OC) source can further stimulate this process (Scalenghe et al. 2002 ). However, to what extent reductive dissolution in flooded soils can also increase the effectiveness of Fe-based P fertilizers is still unknown. Against this background, a pot trial was set up to identify the P fertilizer use efficiency (PFUE) of six granular recycled FeP products (three vivianites and three P-loaded Fe oxides) in the early stages of rice development, in paddy soils with or without flooding (13 days). The PFUE of FePs was compared to that of triple superphosphate (TSP), a conventional soluble P fertilizer and an unamended control treatments. We hypothesized that the recycled FePs will perform better as P fertilizers in the pot trial under flooded conditions due to increased soil P availability after the liberation of P following reductive dissolution of Fe(III) minerals. In addition, a soil incubation experiment was established to determine the P availability of powdered recycled FePs (as measured by 1 mM CaCl 2 extraction), exploring also the effect of longer flooding conditions (up to 60 days) and OM addition (glutamate) and thus expanding the range of soil conditions in comparison with those in the pot experiment. With the incubation experiment, we hypothesized that prolonged flooding and OM addition would promote reduced conditions and thus enhance the P availability of FePs in soils. Materials And Methods Soils The selected physical and chemical properties of the soils used are given in Table 1 . Soil samples were collected from the upper 20–30 cm layer, air-dried, and sieved to < 2 mm before use. These soils were chosen as representative of rice-growing areas with low P availability. Soils were analysed for pH, cation exchange capacity (CEC), particle size distribution, total C and N, and oxalate extractable Fe, Mn, and P (Table 1 ). Table 1 Selected physicochemical properties of soils from pot experiment. acid neutral calcareous Site of origin Cavinti, Laguna, Philippines Dakawa, Tanzania Isla Mayor, Seville, Spain Soil classification a Ferralsol Vertisol Vertisol Clay b (%) 84 32 8 Silt b (%) 14 56 76 Sand b (%) 2 12 16 pH c 4.5; 6.1 c 6.0 7.9 CEC d 7.6 20.7 26.4 C/N e 10.5 14.6 22.0 Organic C e (%) 0.55 0.86 1.84 Inorganic C e (%) - 0.2 2.7 P in soil solution f (mg P /L) < 0.008 < 0.008 0.01 Fe ox g (g Fe /kg) 0.94 2.62 2.91 Al ox g (g Al /kg) 1.86 0.62 0.72 Mn ox g (g Mn /kg) 0.17 0.39 0.32 P ox g (mg P /kg) 10 40 300 FC h (mL /kg) 410 250 325 K i (L/kg) 1065 136 120 n i 0.22 0.29 0.36 PSI j (mg P /kg) 635 70 52 PSC k (mmol /kg) 42.9 35.0 39.4 DPS l (%) 0.7 3.4 24.8 a Major soil groups (IUSS Working Group WRB, 2015) b Clay, silt, sand and texture class based on particle size distribution (Soil Science Division Staff, 2017) determined by laser diffraction method; texture of acid soil determined by pipette method c pH (1:5 S:L ) in 0.01 M CaCl 2 (acid soil was limed to pH 6.1 for the pot trial) d CEC was determined in a 0.0166 M cobalt hexamine (Cohex) extract (ISO, 2007), as the difference between total Co added and Co measured in the extract with ICP-OES. e C/N and organic C and inorganic C as % of total soil mass determined by the combustion method f P in soil solution determined by indirect sorption/desorption method (0.01 M CaCl 2 ); P concentration in filtrate was determined using malachite green method with detection limit of 8 µg P/L (Van Veldhoven and Mannaerts, 1987 ) g Ammonium oxalate extractable Fe, Al, Mn and P (Schwertmann, 1964) h Field capacity (FC) determined through the glistening effect i Fit parameters for the P sorption isotherms described by the Freundlich equation (P sorbed =k (P solution ) n ) j P sorption index (PSI) defined as the amount of added P sorbed on the solid phase at a soil solution concentration of 0.1 mg P/L (Six et al., 2012 ). k P sorption capacity (PSC) defined as 0.5*(Fe ox + Al ox ) l Degree of P saturation (DPS) defined as \(\frac{{P}_{ox}}{PSC}*100\%\) The P adsorption isotherms were also determined for the three soils as detailed by Six et al. ( 2012 ). Briefly, soils were mixed with 0.01 M CaCl 2 with increasing P concentrations. Soil suspensions were then shaken for 16 hrs, centrifuged (2500 g, 10 min), and filtered (0.45 µm, Chromafil ® Xtra PET − 45/25; Macherey- Nagel, Germany). The P concentration in the filtrate was determined using malachite green method (Van Veldhoven and Mannaerts 1987 ) and absorbance was measured at 630 nm using a spectrophotometer (Perkin Elmer, Lambda 20, 1 cm path length). Results showed that the P sorption of the soils ranged acid soil > > neutral soil > calcareous soil (Figure S1). Recycled FeP materials Three vivianites and three Fe(III) phosphates were used (Table 2 ). Two vivianites and two Fe(III) phosphates were collected from different sources. In addition, one extra vivianite was synthesized in the lab by dissolving FeSO 4 and (NH 4 ) 3 PO 4 and one extra Fe(III) phosphate was produced by loading a Fe(III)-rich product with a saturated P solution. As a reference P fertilizer, the commercial soluble fertilizer TSP was used. The total P content (and other elements) of the FeP materials was determined with Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES, Thermo Scientific iCAP 7000 series) after digestion in aqua regia (Table 3 ). Table 2 Description of the FeP materials tested in the experiment. Material Description Vivianites (Fe(II) phosphates) V-WWTP Provided by Wetsus (European Center of Excellence for Sustainable Water Technology), a water treatment facility in the Netherlands V-fert Provided by Fertiberia, a fertilizer company in Spain V-syn Synthesized according to Rosado et al. ( 2002 ) by dissolving 2.5% (w/v) of monoammonium phosphate (MAP) with 7.5% (w/v) ferrous sulphate. The pH is adjusted to 6.5 to 7.5 with 10 M KOH. Suspension is then washed with MilliQ until electrical conductivity (EC) is < 0.2 dS m − 1 . Precipitates were then dried under anaerobic hood. Fe(III) phosphates Fe(III)P-sludge Iron sludge from Veghel pumpstation provided by Aquaminerals (company in the Netherlands that finds application of Fe by-products from water companies) Fe(III)P-gravel Mixture of iron coated gravels from different pumpstations in the Netherlands provided by Aquaminerals. Due to low P content of the material (0.32%), it was artificially loaded with P by incubating the material for 24 h in a 184 mM KH 2 PO 4 solution (liquid:solid ratio of 10 L kg − 1 , end-over-end shaking). After recovery of the material via centrifugation, it was air-dried and stored until further use. Fe(III)P-sand P-loaded iron coated sand provided by Nico Lambert of NuReDrain Project (Lambert et al. 2021 ) Table 3 The elemental composition of the FeP materials, expressed as percentage by weight of air-dried material. Materials P (%) Ca(%) Mg(%) Al(%) Fe(%) Fe:P molar ratio TSP 18.05 22.40 0.007 2.16 3.87 0.01 Vivianites (Fe(II) phosphates) V-WWTP 9.55 0.90 0.96 0.11 25.81 1.50 V-fert 12.65 n.d. n.d. n.d. 35.47 1.55 V-syn 13.45 n.d n.d. n.d. 38.28 1.58 Fe(III) phosphates Fe(III)P-sludge 2.78 7.40 n.d. 0.01 34.70 6.81 Fe(III)P-gravel 3.31 0.002 0.00006 1.23 27.00 4.15 Fe(III)P-sand 1.26 1.90 0.24 0.02 50.18 22.15 n.d. not detected The FeP materials were provided in different forms, i.e., as granule or as powder. Granular materials (i.e., TSP, Fe(III)P-gravel, and Fe(III)P-sand, see Table 2 for abbreviations) were sieved to obtain granules of 2–4 mm (except the small-sized TSP). The powders (i.e., all vivianites), were made into granular particles via extrusion. For this, a paste was made by mixing ultrapure water (MilliQ) with the powders, which was extruded in a mould with a 4-mm diameter hole. Subsequently, the obtained pellets were cut to 3 mm length and dried at 40°C overnight. In the pot trial, all six FePs and TSP applied as granules were tested, while in the incubation experiment only two products were tested, i.e. one Fe(II) phosphate (V-WWTP) and one Fe(III) phosphate (Fe(III)P-sludge). Plant growth trial The experimental design was completely randomized with three factors (soil, amendments, soil flooding) and with three replicates for each treatment. The pot trials were not done simultaneously due to space limitation in the growth cabinet and the late arrival of the calcareous soil. To avoid false positive P response as a result of flooding (raised soil pH under flooded conditions) and the pH neutralizing effect of neutral FeP fertilizers on acid soils, the acid soil was limed at a rate of 1.5 g Ca(OH) 2 /kg, which raised the soil pH from pH 4.5 to 6.1; thus this soil is further termed acid soil. Soils were mixed with macronutrients (other tha n P) as dry salts at the rates of 120 mg N/kg (NH 4 NO 3 ), 120 mg K/kg (KCl, 254 mg K/kg for acid soil due to higher P dose), 75 mg Ca/kg (CaCl 2 ), 30 mg Mg/kg and 40 mg S/kg (MgSO 4 ·7H 2 O). The N and K were split-applied, partly before sowing as dry salts and at 16 days after planting (DAP) as solution. Micronutrients were applied by spraying the soil with a micronutrient solution (20 ml/kg soil) with adequate concentration to obtain rates of 1.2 mg Mn/kg (MnCl 2 ·4H 2 O), 0.6 mg Zn/kg (ZnCl 2 ), 0.6 mg Cu/kg (CuCl 2 ·2H 2 O), 0.2 mg B/kg (Na 2 B 4 O 7 ·10H 2 O), and 0.2 mg Mo/kg (Na 2 MoO 4 ·2H 2 O). After mixing the nutrients with the air-dried soil, soils were transferred individually into 1 L transparent pots (900 g soil for the neutral and calcareous soil, 838 g soil for the acid soil). Then, for each soil, TSP (four doses) and FeP (one P dose; equal to highest TSP dose) granules were added in the center of the pots, 3 cm below the surface. For TSP, maximum doses were 24 mg P/kg for the neutral soil, 50 mg P/kg for the acid soil, and 40 mg P/kg for the calcareous soil. This was based on the P adsorption curves of each soil and previous P fertilizer studies where the estimated difference in P uptake between mixed P (KH 2 PO 4 ) and placed P (TSP) application was a factor of 3 for the neutral soil (de Bauw et al. 2019 ), 4 for the acid soil(de Bauw et al. 2019 ) and 1.3 for the calcareous soil (Everaert et al. 2017 ). Control treatments (without P) were also included for all soils. Subsequently, soils were watered until field capacity and were incubated in the phytotron for six days in dark conditions at 25 ± 2°C. Then, two pre-germinated seedlings of Malagasy rice variety X265 were transplanted (at root length ± 1.5 cm) to each pot after incubation and thinned to one after 5 DAP. At 8 DAP, the contrasting water regime was imposed by adding water to ± 3 cm on top of the soil surface in the flooded treatments. Water management was maintained daily until the end of pot trial. Until harvest, rice was grown in a plant growth cabinet with day/night temperature setting of 25/20°C, at relative humidity of 80% and light intensity of 550–600 µmol / cm 2 s. At 21 DAP, the rice plants were harvested and oven-dried at 60°C for 3 days. Dry shoots were weighed and digested in 10ml HNO 3 using a microwave (MARS 6 microwave digestion system, CEM). The digests were analyzed for concentrations of P and other plant nutrients by ICP-OES. Each batch included 2 blank samples, an internal standard, and a certified reference material (hay powder, Joint research centre, European Commission). The average recovery of P, certified concentration 2360 mg P kg − 1 , was 99%. The internal standard material (rice shoots) is verified relative to certified reference material (hay powder) with P at similar concentrations (e.g., BCR129; Joint research centre European Commission, 2021). For P in the internal standard, verified concentration of 1308 mg P kg − 1 , the average recovery was 91%. Soil analyses after plant growth One week after harvest, a 1mM CaCl 2 soil extraction (solid:liquid ratio = 0.2 kg L − 1 ; 24 h) was performed on two (randomly chosen) out of three replicates of each treatment, the flooded soil was stored and kept flooded between harvest and soil sampling. The upper 3 cm of the soil column from a pot was sampled and mixed. Ten grams of moist soil was taken and added to a 50 mL polyethylene tube. Next, a 1 mM CaCl 2 solution was added to the tube until it was completely filled (i.e., no headspace). Samples were shaken end-over-end for 24 h (0.42 s − 1 ; T = 20 +/- 2°C), centrifuged (2500 g, 10 min), filtered, and acidified using concentrated HNO 3 to a volume percentage of 1%. Next, the P concentration of the acidified samples was determined with Inductively Coupled Plasma Mass Spectrometry (ICP-MS; Agilent 7700x, Agilent Technologies). The soil redox potential (E h ) was also measured in control unamended treatments 24 h and 48 h after the harvest using glass fiber probes (8 mm diameter, 10 cm length) (Paleoterra Products, Amsterdam, The Netherlands) inserted vertically into the soil column. The E h measuring point made of platinum ring was positioned 2 cm from the tip of the probe allowing E h measurement at 2 cm below the soil surface. The Ag-AgCl reference electrode was positioned in the water layer. The E h relative to standard hydrogen electrode was calculated from the measured potential with temperature-dependent correction for the potential of the Ag-AgCl electrode. The temperature and pH were also measured using a pH meter. Incubation Experiment Soils (air-dried and sieved) were mixed with macronutrients at the same dose used in the pot trial. Two hundred grams of soil were placed into 250 ml plastic containers, after which the soil was flooded with deionized water up to 3 cm above the surface. The pots containing the soils were incubated under water in dark conditions for 60 days at 25 ± 2°C. Different treatments were set up, varying the type of powdered iron phosphates (Fe(III)P-sludge or V-WWTP applied at P dose of 200 mg P/kg for acid soil, 70 mg P/kg for neutral soil, and 52 mg P/kg for calcareous soil) and glutamate content (0 or 1 g C/kg soil) for three soils, with three replicates per treatment. Glutamate was added as C source to stimulate reductive dissolution of Fe(III). Control treatments (without FePs) were also included for all soils. After 3, 14, and 60 days of incubation, a 1 mM CaCl 2 soil extraction was performed as described above. For each soil, the redox potential values were also monitored weekly in an additional replicate of control treatments. Data and statistical analysis The phosphorus uptake (PU) in each treatment was calculated as \(PU \left(mg\right)=P concentration in shoot (mg/g) x dry matter yield \left(g\right)\) (Eq. 1) The relative P use efficiency (RPUE) of the FeP materials was determined as (Cabeza et al 2011 ): \(RPUE, x \left(\%\right)=\frac{{PU}_{x}-{PU}_{control}}{{PU}_{TSP}-{PU}_{control}} x 100\) (Eq. 2) with PU x = PU obtained by a specific FeP treatment \(x\) (mg), PU control = mean PU in the unfertilized control (mg), and PU TSP = mean PU in the TSP reference treatment at equal P dose (mg). Statistical analysis was performed using JMP software (JMP pro 15, SAS Institute Inc.). All data were subjected to analysis of variance (ANOVA) with soil, fertilizer type and water as the main factors. Then, for each soil the effects of P dose and water treatments on P uptake and CaCl 2 -extractable soil P in the TSP treatments (each indicated as Y) were assessed using multiple linear regression with the resulting model: Y = β 0 + β 1 *(P dose) + β 2 *(Flooded) + β 3 *(P dose – c) 2 + β 4 *((Pdose – c)*Flooded) (Eq. 3) with β 0 , β 1 , β 2 , β 3 and β 4 the parameter estimates of this model and c the mean P dose. The effect of different FeP fertilizers on P uptake and soil P (in comparison to the unfertilized control and to the same P dose of TSP) was assessed with the Tukey test following the ANOVA test. This was done for each soil separately, and within each soil, for each water treatment separately at 0.05 level of significance. Next, a t-test was used to determine if the P uptake and CaCl 2 - extractable soil P of each FeP fertilizer type is significantly different (P < 0.05) between non-flooded and flooded conditions. For the incubation experiment, the CaCl 2 -extractable P concentrations were subjected to ANOVA with soil, FeP type and glutamate as the main factors. Then, for each soil the effect of glutamate on the CaCl 2 -extractable P for each FeP treatment per sampling time was assessed with the Tukey test following the ANOVA test at 0.05 level of significance. Results Plant growth trial Plant response to TSP application The shoot dry matter and shoot P uptake increased largely and significantly with increasing TSP doses in all soils and all water treatments except in the non-flooded calcareous soil (Figure S2). This supports the fact that the three soils are P deficient, with P deficiency most pronounced in the acid soil in comparison with the neutral and calcareous soils. Shoot P concentrations responded in line with the shoot P uptake, except in the calcareous soil in both water treatments (Figure S3). The plants grown under non-flooded treatments took up more P than corresponding flooded treatments in the acid and neutral soils (Table S1). Plant growth and P uptake were distinctly lower in the calcareous soil than in the other two soils (Figure S3). Plant response to application of recycled FeP products The application of the different FePs resulted in lower shoot P uptake than in TSP treatments at equal P doses. The FePs did not significantly enhance shoot P uptake in comparison with the unfertilized control in most soils and flooding treatments (Fig. 1 ) except for V-syn and V-WWTP, and Fe(III)P-gravel in the acid soil for both water treatments. The Fe(III)P-gravel also enhanced P uptake in the flooded treatments of the two other soils but not in the non-flooded ones. The Fe(III)P-gravel had been artificially loaded with P prior to the pot trial, likely resulting in higher P availability than the other FePs. Flooding the soil for a brief period (13 days) did not have any effect on the P uptake of FePs in the acid soil in contrast to the neutral soil where a negative effect of flooding was observed (Table S2). The average E h values of the unfertilized control treatments were 280 mV (pH 6) for the acid soil and 370 mV (pH 6) for the neutral soil after harvest indicating soil conditions were not reduced enough to transform Fe(III) to Fe(II) (Fig. 5 ). In the calcareous soil, flooding induced either a negative or no effect on the P uptake of the treatments. A lower P uptake was observed in the control, V-fert, Fe(III)P-sand and Fe(III)P-sludge while the P uptake of the other FePs were not affected by the water conditions. In the calcareous soil, under non-flooded conditions, all treatments were not significantly different from each other while P uptake in flooded conditions highly differentiated the TSP treatment from the rest of the FePs. The better performance of Fe(III)P-gravel was not observed in this soil (non-flooded treatments) as the material had likely aged by the time the pot experiment for this soil was performed. The RPUE (Eq. 2) was calculated and is shown in Fig. 2 . The RPUE values of the FePs were all small (2–3%) and RPUE was maximally 24% compared to TSP for the Fe(III)P-gravel in the acid soil. In some cases, a negative RPUE was obtained, indicating that the P uptake for these treatments is even lower than that of control treatments. CaCl 2 -extractable P across soils after plant growth The majority of the CaCl 2 -extractable soil P concentrations in the FeP-amended treatments were not statistically different from those of the corresponding unamended control or TSP treatments (Fig. 3 ). The CaCl 2 -extractable soil P concentrations confirmed the ranking of soil P deficiency as found in the plant growth assay (acid > > neutral > calcareous soil), since the P concentrations in the acid soil were smallest and all were below the detection limit (0.003 mg P/L). These concentrations were also low in the neutral soil, averaging at 0.01 mg P/L in non-flooded and 0.0.02 mg P/L in flooded conditions. In the calcareous soil, the values range from 0.0.03 mg P/L for the control to about 0.06 mg P/L for the highest dose of TSP. These values are all below the adequate P concentration values needed for growing rice (0.1 mg P/L; Beckwith 1965 ). Incubation Experiment Stimulating CaCl 2 -extractable P from FeP amended soils Flooding of the soils in the incubation experiment reduced the soil redox potential for all the treatments (Fig. 4 ) with glutamate-amended treatments reaching the lower limit of -200 mV faster than treatments without OM. The calcareous soil reached negative values within 3 days of flooding, while it took 7 days for the neutral soil. The acid soil treated with glutamate took the longest time (3 weeks) to reach reduced conditions. The CaCl 2 -extractable soil P concentrations are shown in Fig. 5 . In the acid soil, the CaCl 2 -extractable P was lower than the concentration needed to support rice growth (0.1 mg P/L), even with glutamate addition. In the neutral soil, the P concentration of about 0.1 mg P/L was only reached in the treatment amended with Fe(III)P-sludge after 60 days. In contrast, in the calcareous soil, this P concentration was already achieved after two weeks for all treatments. The effect of glutamate on stimulating P release was significant in the Fe(III)P-sludge treatments on the 14th and 60th day (Table S6) in the acid soil. In the neutral soil, the addition of glutamate significantly increased the soil P concentrations in FeP treatments but only at 14th day for V-WWTP and only at 60th day Fe(III)P-sludge. All glutamate-amended treatments in the calcareous soil showed significantly higher P concentrations than those without OM but only the Fe(III)P-sludge treatments had significantly different P values until the end of the incubation period. Discussion The different FePs had very low available P in the short-term pot trial here. It is well established that a high Fe:P ratio in a soil amendment lowers its P availability. For example, the low plant P availability of sewage sludges was found to be correlated to the increased concentration of total Fe and Al of the sludge (Lemming et al. 2017 , O’Connor et al. 2004). A high Fe content (e.g. 0.25 Fe:P molar ratio) in sewage sludge increased the P sorption capacity of soils, thereby decreasing the P availability (Samie and Romer, 2001 ). This can partly explain the observed low P uptakes from vivianites (Fe:P molar ratio of about 1.5) and from Fe(III)Ps that have Fe:P molar ratios ranging from 4 to 22 (Table 3 ). An exception was Fe(III)P-gravel, as this material was loaded with P six weeks prior to the pot experiment with the neutral and acid soil. This was not observed in the calcareous soil as the pot trial with this soil started only 6 months after P loading of the Fe(III)P-gravel. The plant availability of P decreases with time due to diffusion and precipitation reactions, explaining the lower RPUE of the Fe(III)P-gravel in the calcareous soil (Hylander and Simán 2001 ). In addition, the FeP fertilizers were still intact as granules in the soil after the plant growth trial indicating reduced solubility of FePs if granulated, which thus explains the poor P supply from the granules to the soil solution (Fig. 3 ). The low soil P concentration extracted using CaCl 2 implied that the P released (if any), was adsorbed on or precipitated in all soils, becoming unavailable to plants. The P uptake in the flooded treatments is typically higher than that in the corresponding treatments in non-flooded conditions (Huguenin-Elie et al., 2003; Rabeharisoa et al., 2012 ). However, this is in contrast with our observations in the pot trial, where P uptake in non-flooded conditions was either higher in the neutral soil or indifferent in acid soil than in the flooded counterparts. The Fe(III) transforms to Fe(II) under E h around + 300mV at pH 6, + 100 mV at pH 7, -100 mV at pH 8 (Fageria et al. 2011 ). The measured redox values indicated that the soils were only at the edge of Fe(III) reduction (Fageria et al. 2011 ), which most likely was the result of limited flooding time (13 days), low amounts of OC in these soils (Table 1 ) and/or the presence of plant roots that aerate the rhizosphere. In contrast, soil E h values were already negative in the soils after two weeks in the incubation experiment (Fig. 4 ) as the previously mentioned reasons for the positive E h values in the pot trial were absent. The results from the incubation experiment (Fig. 4 ), however, should be interpreted carefully. Here the soils were unplanted, a scenario that does not exactly reflect pot or field conditions. Because of its oxidizing potential, rice roots can significantly delay the onset of reduced conditions necessary for reductive dissolution of Fe(III) minerals particularly if the soils contain low OM. The incubation experiment predicts that prolonged flooding and OM addition are necessary to accelerate the release of P from FePs. Flooding in the short term did not affect P uptake significantly in the calcareous soil for most FePs (Table S2). In such soil, P precipitates with Ca 2+ ions to form poorly soluble calcium phosphates (CaPs), restricting P availability. The solubility of CaPs may increase under reduced conditions, as soil pH drops after flooding due to CO 2 accumulation, and OM complexes Ca 2+ ions (Slaton et al. 2002 ). In calcareous soils, application of vivianites is also of interest because of possible supply of Fe, that can mitigate Fe chlorosis in crops. Nonetheless, the application of FePs in calcareous soil did neither enhance growth (Figure S4) nor shoot Fe concentration (Figure S5) compared to the unamended control and TSP treatments. Higher shoot Fe concentrations were found in flooded compared to non-flooded soils in the acid soils, irrespective of FeP treatments (Figure S5) indicating that Fe(III) reduction already took place in that soil that was flooded. Oxidized conditions can also transform vivianite into highly insoluble Fe(III) (hydr)oxide residue (i.e., lepodocrocite (Roldán et al. 2002 )) and dissolved phosphate. This has been the basis for using vivianites as slow-release P and Fe fertilizer in correcting Fe chlorosis of crops in non-flooded calcareous soils. If vivianite is placed in aerated soils, it may also undergo incongruent dissolution which is boosted by the presence of effective phosphate sinks, such as plant roots and P-sorbing minerals. In our pot trial, these processes may have been restricted in flooded treatments, explaining why vivianite performed better under non-flooded than flooded conditions. The incubation experiment suggested that soil conditions needed to better reduce Fe(III) can be met with prolonged flooding, and even faster with glutamate addition. In the presence of native or added OM, E h values decline more rapidly as OM fuels microorganisms that catalyze the sequential redox reactions following O 2 depletion by mediating the electron transfers involved. Thus, the difference in E h values in this study was large between soils with and without glutamate. This was particularly true for acid and neutral soils owing to the inherently low OM content of these soils; in contrast to calcareous soil that contains higher OM. The addition of glutamate did not increase the CaCl 2 -extractable P except in the calcareous soil. The low P values observed in Fe-rich soils, such as the acid and neutral soils used here, may be attributed to the re-sorption of liberated P onto higher P-sorbing secondary ferrous minerals (Holford and Patrick 1979 ) and precipitation of Fe(II)P compounds (Amery and Smolders 2012 ). However, in the calcareous soil, the P concentration remained sufficient to support rice growth, which indicated that released P can remain available more easily in these soil conditions. This was also demonstrated by the continued increase in the P concentration of vivianite-amended treatments. Hence, it is expected that P released from FePs in the calcareous soil will most likely be depleted by plant uptake or microbial immobilization rather than be resorbed on surfaces of Fe/Al hydroxides. The continued release of P from vivianite treatments can be attributed to a two-step process. First, Fe(II) in vivianite can oxidize to Fe(III) with time as this mineral is not very stable (Wilfert et al. 2018 ). Second, the Fe(III) can be reduced again in flooded conditions which enhances the solubility of the vivianite. Despite the poor performance of the FePs compared to TSP for both water conditions observed in the pot trial, some strategies based on the results of the incubation experiment are suggested to circumvent this issue. Our pot trial lasted for only 3 weeks during which nonlabile inorganic P in FePs may not have been fully mobilized. This duration may not also have also captured the full picture of changes in the concentration of soluble P following flooding, as our incubation experiment indicated that a flooding period for at least several weeks was necessary to obtain reduced soil conditions. The positive effect of glutamate in increasing P concentration in flooded soils amended by FePs suggests that the application of OM may strongly increase the P fertilizer value of FePs particularly on the short term. Rice straw, for example, can be applied to accelerate the reduction of Fe(III) materials (both from FePs and unplanted soils) in submerged conditions (Scalenghe et al. 2022). Furthermore, it may be best to incubate FePs in flooded soil several weeks before sowing. It is assumed that after the incubation period, the liberation of P from FePs, will synchronize with the P demand of rice at its initial growth stages. In addition, FeP minerals were applied as intact granules in the pot experiment, for which the dissolution was likely slower in comparison to its powdered form, as was shown earlier for struvite fertilizers (Degryse et al. 2017 ). Lower P availability has also been observed in biosolids-P when pelletized via heat drying (O’Connor et al. 2004). Possibly, the effectiveness of FePs will be higher if applied as powders than as granules as shown in our incubation experiment. This again was interpreted from a soil scenario where rice roots were present and thus warrants investigating the performance of FePs as P fertilizers in a pot trial applying the parameters used in the incubation experiment (powdered FePs, longer flooding period, and OM addition). Conclusion The P fertilizer efficiency of the different recycled FePs was investigated in a pot trial and an incubation experiment. The results from the pot trial indicated a very limited effectiveness of the recycled FePs as P fertilizer for rice grown under both flooded and non-flooded conditions in the three soils. Their PFUEs were negligible compared to that of TSP due to (1) the intrinsically low solubility of the FeP compounds (high Fe content), (2) a subsequent reduction in solubility in soil as result of FeP application as granule, and (3) a short flooding period, low OM in soils and presence of rice roots resulting in a limited reductive dissolution of Fe(III) minerals. These reasons were overcome (except 1) in an incubation experiment where FePs were applied as powder in unplanted soil that was flooded beyond 2 weeks and with (or without) glutamate. The results from the incubation experiment showed that soil conditions needed to reduce Fe(III) and to subsequently release P from FePs, which were not observed during the pot trial, can be met with prolonged flooding and glutamate addition. Applying FePs as a powder can likely also increase the FeP solubility in comparison with a granular application. These suggested strategies for successful FeP fertilizer utilization will be tested in pot trial and field studies in the future. Declarations The authors have no relevant financial or non-financial interests to disclose. Acknowledgments The authors thank Olaf van der Kolk of Aquaminerals, Nico Lambert of KU Leuven, Leon Korving of Wetsus, and Maria Cinta Cazador Ruiz of Fertiberia for providing the iron phosphates used in this study. Our gratitude also goes to Antonio Delgado and Patrick Rocamora who oversaw the sampling and shipping of soils from Spain and from the Philippines, respectively. Tovohery Rakotoson is also kindly thanked for providing the rice seeds from Madagascar. Funding This research was financially supported by the European Union's Horizon 2020 Research & Innovation Programme under the Marie Skłodowska Curie Grant Agreement No. 813438. References Amery F, Smolders E ( 2012 ) Unlocking fixed soil phosphorus upon waterlogging can be promoted by increasing soil cation exchange capacity . Eur J Soil Sci. https://doi.org/10.1111/j.1365-2389.2012.01478.x Bollyn J, Castelein, L, Smolders E ( 2019 ) Fate and bioavailbility of phosphorus loaded to iron oxyhydroxide nanaparticles added to weathered soils . Plant and Soil. https://doi.org/10.1007/s11104-019-04008-x Beckwith RS ( 1965 ) Sorbed phosphate at standard supernatant concentration as an estimate of the phosphate needs of soils . Aust J Exp Agric Anim Husb. http://dx.doi.org/10.1071/EA9650052 Bodrova EM, Ozolina ZD ( 1965 ) Simultaneous application of organic and mineral fertilizers. Translated from Russian and published pursuant to an agreement with US Dept of Agriculture, Jerusalem. Cabeza R, Steingrobe B, Römer W, Claasen N ( 2011 ) Effectiveness of recycled P products as P fertilizers, as evaluated in pot experiments . Nutr Cycl Agroecosys. DOI : 10.1007/s10705-011-9454-0 de Bauw P, Vandamme E, Senthilkumar K, Lupembe A, Smolders E, Merckx R ( 2019 ) Combining phosphorus placement and water saving technologies enhances rice production in phosphorus-deficient lowlands . Field Crops Res. https://doi.org/10.1016/j.fcr.2019.03.021 Degryse F, Baird R, da Silva RC, McLaughlin MJ ( 2017 ) Dissolution rate and agronomic effectiveness of struvite fertilizers – effect of soil pH, granulation and base excess . Plant Soil. https://doi.org/10.1007/s11104-016-2990-2 Díaz I, Barrón V, del Campillo MC, Torrent J ( 2009 ) Vivianite (ferrous phosphate) alleviates iron chlorosis in grapevine . Vitis, 48 ( 3 ):107–113. Dobbie KE, Heal KV, Smith KA ( 2005 ) Assessing the performance of phosphorus-saturated ochre as a fertilizer and its environmental acceptability . Soil Use Manage. https://doi.org/10.1079/sum2005314 Everaert M, Degryse F, McLaughlin MJ, de Vos D, Smolders E ( 2017 ) Agronomic Effectiveness of Granulated and Powdered P-Exchanged Mg-Al LDH Relative to Struvite and MAP . J Agric Food Chem. https://doi.org/10.1021/acs.jafc.7b01031 Fageria NK, Carvalho GD, Santos AB, Ferreira EPB, Knupp AM ( 2011 ). Chemistry of lowland rice soils and nutrient availability . Commun Soil Sci Plan. https://doi.org/10.1080/00103624.2011.591467 Gamzikov GP, Marmulev AN ( 2007 ) Agrochemical assessment of bog phosphates in Western Siberia . Eurasian Soil Sci+. https://doi.org/10.1134/S1064229307090098 He ZL, Yang X, Yuan KN, Zhu ZX ( 1994 ) Desorption and plant-availability of phosphate sorbed by some important minerals . Plant Soil, 162 :89–97. Holford ICR and Patrick WH ( 1979 ) Effects of reduction and pH changes on phosphate sorption and mobility in an acid soil . Soil Sci Soc Am J. https://doi.org/10.2136/ssaj1979.03615995004300020010x Huguenin-Elie O, Kirk GJD, Frossard E ( 2009 ). Phosphorus uptake by rice from soils that is flooded, drained or flooded then drained . Eur J Soil Sci. https://doi.org/10.1046/j.1365-2389.2002.00489.x Hylander LD, Simán G ( 2001 ) Plant availability of phosphorus sorbed to potential wastewater treatment materials . Biol Fert Soils, 34 :42–48. Joint research centre European Commision. ( 2021 ). BCR-129 hay powder – certified reference materials catalogue of the JRC. Johnston A, Richards I ( 2003 ) Effectiveness of different precipitated phosphates as phosphorus sources for plants . Soil Use Manage. https://doi.org/10.1079/SUM2002162 Kahiluoto H, Kuisma M, Ketoja E, Salo T, Heikkinen J ( 2015 ) Phosphorus in manure and sewage sludge more recyclable than in soluble inorganic fertilizer . Environ Sci Tech. https://doi.org/10.1021/es503387y Lambert N, van Aken P, van den Broeck R, Dewil R ( 2021 ) Adsorption of phosphate on iron-coated sand granules as a robust end-of-pipe purification strategy in the horticulture sector . Chemosphere . https://doi.org/10.1016/j.chemosphere.2020.129276 Lemming C, Bruun S, Jensen LS, Magid J ( 2017 ) Plant availability of phosphorus from dewatered sewage sludge, untreated incineration ashes, and other products recovered from a wastewater treatment system . J Plant Nutr Soil Sci. https://doi.org/10.1002/jpln.201700206 Lindsay WL, DeMent JD ( 1961 ) Effectiveness of some iron phosphates as sources of phosphorus for plants . Plant Soil, 14 :118–126. Liu R, Chi L, Wang X, Sui Y, Wang Y, Arandiyan H ( 2018 ) Review of metal (hydr)oxide and other adsorptive materials for phosphate removal from water . J Environ Chem Eng, https://doi.org/10.1016/.j.jece.2018.08.008 Melia PM, Cundy AB, Sohi SP, Hooda PS, Busquets R ( 2017 ) Trends in the recovery of phosphorus in bioavailable forms from wastewater . Chemosphere . https://doi.org/10.1016/j.chemosphere.2017.07.089 Nieminen M, Lauren A, Hökka H, Sarkkola S, Koivusalo H, Pennanen T ( 2011 ) Recycled iron phosphates as fertilizer raw material for tree stands on drained boreal peatlands . For Ecol Manag. https://doi.org/10.1016/j.foreco.2010.09.036 O’ Connor GA, Sarkar D, Brinton SR, Elliott HA, Martin FG ( 2004 ) Phytoavailability of biosolids phosphorus . J Environ Qual. https://doi.org/10.2134/jeq2004.7030 Rabeharisoa L, Razanakoto O R, Razafimanantsoa M P, Rakotoson T, Amery F and Smolders E ( 2012 ) Larger bioavailability of soil phosphorus for irrigated rice compared with rainfed rice in Madagascar: results from a soil and plant survey . Soil Use and Management 28 :448–456. Rakotoson T, Rabeharisoa L, Smolders E ( 2016 ) Effects of soil flooding and organic matter addition on plant accessible phosphorus in a tropical paddy soil: an isotope dilution study . J Plant Nutr Soil Sci. https://doi.org/10.1002/jpln.201500383 Roldán R, Barrón V, Torrent J ( 2002 ) Experimental alteration of vivianite to lepidocrocite in a calcareous medium . Clay Miner. https://doi.org/10.1180/0009855023740072 Rosado R, del Campillo MC, Martínez MA, Barrón V, Torrent J ( 2002 ) Long-term effectiveness of vivianite in reducing iron chlorosis in olive trees . Plant Soil 241 :139–144. Samie IF and Romer W ( 2001 ) Phosphorus availability to maize plants from sewage sludge treated with Fe compounds. In: Horst WJ , Schenk MK , Bürkert A , Claassen N , Flessa H , Frommer WB , Goldbach H , Olfs HW , Römheld V , Sattelmacher B , Schmidhalter U , Schubert S , Wirén N , Witternmayer L (eds) Plant Nutrition , Springer Netherlands , Dordrecht. pp 846–847 Scalenghe R, Edwards AC, Ajmone Marsan F, Baraberis E ( 2002 ) The effect of reducing conditions on the solubility of phosphorus in a diverse range of European agricultural soils. Eur J Soil Sci. https://doi.org/10.1046/j.1365-2389.2002.00462.x Schwertmann U (1964) Differenzierung der eisen-oxide des bodens durch photochemische extraktion mit sauer ammonium oxalat-lösung. Z Pflanz Bodenkunde 105:194–202. Sikora FJ, Mullins GL ( 1995 ) Bioavailability of citrate-insoluble phosphorus in monoammonium phosphate and triple superphosphate fertilizers . Soil Sci Soc Am J. https://doi.org/10.2136/sssaj1995.03615995005900040034x Six L, Pypers P, Degryse F, Smolders E, Merckx R ( 2012 ). The performance of DGT versus conventional soil phosphorus tests in tropical soils - An isotope dilution study . Plant Soil. https://doi.org/10.1007/s11104-012-1192-9 Slaton NA, Wilson CE, Norman RJ, Ntamatungiro S, Frizzell DL ( 2002 ). Rice response to phosphorus fertilizer application rate and timing on calcareous soils in Arkansas . Agron Journ. http://dx.doi.org/10.2134/agronj2002.1393 Vance CP, Uhde-Stone C, Allan DL ( 2003 ) Phosphorus acquisition and use: critical adaptations by plants for securing a nonrenewable resource . New Phytol. https://doi.org/10.1046/j.1469-8137.2003.00695.x Van Veldhoven PP, Mannaerts GP ( 1987 ) Inorganic and organic phosphate measurements in the nanomolar range . Anal Biochem. DOI : 10.1016/0003-2697(87)-90649-x Wilfert P, Mandalidis A, Dugulan AI, Goubitz K, Korving L, Temmink H, Witkamp GJ, van Loosdrecht MCM ( 2016 ) Vivianite as an important iron phosphate precipitate in sewage treatment plants . Water Res. https://doi.org/10.1016/j.watres.2016.08.032 Wilfert P, Dugulan AI, Goubitz K, Korving L, Witkamp GJ, van Loosdrecht MCM ( 2018 ) Vivianite as the main phosphate mineral in digested sewage sludge and its role for phosphate recovery . Water Res. https://doi.org/10.1016/j.watres.2018.07.020 Yaya F, Nguetnkam J, Tchameni R, Basga S, Penaye J ( 2015 ) Assessment of the Fertilizing effect of Vivianite on the Growth and yield of the Bean “‘phaseolus vulgaris’” on Oxisoils from Ngaoundere (Central North Cameroon) . Int Res J Earth Sci 3 ( 4 ):18–26. Additional Declarations No competing interests reported. Supplementary Files suppfilefinalNutriCycAgroecosys.docx Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-2138400","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":142300780,"identity":"5ddf236f-1db5-42be-ac52-9bc115dbf8dc","order_by":0,"name":"Rochelle Joie Saracanlao","email":"data:image/png;base64,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","orcid":"","institution":"KU Leuven","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Rochelle","middleName":"Joie","lastName":"Saracanlao","suffix":""},{"id":142300783,"identity":"7f69a56b-71f2-4bcc-b3e9-c149b6993404","order_by":1,"name":"Hannah Ryckel","email":"","orcid":"","institution":"KU Leuven","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Hannah","middleName":"","lastName":"Ryckel","suffix":""},{"id":142300785,"identity":"b2b9518d-a67d-44be-9ba0-68985a03acee","order_by":2,"name":"Maarten Everaert","email":"","orcid":"","institution":"KU Leuven","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Maarten","middleName":"","lastName":"Everaert","suffix":""},{"id":142300786,"identity":"9a0f0090-63fa-4c2e-8457-92b31679bbd6","order_by":3,"name":"Mieke Verbeeck","email":"","orcid":"","institution":"Soil Service of Belgium","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Mieke","middleName":"","lastName":"Verbeeck","suffix":""},{"id":142300787,"identity":"330e8abb-96b2-4c9c-8bf9-4207c00b3dd7","order_by":4,"name":"Erik Smolders","email":"","orcid":"","institution":"KU Leuven","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Erik","middleName":"","lastName":"Smolders","suffix":""}],"badges":[],"createdAt":"2022-10-06 11:14:20","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-2138400/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-2138400/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":27627956,"identity":"2a5b739a-f43b-4b26-8b8f-8bf32da45876","added_by":"auto","created_at":"2022-10-11 15:46:20","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":391483,"visible":true,"origin":"","legend":"\u003cp\u003eThe shoot P uptake by rice grown for 3 weeks in the acid (A), neutral (B) and calcareous (C) soils amended by recycled FePs is not significantly different from the unamended control (except Fe(III)P-gravel in A and B) and significantly lower than that of TSP in non-flooded (left) and flooded (right) conditions. Treatments were applied at a dose of 50 mg P/kg in A, 25 mg P/kg in B, and 40 mg P/kg in C. Data are means of 3 replicates (except for control where n=6) and error bars represent standard error of means. Different letters denote significant differences among treatments (Tukey, P\u0026lt;0.05).\u003c/p\u003e","description":"","filename":"Figure1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-2138400/v1/50fb5de075735d36e528f487.jpg"},{"id":27628284,"identity":"a257a1c5-aff6-46f7-b32e-2e2696ce5aa9","added_by":"auto","created_at":"2022-10-11 15:51:20","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":345124,"visible":true,"origin":"","legend":"\u003cp\u003eRelative phosphorus use efficiency (RPUEs) of FePs indicate their low effectiveness as P fertilizers in a 3-week rice pot experiment in the acid (A), neutral (B) and calcareous (C) soils under non-flooded (left) and flooded (right conditions). The RPUE of TSP is 100% by definition. Treatments were applied at a dose of 50 mg P/kg in A, 25 mg P/kg in B and 40 mg P/kg in C. The RPUEs in non-flooded calcareous soil (lowest left graph) were negative and are not shown. Values represent a mean of n=3, except for control treatments where n=6. Error bars represent the standard error of the means. Different letters denote significant differences among treatments (Tukey, P\u0026lt;0.05).\u003c/p\u003e","description":"","filename":"Figure2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-2138400/v1/145cc970c19a8229df9ed351.jpg"},{"id":27628285,"identity":"202ff6ab-4165-412f-8184-ffc842cb05e4","added_by":"auto","created_at":"2022-10-11 15:51:21","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":424059,"visible":true,"origin":"","legend":"\u003cp\u003eThe CaCl\u003csub\u003e2\u003c/sub\u003e-extractable P (mg P/ L) in the acid (A), neutral (B) and calcareous (C) soils amended by FePs and TSP that were either flooded or not flooded. Note the different scales for the different soils and that values for acid soil were below limit of detection (0.003 mg P/L, dashed horizontal lines). These data show the low solubility of FePs and high P sorption capacity of soils that released P from FePs, if any. All P fertilizers were applied at a dose of 50 mg P/kg in A, 25 mg P/kg in B and 40 mg P/kg in C. Values represent a mean of n=2, except for control treatments where n=4. Error bars represent the standard error of the means. Different letters denote significant differences among treatments (Tukey, P\u0026lt;0.05).\u003c/p\u003e","description":"","filename":"Figure3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-2138400/v1/a8e223694b2d0c8c6e919192.jpg"},{"id":27626339,"identity":"22ab315c-548c-41af-9a16-4f75f198d72d","added_by":"auto","created_at":"2022-10-11 15:41:21","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":242609,"visible":true,"origin":"","legend":"\u003cp\u003eChanges in soil redox potential (mV) with time after incubating control treatments of acid, neutral, and calcareous soils with (full lines) and without (dotted lines) glutamate under flooded conditions. Dots are the measured redox values on control (no FeP) treatments after harvest in plant growth trial with flooding period of 13 days.\u003c/p\u003e","description":"","filename":"Figure4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-2138400/v1/8e634c8241fda264367eefbd.jpg"},{"id":27627958,"identity":"141d3bc6-f124-448e-a4f6-fe2bd8fd1325","added_by":"auto","created_at":"2022-10-11 15:46:20","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":375911,"visible":true,"origin":"","legend":"\u003cp\u003eChanges in mean CaCl\u003csub\u003e2\u003c/sub\u003e-extractable P concentrations (mg P/L) with time in acid (A), neutral (B), and calcareous (C) soils amended with recycled FePs with and without glutamate (0C and +C treatment). Error bars represent standard error of means (n=3).\u003c/p\u003e","description":"","filename":"Figure5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-2138400/v1/14d7cb05261383fe506db58b.jpg"},{"id":27628286,"identity":"d0daf885-6a20-455f-bdab-59cecc4bf642","added_by":"auto","created_at":"2022-10-11 15:51:25","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":772272,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-2138400/v1/658252f9-8027-4082-a2df-fdcfc9f99c19.pdf"},{"id":27626334,"identity":"3ae06926-5ceb-4f44-ae4b-f4584cbbdaa1","added_by":"auto","created_at":"2022-10-11 15:41:20","extension":"docx","order_by":10,"title":"","display":"","copyAsset":false,"role":"supplement","size":1019292,"visible":true,"origin":"","legend":"","description":"","filename":"suppfilefinalNutriCycAgroecosys.docx","url":"https://assets-eu.researchsquare.com/files/rs-2138400/v1/c48547e3dc45fa9b8ef9c82f.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Increasing phosphorus fertilizer value of recycled iron phosphates in strong P-fixing soils by prolonged flooding and organic matter addition","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe global use of phosphorus (P) fertilizers has increased, driven primarily by the growing demand for food and feed (Vance et al. \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2003\u003c/span\u003e). This large consumption threatens the stock of phosphate rock and, at the same time, leads to local environmental issues where excess fertilizer has been used. To target both issues, P can be removed from P-rich waste streams and potentially be recycled into an effective fertilizer, thereby closing the P cycle in agriculture (Melia et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2017\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eCurrently, most approaches to recover P from wastewater in wastewater treatment plants (WWTPs) focus on crystallization of struvite, direct application of sewage sludge to agricultural fields, or techniques relying on sludge incineration. Each of these has disadvantages regarding recovery efficiencies and applicability. In contrast, the recovery of P as vivianite (Fe(II)\u003csub\u003e3\u003c/sub\u003e[PO\u003csub\u003e4\u003c/sub\u003e]\u003csub\u003e2\u003c/sub\u003e\u0026sdot;8H\u003csub\u003e2\u003c/sub\u003eO), a mineral that is formed when ferrous iron (Fe) is added to wastewaters to remove P, is promising for several reasons. First, it is naturally ubiquitous in sewage sludge, accounting for 70\u0026ndash;90% of all phosphates (Wilfert et al. \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Second, it has higher P content (Fe:P molar ratio of 1.5) compared to other ferric precipitates in WWTPs. Third, vivianite, owing to its paramagnetic properties, can be separated from sewage sludge, and be collected in relatively pure phase using magnetic separators (Wilfert et al. \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2018\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eFor the removal of P from diffuse agricultural sources, P removal via adsorption processes using low-cost P-sorbing materials (PSMs) has garnered attention due to the fast immobilization of P (Liu et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). These PSMs contain metal cations, typically aluminum (Al), calcium (Ca), magnesium (Mg), and Fe, that form an insoluble compound with dissolved P. Specifically, Fe-coated sands and Fe sludges are Fe(III) based minerals that are very effective at removing P (Lambert et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). These materials are by-products from drinking water production, that are formed during Fe removal to prevent colored and bad-tasting water. Aeration of the groundwater leads to the oxidation of Fe(II) to Fe(OH)\u003csub\u003e3\u003c/sub\u003e, which coats the sand and gravel filter beds, yielding Fe-coated sand. Alternatively, the Fe-coated sand can be washed for reuse of the sand, producing Fe-sludges (Liu et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2018\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe FeP minerals, obtained by trapping P from waste streams using Fe minerals, have the potential to be reused as fertilizers. From the perspective of P recovery, the strong interaction between Fe and P is a clear advantage, however, the poor solubility P from the FeP materials could strongly limit the plant availability of the recovered P (Samie and Romer al., 2001; Kahiluoto et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2015\u003c/span\u003e), particularly in aerobic conditions. The Fe(II) based ones such as vivianites have been used as P fertilizer but are mostly limited to those of geologic origin (Yaya et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2015\u003c/span\u003e) or of peat origin in various crop experiments in Russia (Bodrova and Ozolina, 1968; Gamzikov and Marmulev, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). Next to their potential as P source, vivianites can also be valorized as Fe fertilizers to mitigate Fe chlorosis in various crops growing in calcareous soils in the Mediterranean region (D\u0026iacute;az et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Rosado et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2002\u003c/span\u003e). In contrast, Fe(III) based P fertilizers rarely exhibit positive P fertilizer effects, even when added as nanoparticles to soil (Bollyn et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). However, in some conditions, positive fertilizer values have been found. For example, P sorbed on Fe minerals was used to prepare a P-mineral complex for growing rice in a glasshouse of which 15\u0026ndash;31% of sorbed P was recovered by rice within 3 months (He et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e1994\u003c/span\u003e). Similarly, ochre (hydrous ferrous oxides) from coal mines that were subsequently loaded with P performed well as slow-release P fertilizer in cereals and trees (Dobbie et al. \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). Synthetic iron phosphates showed a slightly higher biomass yield but lower P uptake in comparison with monocalcium phosphates in ryegrass (Johnston and Richards \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2003\u003c/span\u003e), yet no explanation was provided for the relatively good performance of the material. Iron phosphates as by-products of fertilizer reactions in the soil (e.g., hydrogen ammonium iron phosphates and colloidal ferric phosphates) and as impurities of commercial P fertilizers (reported as citrate-insoluble P) were reported to have residual P availability (Lindsay and Demnet 1961; Sikora and Mullins \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e1995\u003c/span\u003e) suggesting the release of P in the long term. This could be beneficial for plants requiring frequent P fertilization like tree stands in peatland forests (Nieminen et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2011\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eHere, we hypothesized that Fe-based P recycling products can be suitable P fertilizers in flooded soils, e.g. in soils used in growing paddy rice. It is well established that soil P availability increases upon soil flooding following reductive dissolution of soil Fe(III) minerals (Rakotoson et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2016\u003c/span\u003e), and the addition of an organic carbon (OC) source can further stimulate this process (Scalenghe et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2002\u003c/span\u003e). However, to what extent reductive dissolution in flooded soils can also increase the effectiveness of Fe-based P fertilizers is still unknown. Against this background, a pot trial was set up to identify the P fertilizer use efficiency (PFUE) of six granular recycled FeP products (three vivianites and three P-loaded Fe oxides) in the early stages of rice development, in paddy soils with or without flooding (13 days). The PFUE of FePs was compared to that of triple superphosphate (TSP), a conventional soluble P fertilizer and an unamended control treatments. We hypothesized that the recycled FePs will perform better as P fertilizers in the pot trial under flooded conditions due to increased soil P availability after the liberation of P following reductive dissolution of Fe(III) minerals. In addition, a soil incubation experiment was established to determine the P availability of powdered recycled FePs (as measured by 1 mM CaCl\u003csub\u003e2\u003c/sub\u003e extraction), exploring also the effect of longer flooding conditions (up to 60 days) and OM addition (glutamate) and thus expanding the range of soil conditions in comparison with those in the pot experiment. With the incubation experiment, we hypothesized that prolonged flooding and OM addition would promote reduced conditions and thus enhance the P availability of FePs in soils.\u003c/p\u003e"},{"header":"Materials And Methods","content":"\u003cp\u003eSoils\u003c/p\u003e \u003cp\u003eThe selected physical and chemical properties of the soils used are given in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Soil samples were collected from the upper 20\u0026ndash;30 cm layer, air-dried, and sieved to \u0026lt;\u0026thinsp;2 mm before use. These soils were chosen as representative of rice-growing areas with low P availability. Soils were analysed for pH, cation exchange capacity (CEC), particle size distribution, total C and N, and oxalate extractable Fe, Mn, and P (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSelected physicochemical properties of soils from pot experiment.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eacid\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eneutral\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003ecalcareous\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSite of origin\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCavinti, Laguna, Philippines\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eDakawa, Tanzania\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eIsla Mayor, Seville, Spain\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSoil classification\u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eFerralsol\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eVertisol\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eVertisol\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eClay\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e84\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e32\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSilt\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e56\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e76\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSand\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e16\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003epH\u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4.5; 6.1\u003csup\u003ec\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e6.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e7.9\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCEC\u003csup\u003ed\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e7.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e20.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e26.4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eC/N\u003csup\u003ee\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e10.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e14.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e22.0\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOrganic C\u003csup\u003ee\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.86\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.84\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eInorganic C\u003csup\u003ee\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.7\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eP in soil solution\u003csup\u003ef\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(mg P /L)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.008\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.008\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.01\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFe\u003csub\u003eox\u003c/sub\u003e\u003csup\u003eg\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(g Fe /kg)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.94\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e2.62\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e2.91\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAl\u003csub\u003eox\u003c/sub\u003e\u003csup\u003eg\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(g Al /kg)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1.86\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.62\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.72\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMn\u003csub\u003eox\u003c/sub\u003e\u003csup\u003eg\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(g Mn /kg)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.39\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.32\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eP\u003csub\u003eox\u003c/sub\u003e\u003csup\u003eg\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(mg P /kg)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e300\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFC\u003csup\u003eh\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(mL /kg)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e410\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e250\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e325\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eK\u003csup\u003ei\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(L/kg)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1065\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e136\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e120\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003en\u003csup\u003ei\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.22\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.29\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.36\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePSI\u003csup\u003ej\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(mg P /kg)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e635\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e70\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e52\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePSC\u003csup\u003ek\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(mmol /kg)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e42.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e35.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e39.4\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDPS\u003csup\u003el\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e3.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e24.8\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003e\u003csup\u003ea\u003c/sup\u003e Major soil groups (IUSS Working Group WRB, 2015)\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003e\u003csup\u003eb\u003c/sup\u003e Clay, silt, sand and texture class based on particle size distribution (Soil Science Division Staff, 2017) determined by laser diffraction method; texture of acid soil determined by pipette method\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003e\u003csup\u003ec\u003c/sup\u003e pH (1:5 S:L ) in 0.01 M CaCl\u003csub\u003e2\u003c/sub\u003e (acid soil was limed to pH 6.1 for the pot trial)\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003e\u003csup\u003ed\u003c/sup\u003e CEC was determined in a 0.0166 M cobalt hexamine (Cohex) extract (ISO, 2007), as the difference between total Co added and Co measured in the extract with ICP-OES.\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003e\u003csup\u003ee\u003c/sup\u003eC/N and organic C and inorganic C as % of total soil mass determined by the combustion method\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003e\u003csup\u003ef\u003c/sup\u003e P in soil solution determined by indirect sorption/desorption method (0.01 M CaCl\u003csub\u003e2\u003c/sub\u003e); P concentration in filtrate was determined using malachite green method with detection limit of 8 \u0026micro;g P/L (Van Veldhoven and Mannaerts, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e1987\u003c/span\u003e)\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003e\u003csup\u003eg\u003c/sup\u003e Ammonium oxalate extractable Fe, Al, Mn and P (Schwertmann, 1964)\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003e\u003csup\u003eh\u003c/sup\u003e Field capacity (FC) determined through the glistening effect\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003e\u003csup\u003ei\u003c/sup\u003e Fit parameters for the P sorption isotherms described by the Freundlich equation (P \u003csub\u003esorbed\u003c/sub\u003e =k (P\u003csub\u003esolution\u003c/sub\u003e)\u003csup\u003en\u003c/sup\u003e)\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003e\u003csup\u003ej\u003c/sup\u003e P sorption index (PSI) defined as the amount of added P sorbed on the solid phase at a soil solution concentration of 0.1 mg P/L (Six et al., \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2012\u003c/span\u003e).\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003e\u003csup\u003ek\u003c/sup\u003e P sorption capacity (PSC) defined as 0.5*(Fe\u003csub\u003eox\u003c/sub\u003e + Al\u003csub\u003eox\u003c/sub\u003e)\u003c/td\u003e\u003c/tr\u003e \u003ctr\u003e\u003ctd colspan=\"5\"\u003e\u003csup\u003el\u003c/sup\u003e Degree of P saturation (DPS) defined as\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\frac{{P}_{ox}}{PSC}*100\\%\\)\u003c/span\u003e\u003c/span\u003e\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe P adsorption isotherms were also determined for the three soils as detailed by Six et al. (\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). Briefly, soils were mixed with 0.01 M CaCl\u003csub\u003e2\u003c/sub\u003e with increasing P concentrations. Soil suspensions were then shaken for 16 hrs, centrifuged (2500 g, 10 min), and filtered (0.45 \u0026micro;m, Chromafil \u0026reg; Xtra PET \u0026minus;\u0026thinsp;45/25; Macherey- Nagel, Germany). The P concentration in the filtrate was determined using malachite green method (Van Veldhoven and Mannaerts \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e1987\u003c/span\u003e) and absorbance was measured at 630 nm using a spectrophotometer (Perkin Elmer, Lambda 20, 1 cm path length). Results showed that the P sorption of the soils ranged acid soil\u0026thinsp;\u0026gt;\u0026thinsp;\u0026gt;\u0026thinsp;neutral soil\u0026thinsp;\u0026gt;\u0026thinsp;calcareous soil (Figure S1).\u003c/p\u003e \u003cp\u003eRecycled FeP materials\u003c/p\u003e \u003cp\u003eThree vivianites and three Fe(III) phosphates were used (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Two vivianites and two Fe(III) phosphates were collected from different sources. In addition, one extra vivianite was synthesized in the lab by dissolving FeSO\u003csub\u003e4\u003c/sub\u003e and (NH\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e and one extra Fe(III) phosphate was produced by loading a Fe(III)-rich product with a saturated P solution. As a reference P fertilizer, the commercial soluble fertilizer TSP was used. The total P content (and other elements) of the FeP materials was determined with Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES, Thermo Scientific iCAP 7000 series) after digestion in aqua regia (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eDescription of the FeP materials tested in the experiment.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMaterial\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDescription\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003e\u003cb\u003eVivianites (Fe(II) phosphates)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eV-WWTP\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eProvided by Wetsus (European Center of Excellence for Sustainable Water Technology), a water treatment facility in the Netherlands\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eV-fert\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eProvided by Fertiberia, a fertilizer company in Spain\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eV-syn\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSynthesized according to Rosado et al. (\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2002\u003c/span\u003e) by dissolving 2.5% (w/v) of monoammonium phosphate (MAP) with 7.5% (w/v) ferrous sulphate. The pH is adjusted to 6.5 to 7.5 with 10 M KOH. Suspension is then washed with MilliQ until electrical conductivity (EC) is \u0026lt;\u0026thinsp;0.2 dS m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Precipitates were then dried under anaerobic hood.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003e\u003cb\u003eFe(III) phosphates\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFe(III)P-sludge\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eIron sludge from Veghel pumpstation provided by Aquaminerals (company in the Netherlands that finds application of Fe by-products from water companies)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFe(III)P-gravel\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMixture of iron coated gravels from different pumpstations in the Netherlands provided by Aquaminerals. Due to low P content of the material (0.32%), it was artificially loaded with P by incubating the material for 24 h in a 184 mM KH\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e solution (liquid:solid ratio of 10 L kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, end-over-end shaking). After recovery of the material via centrifugation, it was air-dried and stored until further use.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFe(III)P-sand\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eP-loaded iron coated sand provided by Nico Lambert of NuReDrain Project (Lambert et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2021\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eThe elemental composition of the FeP materials, expressed as percentage by weight of air-dried material.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"13\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c11\" colnum=\"11\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c12\" colnum=\"12\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c13\" colnum=\"13\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003eMaterials\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003eP (%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e \u003cp\u003eCa(%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e \u003cp\u003eMg(%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e \u003cp\u003eAl(%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e \u003cp\u003eFe(%)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c13\"\u003e \u003cp\u003eFe:P molar ratio\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eTSP\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c3\" namest=\"c2\"\u003e \u003cp\u003e18.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e \u003cp\u003e22.40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e \u003cp\u003e0.007\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c9\" namest=\"c8\"\u003e \u003cp\u003e2.16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c11\" namest=\"c10\"\u003e \u003cp\u003e3.87\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c13\" namest=\"c12\"\u003e \u003cp\u003e0.01\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"13\" nameend=\"c13\" namest=\"c1\"\u003e \u003cp\u003e\u003cb\u003eVivianites (Fe(II) phosphates)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003eV-WWTP\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003e9.55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e \u003cp\u003e0.90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e \u003cp\u003e0.96\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e \u003cp\u003e0.11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e \u003cp\u003e25.81\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003e1.50\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003eV-fert\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003e12.65\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e \u003cp\u003en.d.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e \u003cp\u003en.d.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e \u003cp\u003en.d.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e \u003cp\u003e35.47\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003e1.55\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003eV-syn\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003e13.45\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e \u003cp\u003en.d\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e \u003cp\u003en.d.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e \u003cp\u003en.d.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e \u003cp\u003e38.28\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003e1.58\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"13\" nameend=\"c13\" namest=\"c1\"\u003e \u003cp\u003e\u003cb\u003eFe(III) phosphates\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003eFe(III)P-sludge\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003e2.78\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e \u003cp\u003e7.40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e \u003cp\u003en.d.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e \u003cp\u003e0.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e \u003cp\u003e34.70\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003e6.81\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003eFe(III)P-gravel\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003e3.31\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e \u003cp\u003e0.002\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e \u003cp\u003e0.00006\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e \u003cp\u003e1.23\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e \u003cp\u003e27.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003e4.15\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003eFe(III)P-sand\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003e1.26\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e \u003cp\u003e1.90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c8\" namest=\"c7\"\u003e \u003cp\u003e0.24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e \u003cp\u003e0.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c12\" namest=\"c11\"\u003e \u003cp\u003e50.18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003e22.15\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"13\"\u003en.d. not detected\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eThe FeP materials were provided in different forms, i.e., as granule or as powder. Granular materials (i.e., TSP, Fe(III)P-gravel, and Fe(III)P-sand, see Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e for abbreviations) were sieved to obtain granules of 2\u0026ndash;4 mm (except the small-sized TSP). The powders (i.e., all vivianites), were made into granular particles via extrusion. For this, a paste was made by mixing ultrapure water (MilliQ) with the powders, which was extruded in a mould with a 4-mm diameter hole. Subsequently, the obtained pellets were cut to 3 mm length and dried at 40\u0026deg;C overnight.\u003c/p\u003e \u003cp\u003eIn the pot trial, all six FePs and TSP applied as granules were tested, while in the incubation experiment only two products were tested, i.e. one Fe(II) phosphate (V-WWTP) and one Fe(III) phosphate (Fe(III)P-sludge).\u003c/p\u003e \u003cp\u003ePlant growth trial\u003c/p\u003e \u003cp\u003eThe experimental design was completely randomized with three factors (soil, amendments, soil flooding) and with three replicates for each treatment. The pot trials were not done simultaneously due to space limitation in the growth cabinet and the late arrival of the calcareous soil. To avoid false positive P response as a result of flooding (raised soil pH under flooded conditions) and the pH neutralizing effect of neutral FeP fertilizers on acid soils, the acid soil was limed at a rate of 1.5 g Ca(OH)\u003csub\u003e2\u003c/sub\u003e/kg, which raised the soil pH from pH 4.5 to 6.1; thus this soil is further termed acid soil. Soils were mixed with macronutrients (other tha n P) as dry salts at the rates of 120 mg N/kg (NH\u003csub\u003e4\u003c/sub\u003eNO\u003csub\u003e3\u003c/sub\u003e), 120 mg K/kg (KCl, 254 mg K/kg for acid soil due to higher P dose), 75 mg Ca/kg (CaCl\u003csub\u003e2\u003c/sub\u003e), 30 mg Mg/kg and 40 mg S/kg (MgSO\u003csub\u003e4\u003c/sub\u003e\u0026middot;7H\u003csub\u003e2\u003c/sub\u003eO). The N and K were split-applied, partly before sowing as dry salts and at 16 days after planting (DAP) as solution. Micronutrients were applied by spraying the soil with a micronutrient solution (20 ml/kg soil) with adequate concentration to obtain rates of 1.2 mg Mn/kg (MnCl\u003csub\u003e2\u003c/sub\u003e\u0026middot;4H\u003csub\u003e2\u003c/sub\u003eO), 0.6 mg Zn/kg (ZnCl\u003csub\u003e2\u003c/sub\u003e), 0.6 mg Cu/kg (CuCl\u003csub\u003e2\u003c/sub\u003e\u0026middot;2H\u003csub\u003e2\u003c/sub\u003eO), 0.2 mg B/kg (Na\u003csub\u003e2\u003c/sub\u003eB\u003csub\u003e4\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e\u0026middot;10H\u003csub\u003e2\u003c/sub\u003eO), and 0.2 mg Mo/kg (Na\u003csub\u003e2\u003c/sub\u003eMoO\u003csub\u003e4\u003c/sub\u003e\u0026middot;2H\u003csub\u003e2\u003c/sub\u003eO). After mixing the nutrients with the air-dried soil, soils were transferred individually into 1 L transparent pots (900 g soil for the neutral and calcareous soil, 838 g soil for the acid soil). Then, for each soil, TSP (four doses) and FeP (one P dose; equal to highest TSP dose) granules were added in the center of the pots, 3 cm below the surface. For TSP, maximum doses were 24 mg P/kg for the neutral soil, 50 mg P/kg for the acid soil, and 40 mg P/kg for the calcareous soil. This was based on the P adsorption curves of each soil and previous P fertilizer studies where the estimated difference in P uptake between mixed P (KH\u003csub\u003e2\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e) and placed P (TSP) application was a factor of 3 for the neutral soil (de Bauw et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2019\u003c/span\u003e), 4 for the acid soil(de Bauw et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2019\u003c/span\u003e) and 1.3 for the calcareous soil (Everaert et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Control treatments (without P) were also included for all soils. Subsequently, soils were watered until field capacity and were incubated in the phytotron for six days in dark conditions at 25\u0026thinsp;\u0026plusmn;\u0026thinsp;2\u0026deg;C. Then, two pre-germinated seedlings of Malagasy rice variety X265 were transplanted (at root length\u0026thinsp;\u0026plusmn;\u0026thinsp;1.5 cm) to each pot after incubation and thinned to one after 5 DAP. At 8 DAP, the contrasting water regime was imposed by adding water to \u0026plusmn;\u0026thinsp;3 cm on top of the soil surface in the flooded treatments. Water management was maintained daily until the end of pot trial. Until harvest, rice was grown in a plant growth cabinet with day/night temperature setting of 25/20\u0026deg;C, at relative humidity of 80% and light intensity of 550\u0026ndash;600 \u0026micro;mol / cm\u003csup\u003e2\u003c/sup\u003e s. At 21 DAP, the rice plants were harvested and oven-dried at 60\u0026deg;C for 3 days. Dry shoots were weighed and digested in 10ml HNO\u003csub\u003e3\u003c/sub\u003e using a microwave (MARS 6 microwave digestion system, CEM). The digests were analyzed for concentrations of P and other plant nutrients by ICP-OES.\u003c/p\u003e \u003cp\u003eEach batch included 2 blank samples, an internal standard, and a certified reference material (hay powder, Joint research centre, European Commission). The average recovery of P, certified concentration 2360 mg P kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, was 99%. The internal standard material (rice shoots) is verified relative to certified reference material (hay powder) with P at similar concentrations (e.g., BCR129; Joint research centre European Commission, 2021). For P in the internal standard, verified concentration of 1308 mg P kg\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, the average recovery was 91%.\u003c/p\u003e \u003cp\u003eSoil analyses after plant growth\u003c/p\u003e \u003cp\u003eOne week after harvest, a 1mM CaCl\u003csub\u003e2\u003c/sub\u003e soil extraction (solid:liquid ratio\u0026thinsp;=\u0026thinsp;0.2 kg L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e; 24 h) was performed on two (randomly chosen) out of three replicates of each treatment, the flooded soil was stored and kept flooded between harvest and soil sampling. The upper 3 cm of the soil column from a pot was sampled and mixed. Ten grams of moist soil was taken and added to a 50 mL polyethylene tube. Next, a 1 mM CaCl\u003csub\u003e2\u003c/sub\u003e solution was added to the tube until it was completely filled (i.e., no headspace). Samples were shaken end-over-end for 24 h (0.42 s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e; T\u0026thinsp;=\u0026thinsp;20 +/- 2\u0026deg;C), centrifuged (2500 g, 10 min), filtered, and acidified using concentrated HNO\u003csub\u003e3\u003c/sub\u003e to a volume percentage of 1%. Next, the P concentration of the acidified samples was determined with Inductively Coupled Plasma Mass Spectrometry (ICP-MS; Agilent 7700x, Agilent Technologies).\u003c/p\u003e \u003cp\u003eThe soil redox potential (E\u003csub\u003eh\u003c/sub\u003e) was also measured in control unamended treatments 24 h and 48 h after the harvest using glass fiber probes (8 mm diameter, 10 cm length) (Paleoterra Products, Amsterdam, The Netherlands) inserted vertically into the soil column. The E\u003csub\u003eh\u003c/sub\u003e measuring point made of platinum ring was positioned 2 cm from the tip of the probe allowing E\u003csub\u003eh\u003c/sub\u003e measurement at 2 cm below the soil surface. The Ag-AgCl reference electrode was positioned in the water layer. The E\u003csub\u003eh\u003c/sub\u003e relative to standard hydrogen electrode was calculated from the measured potential with temperature-dependent correction for the potential of the Ag-AgCl electrode. The temperature and pH were also measured using a pH meter.\u003c/p\u003e \u003cp\u003eIncubation Experiment\u003c/p\u003e \u003cp\u003eSoils (air-dried and sieved) were mixed with macronutrients at the same dose used in the pot trial. Two hundred grams of soil were placed into 250 ml plastic containers, after which the soil was flooded with deionized water up to 3 cm above the surface. The pots containing the soils were incubated under water in dark conditions for 60 days at 25\u0026thinsp;\u0026plusmn;\u0026thinsp;2\u0026deg;C. Different treatments were set up, varying the type of powdered iron phosphates (Fe(III)P-sludge or V-WWTP applied at P dose of 200 mg P/kg for acid soil, 70 mg P/kg for neutral soil, and 52 mg P/kg for calcareous soil) and glutamate content (0 or 1 g C/kg soil) for three soils, with three replicates per treatment. Glutamate was added as C source to stimulate reductive dissolution of Fe(III). Control treatments (without FePs) were also included for all soils. After 3, 14, and 60 days of incubation, a 1 mM CaCl\u003csub\u003e2\u003c/sub\u003e soil extraction was performed as described above. For each soil, the redox potential values were also monitored weekly in an additional replicate of control treatments.\u003c/p\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eData and statistical analysis\u003c/h2\u003e \u003cdiv id=\"Sec4\" class=\"Section3\"\u003e \u003ch2\u003eThe phosphorus uptake (PU) in each treatment was calculated as\u003c/h2\u003e \u003cp\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\(PU \\left(mg\\right)=P concentration in shoot (mg/g) x dry matter yield \\left(g\\right)\\)\u003c/span\u003e \u003c/span\u003e (Eq.\u0026nbsp;1)\u003c/p\u003e \u003cp\u003eThe relative P use efficiency (RPUE) of the FeP materials was determined as (Cabeza et al \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2011\u003c/span\u003e):\u003c/p\u003e \u003cp\u003e \u003cspan class=\"InlineEquation\"\u003e \u003cspan class=\"mathinline\"\u003e\\(RPUE, x \\left(\\%\\right)=\\frac{{PU}_{x}-{PU}_{control}}{{PU}_{TSP}-{PU}_{control}} x 100\\)\u003c/span\u003e \u003c/span\u003e (Eq.\u0026nbsp;2)\u003c/p\u003e \u003cp\u003ewith PU\u003csub\u003ex\u003c/sub\u003e = PU obtained by a specific FeP treatment \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(x\\)\u003c/span\u003e\u003c/span\u003e (mg), PU\u003csub\u003econtrol\u003c/sub\u003e = mean PU in the unfertilized control (mg), and PU\u003csub\u003eTSP\u003c/sub\u003e = mean PU in the TSP reference treatment at equal P dose (mg).\u003c/p\u003e \u003cp\u003eStatistical analysis was performed using JMP software (JMP pro 15, SAS Institute Inc.). All data were subjected to analysis of variance (ANOVA) with soil, fertilizer type and water as the main factors. Then, for each soil the effects of P dose and water treatments on P uptake and CaCl\u003csub\u003e2\u003c/sub\u003e-extractable soil P in the TSP treatments (each indicated as Y) were assessed using multiple linear regression with the resulting model:\u003c/p\u003e \u003cp\u003eY\u0026thinsp;=\u0026thinsp;β\u003csub\u003e0\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;β\u003csub\u003e1\u003c/sub\u003e*(P dose) + β\u003csub\u003e2\u003c/sub\u003e*(Flooded) + β\u003csub\u003e3\u003c/sub\u003e*(P dose \u0026ndash; c)\u003csup\u003e2\u003c/sup\u003e + β\u003csub\u003e4\u003c/sub\u003e*((Pdose \u0026ndash; c)*Flooded)\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e(Eq.\u0026nbsp;3)\u003c/h2\u003e \u003cp\u003ewith β\u003csub\u003e0\u003c/sub\u003e, β\u003csub\u003e1\u003c/sub\u003e, β\u003csub\u003e2\u003c/sub\u003e, β\u003csub\u003e3\u003c/sub\u003e and β\u003csub\u003e4\u003c/sub\u003e the parameter estimates of this model and c the mean P dose.\u003c/p\u003e \u003cp\u003eThe effect of different FeP fertilizers on P uptake and soil P (in comparison to the unfertilized control and to the same P dose of TSP) was assessed with the Tukey test following the ANOVA test. This was done for each soil separately, and within each soil, for each water treatment separately at 0.05 level of significance. Next, a t-test was used to determine if the P uptake and CaCl\u003csub\u003e2\u003c/sub\u003e- extractable soil P of each FeP fertilizer type is significantly different (P\u0026thinsp;\u0026lt;\u0026thinsp;0.05) between non-flooded and flooded conditions.\u003c/p\u003e \u003cp\u003eFor the incubation experiment, the CaCl\u003csub\u003e2\u003c/sub\u003e-extractable P concentrations were subjected to ANOVA with soil, FeP type and glutamate as the main factors. Then, for each soil the effect of glutamate on the CaCl\u003csub\u003e2\u003c/sub\u003e-extractable P for each FeP treatment per sampling time was assessed with the Tukey test following the ANOVA test at 0.05 level of significance.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003ePlant growth trial\u003c/h2\u003e \u003cp\u003ePlant response to TSP application\u003c/p\u003e \u003cp\u003eThe shoot dry matter and shoot P uptake increased largely and significantly with increasing TSP doses in all soils and all water treatments except in the non-flooded calcareous soil (Figure S2). This supports the fact that the three soils are P deficient, with P deficiency most pronounced in the acid soil in comparison with the neutral and calcareous soils. Shoot P concentrations responded in line with the shoot P uptake, except in the calcareous soil in both water treatments (Figure S3). The plants grown under non-flooded treatments took up more P than corresponding flooded treatments in the acid and neutral soils (Table S1). Plant growth and P uptake were distinctly lower in the calcareous soil than in the other two soils (Figure S3).\u003c/p\u003e \u003cp\u003ePlant response to application of recycled FeP products\u003c/p\u003e \u003cp\u003eThe application of the different FePs resulted in lower shoot P uptake than in TSP treatments at equal P doses. The FePs did not significantly enhance shoot P uptake in comparison with the unfertilized control in most soils and flooding treatments (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) except for V-syn and V-WWTP, and Fe(III)P-gravel in the acid soil for both water treatments. The Fe(III)P-gravel also enhanced P uptake in the flooded treatments of the two other soils but not in the non-flooded ones. The Fe(III)P-gravel had been artificially loaded with P prior to the pot trial, likely resulting in higher P availability than the other FePs.\u003c/p\u003e \u003cp\u003eFlooding the soil for a brief period (13 days) did not have any effect on the P uptake of FePs in the acid soil in contrast to the neutral soil where a negative effect of flooding was observed (Table S2). The average E\u003csub\u003eh\u003c/sub\u003e values of the unfertilized control treatments were 280 mV (pH 6) for the acid soil and 370 mV (pH 6) for the neutral soil after harvest indicating soil conditions were not reduced enough to transform Fe(III) to Fe(II) (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). In the calcareous soil, flooding induced either a negative or no effect on the P uptake of the treatments. A lower P uptake was observed in the control, V-fert, Fe(III)P-sand and Fe(III)P-sludge while the P uptake of the other FePs were not affected by the water conditions. In the calcareous soil, under non-flooded conditions, all treatments were not significantly different from each other while P uptake in flooded conditions highly differentiated the TSP treatment from the rest of the FePs. The better performance of Fe(III)P-gravel was not observed in this soil (non-flooded treatments) as the material had likely aged by the time the pot experiment for this soil was performed.\u003c/p\u003e \u003cp\u003eThe RPUE (Eq.\u0026nbsp;2) was calculated and is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The RPUE values of the FePs were all small (2\u0026ndash;3%) and RPUE was maximally 24% compared to TSP for the Fe(III)P-gravel in the acid soil. In some cases, a negative RPUE was obtained, indicating that the P uptake for these treatments is even lower than that of control treatments.\u003c/p\u003e \u003cp\u003eCaCl\u003csub\u003e2\u003c/sub\u003e-extractable P across soils after plant growth\u003c/p\u003e \u003cp\u003eThe majority of the CaCl\u003csub\u003e2\u003c/sub\u003e-extractable soil P concentrations in the FeP-amended treatments were not statistically different from those of the corresponding unamended control or TSP treatments (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). The CaCl\u003csub\u003e2\u003c/sub\u003e-extractable soil P concentrations confirmed the ranking of soil P deficiency as found in the plant growth assay (acid\u0026thinsp;\u0026gt;\u0026thinsp;\u0026gt;\u0026thinsp;neutral\u0026thinsp;\u0026gt;\u0026thinsp;calcareous soil), since the P concentrations in the acid soil were smallest and all were below the detection limit (0.003 mg P/L). These concentrations were also low in the neutral soil, averaging at 0.01 mg P/L in non-flooded and 0.0.02 mg P/L in flooded conditions. In the calcareous soil, the values range from 0.0.03 mg P/L for the control to about 0.06 mg P/L for the highest dose of TSP. These values are all below the adequate P concentration values needed for growing rice (0.1 mg P/L; Beckwith \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e1965\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eIncubation Experiment\u003c/h3\u003e\n\u003cp\u003eStimulating CaCl\u003csub\u003e2\u003c/sub\u003e-extractable P from FeP amended soils\u003c/p\u003e \u003cp\u003eFlooding of the soils in the incubation experiment reduced the soil redox potential for all the treatments (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e) with glutamate-amended treatments reaching the lower limit of\u003c/p\u003e \u003cp\u003e-200 mV faster than treatments without OM. The calcareous soil reached negative values within 3 days of flooding, while it took 7 days for the neutral soil. The acid soil treated with glutamate took the longest time (3 weeks) to reach reduced conditions.\u003c/p\u003e \u003cp\u003eThe CaCl\u003csub\u003e2\u003c/sub\u003e-extractable soil P concentrations are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. In the acid soil, the CaCl\u003csub\u003e2\u003c/sub\u003e-extractable P was lower than the concentration needed to support rice growth (0.1 mg P/L), even with glutamate addition. In the neutral soil, the P concentration of about 0.1 mg P/L was only reached in the treatment amended with Fe(III)P-sludge after 60 days. In contrast, in the calcareous soil, this P concentration was already achieved after two weeks for all treatments.\u003c/p\u003e \u003cp\u003eThe effect of glutamate on stimulating P release was significant in the Fe(III)P-sludge treatments on the 14th and 60th day (Table S6) in the acid soil. In the neutral soil, the addition of glutamate significantly increased the soil P concentrations in FeP treatments but only at 14th day for V-WWTP and only at 60th day Fe(III)P-sludge. All glutamate-amended treatments in the calcareous soil showed significantly higher P concentrations than those without OM but only the Fe(III)P-sludge treatments had significantly different P values until the end of the incubation period.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eThe different FePs had very low available P in the short-term pot trial here. It is well established that a high Fe:P ratio in a soil amendment lowers its P availability. For example, the low plant P availability of sewage sludges was found to be correlated to the increased concentration of total Fe and Al of the sludge (Lemming et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2017\u003c/span\u003e, O\u0026rsquo;Connor et al. 2004). A high Fe content (e.g. 0.25 Fe:P molar ratio) in sewage sludge increased the P sorption capacity of soils, thereby decreasing the P availability (Samie and Romer, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2001\u003c/span\u003e). This can partly explain the observed low P uptakes from vivianites (Fe:P molar ratio of about 1.5) and from Fe(III)Ps that have Fe:P molar ratios ranging from 4 to 22 (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). An exception was Fe(III)P-gravel, as this material was loaded with P six weeks prior to the pot experiment with the neutral and acid soil. This was not observed in the calcareous soil as the pot trial with this soil started only 6 months after P loading of the Fe(III)P-gravel. The plant availability of P decreases with time due to diffusion and precipitation reactions, explaining the lower RPUE of the Fe(III)P-gravel in the calcareous soil (Hylander and Sim\u0026aacute;n \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2001\u003c/span\u003e). In addition, the FeP fertilizers were still intact as granules in the soil after the plant growth trial indicating reduced solubility of FePs if granulated, which thus explains the poor P supply from the granules to the soil solution (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). The low soil P concentration extracted using CaCl\u003csub\u003e2\u003c/sub\u003e implied that the P released (if any), was adsorbed on or precipitated in all soils, becoming unavailable to plants.\u003c/p\u003e \u003cp\u003eThe P uptake in the flooded treatments is typically higher than that in the corresponding treatments in non-flooded conditions (Huguenin-Elie et al., 2003; Rabeharisoa et al., \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). However, this is in contrast with our observations in the pot trial, where P uptake in non-flooded conditions was either higher in the neutral soil or indifferent in acid soil than in the flooded counterparts. The Fe(III) transforms to Fe(II) under E\u003csub\u003eh\u003c/sub\u003e around +\u0026thinsp;300mV at pH 6, +\u0026thinsp;100 mV at pH 7, -100 mV at pH 8 (Fageria et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). The measured redox values indicated that the soils were only at the edge of Fe(III) reduction (Fageria et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2011\u003c/span\u003e), which most likely was the result of limited flooding time (13 days), low amounts of OC in these soils (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) and/or the presence of plant roots that aerate the rhizosphere. In contrast, soil E\u003csub\u003eh\u003c/sub\u003e values were already negative in the soils after two weeks in the incubation experiment (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e) as the previously mentioned reasons for the positive E\u003csub\u003eh\u003c/sub\u003e values in the pot trial were absent.\u003c/p\u003e \u003cp\u003eThe results from the incubation experiment (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e), however, should be interpreted carefully. Here the soils were unplanted, a scenario that does not exactly reflect pot or field conditions. Because of its oxidizing potential, rice roots can significantly delay the onset of reduced conditions necessary for reductive dissolution of Fe(III) minerals particularly if the soils contain low OM. The incubation experiment predicts that prolonged flooding and OM addition are necessary to accelerate the release of P from FePs.\u003c/p\u003e \u003cp\u003eFlooding in the short term did not affect P uptake significantly in the calcareous soil for most FePs (Table S2). In such soil, P precipitates with Ca\u003csup\u003e2+\u003c/sup\u003e ions to form poorly soluble calcium phosphates (CaPs), restricting P availability. The solubility of CaPs may increase under reduced conditions, as soil pH drops after flooding due to CO\u003csub\u003e2\u003c/sub\u003e accumulation, and OM complexes Ca\u003csup\u003e2+\u003c/sup\u003e ions (Slaton et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2002\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn calcareous soils, application of vivianites is also of interest because of possible supply of Fe, that can mitigate Fe chlorosis in crops. Nonetheless, the application of FePs in calcareous soil did neither enhance growth (Figure S4) nor shoot Fe concentration (Figure S5) compared to the unamended control and TSP treatments. Higher shoot Fe concentrations were found in flooded compared to non-flooded soils in the acid soils, irrespective of FeP treatments (Figure S5) indicating that Fe(III) reduction already took place in that soil that was flooded.\u003c/p\u003e \u003cp\u003eOxidized conditions can also transform vivianite into highly insoluble Fe(III) (hydr)oxide residue (i.e., lepodocrocite (Rold\u0026aacute;n et al. \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2002\u003c/span\u003e)) and dissolved phosphate. This has been the basis for using vivianites as slow-release P and Fe fertilizer in correcting Fe chlorosis of crops in non-flooded calcareous soils. If vivianite is placed in aerated soils, it may also undergo incongruent dissolution which is boosted by the presence of effective phosphate sinks, such as plant roots and P-sorbing minerals. In our pot trial, these processes may have been restricted in flooded treatments, explaining why vivianite performed better under non-flooded than flooded conditions.\u003c/p\u003e \u003cp\u003eThe incubation experiment suggested that soil conditions needed to better reduce Fe(III) can be met with prolonged flooding, and even faster with glutamate addition. In the presence of native or added OM, E\u003csub\u003eh\u003c/sub\u003e values decline more rapidly as OM fuels microorganisms that catalyze the sequential redox reactions following O\u003csub\u003e2\u003c/sub\u003e depletion by mediating the electron transfers involved. Thus, the difference in E\u003csub\u003eh\u003c/sub\u003e values in this study was large between soils with and without glutamate. This was particularly true for acid and neutral soils owing to the inherently low OM content of these soils; in contrast to calcareous soil that contains higher OM. The addition of glutamate did not increase the CaCl\u003csub\u003e2\u003c/sub\u003e-extractable P except in the calcareous soil. The low P values observed in Fe-rich soils, such as the acid and neutral soils used here, may be attributed to the re-sorption of liberated P onto higher P-sorbing secondary ferrous minerals (Holford and Patrick \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e1979\u003c/span\u003e) and precipitation of Fe(II)P compounds (Amery and Smolders \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). However, in the calcareous soil, the P concentration remained sufficient to support rice growth, which indicated that released P can remain available more easily in these soil conditions. This was also demonstrated by the continued increase in the P concentration of vivianite-amended treatments. Hence, it is expected that P released from FePs in the calcareous soil will most likely be depleted by plant uptake or microbial immobilization rather than be resorbed on surfaces of Fe/Al hydroxides. The continued release of P from vivianite treatments can be attributed to a two-step process. First, Fe(II) in vivianite can oxidize to Fe(III) with time as this mineral is not very stable (Wilfert et al. \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Second, the Fe(III) can be reduced again in flooded conditions which enhances the solubility of the vivianite.\u003c/p\u003e \u003cp\u003eDespite the poor performance of the FePs compared to TSP for both water conditions observed in the pot trial, some strategies based on the results of the incubation experiment are suggested to circumvent this issue. Our pot trial lasted for only 3 weeks during which nonlabile inorganic P in FePs may not have been fully mobilized. This duration may not also have also captured the full picture of changes in the concentration of soluble P following flooding, as our incubation experiment indicated that a flooding period for at least several weeks was necessary to obtain reduced soil conditions. The positive effect of glutamate in increasing P concentration in flooded soils amended by FePs suggests that the application of OM may strongly increase the P fertilizer value of FePs particularly on the short term. Rice straw, for example, can be applied to accelerate the reduction of Fe(III) materials (both from FePs and unplanted soils) in submerged conditions (Scalenghe et al. 2022). Furthermore, it may be best to incubate FePs in flooded soil several weeks before sowing. It is assumed that after the incubation period, the liberation of P from FePs, will synchronize with the P demand of rice at its initial growth stages. In addition, FeP minerals were applied as intact granules in the pot experiment, for which the dissolution was likely slower in comparison to its powdered form, as was shown earlier for struvite fertilizers (Degryse et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Lower P availability has also been observed in biosolids-P when pelletized via heat drying (O\u0026rsquo;Connor et al. 2004). Possibly, the effectiveness of FePs will be higher if applied as powders than as granules as shown in our incubation experiment. This again was interpreted from a soil scenario where rice roots were present and thus warrants investigating the performance of FePs as P fertilizers in a pot trial applying the parameters used in the incubation experiment (powdered FePs, longer flooding period, and OM addition).\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThe P fertilizer efficiency of the different recycled FePs was investigated in a pot trial and an incubation experiment. The results from the pot trial indicated a very limited effectiveness of the recycled FePs as P fertilizer for rice grown under both flooded and non-flooded conditions in the three soils. Their PFUEs were negligible compared to that of TSP due to (1) the intrinsically low solubility of the FeP compounds (high Fe content), (2) a subsequent reduction in solubility in soil as result of FeP application as granule, and (3) a short flooding period, low OM in soils and presence of rice roots resulting in a limited reductive dissolution of Fe(III) minerals. These reasons were overcome (except 1) in an incubation experiment where FePs were applied as powder in unplanted soil that was flooded beyond 2 weeks and with (or without) glutamate. The results from the incubation experiment showed that soil conditions needed to reduce Fe(III) and to subsequently release P from FePs, which were not observed during the pot trial, can be met with prolonged flooding and glutamate addition. Applying FePs as a powder can likely also increase the FeP solubility in comparison with a granular application. These suggested strategies for successful FeP fertilizer utilization will be tested in pot trial and field studies in the future.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003eThe authors have no relevant financial or non-financial interests to disclose.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors thank Olaf van der Kolk of Aquaminerals, Nico Lambert of KU Leuven, Leon Korving of Wetsus, and Maria Cinta Cazador Ruiz of Fertiberia for providing the iron phosphates used in this study. Our gratitude also goes to Antonio Delgado and Patrick Rocamora who oversaw the sampling and shipping of soils from Spain and from the Philippines, respectively. Tovohery Rakotoson is also kindly thanked for providing the rice seeds from Madagascar.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research was financially supported by the European Union\u0026apos;s Horizon 2020 Research \u0026amp; Innovation Programme under the Marie Skłodowska Curie Grant Agreement No. 813438.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAmery F, Smolders E \u003cem\u003e(\u003c/em\u003e2012\u003cem\u003e) Unlocking fixed soil phosphorus upon waterlogging can be promoted by increasing soil cation exchange capacity\u003c/em\u003e. Eur J Soil Sci. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1111/j.1365-2389.2012.01478.x\u003c/span\u003e\u003cspan address=\"10.1111/j.1365-2389.2012.01478.x\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBollyn J, Castelein, L, Smolders E \u003cem\u003e(\u003c/em\u003e2019\u003cem\u003e) Fate and bioavailbility of phosphorus loaded to iron oxyhydroxide nanaparticles added to weathered soils\u003c/em\u003e. Plant and Soil. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s11104-019-04008-x\u003c/span\u003e\u003cspan address=\"10.1007/s11104-019-04008-x\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBeckwith RS \u003cem\u003e(\u003c/em\u003e1965\u003cem\u003e) Sorbed phosphate at standard supernatant concentration as an estimate of the phosphate needs of soils\u003c/em\u003e. Aust J Exp Agric Anim Husb. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttp://dx.doi.org/10.1071/EA9650052\u003c/span\u003e\u003cspan address=\"10.1071/EA9650052\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBodrova EM, Ozolina ZD \u003cem\u003e(\u003c/em\u003e1965\u003cem\u003e) Simultaneous application of organic and mineral fertilizers. Translated from Russian and published pursuant to an agreement with US Dept of Agriculture, Jerusalem.\u003c/em\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCabeza R, Steingrobe B, R\u0026ouml;mer W, Claasen N \u003cem\u003e(\u003c/em\u003e2011\u003cem\u003e) Effectiveness of recycled P products as P fertilizers, as evaluated in pot experiments\u003c/em\u003e. Nutr Cycl Agroecosys. \u003cem\u003eDOI\u003c/em\u003e:\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1007/s10705-011-9454-0\u003c/span\u003e\u003cspan address=\"10.1007/s10705-011-9454-0\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003e\u003cem\u003ede\u003c/em\u003e Bauw P, Vandamme E, Senthilkumar K, Lupembe A, Smolders E, Merckx R \u003cem\u003e(\u003c/em\u003e2019\u003cem\u003e) Combining phosphorus placement and water saving technologies enhances rice production in phosphorus-deficient lowlands\u003c/em\u003e. Field Crops Res. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.fcr.2019.03.021\u003c/span\u003e\u003cspan address=\"10.1016/j.fcr.2019.03.021\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDegryse F, Baird R, \u003cem\u003eda\u003c/em\u003e Silva RC, McLaughlin MJ \u003cem\u003e(\u003c/em\u003e2017\u003cem\u003e) Dissolution rate and agronomic effectiveness of struvite fertilizers \u0026ndash; effect of soil pH, granulation and base excess\u003c/em\u003e. Plant Soil. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s11104-016-2990-2\u003c/span\u003e\u003cspan address=\"10.1007/s11104-016-2990-2\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eD\u0026iacute;az I, Barr\u0026oacute;n V, \u003cem\u003edel\u003c/em\u003e Campillo MC, Torrent J \u003cem\u003e(\u003c/em\u003e2009\u003cem\u003e) Vivianite (ferrous phosphate) alleviates iron chlorosis in grapevine\u003c/em\u003e. Vitis, \u003cem\u003e48\u003c/em\u003e(\u003cem\u003e3\u003c/em\u003e):107\u0026ndash;113.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDobbie KE, Heal KV, Smith KA \u003cem\u003e(\u003c/em\u003e2005\u003cem\u003e) Assessing the performance of phosphorus-saturated ochre as a fertilizer and its environmental acceptability\u003c/em\u003e. Soil Use Manage. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1079/sum2005314\u003c/span\u003e\u003cspan address=\"10.1079/sum2005314\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eEveraert M, Degryse F, McLaughlin MJ, \u003cem\u003ede\u003c/em\u003e Vos D, Smolders E \u003cem\u003e(\u003c/em\u003e2017\u003cem\u003e) Agronomic Effectiveness of Granulated and Powdered P-Exchanged Mg-Al LDH Relative to Struvite and MAP\u003c/em\u003e. J Agric Food Chem. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1021/acs.jafc.7b01031\u003c/span\u003e\u003cspan address=\"10.1021/acs.jafc.7b01031\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFageria NK, Carvalho GD, Santos AB, Ferreira EPB, Knupp AM \u003cem\u003e(\u003c/em\u003e2011\u003cem\u003e). Chemistry of lowland rice soils and nutrient availability\u003c/em\u003e. Commun Soil Sci Plan.\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1080/00103624.2011.591467\u003c/span\u003e\u003cspan address=\"10.1080/00103624.2011.591467\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGamzikov GP, Marmulev AN \u003cem\u003e(\u003c/em\u003e2007\u003cem\u003e) Agrochemical assessment of bog phosphates in Western Siberia\u003c/em\u003e. Eurasian Soil Sci+. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1134/S1064229307090098\u003c/span\u003e\u003cspan address=\"10.1134/S1064229307090098\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHe ZL, Yang X, Yuan KN, Zhu ZX \u003cem\u003e(\u003c/em\u003e1994\u003cem\u003e) Desorption and plant-availability of phosphate sorbed by some important minerals\u003c/em\u003e. Plant Soil, \u003cem\u003e162\u003c/em\u003e:89\u0026ndash;97.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHolford ICR and Patrick WH \u003cem\u003e(\u003c/em\u003e1979\u003cem\u003e) Effects of reduction and pH changes on phosphate sorption and mobility in an acid soil\u003c/em\u003e. Soil Sci Soc Am J. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.2136/ssaj1979.03615995004300020010x\u003c/span\u003e\u003cspan address=\"10.2136/ssaj1979.03615995004300020010x\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHuguenin-Elie O, Kirk GJD, Frossard E \u003cem\u003e(\u003c/em\u003e2009\u003cem\u003e). Phosphorus uptake by rice from soils that is flooded, drained or flooded then drained\u003c/em\u003e. Eur J Soil Sci. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1046/j.1365-2389.2002.00489.x\u003c/span\u003e\u003cspan address=\"10.1046/j.1365-2389.2002.00489.x\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHylander LD, Sim\u0026aacute;n G \u003cem\u003e(\u003c/em\u003e2001\u003cem\u003e) Plant availability of phosphorus sorbed to potential wastewater treatment materials\u003c/em\u003e. Biol Fert Soils, \u003cem\u003e34\u003c/em\u003e:42\u0026ndash;48.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003e\u003cem\u003eJoint research centre European Commision. (\u003c/em\u003e2021\u003cem\u003e). BCR-129 hay powder \u0026ndash; certified reference materials catalogue of the JRC.\u003c/em\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJohnston A, Richards I \u003cem\u003e(\u003c/em\u003e2003\u003cem\u003e) Effectiveness of different precipitated phosphates as phosphorus sources for plants\u003c/em\u003e. Soil Use Manage. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1079/SUM2002162\u003c/span\u003e\u003cspan address=\"10.1079/SUM2002162\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKahiluoto H, Kuisma M, Ketoja E, Salo T, Heikkinen J \u003cem\u003e(\u003c/em\u003e2015\u003cem\u003e) Phosphorus in manure and sewage sludge more recyclable than in soluble inorganic fertilizer\u003c/em\u003e. Environ Sci Tech. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1021/es503387y\u003c/span\u003e\u003cspan address=\"10.1021/es503387y\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLambert N, \u003cem\u003evan\u003c/em\u003e Aken P, \u003cem\u003evan den\u003c/em\u003e Broeck R, Dewil R \u003cem\u003e(\u003c/em\u003e2021\u003cem\u003e) Adsorption of phosphate on iron-coated sand granules as a robust end-of-pipe purification strategy in the horticulture sector\u003c/em\u003e. \u003cem\u003eChemosphere\u003c/em\u003e. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.chemosphere.2020.129276\u003c/span\u003e\u003cspan address=\"10.1016/j.chemosphere.2020.129276\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLemming C, Bruun S, Jensen LS, Magid J \u003cem\u003e(\u003c/em\u003e2017\u003cem\u003e) Plant availability of phosphorus from dewatered sewage sludge, untreated incineration ashes, and other products recovered from a wastewater treatment system\u003c/em\u003e. J Plant Nutr Soil Sci. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1002/jpln.201700206\u003c/span\u003e\u003cspan address=\"10.1002/jpln.201700206\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLindsay WL, DeMent JD \u003cem\u003e(\u003c/em\u003e1961\u003cem\u003e) Effectiveness of some iron phosphates as sources of phosphorus for plants\u003c/em\u003e. Plant Soil, \u003cem\u003e14\u003c/em\u003e:118\u0026ndash;126.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLiu R, Chi L, Wang X, Sui Y, Wang Y, Arandiyan H \u003cem\u003e(\u003c/em\u003e2018\u003cem\u003e) Review of metal (hydr)oxide and other adsorptive materials for phosphate removal from water\u003c/em\u003e. J Environ Chem Eng, \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/.j.jece.2018.08.008\u003c/span\u003e\u003cspan address=\"10.1016/.j.jece.2018.08.008\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMelia PM, Cundy AB, Sohi SP, Hooda PS, Busquets R \u003cem\u003e(\u003c/em\u003e2017\u003cem\u003e) Trends in the recovery of phosphorus in bioavailable forms from wastewater\u003c/em\u003e. \u003cem\u003eChemosphere\u003c/em\u003e. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.chemosphere.2017.07.089\u003c/span\u003e\u003cspan address=\"10.1016/j.chemosphere.2017.07.089\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNieminen M, Lauren A, H\u0026ouml;kka H, Sarkkola S, Koivusalo H, Pennanen T \u003cem\u003e(\u003c/em\u003e2011\u003cem\u003e) Recycled iron phosphates as fertilizer raw material for tree stands on drained boreal peatlands\u003c/em\u003e. For Ecol Manag. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.foreco.2010.09.036\u003c/span\u003e\u003cspan address=\"10.1016/j.foreco.2010.09.036\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eO\u0026rsquo; Connor GA, Sarkar D, Brinton SR, Elliott HA, Martin FG \u003cem\u003e(\u003c/em\u003e2004\u003cem\u003e) Phytoavailability of biosolids phosphorus\u003c/em\u003e. J Environ Qual. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.2134/jeq2004.7030\u003c/span\u003e\u003cspan address=\"10.2134/jeq2004.7030\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRabeharisoa L, Razanakoto O R, Razafimanantsoa M P, Rakotoson T, Amery F and Smolders E \u003cem\u003e(\u003c/em\u003e2012\u003cem\u003e) Larger bioavailability of soil phosphorus for irrigated rice compared with rainfed rice in Madagascar: results from a soil and plant survey\u003c/em\u003e. Soil Use and Management \u003cem\u003e28\u003c/em\u003e:448\u0026ndash;456.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRakotoson T, Rabeharisoa L, Smolders E \u003cem\u003e(\u003c/em\u003e2016\u003cem\u003e) Effects of soil flooding and organic matter addition on plant accessible phosphorus in a tropical paddy soil: an isotope dilution study\u003c/em\u003e. J Plant Nutr Soil Sci. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1002/jpln.201500383\u003c/span\u003e\u003cspan address=\"10.1002/jpln.201500383\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRold\u0026aacute;n R, Barr\u0026oacute;n V, Torrent J \u003cem\u003e(\u003c/em\u003e2002\u003cem\u003e) Experimental alteration of vivianite to lepidocrocite in a calcareous medium\u003c/em\u003e. Clay Miner. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1180/0009855023740072\u003c/span\u003e\u003cspan address=\"10.1180/0009855023740072\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRosado R, \u003cem\u003edel\u003c/em\u003e Campillo MC, Mart\u0026iacute;nez MA, Barr\u0026oacute;n V, Torrent J \u003cem\u003e(\u003c/em\u003e2002\u003cem\u003e) Long-term effectiveness of vivianite in reducing iron chlorosis in olive trees\u003c/em\u003e. Plant Soil \u003cem\u003e241\u003c/em\u003e:139\u0026ndash;144.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSamie IF and Romer W \u003cem\u003e(\u003c/em\u003e2001\u003cem\u003e) Phosphorus availability to maize plants from sewage sludge treated with Fe compounds. In: Horst WJ\u003c/em\u003e, \u003cem\u003eSchenk MK\u003c/em\u003e, \u003cem\u003eB\u0026uuml;rkert A\u003c/em\u003e, \u003cem\u003eClaassen N\u003c/em\u003e, \u003cem\u003eFlessa H\u003c/em\u003e, \u003cem\u003eFrommer WB\u003c/em\u003e, \u003cem\u003eGoldbach H\u003c/em\u003e, \u003cem\u003eOlfs HW\u003c/em\u003e, \u003cem\u003eR\u0026ouml;mheld V\u003c/em\u003e, \u003cem\u003eSattelmacher B\u003c/em\u003e, \u003cem\u003eSchmidhalter U\u003c/em\u003e, \u003cem\u003eSchubert S\u003c/em\u003e, \u003cem\u003eWir\u0026eacute;n N\u003c/em\u003e, \u003cem\u003eWitternmayer L (eds) Plant Nutrition\u003c/em\u003e, \u003cem\u003eSpringer Netherlands\u003c/em\u003e, \u003cem\u003eDordrecht. pp\u003c/em\u003e 846\u0026ndash;847\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eScalenghe R, Edwards AC, Ajmone Marsan F, Baraberis E \u003cem\u003e(\u003c/em\u003e2002\u003cem\u003e) The effect of reducing conditions on the solubility of phosphorus in a diverse range of European agricultural soils. Eur J Soil Sci.\u003c/em\u003e \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1046/j.1365-2389.2002.00462.x\u003c/span\u003e\u003cspan address=\"10.1046/j.1365-2389.2002.00462.x\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e Schwertmann U \u003cem\u003e(1964) Differenzierung der eisen-oxide des bodens durch photochemische extraktion mit sauer ammonium oxalat-l\u0026ouml;sung. Z Pflanz Bodenkunde 105:194\u0026ndash;202.\u003c/em\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSikora FJ, Mullins GL \u003cem\u003e(\u003c/em\u003e1995\u003cem\u003e) Bioavailability of citrate-insoluble phosphorus in monoammonium phosphate and triple superphosphate fertilizers\u003c/em\u003e. Soil Sci Soc Am J. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.2136/sssaj1995.03615995005900040034x\u003c/span\u003e\u003cspan address=\"10.2136/sssaj1995.03615995005900040034x\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSix L, Pypers P, Degryse F, Smolders E, Merckx R \u003cem\u003e(\u003c/em\u003e2012\u003cem\u003e). The performance of DGT versus conventional soil phosphorus tests in tropical soils - An isotope dilution study\u003c/em\u003e. Plant Soil. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s11104-012-1192-9\u003c/span\u003e\u003cspan address=\"10.1007/s11104-012-1192-9\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSlaton NA, Wilson CE, Norman RJ, Ntamatungiro S, Frizzell DL \u003cem\u003e(\u003c/em\u003e2002\u003cem\u003e). Rice response to phosphorus fertilizer application rate and timing on calcareous soils in Arkansas\u003c/em\u003e. Agron Journ. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttp://dx.doi.org/10.2134/agronj2002.1393\u003c/span\u003e\u003cspan address=\"10.2134/agronj2002.1393\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eVance CP, Uhde-Stone C, Allan DL \u003cem\u003e(\u003c/em\u003e2003\u003cem\u003e) Phosphorus acquisition and use: critical adaptations by plants for securing a nonrenewable resource\u003c/em\u003e. New Phytol. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1046/j.1469-8137.2003.00695.x\u003c/span\u003e\u003cspan address=\"10.1046/j.1469-8137.2003.00695.x\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003e\u003cem\u003eVan\u003c/em\u003e Veldhoven PP, Mannaerts GP \u003cem\u003e(\u003c/em\u003e1987\u003cem\u003e) Inorganic and organic phosphate measurements in the nanomolar range\u003c/em\u003e. Anal Biochem. \u003cem\u003eDOI\u003c/em\u003e:\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/0003-2697(87)-90649-x\u003c/span\u003e\u003cspan address=\"10.1016/0003-2697(87)-90649-x\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWilfert P, Mandalidis A, Dugulan AI, Goubitz K, Korving L, Temmink H, Witkamp GJ, \u003cem\u003evan\u003c/em\u003e Loosdrecht MCM \u003cem\u003e(\u003c/em\u003e2016\u003cem\u003e) Vivianite as an important iron phosphate precipitate in sewage treatment plants\u003c/em\u003e. Water Res. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.watres.2016.08.032\u003c/span\u003e\u003cspan address=\"10.1016/j.watres.2016.08.032\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWilfert P, Dugulan AI, Goubitz K, Korving L, Witkamp GJ, \u003cem\u003evan\u003c/em\u003e Loosdrecht MCM \u003cem\u003e(\u003c/em\u003e2018\u003cem\u003e) Vivianite as the main phosphate mineral in digested sewage sludge and its role for phosphate recovery\u003c/em\u003e. Water Res. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.watres.2018.07.020\u003c/span\u003e\u003cspan address=\"10.1016/j.watres.2018.07.020\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYaya F, Nguetnkam J, Tchameni R, Basga S, Penaye J \u003cem\u003e(\u003c/em\u003e2015\u003cem\u003e) Assessment of the Fertilizing effect of Vivianite on the Growth and yield of the Bean \u0026ldquo;\u0026lsquo;phaseolus vulgaris\u0026rsquo;\u0026rdquo; on Oxisoils from Ngaoundere (Central North Cameroon)\u003c/em\u003e. Int Res J Earth Sci \u003cem\u003e3\u003c/em\u003e(\u003cem\u003e4\u003c/em\u003e):18\u0026ndash;26.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Phosphorus fertilizer efficiency, P recycled products, P-loaded Fe(III) oxides, vivianite ","lastPublishedDoi":"10.21203/rs.3.rs-2138400/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-2138400/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eIron (Fe) minerals are commonly used to remove phosphorus (P) from waste streams, producing P-loaded Fe(III) oxides or Fe(II)P minerals (e.g. vivianite). These minerals may be used as fertilizers to enhance P circularity if solubilized in soil. Here, we tested the P fertilizer value of recycled iron phosphates (FePs) in a pot trial and in an incubation experiment, hypothesizing that P release from FePs is possible under Fe(III) reducing conditions. First, a pot trial was set up with rice (Oryza sativa) in all combinations of soil flooding or not, three P-deficient soils (acid, neutral, calcareous) and six FePs (three Fe(III) and three Fe(II)phosphates) referenced to triple superphosphate (TSP) or zero amendments. Shoot P uptake responded to TSP applications in all treatments but only marginally to FePs. The redox potential did not decrease below 200 mV by flooding for a brief period during the pot trial. A longer incubation experiment (60 days) was performed which included a treatment of glutamate addition to stimulate reductive conditions and P availability was assessed with CaCl\u003csub\u003e2\u003c/sub\u003e extraction of soils. Glutamate addition and/or longer incubation lowered soil redox potential to \u0026lt;-100 mV. On the longer term, Fe(III) minerals released P and adequate P was reached in the calcareous soil and in the neutral soil amended with Fe(III)P-sludge. It can be concluded that prolonged soil flooding and organic matter (OM) addition can enhance the P fertilizer efficiency of FePs. Additional treatments showed that application of FeP in powder form may enhance P availability.\u003c/p\u003e","manuscriptTitle":"Increasing phosphorus fertilizer value of recycled iron phosphates in strong P-fixing soils by prolonged flooding and organic matter addition","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2022-10-11 15:41:18","doi":"10.21203/rs.3.rs-2138400/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"8d0cc555-c826-48a8-a17d-4967c15c16ac","owner":[],"postedDate":"October 11th, 2022","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2022-10-11T15:41:20+00:00","versionOfRecord":[],"versionCreatedAt":"2022-10-11 15:41:18","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-2138400","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-2138400","identity":"rs-2138400","version":["v1"]},"buildId":"WrCJVZZCHTDjtuVLN7oU0","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}