Fodder oats as catch crop: potential to reduce nitrogen losses from soil

Reducing nitrogen (N) losses and associated nitrate (NO 3-) leaching and nitrous oxide emissions from agricultural land is a critical target worldwide. This is particularly urgent in areas with low fertility soils and a climate that increases the risk of N loss, such as the arid and temperate regions of South Africa. Here, we assessed the potential of fodder oats (Avena sativa) as a winter catch crop to deplete residual N in a field laid fallow for the previous four years, where vetch had proliferated. The soil presented a high clay content (34-44%), with the main exchangeable bases being calcium and magnesium hence, ammonium (NH4+) deposited by the vetch was expected to be rapidly adsorbed and slowly released. A significant decrease in the concentrations of NO3- (49%) and NH4+ (30%) throughout the soil profile (0-90 cm) was observed following harvest of the oats compared to the concentrations measured before sowing. The effectiveness of the oats to uptake both forms of N from top and deep soil layers enhances their potential to reduce N losses. Our results are useful to fill current knowledge gaps on N dynamics in understudied, vulnerable soils such as agricultural land in South Africa, and to advance crop rotation strategies that reduce risk of N leaching.

Catch crop; Oats; Soil nitrogen; Nitrate leaching; Agricultural soil .CC-BY-NC-ND 4.0 International licensemade available under a (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is The copyright holder for this preprintthis version posted June 30, 2024. ; https://doi.org/10.1101/2024.06.26.600925doi: bioRxiv preprint 1. INTRODUCTION Humanity is reliant on fertile agricultural soils to ensure food supply for the ever -growing population, but at least 33% of all croplands are moderately or highly degraded globally (Itps, 2015; Davis et al., 2023) . This threat to food security is particularly severe in countries like South Africa (Ighodaro et al., 2016; Daniell and van Tonder, 2023; Roopnarain et al., 2024). Mitigation of low soil fertility through application of synthetic nitrogen (N) fertilizers currently supports the production of half of the food humans consume (Ritchie, 2017), but half of the N- fertilizer inputs are lost to the environment worldwide (Havlin, 2020; Duncombe, 2021) with a detrimental impact on yields, agricultural wealth and the environment. Nitrate (NO3-) leaching contributes to eutrophication and the emission of nitrous oxide plays a major role in global warming (Rezaei Rashti et al., 2015; Henryson et al., 2020; Maaz et al., 2021) . N itrogen leaching from crop land in South Africa is particularly acute during high rainfall events (Tongwane et al., 2020). Consequently, mitigating N losses from agricultural soils, particularly through leaching of nitrates to deeper soil layers and groundwater, is a critical economic and environmental demand. Efforts to improve N use efficiency (NUE) to enhance crop production and minimise environmental pollution have been proven challenging (Timilsena et al., 2015; Tian et al., 2021). Strategies such as use of nitrification inhibitors and organic amendments have been reported as rather ineffective in mitigating N-fertilizer losses (Coskun et al., 2017; Bossolani et al., 2023) . Nitrogen recovery by catch crops in soils with high N residual content is a n increasingly recognized strategy to optimize NUE and minimize N losses (Abdalla et al., 2019; Malcolm et al., 2022). Catch crops can utilize excess soil nutrients and gradually release them to the soil when decomposing during the following cropping season (Berntsen et al., 2006; Constantin et al., 2011) . Besides their nutritional advantages (Rasane et al., 2015) , oats (Avena sativa ) are a reportedly effective catch crop candidate (Gentsch et al., 2022) to decrease NO3- leaching and enhance soil health and crop profitability (Talanow et al., 2021; Vogeler et al., 2023) , particularly relevant in semiarid regions like South Africa (Milton and .CC-BY-NC-ND 4.0 International licensemade available under a (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is The copyright holder for this preprintthis version posted June 30, 2024. ; https://doi.org/10.1101/2024.06.26.600925doi: bioRxiv preprint Dean, 1995; Acharya et al., 2022) . Fodder oats are highly valuable for farming systems, especially for smallholders (FAO, 2004). Additionally, oats as a catch crop provides protection against soil borne diseases (Leveau et al., 2019) that affect cash crops like wheat (Tadesse et al., 2019; Shew et al., 2020). The present study therefore aimed to investigate the potential of fodder oats as a winter catch crop on a South African soil. Previous studies have focused on the impact of catch crops on N levels in the topsoil, with limited information on their ability to access and take up N from deeper soil horizons. Here, we assess the impact of fodder oats through the soil profile. Also, this study focused on a soil with high clay content (34 -44%), prevalent in South Africa (Sumner, 2015; Daniell and van Tonder, 2023), where ammonium (NH4+) is expected to be rapidly adsorbed onto clay minerals and slowly released over time (Yu et al., 2023). 2. MATERIALS AND METHODS A field study was conducted in 2022 in South Africa (Agricultural Research Council research farm, Brits (25,5849 N, 27,7692 E), to assess the ability of fodder oats to reduce N levels in the soil profile. The field was laid fallow for four years prior to this study, with mostly couch grass (Cynodon dactylon) and broad-leafed purple vetch (Vicia sativa) growing in the field. Fodder oats were obtained from a local provider and sown in May 2022. No N -fertilizer or herbicides were applied throughout the study. The oats were irrigated using sprinklers with water being sourced from the Hartbeespoort dam, with a recorded low N content. Three sets of soil samples were collected throughout the study using a Dutch soil auger. Samples were collected at three depths (0-30 cm, 30-60 cm, and 60-90 cm) at relevant times: prior to sowing (May 2022), at plant ripening (September 2022) and following harvest (October 2022). Soil fertility and soil texture were determined from the first set of samples through chemical characterization (Jackson, 2005; Hailu et al., 2015) and particle size analysis (Murano et al., 2015). Nitrate and NH4+ content in the soil profile were determined for the first and third sets .CC-BY-NC-ND 4.0 International licensemade available under a (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is The copyright holder for this preprintthis version posted June 30, 2024. ; https://doi.org/10.1101/2024.06.26.600925doi: bioRxiv preprint of samples by soil extraction with KCl 1 M and measured in a SEAL Analytical AAIII segmented flow, colorimetric, auto-analyser (Technicon AutoAnalyzer, n.d.). To determine the impact of the oats on soil microbial activity, N potential release (NPR) and potentially mineralisable N (PMN) (Moore et al., 2019) were determined using the Solvita CO 2 burst test (Haney et al., 2008; Chahal et al., 2021) for the second and third set of samples. 3. RESULTS AND DISCUSSION The soil was classified as Cambic calcisol (Chromic) (van Huyssteen, 2020), Kimberley form (Classification Working Group, n.d.; van Zijl et al., 2020), according to the particle size analysis (Table S1), this being consistent with the arid climate of the area (Köppen, 1931; Cui et al., 2021). Base saturation analysis indicated that f or this soil exchangeable sites are occupied mainly by calcium (Ca) and magnesium (Mg) (Table 1). The ratio of potassium (K) to Mg suggests a Mg -induced K deficiency (Hailu et al., 2015) . The ratio Ca to Mg and the Na saturation lower than 3% suggest that the soil has potential for self -mulching (Laker and Nortjé, 2019) and a moderate tendency to disperse (Rengasamy et al., 1986). The clay content ranged 34-44% through the soil profile (Table S1), with a gradual decrease of resistivity with depth (Table 1) likely related to the clay content increase (Long et al., 2012) . The low soil resistivity values recorded can be partly attributed to the proliferation of vetch over the four years before the study (Gabriel et al., 2021). The initial NO3- concentrations in the soil studied (Figure 1) were comparable to those reported by previous studies in NE South Africa (Ntalo et al., 2022), while the NH4+ concentrations were above average, likely due to rhizodeposition of N by the vetch (Ozpinar and Baytekin, 2006) and the adsorption of N on the clay fraction. Soils in the area are rich in smectite, which hold high quantities of essential nutrients that are easily available for plant uptake (Daniell and van Tonder, 2023). This is conf irmed by the high percentage of exchangeable Ca2+ and Mg 2+ .CC-BY-NC-ND 4.0 International licensemade available under a (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is The copyright holder for this preprintthis version posted June 30, 2024. ; https://doi.org/10.1101/2024.06.26.600925doi: bioRxiv preprint (Table 1) which reportedly increase the soil capacity to adsorb N (Dontsova et al., 2005; Nieder et al., 2011). Sowing fodder oats over winter significantly decreased the concentrations of NO3- (49%) and NH4+ (30%) at the three depths of the soil profile studied (Figure 1) (Bonferroni t-test, p=2.31e- 5 for NH 4+ and p=4.3e -4 for NO 3-). These results are consistent with previous research reporting that oats can access N from deeper soil levels than other crops (Af Geijersstam and Mårtensson, 2006) and with previous studies showing a reduction of N losses by planting oats over winter (Michel et al., 2021; Malcolm et al., 2022) , therefore confirming their potential to reduce N leaching (Carey et al., 2018) . No significant differences were obtained for the NH4+/NO3- ratio (Figure 2), with only a minor increase of the ratio in the top layer, which indicates that oats take up both forms of N (van Lierop and Tran, 1980). The uptake of NH 4+ adsorbed to the clay minerals by the oats can be explained by different mechanisms. Firstly, the decrease of NH4+ ions in the soil solution might lead to their diffusion from the clay minerals but the dynamics remain unclear (Nieder et al., 2011). Second, recently adsorbed NH4+ such as that likely deposited by the vetch can be released over the three following months and therefore it would have become available for the oats to uptake (Kowalenko and Cameron, 1976; Scherer, 1993). Thirdly, the roots of the oats likely released exudates that might have promoted the desorption and depletion of NH4+ by the plant (Trofymow et al., 1987; Fisk et al., 2015). Release of exudates is also expected to affect the soil biological activity in relation to N availability (Zhalnina et al., 2018; Morales et al., 2023). Although the results from the Solvita CO2 burst test were not conclusive due to the variability of the measurements (Table 2, Table S2), we determined a significant decrease in NH 4+ as plants grew to full maturity, which confirms that the NH 4+ released by desorption was the main source of N for the oats. In summary, growing oats through winter can significantly decrease the risk of N losses by leaching or gas emission, particularly when grown in land previously laid fallow (Tongwane et al., 2020). .CC-BY-NC-ND 4.0 International licensemade available under a (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is The copyright holder for this preprintthis version posted June 30, 2024. ; https://doi.org/10.1101/2024.06.26.600925doi: bioRxiv preprint 4. CONCLUSION Fodder oats can be used as an effective catch crop over winter to deplete N from soil since this crop can uptake both NO3- and NH4+ recently adsorbed on to the clay minerals. This makes them particularly suitable for soils with high clay content where NH 4+ is rapidly adsorbed and slowly released. Our results confirm that oats can uptake both forms of N from deep soil layers, which enhances their potential to reduce N losses by leaching. The results presented are useful to fill current knowledge gaps on N dynamics in understudied, low fertility soils such as agricultural land in South Africa, and to develop crop rotation strategies that reduce risk of N leaching. AUTHOR CONTRIBUTIONS Michael Kidson : Conceptualisation, writing, editing, data an alysis. Maria C. Hernandez - Soriano: writing - review and editing; data analysis. Buhlebelive Mndzebele: sampling, analysis, review. Busiswa Ndaba: review. Rasheed Adeleke: review. Adornis Nciizah: review & editing. Ashira Roopnarain: review, editing.

The project is funded by the European Joint Programme Soil ERA-NET (HORIZON 2020) and the New Zealand Government to support the objectives of the Global Research Alliance on Agricultural Greenhouse Gases (Project P07000201). MCHS gratefully acknowledges th e support of the Biotechnology and Biological Sciences Research Council (BBSRC); her research is funded by the BBSRC project BB/X003000/1. CONFLICT OF INTEREST STATEMENT .CC-BY-NC-ND 4.0 International licensemade available under a (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is The copyright holder for this preprintthis version posted June 30, 2024. ; https://doi.org/10.1101/2024.06.26.600925doi: bioRxiv preprint The authors declare no conflict of interest. DATA AVAILABILITY STATEMENT The data that support the findings of this study are partially available from the supporting

and further from the corresponding author upon reasonable request. ORCID Michael Kidson https://orcid.org/0000-0001-9991-2808 Maria C. Hernandez-Soriano https://orcid.org/0000-0002-8006-9192 Buhlebelive Mndzebele https://orcid.org/0000-0001-9372-4523 Busiswa Ndaba https://orcid.org/0000-0002-7208-8174 Rasheed Adeleke https://orcid.org/0000-0002-8974-422X Adornis Nciizah https://orcid.org/0000-0002-2481-5218 Ashira Roopnarain https://orcid.org/0000-0002-8866-3049 .CC-BY-NC-ND 4.0 International licensemade available under a (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is The copyright holder for this preprintthis version posted June 30, 2024. ; https://doi.org/10.1101/2024.06.26.600925doi: bioRxiv preprint Figure 1. Average values (n=3) of ammonium (NH4+) and nitrate (NO3-) across the soil profile before (Start) and after (End) growing oats. Significant decrease was confirmed for both forms of nitrogen (Bonferroni t-test, p=2.31e-5 for (n=3) and p=4.3e-4 for NO3-), for the three depths sampled. Figure 2. Ammonia (NH 4+) to nitrate (NO 3-) ratios (n=3) across the soil profile before (Start) and after (End) growing oats. No significant differences were observed but significant decrease was confirmed for both forms of nitrogen ( t-test, p>0.05) .CC-BY-NC-ND 4.0 International licensemade available under a (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is The copyright holder for this preprintthis version posted June 30, 2024. ; https://doi.org/10.1101/2024.06.26.600925doi: bioRxiv preprint Table 1. Exchangeable bases, cation exchange capacity (CEC), base saturation percentage, K to Mg ratio, Ca to Mg, available phosphorus (P), resistivity (R) and pH of the study site at three depths (n=3). Depth P Exchangeable bases cmol(+) kg-1 K:Mg Ca:Mg CEC Base saturation % CEC R pH* cm mg kg-1 Ca Mg K Na cmol(+) kg-1 Ca Mg K Na ohm.cm 0-30 3.5 1.3 9.5 0.30 0.36 0.03 :1 0.14 :1 11.5 11 83 2.6 3.2 510 7.23 2.8 12 7.2 0.24 0.38 0.03 :1 1.67 :1 19.8 61 36 1.2 1.9 640 7.33 13 12 7.9 0.35 0.35 0.04 :1 1.53 :1 20.6 58 38 1.7 1.7 720 7.13 11 12 6.8 0.33 0.32 0.05 :1 1.76 :1 19.5 62 35 1.7 1.6 560 7.3 30-60 0.13 18 12.0 0.32 0.71 0.03 :1 1.50 :1 31.0 58 39 1.0 2.3 340 7.86 0.58 19 8.3 0.30 0.57 0.04 :1 2.28 :1 28.2 67 30 1.1 2.0 530 7.46 1.1 13 9.6 0.26 0.53 0.03 :1 1.36 :1 23.4 56 41 1.1 2.3 650 7.54 0.42 15 9.8 0.28 0.50 0.03 :1 1.53 :1 25.6 59 38 1.1 2.0 480 7.54 60-90 0.05 30 13.0 0.35 0.81 0.03 :1 2.31 :1 44.2 68 29 0.8 1.8 360 8.22 0.08 14 7.9 0.26 0.50 0.03 :1 1.78 :1 22.6 62 35 1.1 2.2 430 7.86 0.30 12 9.7 0.26 0.54 0.03 :1 1.24 :1 22.5 53 43 1.1 2.4 630 7.69 0.18 19 11.3 0.32 0.62 0.03 :1 1.68 :1 31.3 61 36 1.0 2.0 410 7.86 .CC-BY-NC-ND 4.0 International licensemade available under a (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is The copyright holder for this preprintthis version posted June 30, 2024. ; https://doi.org/10.1101/2024.06.26.600925doi: bioRxiv preprint Table 2. Average soil microbial activity (n=3) in the topsoil (0-30 cm) determined by the Solvita CO2 burst test and Potentially Mineralisable Nitrogen (PMN) analysis. Soil microbial activity and nitrogen potential release (NPR) were estimated according to the scale of microbial soil activity (Solvita® Guidelines, 2013) and consistently medium-high at the three sampling times. Sampling date CO2 (ppm) NH4-N (mg/kg) NO3-N (mg/kg) PMN (mg/kg) Sep-2022 64 ± 24a 1.57 ± 0.21a 1.19 ± 0.54a 1.05 ± 1.17a Oct-2022 77 ± 28a 1.20 ± 0.14b 0.64 ± 0.10a 1.37 ± 1.34a .CC-BY-NC-ND 4.0 International licensemade available under a (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is The copyright holder for this preprintthis version posted June 30, 2024. ; https://doi.org/10.1101/2024.06.26.600925doi: bioRxiv preprint

Abdalla, M., Hastings, A., Cheng, K., Yue, Q., Chadwick, D., Espenberg, M., Truu, J., Rees, R.M., Smith, P., 2019. A critical review of the impacts of cover crops on nitrogen leaching, net greenhouse gas balance and crop productivity. Global Change Biology 25, 2530– 2543. Acharya, P., Ghimire, R., Cho, Y., Thapa, V.R., Sainju, U.M., 2022. Soil profile carbon, nitrogen, and crop yields affected by cover crops in semiarid regions. Nutrient Cycling in Agroecosystems 122, 191–203. Af Geijersstam, L., Mårtensson, A., 2006. Nitrogen fixation and residual effects of field pea intercropped with oats. Acta Agriculturae Scandinavica. Section B. Soil and Plant Science 56, 186–196. Berntsen, J., Olesen, J.E., Petersen, B.M., Hansen, E.M., 2006. Long -term fate of nitrogen uptake in catch crops. European Journal of Agronomy: The Journal of the European Society for Agronomy 25, 383–390. Bossolani, J.W., Leite, M.F.A., Momesso, L., ten Berge, H., Bloem, J., Kuramae, E.E., 2023. Nitrogen input on organic amendments alters the pattern of soil –microbe-plant co - dependence. The Science of the Total Environment 890, 164347. Carey, P.L., Cameron, K.C., Di, H.J., Edwards, G.R., 2018. Does sowing an oats catch crop reduce nitrate leaching from urine deposition following simulated winter forage grazing? - a growth chamber experiment. Plant and Soil 431, 37–52. Chahal, I., Hooker, D.C., Deen, B., Janovicek, K., Van Eerd, L.L., 2021. Long-term effects of crop rotation, tillage, and fertilizer nitrogen on soil health indicators and crop productivity in a temperate climate. Soil and Tillage Research 213, 105121. Classification Working Group, S., n.d. Soil classification: a natural and anthropogenic system for South Africa. Agricultural Research Council, Institute for Soil. Constantin, J., Beaudoin, N., Laurent, F., Cohan, J.-P., Duyme, F., Mary, B., 2011. Cumulative effects of catch crops on nitrogen uptake, leaching and net mineralization. Plant and Soil 341, 137–154. Coskun, D., Britto, D.T., Shi, W., Kronzucker, H.J., 2017. Nitrogen transformations in modern agriculture and the role of biological nitrification inhibition. Nature Plants 3, 1–10. Cui, D., Liang, S., Wang, D., 2021. Observed and projected changes in global climate zones based on Köppen climate classification. Wiley Interdisciplinary Reviews. Climate Change 12. doi:10.1002/wcc.701 Davis, A.G., Huggins, D.R., Reganold, J.P., 2023. Linking soil health and ecological resilience to achieve agricultural sustainability. Frontiers in Ecology and the Environment 21, 131– 139. Daniell, A. and van Tonder, D.M., 2023. Opportunity for increasing the soil quality of non - arable and depleted soils in South Africa: A review. Journal of Soil Science and Plant Nutrition, 23(2), pp.2476-2487. Dontsova, K.M., Norton, L.D., Johnston, C.T., 2005. Calcium and magnesium effects on ammonia adsorption by soil clays. Soil Science Society of America Journal. Soil Science Society of America 69, 1225–1232. Duncombe, J., 2021. Index suggests that half of nitrogen applied to crops is lost. Eos 102. doi:10.1029/2021eo162300 FAO, 2004. Fodder Oats: A World Overview. Food & Agriculture Org. Fisk, L.M., Barton, L., Jones, D.L., Glanville, H.C., Murphy, D.V., 2015. Root exudate carbon .CC-BY-NC-ND 4.0 International licensemade available under a (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is The copyright holder for this preprintthis version posted June 30, 2024. ; https://doi.org/10.1101/2024.06.26.600925doi: bioRxiv preprint mitigates nitrogen loss in a semi-arid soil. Soil Biology & Biochemistry 88, 380–389. Gabriel, J.L., García-González, I., Quemada, M., Martin-Lammerding, D., Alonso-Ayuso, M., Hontoria, C., 2021. Cover crops reduce soil resistance to penetration by preserving soil surface water content. Geoderma 386, 114911. Gentsch, N., Heuermann, D., Boy, J., Schierding, S., von Wirén, N., Schweneker, D., Feuerstein, U., Kümmerer, R., Bauer, B., Guggenberger, G., 2022. Soil nitrogen and water management by winter-killed catch crops. SOIL 8, 269–281. Hailu, H., Mamo, T., Keskinen, R., Karltun, E., Gebrekidan, H., Bekele, T., 2015. Soil fertility status and wheat nutrient content in Vertisol cropping systems of central highlands of Ethiopia. Agriculture & Food Security 4, 19. Haney, R.L., Brinton, W.H., Evans, E., 2008. Estimating Soil Carbon, Nitrogen, and Phosphorus Mineralization from Short ‐Term Carbon Dioxide Respiration. Communications in Soil Science and Plant Analysis 39, 2706–2720. Havlin, J., 2020. Soil: Fertility and nutrient management. Landscape and Land Capacity 251– 265. Henryson, K., Kätterer, T., Tidåker, P., Sundberg, C., 2020. Soil N2O emissions, N leaching and marine eutrophication in life cycle assessment - A comparison of modelling approaches. The Science of the Total Environment 725, 138332. Ighodaro, I.D., Lategan, F., Mupindu, W., 2016. The impact of soil erosion as a food security and rural livelihoods risk in South Africa. The Journal of Agricultural Science 8, 1. Itps, F., 2015. Status of the world’s soil resources (SWSR)—Main report. Food and Agriculture Organization of the United Nations and Intergovernmental Technical Panel on Soils 650. Jackson, M.L., 2005. Soil Chemical Analysis: Advanced Course : a Manual of Methods Useful for Instruction and Research in Soil Chemistry, Physical Chemistry of Soils, Soil Fertility, and Soil Genesis. UW-Madison Libraries Parallel Press. Köppen, W.P., 1931. Grundriss der Klimakunde. W. de Gruyter. Kowalenko, C.G., Cameron, D.R., 1976. Nitrogen transformations in an incubated soil as affected by combinations of moisture content and temperature and adsorption-fixation of ammonium. Canadian Journal of Soil Science 56, 63–70. Laker, M.C., Nortjé, G.P., 2019. Review of existing knowledge on soil crusting in South Africa. Advances in Agronomy 155, 189–242. Leveau, A., Reed, J., Qiao, X., Stephenson, M.J., Mugford, S.T., Melton, R.E., Rant, J.C., Vickerstaff, R., Langdon, T., Osbourn, A., 2019. Towards take-all control: a C-21β oxidase required for acylation of triterpene defence compounds in oat. The New Phytologist 221, 1544–1555. Long, M., Donohue, S., L’Heureux, J. -S., Solberg, I. -L., Rønning, J.S., Limacher, R., O’Connor, P., Sauvin, G., Rømoen, M., Lecomte, I., 2012. Relationship between electrical resistivity and basic geotechnical parameters for marine clays. Canadian Geotechn ical Journal 49, 1158–1168. Maaz, T.M., Sapkota, T.B., Eagle, A.J., Kantar, M.B., Bruulsema, T.W., Majumdar, K., 2021. Meta-analysis of yield and nitrous oxide outcomes for nitrogen management in agriculture. Global Change Biology 27, 2343–2360. Malcolm, B.J., Cameron, K.C., Beare, M.H., Carrick, S.T., Payne, J.J., Maley, S.C., Di, H.J., Richards, K.K., Dalley, D.E., de Ruiter, J.M., 2022. Oat catch crop efficacy on nitrogen leaching varies after forage crop grazing. Nutrient Cycling in Agroecosystems 122, 273– 288. Michel, A.J., Malcolm, B.J., Maley, S., Jenkins, H.K., 2021. Sowing strategy of winter -sown oats catch crops affects crop development and nitrogen uptake [WWW Document]. URL .CC-BY-NC-ND 4.0 International licensemade available under a (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is The copyright holder for this preprintthis version posted June 30, 2024. ; https://doi.org/10.1101/2024.06.26.600925doi: bioRxiv preprint https://www.agronomysociety.org.nz/files/ASNZ_2021_05._Oat_catch_crops_sowing_st rategy.pdf (accessed 4.24.24). Milton, S.J., Dean, W.R., 1995. South Africa’s arid and semiarid rangelands: Why are they changing and can they be restored? Environmental Monitoring and Assessment 37, 245– 264. Moore, D.B., Guillard, K., Morris, T.F., Brinton, W.F., 2019. Correlation between Solvita Labile Amino-Nitrogen and CO2-Burst Soil Health Tests and Response to Organic Fertilizer in a Turfgrass Soil. Communications in Soil Science and Plant Analysis 50, 2948–2959. Morales, M.E., Iocoli, G.A., Allegrini, M., Villamil, M.B., Zabaloy, M.C., 2023. Response of root exudates and bacterial community to N fertilization and termination methods in Avena sativa L. as a winter cover crop model. European Journal of Soil Biology 114, 103453. Murano, H., Takata, Y., Isoi, T., 2015. Origin of the soil texture classification system used in Japan. Soil Science and Plant Nutrition 61, 688–697. Nieder, R., Benbi, D.K., Scherer, H.W., 2011. Fixation and defixation of ammonium in soils: a review. Biology and Fertility of Soils 47, 1–14. Ntalo, M., Ravhuhali, K.E., Moyo, B., Mmbi, N.E., Mokoboki, K.H., 2022. Physical and chemical properties of the soils in selected communal property associations of South Africa. PeerJ 10, e13960. Ozpinar, S., Baytekin, H., 2006. Effects of tillage on biomass, roots, N-accumulation of vetch (Vicia sativa L.) on a clay loam soil in semi -arid conditions. Field Crops Research 96, 235–242. Quemada, M., Delgado, A., Mateos, L., Villalobos, F.J., 2016. Nitrogen Fertilization I: The Nitrogen Balance, in: Villalobos, F.J., Fereres, E. (Eds.), Principles of Agronomy for Sustainable Agriculture. Springer International Publishing, Cham, pp. 341–368. Rasane, P., Jha, A., Sabikhi, L., Kumar, A., Unnikrishnan, V.S., 2015. Nutritional advantages of oats and opportunities for its processing as value added foods - a review. Journal of Food Science and Technology 52, 662–675. Rengasamy, P., Greene, R.S.B., Ford, G.W., 1986. Influence of magnesium on aggregate stability in sodic red-brown earths. Soil Research 24, 229–237. Rezaei Rashti, M., Wang, W., Moody, P., Chen, C., Ghadiri, H., 2015. Fertiliser -induced nitrous oxide emissions from vegetable production in the world and the regulating factors: A review. Atmospheric Environment 112, 225–233. Ritchie, H., 2017. How many people does synthetic fertilizer feed? Our World in Data. Roopnarain, A., Kidson, M.V., Mndzebele, B., Hernandez -Soriano, M.C., Ndaba, B., 2024. Role of Targeted Breeding to Improve Wheat Production on the Marginal Lands of Africa, in: Nciizah, A.D., Roopnarain, A., Ndaba, B., Malobane, M.E. (Eds.), The Marginal Soils of Africa: Rethinking Uses, Management and Reclamation. Springer Nature Switzerland, Cham, pp. 229–252. Scherer, H.W., 1993. Dynamics and availability of the non-exchangeable NH4-N — a review. European Journal of Agronomy: The Journal of the European Society for Agronomy 2, 149–160. Shew, A.M., Tack, J.B., Nalley, L.L., Chaminuka, P., 2020. Yield reduction under climate warming varies among wheat cultivars in South Africa. Nature Communications 11, 4408. Sumner, M., 2015. Soils of South Africa: Their distribution, properties, classification, genesis, use and environmental significance. Soil Science Society of America Journal, 79(4), p.1265. Tadesse, W., Bishaw, Z., Assefa, S., 2019. Wheat production and breeding in Sub -Saharan Africa. International Journal of Climate Change Strategies and Management 11, 696 – .CC-BY-NC-ND 4.0 International licensemade available under a (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is The copyright holder for this preprintthis version posted June 30, 2024. ; https://doi.org/10.1101/2024.06.26.600925doi: bioRxiv preprint 715. Talanow, K., Topp, E.N., Loos, J., Martín -López, B., 2021. Farmers’ perceptions of climate change and adaptation strategies in South Africa's Western Cape. Journal of Rural Studies 81, 203–219. Technicon AutoAnalyzer, I.I., n.d. Industrial/simulation determination of nitrogen and/or phosphorus in BD acid digests. Industrial Method. Tian, Z., Wang, J.-W., Li, J., Han, B., 2021. Designing future crops: challenges and strategies for sustainable agriculture. The Plant Journal: For Cell and Molecular Biology 105, 1165– 1178. Timilsena, Y.P., Adhikari, R., Casey, P., Muster, T., Gill, H., Adhikari, B., 2015. Enhanced efficiency fertilisers: a review of formulation and nutrient release patterns. Journal of the Science of Food and Agriculture 95, 1131–1142. Tongwane, M.I., Moeletsi, M.E., Tsubo, M., 2020. Trends of carbon emissions from applications of nitrogen fertiliser and crop residues to agricultural soils in South Africa. Journal of Environmental Management 272, 111056. Trofymow, J.A., Coleman, D.C., Cambardella, C., 1987. Rates of rhizodeposition and ammonium depletion in the rhizosphere of axenic oat roots. Plant and Soil 97, 333–344. Turner, T.R., Ramakrishnan, K., Walshaw, J., Heavens, D., Alston, M., Swarbreck, D., Osbourn, A., Grant, A., Poole, P.S., 2013. Comparative metatranscriptomics reveals kingdom level changes in the rhizosphere microbiome of plants. The ISME Journal 7, 2248–2258. van Huyssteen, C.W., 2020. Relating the South African soil taxonomy to the World Reference Base for soil resources. SunBonani Scholar. van Lierop, W., Tran, T.S., 1980. The comparative use of nitrate, ammonium and urea fertilizers by oats and wheat as determined by 15N ‐techniques. Communications in Soil Science and Plant Analysis 11, 231–250. van Zijl, G.V., Turner, D., Paterson, G., Koch, J., van Tol, J.V., Barichievy, K., Clarke, C., du Plessis, M., van Deventer, P.V., 2020. The new soil classification system in South Africa, its history, important changes made and implications for users. Sou th African Journal of Plant and Soil/Suid-Afrikaanse Tydskrift Plant En Grond 37, 331–342. Vogeler, I., Hansen, E.M., Thomsen, I.K., 2023. The effect of catch crops in spring barley on nitrate leaching and their fertilizer replacement value. Agriculture, Ecosystems & Environment 343, 108282. Yu, A.J., Lin, X., Zhu, J., He, H., Li, L. 2023. Environmental effects on ammonium adsorption onto clay minerals: Experimental constraints and applications, Applied Clay Science, 246. 107165 Zhalnina, K., Louie, K.B., Hao, Z., Mansoori, N., da Rocha, U.N., Shi, S., Cho, H., Karaoz, U., Loqué, D., Bowen, B.P., Firestone, M.K., Northen, T.R., Brodie, E.L., 2018. Dynamic root exudate chemistry and microbial substrate preferences drive patterns in rhizosp here microbial community assembly. Nature Microbiology 3, 470–480. .CC-BY-NC-ND 4.0 International licensemade available under a (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is The copyright holder for this preprintthis version posted June 30, 2024. ; https://doi.org/10.1101/2024.06.26.600925doi: bioRxiv preprint