Polyurethane Foam as a model platform for evaluating properties of soilless growing media

Polyurethane Foam as a model platform for evaluating properties of soilless growing media | 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 Polyurethane Foam as a model platform for evaluating properties of soilless growing media Harry C Wright, Samuel W Wilkinson, Stephen A Rolfe, Duncan D Cameron, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6890616/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 14 Oct, 2025 Read the published version in Frontiers in Horticulture → Version 1 posted You are reading this latest preprint version Abstract The increasing adoption of hydroponics and soilless cultivation techniques in food production has increased the demand for novel soilless growing media, presenting a unique opportunity for the development of customised media. Given the wide variety of crops and cultivation techniques used in soilless systems, optimising the physical properties of novel media for specific crops and systems presents both a challenge and an opportunity, as many growing media components provide only a single set of physical properties to work with. Polyurethane foams (PUFs), a promising soilless growing media, offer flexibility, as their formulation chemistry can be adjusted to produce foams with a diverse range of physical properties. This adaptability enables the tailoring of foams for specific crops and systems, providing valuable insights into optimised growing media “recipes” for various conditions. In this study, we examined 10 distinct PUF formulations with a range of physical properties through germination and growth trials. A preliminary investigation into whether physical or chemical characteristics of these media influence disease susceptibility was conducted by inoculating tomato plants with Pythium sp . An initial germination trial using lettuce and tomato identified four PUF formulations as unsuitable. A subsequent small scale growth trial demonstrated that the remaining six formulations performed comparably to mineral wool (MW) in terms of yield. Three of these formulations, which showed the highest yields, were then tested in yield trials for lettuce and pak choi in a nutrient film technique (NFT) system and for tomato using a dripper-fed system. Results indicated that two PUF formulations surpassed MW in vegetative yield in tomato trials, while two PUF formulations matched MW in lettuce yield in NFT trials. However, pak choi plants grown in foam displayed slightly lower yields than those in MW, although differences were not significant. All foam samples suppressed Pythium , as evidenced by no observed reductions in germination rates or seedling mass when compared to the uninfected samples, warranting further investigation into disease suppression potential. Overall, these yield results underscore that a “one size fits all” approach to soilless media formulation is inappropriate; rather, media should be optimised according to both hydroponic technique and crop type to maximise yields and other benefits. This study demonstrates that PUFs offer a valuable platform for developing tailored growing media "recipes" aligned with specific crop and system requirements. Horticulture Polymer Science growing media horticulture hydroponic mineral wool polyurethane foam soilless Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 1. Introduction The escalating challenges posed by global soil degradation and the increasing unpredictability of weather patterns due to climate change are placing significant pressure on traditional agricultural practices (FAO, 2015 ). This necessitates the exploration and adoption of alternative food production systems that are less reliant on conventional arable land. Among these alternatives, hydroponics or soilless cultivation, a controlled environment agriculture (CEA) technology, has emerged as a promising method for cultivating crops without soil whilst controlling the crop environment and circumventing many of the limitations associated with traditional farming, especially soil degradation and unpredictable changing weather patterns (Cowan et al., 2022 ). The remarkable advancements in the development of a large range soilless growing techniques over the past three to four decades have led to commercial scale cultivation of a range of crops, including leafy greens, herbs, flowers, vegetables, medicinal crops, fodder and fruits (Velazquez-Gonzalez et al., 2022 ), confirming soilless growing techniques as a leading technology in modern horticulture. In hydroponic and soilless cultivation, the soilless growing media serves as the foundational matrix that directly influences plant health and productivity by providing essential support, facilitating aeration, retaining crucial moisture, and enabling the delivery of nutrients to the plant roots (Gruda, 2019 ). Key physical attributes such as water holding capacity, aeration, porosity, bulk density, and drainage collectively determine the suitability of a media for optimal plant yield (Fields and Gruda, 2021 ). Water holding is crucial for maintaining adequate hydration of the root system without leading to waterlogged conditions. A media with good water retention ensures that plants can endure periods of reduced irrigation or fluctuating environmental conditions. Aeration, the provision of sufficient airflow around the roots, is equally vital for preventing root rot and promoting healthy plant growth. Inadequate aeration can lead to the buildup of carbon dioxide, which can be toxic to roots, and create an environment conducive to anaerobic pathogens that cause detrimental root diseases. Porosity, referring to the empty spaces within the growing media, is fundamental for both air circulation and water movement. Total porosity comprises both air porosity and water holding porosity, and an ideal medium typically exhibits a total porosity exceeding 60–70%, with an aeration porosity of at least 20–30% on a volume basis (Caron and Michel, 2021 ). The distribution of pore sizes is also critical, with macro pores (> 75 µm) facilitating aeration and drainage, while micro pores (< 30 µm) are responsible for water retention. A balanced distribution ensures both adequate oxygen supply and moisture availability. Bulk density of a porous material, the measure of a growing medium's mass relative to its volume, influences the stability of plant containers and can impact aeration. Generally, lower bulk density is associated with higher total porosity, which is beneficial for root health. However, sufficient bulk density is necessary to provide adequate physical support for larger plants, preventing them from toppling over. In addition to physical properties, chemical and biological properties are also important when designing a growing media. However, for this work, we examine chemically and biologically “inert” media, and therefore focus on physical properties. The inherent flexibility of soilless production systems allows growers to exercise greater control over environmental parameters, including the precise tailoring of growing media to meet the specific needs of different crops. It is well established that various plant species exhibit distinct preferences for the physical properties of their growing media, particularly concerning water retention and aeration. Furthermore, the requirements for the growing medium can also vary depending on the specific type of hydroponic system employed (Fussy and Papenbrock, 2022 ). The ability to precisely adjust the physical characteristics of a growing media for specific plant species and hydroponic systems holds significant potential for optimising root zone conditions, enhancing nutrient uptake efficiency, improving water utilisation, and ultimately achieving higher crop yields and superior quality (Fields and Gruda, 2021 ). For instance, leafy greens might thrive in lightweight, well aerated media, while fruiting plants may require media with higher water retention. Similarly, an ebb and flow system might benefit from a media with good water retention, whereas a deep-water culture system might perform better with a lightweight media that promotes oxygenation. A model growing media platform, based on a single type of material, that allows for the manipulation of physical properties would offer an invaluable tool for researchers and growers to systematically investigate and optimise growing conditions for a diverse range of plants and systems, potentially streamlining both experimentation and commercial production. Polyurethane (PU) foams, a versatile solid polymeric foam have long found application in horticulture with, in 1976, the issuance of the first patent for its use as a synthetic soil (Bardsley, 1976 ). Early investigations often utilised PU foam sourced from other industries, which were not specifically designed or optimised for horticultural purposes. However, more recent research endeavours, often in collaboration with polyurethane manufacturers, have focused on developing tailored foam formulations that can match or even surpass the performance of established synthetic media like mineral wool. Notably, PU foam media have demonstrated the potential for reuse over extended periods, lasting up to 10 years (Benoit and Ceustermans, 1995 ) and can even exhibit improved water holding capacity over successive cropping cycles due to the retention of organic matter from roots (Hardgrave, 1995 ). Even PUF that have not been optimised for plant growth have been shown to be useable for soilless horticulture, with recycled mattresses being used in NFT systems (Al Meselmani et al., 2020 ). Polyurethane foam plugs are now commonly employed as collars or supports in solution culture systems, indicating a specific and established role for this material in hydroponics. Flexible polyurethane foams (fPUF) possess many of the inherent characteristics required for successful soilless cultivation, including the mechanical strength necessary to anchor plants and a highly porous structure that facilitates the essential transfer of liquids and gases. The promising results observed with early, non-optimised foams spurred further scientific inquiry and development, leading to the creation of specialised formulations designed to enhance plant growth. The structural versatility of fPUF offers a platform for modelling plant media interactions due to the nature of their formulation chemistry which offer the ability to synthesise foams with a wide array of physical properties based on the same materials chemistry. By carefully adjusting the quantities of polyols, isocyanates, catalysts, stabilisers, and blowing agents during the manufacturing process, the cell size and overall pore architecture of flexible polyurethane foam can be controlled. Design of Experiment (DoE) techniques have been successfully employed to generate polyurethane foams with a broad spectrum of physical properties by systematically varying the ratios of catalysts, surfactants and additives (Wright et al., 2021a , b ) These experimental approaches have also enabled researchers to model the complex relationships between the physical properties of the foam and plant growth (Wright et al., 2021a , 2021b ).The inherent tunability of polyurethane foam makes it an ideal candidate for a model growing media, allowing researchers to systematically vary specific physical properties, such as water holding capacity and aeration, while maintaining other factors relatively constant. This controlled manipulation enables the isolation and study of the specific impact of these individual properties on plant growth and physiology, providing valuable insights into plant media interactions. By exploiting these properties of fPUF, the aim of this study is to determine whether fPUF growing media can be used as a model growing media platform to gain insight into plant media interactions, with particular interest in the effect of physical properties of the media on crop yield. 2. Materials and Methods 2.1. Materials To produce PUF materials, raw ingredients were as follows. DOW Chemical Company (Michigan, United States) kindly supplied Polyols, Voranol™ 3322 (a high propylene oxide content polyether triol), Voranol™ 1447 (a high ethylene oxide content polyether), isocyanate, SpecFlex™ NE 112, a low functionality methylene diphenyl diisocyanate (MDI) and surfactants Vorasurf™ 5906, a medium to high efficiency silicone siloxane and Vorasurf™ 5959, a silicone surfactant to be used as a cosurfactant to introduce finer cells/pneumaticity in production of flexible slabstock polyurethane foams. The catalyst Dabco® T (N-Methyl-N-(N,N-dimethylaminoethyl)-aminoethanol), a non-emissive amine catalyst that promotes the urea reaction, was kindly provided by Evonik Industries (Essen, Germany). The additive, Cloisite® NE 116, a sodium bentonite clay, was kindly provided by BYK-Chemie GmbH (Wesel, Germany). Deionised water was used as the blowing agent and all reagents were used as received. 2.2. Foam Formulation and Synthesis The ten foam formulations are given in Table 1 . The amounts of the two surfactants: S1 (Vorasurf™ 5906) and S2 (Vorasurf™ 5959) were varied systematically. This was based on previous work (Wright et al., 2022b ) that showed varying these two surfactants produced a set of foams with a large range of physical properties, particularly foams with varying cell size and open to closed cell ratios, the target of this study. For all formulations the isocyanate index (R) was kept constant at 1.2. All masses are reported in parts per hundred polyol (PPHP). Table 1 Polyurethane formulation for experiments, only the two surfactant concentrations are varied (slight MDI changes to ensure R = 1.2) Foam Voranol 1446 /PPHP Voranol 3322 /PPHP Water /PPHP Dabco T /PPHP S1 /PPHP S2 /PPHP Cloisite /PPHP MDI /PPHP F01 75 25 4 0.5 1.5 0 5 81.2 F02 75 25 4 0.5 1.5 0.5 5 81.7 F03 75 25 4 0.5 1.5 1 5 82.1 F04 75 25 4 0.5 1.5 2 5 82.8 F05 75 25 4 0.5 1.5 3 5 83.6 F06 75 25 4 0.5 0.6 0 5 80.9 F07 75 25 4 0.5 0.6 0.5 5 81.3 F08 75 25 4 0.5 0.6 1 5 81.7 F09 75 25 4 0.5 0.6 2 5 82.4 F10 75 25 4 0.5 0.6 3 5 83.2 Small scale isocyanate conversion foam trials were completed as follows. The polyisocyanate was weighed into a 30 ml syringe. The remaining reaction components were weighed into a 568 ml polypropylene cup and mixed at 3000 RPM for 45 seconds with an overhead mixer with a straight blade disk agitator. This mixture was allowed to debubble in a fume hood for 5 minutes before reacting. The polyisocyanate was added to the polypropylene cup and mixed at 1500 RPM for 6 seconds using the same overhead mixer/ stirrer combination. The reacting mixture was transferred immediately from the reaction vessel into a FoamPi (Wright et al., 2022a ) an apparatus developed specifically for measuring foam reaction kinetics, for 10 minutes before being transferred to a curing oven at 120°C for 20 minutes. The FoamPi was employed to ensure full isocyanate conversion, with the calculation detailed in Wright et al., 2022a . For determining all other properties, and for yield trials, PUF synthesis was scaled up by using a 25 x 25 x 25 cm box as the reaction vessel. This was lined with PTFE film to allow easy removal of the PUF. Mixing and reaction conditions were the same as the small-scale foam experiments. 2.3. Foam Characterisation Methods PUF density was determined according to ASTM D3574-11 Test A (ASTM Standard D3574-11, 2012 ). Foam pieces of size 50 mm × 50 mm × 25 mm were cut perpendicular to the foam rise direction, their dimensions determined using a digital Vernier calliper and their mass recorded. Mass and volume were used to determine PUF density. Analysis was done in triplicate and the mean and standard error are reported. PUF media cell size was determined according to ASTM D3576-15 (ASTM Standard D3576-15, 2014 ). A thin piece of foam was cut perpendicular to the rise direction. The surface of the foam was stained using a marker pen and imaged using optical microscopy. ImageJ (Rasband, n.d.) software was used to determine the cell size. A minimum of 200 cells was counted and the mean diameter and standard error reported. Water uptake of media was measured using an adaptation of the apparatus described by Schulker et al. (Schulker et al., 2021 ). Briefly, media samples were cut into 20 mm × 20 mm × 50 mm pieces and placed vertically in a sub irrigation system which irrigated the media for known time intervals to a height of 25 mm. This irrigation is repeated over several cycles to generate a water uptake curve. Sample mass was determined between each irrigation cycle. Triplicate samples were measured, and a water uptake curve is generated from this data with a fitted exponential decay curve. The fitting parameters of this curve give important insight into the water uptake of the media. Eq. ( 1 ) shows the equation used to fit the capillary rise data. where, H max is the maximum capillary rise height in cm, W UR is the rate of water uptake in cm s − 1 and t is the total sub irrigation time in seconds. The mean and standard error of these two fitting parameters is reported. Airflow through the foam was calculated according to ASTM D3574-11 test G (ASTM Standard D3574-11, 2012 ), whereby airflow (in L min -1 ) was measured through the sample at a standard pressure difference (125 Pa). A calibration curve was generated for determining the linear relationship between airflow and open cell content (Yasunaga et al., 1996 ) and the effective open cell fraction is reported. Analysis was done in triplicate and the mean and standard error are reported. 2.4. Germination / Growth Trials The two germination trials and two vegetative yield trials were performed in a temperature-controlled greenhouse at the Arthur Willis Environmental Centre (AWEC) at the University of Sheffield with a day/night regime of 12 h at 20°C/12 h at 15°C. Germination Trial 1 (GT1) was conducted between 2023/02/15 and 2023/02/22. Vegetative yield trial 1 (VYT1) was conducted between 2023/02/22 and 2023/03/29, using seedlings from GT1. Germination trial (GT2) was conducted between 2023/05/17 and 2023/05/25, Vegetative yield Trial 2 (VYT2) was conducted between 2023/05/25 and 2023/06/19 using seedlings from GT2. Tomato “Moneymaker” ( Solanum lycopersicum ), lettuce “little gem” ( Lactuca sativa ) and pak choi ( Brassica rapa var chinensis ) seeds were purchased from Suttons seeds (Devon, UK). Vitalink Hydromax SW two-part hydroponic nutrient was used for all germination and vegetative yield trials. For germination trials, media plugs were soaked in 4 mL L − 1 nutrient solution (2 mL L − 1 part A and 2 mL L − 1 part B) for 5 minutes before planting. For all vegetative yield trials, the nutrient concentration was 8 mL L − 1 (4 mL L − 1 part A and 4 mL L − 1 part B). All experiments were maintained at pH 6 using dilute phosphoric acid. For GT1 and GT2 20 seeds of each crop were germinated in individual growing media starter cubes of size 25 mm × 25 mm × 40 mm. Two separate hydroponic systems were used in VYT1 and VYT2, a recirculating hydroponic nutrient film technique (NFT) system, for lettuce and pak choi and a dripper fed open system for tomato. Drippers were pressure compensated 2 L h − 1 drippers used to provide irrigation for 5 equally spaced one-minute intervals in the daytime. For the dripper trial, tomato seedlings were transferred into larger media blocks of size 100 mm × 100 mm × 65 mm. For NFT crops, seedlings were transferred into the channels in their starter media blocks. For VYT1 four replicates were used for the tomato vegetative yield trial and seven replicates for the lettuce trial, the number of replicates was dictated by the maximum number of samples that could be run in the system. The reduced number of media in VYT2 meant more replicates could be completed. For this trial eight replicates were used in the tomato trial and ten replicates were used in the lettuce and pak choi trial. For germination and vegetative yield trials, days after planting is reported (DAP) as the number of days since seeds were sown in the media. 2.5. Pythium Infection Trial Pythium sp. isolates 2021 − 110 and 2021 − 116 were sourced from the Norwegian Institute of Bioeconomy Research (NIBIO) fungal culture collection. Both strains were isolated in 2012 from a tomato greenhouse. Isolates were confirmed as Pythium sp. by sequencing internal transcribed spacer 1, 5.8S ribosomal RNA gene, and internal transcribed spacer 2 using the ITS1oo (Riit et al., 2016 ) and ITS4 (White et al., 1990 ) primers, producing consensus sequences and searching for alignments in GenBank using BLASTN (Benson et al., 2012 ). Pythium sp. isolates were cultured for 7 days at 25°C in the dark and without shaking (Postma et al., 2005 ). Cultures consisted of a glycerol stock (1 mL 15% glycerol and plug of V8 juice agar covered in mycelium), revived from storage at -70°C, in V8 juice media which contained 4 mL V8 Juice (Campbell Soup Co., Camden, NJ, USA), 16 mL deionised H 2 O (dH 2 O) and 60 mg CaCO 3 . Inoculums were prepared by washing mycelial mats three or four times in dH 2 O, weighing mats to determine inoculum dose, blitzing for 30 s at low speed with a D-8 homogeniser (MICCRA, Buggingen, Germany) in 50–100 mL dH 2 0 and topping up to a final volume of 200–330 mL with dH 2 O. The final Pythium inoculum contained 5.5–9.5 g of mycelial mat per L per isolate. Seeds of tomato, lettuce, and pak choi were sown in individual growing media starter cubes (25 mm × 25 mm × 40 mm) pre-soaked in 4 ml per L of PlantStart propagation feed (Vitalink, Coventry, UK). For each crop and medium combination, 24 seeds were sown. Following sowing, starter plugs were inoculated with 1 mL of Pythium inoculum or 1 mL of dH 2 O as a control. In repeat three, 1 mL of Pythium inoculum or 1 mL of dH 2 O were added again at 2 days post sowing. Plugs were maintained for 14 days post sowing at the Arthur Willis Environmental Centre (AWEC), University of Sheffield, under a 12 h day/12 h night regime (20°C/15°C) within propagators at 100% relative humidity (RH). Germination was recorded every day and at 14 days post sowing (DAP) fresh weight of above ground tissue was measured. 2.6. Statistics For the analysis of the physical properties of the foams, the mean and standard error were reported. Germination trials, GT1 and GT2, were evaluated using Kaplan-Meier survival analyses for germination and cotyledon expansion, generated with the Lifelines package in Python (Davidson-Pilon, 2019 ). These survival curves were compared using pairwise log-rank tests, and media that exhibited significant differences from the mineral wool control were reported. For vegetative yield trials, VYT1 and VYT2, shoot fresh mass (SFM) and shoot dry mass (SDM) were analysed using a one-way ANOVA with growing media as the factor. These analyses were performed with the Statsmodels package in Python (Seabold and Perktold, 2010 ). When the ANOVA indicated significant differences between means, post hoc Tukey HSD tests were conducted using the SciPy stats package (Virtanen et al., 2020 ). Python 3.12.4 was used for all analyses and figure generation. 3. Results 3.1. PUF Physical Properties The density of the foams showed minimal variation, ranging from 24 to 29 kg m − 3 , classifying them as low-density foams. This limited density variation was expected, as only surfactant quantities were altered, which have a minimal impact on foam density (Fig. 1 A). Foam density decreased with increasing S2 concentration, reaching a minimum when S2 was 1 PPHP. Cell diameters ranged from 600 µm to 800 µm, typical for polyether flexible foams. Cell diameter decreased with increasing concentrations of either surfactant, reaching a minimum of approximately 600 µm (Fig. 1 B). The ten foams exhibited a uniform distribution of cell diameters, providing a spectrum suitable for testing. Effective open cell content ranged from 0.13 to 1 (zero indicates every cell is closed, and one that every cell is fully open), with several foams exhibiting fully open cells and others nearly completely closed cells (Fig. 1 C). Prior to this research (Wright et al., 2022b ) we have demonstrated that these properties are predictive of polyurethane foam hydrodynamic behaviour, a critical factor influencing plant growth (Wright et al., 2021a ). Consequently, the primary objective of the formulation was to generate foams with a wide range of cell structures. This variation in cell properties resulted in foams with diverse water uptake capacities, with fully closed cell foams exhibiting minimal water uptake (< 0.5 cm) and partially or fully open cell foams, particularly those with smaller cells, absorbing up to 3 cm of water (Fig. 1 D). Similarly, a broad range of water uptake rates (WUR) was achieved. WUR varied from near zero (~ 0 cm s − 1 ), particularly in samples with low effective open cell content due to restricted water ingress, with majority of samples having rates around 1 cm s − 1 and a few with the lowest surfactant loadings having rates nearing 0.15 cm s − 1 (Fig. 1 E). Physical properties for each formulation are summarised in Table 2 . Table 2 Physical properties of PUF formulations PUF Formulation ρ / kg m -3 d /µm P eff H max / cm W UR / cm s -1 F01 27.4 ± 0.20 784 ± 29 1 1.90 ± 0.02 0.129 ± 0.003 F02 26.6 ± 0.11 718 ± 21 1 2.76 ± 0.06 0.135 ± 0.016 F03 24.5 ± 0.05 679 ± 18 1 2.84 ± 0.03 0.074 ± 0.003 F04 (*) 24.8 ± 0.14 669 ± 17 0.694 ± 0.01 2.94 ± 0.14 0.023 ± 0.001 F05 23.7 ± 0.03 611 ± 13 0.373 ± 0.04 2.63 ± 0.21 0.010 ± 0.001 F06 28.8 ± 0.33 801 ± 28 1 1.85 ± 0.06 0.134 ± 0.018 F07 (**) 27.0 ± 0.14 683 ± 26 0.897 ± 0.07 3.07 ± 0.15 0.055 ± 0.003 F08 (*) 26.2 ± 0.04 624 ± 15 0.380 ± 0.03 2.35 ± 0.15 0.012 ± 0.001 F09 26.6 ± 0.13 569 ± 12 0.135 ± 0.01 0.397 ± 0.04 0.033 ± 0.003 F10 25.1 ± 0.09 594 ± 13 0.180 ± 0.01 0.613 ± 0.11 0.015 ± 0.001 *Indicates the two best performing foams in VYT2 for drip fed tomatoes; **indicates the best performing foam in VYT2 for lettuce in NFT systems . 3.2. Germination Trial (GT1) Germination fraction (Fig. 2 ) for the mineral wool control (MW) were 75% for tomato, and 70% for lettuce seeds germinating within 8 days. Germination fraction and Kaplan-Meier survivability curves for tomato and lettuce in foams F02 - F05, F07 and F08 were not significantly different from MW controls. Germination was notably reduced in four polyurethane foam (PUF) formulations: F01, F06, F09, and F10. This reduction was observed for both tomatoes (Fig. 2 A and B) and lettuce (Fig. 2 C and D) with all four Kaplan-Meier curves exhibiting significant deviations from the MW curve ( p < .05, pairwise log-rank test). Consequently, vegetative yield trial 1 (VYT1) proceeded with seedlings from the MW control and the six foam formulations (F02-F05, F07, and F08) where the Kaplan-Meier curves did not differ significantly from the MW curve. 3.3. Vegetative Yield Trial (VYT1) Seedlings from GT1 were transferred into an NFT hydroponic system (lettuce) and a dripper fed hydroponic system (tomato) for vegetative yield trial (VYT1). Lettuce was grown to yield, and tomatoes were grown until flowering began. The shoot fresh mass (SFM) and shoot dry mass (SDM) was measured for both lettuce and tomato. One way ANOVA indicated that there was no significant effect of media on the SFM or SDM for either of the crops (Fig. 3 and Table 3 ). Table 3 ANOVA table for VYT1. Crop Mass Sum Sq d.f. F value p Tomato SFM 4043 6,21 1.02 .434 Tomato SDM 31.13 6,21 1.25 .321 Lettuce SFM 6681 6,24 1.22 .314 Lettuce SDM 7.107 6,42 0.905 .500 Following the first vegetative yield trial (VYT1) the number of growing media formulations was reduced. This step was required to increase the number of replicates for the remaining candidates, thereby enhancing the statistical power of the experiment. However, due to limitations in the number of plants that could be accommodated in each system, increasing the number of replicates necessitated a reduction in the number of growing media tested. The two best performing foam media (based on mean shoot fresh mass) for each crop were carried forward to GT2 and VYT2. The best performing foam media were F07 and F08 for tomato, and F04 and F07 for lettuce with MW as a control as shown by the purple asterisk in Fig. 3 . Therefore, three foams were taken forward into GT2 and VYT2: F04, F07 and F08. 3.4. Multicrop/system Trial 3.4.1. Germination Trial (GT2) Germination rates in mineral wool (MW) control were > 0.85 for all three crops. All three foams matched the performance of MW for each crop. Kaplan-Meier survival analysis, followed by pairwise Log-rank tests, showed no significant differences in germination timing or rates between the foams the MW control in any of the crops (Fig. 4 ). This result was consistent with findings from GT1 and confirms that the foam media also supported pak choi germination comparably to the MW control. However, pak choi cotyledon emergence differed in the foam media compared to MW. Pak choi seedlings in foam opened their cotyledons under the media surface, likely due to light penetration through the foam structure (Fig. 5 ). This caused a slight initial lag in growth of pak choi grown in foams compared to MW. Further studies into optimal planting depth in foam, as well as the option of germinating seedlings in the dark, should be explored to mitigate this effect. 3.4.2. Vegetative yield Trial (VYT2) Seedlings from GT2 were transferred into an NFT hydroponic system (lettuce and pak choi) and a dripper fed hydroponic system (tomato) for the vegetative yield trial (VYT2). Lettuce and pak choi were grown to a harvestable stage, while tomatoes were grown until the onset of flowering. Shoot fresh mass (SFM) and shoot dry mass (SDM) were measured for both lettuce and tomato (Fig. 6 ). Growing media significantly affected SFM (ANOVA; F[3,28] = 5.38, p = .0047) and SDM (ANOVA; F[3,28] = 8.22, p = .0044) in the dripper fed tomato growth trial. Post-hoc analysis revealed that two foam based media (F04 and F08) yielded significantly higher SFM and SDM than the MW control (Tukey HSD test; p < .05). In contrast, F07 did not perform significantly differently from the MW control in VYT2, this is consistent with the results from VYT01. Consequently, two of the three foam media tested (F04 and F08) resulted in tomato growth that met or exceeded that observed in the MW control within this dripper fed system. Furthermore, the variation in both SFM and SDM for the tomato crops grown in the foams was similar to that of the MW crops. Notably, F04 produced the highest mean biomass (mean SFM and mean SDM). F08 yielded the second highest mean SFM and SDM, performing consistently with performance in VYT1. For the NFT system, growing media significantly affected the SFM (ANOVA; F[3,36] = 3.38, p = .029) and the SDM (ANOVA; F[3,36] = 6.81, p < 0.001) of the lettuce crop in VYT2. Post-hoc analysis showed that all three-foam media yielded similar SFM compared to the MW control; however, F08 showed slightly suppressed SFM, with two replicates having particularly low values. Post-hoc analysis of SDM indicated that F08 produced significantly lower SDM than the other two foam samples (F04, F07) and the MW control. The results of the VYT2 lettuce trial showed good agreement with VYT1 results compared to the tomato trial, particularly as F04 and F07 were the best performing media in terms of mean biomass in both VYT1 and VYT2. Consistent with this, F08, which was the fourth best performing medium in VYT1, was the lowest performing of the foam media in the VYT2 lettuce trial and was only selected for this trial due to performing well in tomato growth trials. For pak choi NFT trials, growing media did not significantly affect SFM (ANOVA; F[3,36] = 2.12, p = .115). However, growing media significantly affected SDM (ANOVA; F[3,36] = 3.17, p = .0357). Further post-hoc analysis on SDM indicated that there were no statistically significant differences between any two groups. All three-foam media exhibited a marginal decrease in total biomass (mean SFM and mean SDM) when compared to mineral wool. This reduction was likely a combination of suppressed early growth due to cotyledon emergence below the surface of the foam media and the pak choi exhibiting a preference for the root zone conditions provided by mineral wool, potentially due to differences in aeration or moisture retention. 3.5. Pythium infection trial Damping off, caused by oomycete pathogens of the genus Pythium is a problematic disease in hydroponic horticulture, particularly for young plants (Amrhein et al., 2025 ). To evaluate whether the physical properties of soilless growing media influences disease susceptibility in hydroponic systems, we inoculated plants grown in MW, F04, F07 or F08 with Pythium . As these Pythium isolates were sourced from a tomato greenhouse, only tomato was focused on for the disease assays. In tomato, Pythium sp. can cause seed decay along with pre- and post-emergence damping off (Gravel et al., 2005 ) Thus, we monitored germination and cotyledon emergence along with post emergence growth. In media inoculated with Pythium , the total fraction and timing of cotyledon emergence showed little change for the three-foam media (F04, F07, F08) compared to their respective controls. However, a marked decrease in cotyledon emergence was observed in mineral wool (MW), dropping from 0.95 (control) to 0.33 when challenged with Pythium . Pairwise Log-rank tests comparing the Pythium challenged groups indicated that the Kaplan-Meier survival curve for MW differed significantly from those for F07 and F08. No significant difference was found between the curves for the Pythium challenged F04 and MW media (Fig. 7 A-D). After 14 days, plants which had emerged were harvested, and weighted, shoot fresh mass (SFM) exhibited high variance across all samples, and mean SFM was comparable across all media types and treatments ( Pythium vs. control) for the surviving plants (Fig. 7 E). The reduced germination in MW but comparable SFM values among surviving plants across treatments (Fig. 7 D & E) suggests that pathogen induced mortality primarily occurred pre-emergence (damping off or seed decay), with minimal effects attributable to post-emergence damping off in this experiment. 4. Discussion To investigate the potential of polyurethane foams (PUF) as customisable hydroponic growing media, a set of ten foams exhibiting a range of physical properties was synthesised. The objective was to determine if optimising these properties could benefit specific crops or hydroponic systems compared to a 'one size fits all' growing media such as mineral wool. Formulation and synthesis were successful in generating variation among the ten foams regarding key target properties: open cell fraction, cell size, water uptake rate (W UR ), and maximum water uptake (H max ). These foams subsequently underwent two germination and two vegetative yield trials to evaluate their performance against a standard mineral wool (MW) control. Following the initial germination trial, four foam formulations were excluded from further testing due to significantly lower germination and/or germination rates compared to the MW control. Examination of the normalised physical properties of these four unsuccessful formulations provides insight into potential reasons for their poor performance. Analysis revealed that these four foams had properties at the extremes of the range. They included the two formulations with the largest and the two with the smallest cell sizes as well as those with the highest and lowest effective open cell fractions (Table 2 ). As previously demonstrated (Wright et al., 2022b ) cell size and open cell fraction strongly influence water uptake characteristics. Correspondingly, these four foams exhibited the lowest H max values among all ten formulations. Furthermore, PCA analysis (Fig. 8 ) revealed that this group was made up of two subgroups, each consisting of two foams (Fig. 8 ; pink dots). These two groups different along axis that correlated with the vectors W ur and p eff . Two had very high-water uptake rates, and two had low water uptake rates. These findings suggest two distinct failure modes related to inadequate water management within the root zone. Firstly, the two foams characterised by small, predominantly closed cells likely impeded capillary action, resulting in both slow water uptake rates and low maximum capillary rise. (H max ). Secondly, the two foams with large, mostly open cells, while potentially allowing rapid initial water uptake, likely also exhibited excessive drainage, ultimately leading to similarly low H max values. In both scenarios, the resulting suboptimal water availability (either too little retention or too rapid drainage) likely contributed directly to the observed poor germination rates. The poor performance of these four formulations provides important insights into the boundary conditions for designing effective PUF based growing media. Notably, these results suggest that successful PUF media require a sufficient minimum water retention (H max ). Achieving this appears dependent on attaining a balanced pore structure, likely characterised by partially interconnected pores (avoiding extremes of fully open or closed structures) and moderate cell sizes. In the initial vegetative yield trial (VYT1), tomato and lettuce yields were comparable across the tested media. Based on performance in the initial germination (GT1) and vegetative yield (VYT1) trials, the three most promising foam formulations (F04, F07, and F08) were selected for further evaluation. In subsequent germination tests (GT2), these three selected foams demonstrated germination and rates comparable to MW for all three tested crops: tomato, lettuce, and pak choi. A second vegetative yield trial (VYT2) directly compared these three selected foams against MW using two distinct hydroponic systems tailored to different crops: a dripper fed system for tomatoes and a nutrient film technique (NFT) system for lettuce and pak choi. In the dripper system used for tomatoes, foams F04 and F08 produced significantly higher vegetative yields than MW, whilst F07 yielded comparably to the MW control. Conversely, in the NFT system used for lettuce, foams F04 and F07 produced yields comparable to MW, whereas F08 performed significantly worse ( p < .05). Between the two foams matching MW performance in the lettuce/NFT trial, F07 achieved the higher mean vegetative yield. Yield in the pak choi trial was similar between the three-foam media and the MW control, with all three foams performing slightly worse than the MW control, likely due to crops germinating below the surface of the foam, hampering early growth. Analysis of the relationship between hydroponic performance and material properties provides insights into optimisation for specific systems. Examination of the hydrodynamic properties associated with the highest yielding foams in the tomato/dripper system (F04 and F08; Fig. 8 ; purple triangles and asterisks in Table 2 ) reveals relatively slow water uptake rates coupled with high maximum capillary rise. These characteristics are advantageous for an intermittent dripper system, as slower water uptake and potentially slower release (implied by high capillary retention) help maintain media moisture and nutrient availability between irrigation events. Structurally, these foams (F04, F08) possessed moderate cell sizes and effective open cell contents relative to the full range synthesised. In contrast, the best performing foam for lettuce in the NFT system (F07) exhibited faster water uptake rates compared to F04/F08, slightly higher maximum capillary rise, a more open cell structure (higher open cell content), but similarly moderate cell sizes (Fig. 8 ; yellow inverted triangle and asterisks in Table 2 ). This more open structure is likely advantageous in an NFT system, where the media's role in water retention is less critical due to continuous nutrient solution flow. Furthermore, the open cells may facilitate easier root anchorage and subsequent penetration through the media into the NFT channel. These initial trials indicate that a “one size fits all” approach to growing media is unlikely to produce media that is crop and system optimised and furthermore that PUF media can be used as a platform to determine growing media physical property “recipes”, that are both crop and system optimised. Finally, these media were also subjected to a pathogen screen to determine whether PUF influences the biological facet of growing media use. PUF appeared to reduce the effect of a Pythium pathogen on germination of tomato plants. Compared to the MW medium, the reduced early mortality observed in two of the foam media (F07 and F08) under Pythium challenge was an unexpected finding, suggesting that these foam media may possess disease suppressive properties against this pathogen. Potential explanations warrant investigation: the physical properties of the foam surface may be less conducive to Pythium proliferation compared to MW; a chemical component or property of the foam might possess antimicrobial activity effective against the oomycete pathogen, or the foams alter root properties or induce resistance mechanisms in the host. Further investigation of the mechanism of this disease suppression is required to understand how microbes interact with the foam media before utilising these foams as model growing platforms in experiments involving biological factors, such as pathogen screening or the application of beneficial plant health or growth promoting microorganisms. In conclusion, this study demonstrates that a single 'one size fits all' growing media formulation is not optimal for different crops and hydroponic systems. Furthermore, it demonstrates the potential of PUFs as a versatile platform for developing tailored growing media recipes, allowing for the identification of physical property attributes optimal for a given crop and system requirements. Declarations Authors Contributions Conceptualisation: HCW, AJR, SWW, SAR; Methodology: HCW, SWW; Software: HCW; Validation: HCW, SWW; Investigation: HCW, SWW; Data Curation: HCW, SWW; Formal Analysis: HCW, SWW; Writing – Original Draft: HCW; Writing Review and Editing: HCW, SAR, DDC, AJR, SWW; Visualization: HCW; Supervision: DDC, AJR, SAR; Funding Acquisition: DDC, AJR, SAR, HCW. Acknowledgements The authors would like to acknowledge the contributions of Caleb Morgan who conducted ITS sequencing of the Pythium strains. This work is supported by the ‘Transforming UK food systems’ research programme via UKRI’s Strategic Priorities Fund (BB/V004719/1) as well as BBSRC Protected and Controlled Environment horticulture research programme (BB/Z514433/1). Data availability statement. The data that support the findings of this study are openly available at : 10.15131/shef.data.29314193 References Al Meselmani, M. A., Wright, H. C., Cameron, D. D., and Ryan, A. J. (2020). How scientists and refugees brought green to the Desert Garden. Nat. Rev. Earth Environ. 1, 439. doi: 10.1038/s43017-020-0081-7 Amrhein, J. J., Rotondo, F., Kubota, C., Miller, S. A., and Testen, A. L. (2025). Diagnostic Guide for Pythium Root Rot in Hydroponic Leafy Green and Herb Production. Plant Heal. Prog. 26, 87–95. doi: 10.1094/PHP-07-24-0070-DG ASTM Standard D3574-11 (2012). Standard Test Methods for Flexible Cellular Materials—Slab, Bonded, and Molded Urethane Foams . 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(1990). “AMPLIFICATION AND DIRECT SEQUENCING OF FUNGAL RIBOSOMAL RNA GENES FOR PHYLOGENETICS,” in PCR Protocols , (Elsevier), 315–322. doi: 10.1016/B978-0-12-372180-8.50042-1 Wright, H. C., Cameron, D. D., and Ryan, A. J. (2021a). Experimental design as a framework for optimising polyurethane foam as a soilless growing media. Acta Hortic. 1317, 125–132. doi: 10.17660/ActaHortic.2021.1317.15 Wright, H. C., Cameron, D. D., and Ryan, A. J. (2022a). FoamPi: An open-source raspberry Pi based apparatus for monitoring polyurethane foam reactions. HardwareX 12, e00365. doi: 10.1016/j.ohx.2022.e00365 Wright, H. C., Cameron, D. D., and Ryan, A. J. (2022b). Rational Design of a Polyurethane Foam. Polymers (Basel). 14, 5111. doi: 10.3390/polym14235111 Wright, H. C., Zhu, J., Cameron, D. D., and Ryan, A. J. (2021b). Flexible polyurethane foam with sodium bentonite: improving the properties of foams for use as a synthetic growing media. Acta Hortic. , 47–54. doi: 10.17660/ActaHortic.2021.1305.7 Yasunaga, K., Neff, R. A., Zhang, X. D., and Macosko, C. W. (1996). Study of Cell Opening in Flexible Polyurethane Foam. J. Cell. Plast. 32, 427–448. doi: 10.1177/0021955X9603200502 Additional Declarations The authors declare no competing interests. Cite Share Download PDF Status: Published Journal Publication published 14 Oct, 2025 Read the published version in Frontiers in Horticulture → 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. 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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-6890616","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":471075369,"identity":"ede96d62-5898-4c3f-9247-755e044f8adf","order_by":0,"name":"Harry C Wright","email":"data:image/png;base64,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","orcid":"https://orcid.org/0000-0003-0741-1251","institution":"University of Sheffield","correspondingAuthor":true,"prefix":"","firstName":"Harry","middleName":"C","lastName":"Wright","suffix":""},{"id":471075370,"identity":"f965176b-5831-4529-b0c2-f6f2cc306084","order_by":1,"name":"Samuel W Wilkinson","email":"","orcid":"https://orcid.org/0000-0002-4908-8766","institution":"University of York","correspondingAuthor":false,"prefix":"","firstName":"Samuel","middleName":"W","lastName":"Wilkinson","suffix":""},{"id":471075371,"identity":"655b0abd-2b69-4106-97d7-2eb1916a324c","order_by":2,"name":"Stephen A Rolfe","email":"","orcid":"https://orcid.org/0000-0003-2141-4707","institution":"University of Sheffield","correspondingAuthor":false,"prefix":"","firstName":"Stephen","middleName":"A","lastName":"Rolfe","suffix":""},{"id":471075372,"identity":"adc37834-bf9c-47c8-947f-5d429441a746","order_by":3,"name":"Duncan D Cameron","email":"","orcid":"https://orcid.org/0000-0002-5439-6544","institution":"University of Manchester","correspondingAuthor":false,"prefix":"","firstName":"Duncan","middleName":"D","lastName":"Cameron","suffix":""},{"id":471075373,"identity":"f3702ab4-30a5-4f6e-9594-5617d6e00ebf","order_by":4,"name":"Anthony J Ryan","email":"","orcid":"https://orcid.org/0000-0001-7737-0526","institution":"University of Sheffield","correspondingAuthor":false,"prefix":"","firstName":"Anthony","middleName":"J","lastName":"Ryan","suffix":""}],"badges":[],"createdAt":"2025-06-13 20:23:10","currentVersionCode":1,"declarations":{"humanSubjects":false,"vertebrateSubjects":false,"conflictsOfInterestStatement":false,"humanSubjectEthicalGuidelines":false,"humanSubjectConsent":false,"humanSubjectClinicalTrial":false,"humanSubjectCaseReport":false,"vertebrateSubjectEthicalGuidelines":false},"doi":"10.21203/rs.3.rs-6890616/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6890616/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.3389/fhort.2025.1646783","type":"published","date":"2025-10-15T00:00:00+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":84956699,"identity":"c7eef34a-4474-442b-b713-51d1b48e0252","added_by":"auto","created_at":"2025-06-19 08:23:11","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":583473,"visible":true,"origin":"","legend":"\u003cp\u003ePhysical and hydrodynamic properties of PUF growing media at different surfactant-1 (S1) and surfactant-2 loadings (S2). Properties are shown for: density, ρ, (A), cell diameter, d, (B), effective open cell content, P\u003csub\u003eeff\u003c/sub\u003e, (C), maximum water uptake height, H\u003csub\u003emax\u003c/sub\u003e, (D) and water uptake rate, W\u003csub\u003eUR\u003c/sub\u003e, (E). Results are means +/- SE.\u003c/p\u003e","description":"","filename":"Figure1.png","url":"https://assets-eu.researchsquare.com/files/rs-6890616/v1/74b8c87c07419b441e8f6d48.png"},{"id":84956749,"identity":"bdeff763-7f73-442c-a94d-b9d31f59302f","added_by":"auto","created_at":"2025-06-19 08:23:13","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":692217,"visible":true,"origin":"","legend":"\u003cp\u003eKaplan-Meier curves for the probability of a seed not germinating over time as well as the germination fraction for tomato seeds (A and B respectively) and lettuce seeds (C and D respectively). Black lines indicate mineral wool samples, pink indicates PUF samples where \u003cem\u003ep \u0026gt; \u003c/em\u003e.05 (pairwise Log-rank test) when compared to mineral wool curves and blue lines indicate where \u003cem\u003ep \u0026lt; \u003c/em\u003e.05 (pairwise Log-rank test) when compared to mineral wool curves.\u003c/p\u003e","description":"","filename":"Figure2.png","url":"https://assets-eu.researchsquare.com/files/rs-6890616/v1/5d90e5e80d8f0532513eaf8c.png"},{"id":84956733,"identity":"209d972b-ee54-405c-aab2-8470d6eae904","added_by":"auto","created_at":"2025-06-19 08:23:12","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":957963,"visible":true,"origin":"","legend":"\u003cp\u003eShoot fresh mass and shoot dry mass for tomato (A and B respectively) and lettuce (C and D respectively) grown in different growing media. Mineral wool is shown in black; pink indicates PUF formulations where \u003cem\u003ep\u003c/em\u003e \u0026gt; .05 between the formulation and mineral wool samples and blue indicates PUF formulations where \u003cem\u003ep\u003c/em\u003e \u0026lt; .05 between the formulation and mineral wool samples (Tukey’s HSD test). The thick black line in the box plots indicate the median, the box indicates the IQR, and the whiskers show 1.5 × IQR. The purple asterisks indicate the two foam media for each crop that had the largest mean SFM value.\u003c/p\u003e","description":"","filename":"Figure3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6890616/v1/b59a73324a4bceec36a243ac.jpg"},{"id":84956709,"identity":"aa0ff1a3-2c30-4b1b-b38f-f282adf1cfe1","added_by":"auto","created_at":"2025-06-19 08:23:11","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":456210,"visible":true,"origin":"","legend":"\u003cp\u003eKaplan-Meier curves for the probability of a seed not germinating over time and the germination fraction for tomato seeds (A and D respectively). Kaplan-Meier curves for probability of not germinating and germination fraction for lettuce seeds (B and E respectively) and Kaplan-Meier curves for probability of not germinating and fraction for pak choi seeds (C and F respectively). Black lines indicate mineral wool samples, pink indicates PUF samples where \u003cem\u003ep \u0026gt; \u003c/em\u003e.05 (pairwise Log-rank test) when compared to mineral wool curves.\u003c/p\u003e","description":"","filename":"Figure4.png","url":"https://assets-eu.researchsquare.com/files/rs-6890616/v1/86ea8fa5cf0d4213dbe6c237.png"},{"id":84956737,"identity":"2fca75dc-6750-4b93-90f7-19fe9918eba1","added_by":"auto","created_at":"2025-06-19 08:23:12","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":2748973,"visible":true,"origin":"","legend":"\u003cp\u003ePak Choi seedling grown in MW (A) and foam (B) growing media, showing cotyledons opening under the surface of the foam media.\u003c/p\u003e","description":"","filename":"Figure5.png","url":"https://assets-eu.researchsquare.com/files/rs-6890616/v1/1642d2e15a394a11775b0c18.png"},{"id":84956720,"identity":"f213b51e-50e8-4079-91f3-c896b3457485","added_by":"auto","created_at":"2025-06-19 08:23:11","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":1243160,"visible":true,"origin":"","legend":"\u003cp\u003eShoot fresh mass and shoot dry mass for tomato (A and B respectively), lettuce (C and D respectively) and pak choi (E and F respectively) grown in different growing media. Differing letters indicate \u003cem\u003ep \u0026lt; \u003c/em\u003e.05 (Tukey’s HSD test), mineral wool is shown in black, pink indicates where PUF formulations where \u003cem\u003ep\u003c/em\u003e \u0026gt; .05 between the formulation and mineral wool samples and blue indicates PUF formulations where \u003cem\u003ep\u003c/em\u003e\u0026lt; .05 between the formulation and mineral wool samples (Tukey’s HSD test). The thick black line in the box plots indicate the median, the box indicates the IQR, and the whiskers show 1.5 × IQR.\u003c/p\u003e","description":"","filename":"Figure6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6890616/v1/f0a0b5dcad46007777f58776.jpg"},{"id":84956717,"identity":"88d26ab7-b012-4da3-a55a-c35307cda0cc","added_by":"auto","created_at":"2025-06-19 08:23:11","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":592344,"visible":true,"origin":"","legend":"\u003cp\u003eKaplan-Meier plots showing the probability of cotyledons not emerging, for the three-foam media, F04 (A); F07 (B); F08 (C) and the MW control (D), in the \u003cem\u003ePythium\u003c/em\u003e infection germination trial. The pink line indicates plants infected with \u003cem\u003ePythium\u003c/em\u003eand the blue indicates those inoculated with distilled water control. The mass of the SFM harvested at 14 DAP for the four media as well as the MW control (E). The thick black line in the box plots indicate the median, the box indicates the IQR, and the whiskers show 1.5 × IQR. The results shown are representative of three experimental repeats.\u003c/p\u003e","description":"","filename":"Figure7.png","url":"https://assets-eu.researchsquare.com/files/rs-6890616/v1/006a1ff1cd6d4a61d38935bb.png"},{"id":84957725,"identity":"eab6fb0b-5d67-4857-8ad4-f50462caadd1","added_by":"auto","created_at":"2025-06-19 08:31:11","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":357130,"visible":true,"origin":"","legend":"\u003cp\u003ePrincipal component analysis (PCA) of the physical properties of the FPUF growing media. The plot visualises the relationships between media based on their physical properties and shows their progression through the experimental selection process. PC1 (65.8 %) and PC2 (26.5 %) are displayed. Each point represents a unique PUF foam (means of physical properties used) and they are categorised as follows. Pink dots are formulations that were dropped after GT1, blue squares are formulations dropped after VYT1, purple triangles are the best performing formulations for tomato in VYT2 and yellow upside-down triangles is the best performing formulation for lettuce in VYT2. The vectors show the loadings of the measured physical properties.\u003c/p\u003e","description":"","filename":"Figure8.png","url":"https://assets-eu.researchsquare.com/files/rs-6890616/v1/09d873df845ba7f6d4898fe6.png"},{"id":93693860,"identity":"c7002686-4edd-440b-9c36-de647568a80d","added_by":"auto","created_at":"2025-10-16 14:24:30","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":11433361,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6890616/v1/60e8ea1a-3132-4a4c-92e0-a1c17ab04b73.pdf"}],"financialInterests":"The authors declare no competing interests.","formattedTitle":"\u003cp\u003ePolyurethane Foam as a model platform for evaluating properties of soilless growing media\u003c/p\u003e","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThe escalating challenges posed by global soil degradation and the increasing unpredictability of weather patterns due to climate change are placing significant pressure on traditional agricultural practices (FAO, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). This necessitates the exploration and adoption of alternative food production systems that are less reliant on conventional arable land. Among these alternatives, hydroponics or soilless cultivation, a controlled environment agriculture (CEA) technology, has emerged as a promising method for cultivating crops without soil whilst controlling the crop environment and circumventing many of the limitations associated with traditional farming, especially soil degradation and unpredictable changing weather patterns (Cowan et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). The remarkable advancements in the development of a large range soilless growing techniques over the past three to four decades have led to commercial scale cultivation of a range of crops, including leafy greens, herbs, flowers, vegetables, medicinal crops, fodder and fruits (Velazquez-Gonzalez et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), confirming soilless growing techniques as a leading technology in modern horticulture.\u003c/p\u003e \u003cp\u003eIn hydroponic and soilless cultivation, the soilless growing media serves as the foundational matrix that directly influences plant health and productivity by providing essential support, facilitating aeration, retaining crucial moisture, and enabling the delivery of nutrients to the plant roots (Gruda, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Key physical attributes such as water holding capacity, aeration, porosity, bulk density, and drainage collectively determine the suitability of a media for optimal plant yield (Fields and Gruda, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Water holding is crucial for maintaining adequate hydration of the root system without leading to waterlogged conditions. A media with good water retention ensures that plants can endure periods of reduced irrigation or fluctuating environmental conditions. Aeration, the provision of sufficient airflow around the roots, is equally vital for preventing root rot and promoting healthy plant growth. Inadequate aeration can lead to the buildup of carbon dioxide, which can be toxic to roots, and create an environment conducive to anaerobic pathogens that cause detrimental root diseases. Porosity, referring to the empty spaces within the growing media, is fundamental for both air circulation and water movement. Total porosity comprises both air porosity and water holding porosity, and an ideal medium typically exhibits a total porosity exceeding 60\u0026ndash;70%, with an aeration porosity of at least 20\u0026ndash;30% on a volume basis (Caron and Michel, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). The distribution of pore sizes is also critical, with macro pores (\u0026gt;\u0026thinsp;75 \u0026micro;m) facilitating aeration and drainage, while micro pores (\u0026lt;\u0026thinsp;30 \u0026micro;m) are responsible for water retention. A balanced distribution ensures both adequate oxygen supply and moisture availability. Bulk density of a porous material, the measure of a growing medium's mass relative to its volume, influences the stability of plant containers and can impact aeration. Generally, lower bulk density is associated with higher total porosity, which is beneficial for root health. However, sufficient bulk density is necessary to provide adequate physical support for larger plants, preventing them from toppling over. In addition to physical properties, chemical and biological properties are also important when designing a growing media. However, for this work, we examine chemically and biologically \u0026ldquo;inert\u0026rdquo; media, and therefore focus on physical properties.\u003c/p\u003e \u003cp\u003eThe inherent flexibility of soilless production systems allows growers to exercise greater control over environmental parameters, including the precise tailoring of growing media to meet the specific needs of different crops. It is well established that various plant species exhibit distinct preferences for the physical properties of their growing media, particularly concerning water retention and aeration. Furthermore, the requirements for the growing medium can also vary depending on the specific type of hydroponic system employed (Fussy and Papenbrock, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). The ability to precisely adjust the physical characteristics of a growing media for specific plant species and hydroponic systems holds significant potential for optimising root zone conditions, enhancing nutrient uptake efficiency, improving water utilisation, and ultimately achieving higher crop yields and superior quality (Fields and Gruda, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). For instance, leafy greens might thrive in lightweight, well aerated media, while fruiting plants may require media with higher water retention. Similarly, an ebb and flow system might benefit from a media with good water retention, whereas a deep-water culture system might perform better with a lightweight media that promotes oxygenation. A model growing media platform, based on a single type of material, that allows for the manipulation of physical properties would offer an invaluable tool for researchers and growers to systematically investigate and optimise growing conditions for a diverse range of plants and systems, potentially streamlining both experimentation and commercial production.\u003c/p\u003e \u003cp\u003ePolyurethane (PU) foams, a versatile solid polymeric foam have long found application in horticulture with, in 1976, the issuance of the first patent for its use as a synthetic soil (Bardsley, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e1976\u003c/span\u003e). Early investigations often utilised PU foam sourced from other industries, which were not specifically designed or optimised for horticultural purposes. However, more recent research endeavours, often in collaboration with polyurethane manufacturers, have focused on developing tailored foam formulations that can match or even surpass the performance of established synthetic media like mineral wool. Notably, PU foam media have demonstrated the potential for reuse over extended periods, lasting up to 10 years (Benoit and Ceustermans, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e1995\u003c/span\u003e) and can even exhibit improved water holding capacity over successive cropping cycles due to the retention of organic matter from roots (Hardgrave, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e1995\u003c/span\u003e). Even PUF that have not been optimised for plant growth have been shown to be useable for soilless horticulture, with recycled mattresses being used in NFT systems (Al Meselmani et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Polyurethane foam plugs are now commonly employed as collars or supports in solution culture systems, indicating a specific and established role for this material in hydroponics. Flexible polyurethane foams (fPUF) possess many of the inherent characteristics required for successful soilless cultivation, including the mechanical strength necessary to anchor plants and a highly porous structure that facilitates the essential transfer of liquids and gases. The promising results observed with early, non-optimised foams spurred further scientific inquiry and development, leading to the creation of specialised formulations designed to enhance plant growth.\u003c/p\u003e \u003cp\u003eThe structural versatility of fPUF offers a platform for modelling plant media interactions due to the nature of their formulation chemistry which offer the ability to synthesise foams with a wide array of physical properties based on the same materials chemistry. By carefully adjusting the quantities of polyols, isocyanates, catalysts, stabilisers, and blowing agents during the manufacturing process, the cell size and overall pore architecture of flexible polyurethane foam can be controlled. Design of Experiment (DoE) techniques have been successfully employed to generate polyurethane foams with a broad spectrum of physical properties by systematically varying the ratios of catalysts, surfactants and additives (Wright et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2021a\u003c/span\u003e, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003eb\u003c/span\u003e) These experimental approaches have also enabled researchers to model the complex relationships between the physical properties of the foam and plant growth (Wright et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2021a\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2021b\u003c/span\u003e).The inherent tunability of polyurethane foam makes it an ideal candidate for a model growing media, allowing researchers to systematically vary specific physical properties, such as water holding capacity and aeration, while maintaining other factors relatively constant. This controlled manipulation enables the isolation and study of the specific impact of these individual properties on plant growth and physiology, providing valuable insights into plant media interactions.\u003c/p\u003e \u003cp\u003eBy exploiting these properties of fPUF, the aim of this study is to determine whether fPUF growing media can be used as a model growing media platform to gain insight into plant media interactions, with particular interest in the effect of physical properties of the media on crop yield.\u003c/p\u003e"},{"header":"2. Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n \u003ch2\u003e2.1. Materials\u003c/h2\u003e\n \u003cp\u003eTo produce PUF materials, raw ingredients were as follows. DOW Chemical Company (Michigan, United States) kindly supplied Polyols, Voranol\u0026trade; 3322 (a high propylene oxide content polyether triol), Voranol\u0026trade; 1447 (a high ethylene oxide content polyether), isocyanate, SpecFlex\u0026trade; NE 112, a low functionality methylene diphenyl diisocyanate (MDI) and surfactants Vorasurf\u0026trade; 5906, a medium to high efficiency silicone siloxane and Vorasurf\u0026trade; 5959, a silicone surfactant to be used as a cosurfactant to introduce finer cells/pneumaticity in production of flexible slabstock polyurethane foams. The catalyst Dabco\u0026reg; T (N-Methyl-N-(N,N-dimethylaminoethyl)-aminoethanol), a non-emissive amine catalyst that promotes the urea reaction, was kindly provided by Evonik Industries (Essen, Germany). The additive, Cloisite\u0026reg; NE 116, a sodium bentonite clay, was kindly provided by BYK-Chemie GmbH (Wesel, Germany). Deionised water was used as the blowing agent and all reagents were used as received.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\n \u003ch2\u003e2.2. Foam Formulation and Synthesis\u003c/h2\u003e\n \u003cp\u003eThe ten foam formulations are given in Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e. The amounts of the two surfactants: S1 (Vorasurf\u0026trade; 5906) and S2 (Vorasurf\u0026trade; 5959) were varied systematically. This was based on previous work (Wright et al., \u003cspan class=\"CitationRef\"\u003e2022b\u003c/span\u003e) that showed varying these two surfactants produced a set of foams with a large range of physical properties, particularly foams with varying cell size and open to closed cell ratios, the target of this study. For all formulations the isocyanate index (R) was kept constant at 1.2. All masses are reported in parts per hundred polyol (PPHP).\u003c/p\u003e\n \u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003ePolyurethane formulation for experiments, only the two surfactant concentrations are varied (slight MDI changes to ensure R\u0026thinsp;=\u0026thinsp;1.2)\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eFoam\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eVoranol 1446 /PPHP\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eVoranol 3322 /PPHP\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eWater /PPHP\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eDabco T /PPHP\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eS1 /PPHP\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eS2 /PPHP\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCloisite /PPHP\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMDI /PPHP\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eF01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e75\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e81.2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eF02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e75\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e81.7\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eF03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e75\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e82.1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eF04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e75\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e82.8\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eF05\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e75\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e83.6\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eF06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e75\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e80.9\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eF07\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e75\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e81.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eF08\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e75\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e81.7\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eF09\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e75\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e82.4\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eF10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e75\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e83.2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003eSmall scale isocyanate conversion foam trials were completed as follows. The polyisocyanate was weighed into a 30 ml syringe. The remaining reaction components were weighed into a 568 ml polypropylene cup and mixed at 3000 RPM for 45 seconds with an overhead mixer with a straight blade disk agitator. This mixture was allowed to debubble in a fume hood for 5 minutes before reacting. The polyisocyanate was added to the polypropylene cup and mixed at 1500 RPM for 6 seconds using the same overhead mixer/ stirrer combination. The reacting mixture was transferred immediately from the reaction vessel into a FoamPi (Wright et al., \u003cspan class=\"CitationRef\"\u003e2022a\u003c/span\u003e) an apparatus developed specifically for measuring foam reaction kinetics, for 10 minutes before being transferred to a curing oven at 120\u0026deg;C for 20 minutes. The FoamPi was employed to ensure full isocyanate conversion, with the calculation detailed in Wright et al., \u003cspan class=\"CitationRef\"\u003e2022a\u003c/span\u003e.\u003c/p\u003e\n \u003cp\u003eFor determining all other properties, and for yield trials, PUF synthesis was scaled up by using a 25 x 25 x 25 cm box as the reaction vessel. This was lined with PTFE film to allow easy removal of the PUF. Mixing and reaction conditions were the same as the small-scale foam experiments.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\n \u003ch2\u003e2.3. Foam Characterisation Methods\u003c/h2\u003e\n \u003cp\u003ePUF density was determined according to ASTM D3574-11 Test A (ASTM Standard D3574-11, \u003cspan class=\"CitationRef\"\u003e2012\u003c/span\u003e). Foam pieces of size 50 mm \u0026times; 50 mm \u0026times; 25 mm were cut perpendicular to the foam rise direction, their dimensions determined using a digital Vernier calliper and their mass recorded. Mass and volume were used to determine PUF density. Analysis was done in triplicate and the mean and standard error are reported.\u003c/p\u003e\n \u003cp\u003ePUF media cell size was determined according to ASTM D3576-15 (ASTM Standard D3576-15, \u003cspan class=\"CitationRef\"\u003e2014\u003c/span\u003e). A thin piece of foam was cut perpendicular to the rise direction. The surface of the foam was stained using a marker pen and imaged using optical microscopy. ImageJ (Rasband, n.d.) software was used to determine the cell size. A minimum of 200 cells was counted and the mean diameter and standard error reported.\u003c/p\u003e\n \u003cp\u003eWater uptake of media was measured using an adaptation of the apparatus described by Schulker \u003cem\u003eet al.\u003c/em\u003e (Schulker et al., \u003cspan class=\"CitationRef\"\u003e2021\u003c/span\u003e). Briefly, media samples were cut into 20 mm \u0026times; 20 mm \u0026times; 50 mm pieces and placed vertically in a sub irrigation system which irrigated the media for known time intervals to a height of 25 mm. This irrigation is repeated over several cycles to generate a water uptake curve. Sample mass was determined between each irrigation cycle. Triplicate samples were measured, and a water uptake curve is generated from this data with a fitted exponential decay curve. The fitting parameters of this curve give important insight into the water uptake of the media. Eq.\u0026nbsp;(\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e) shows the equation used to fit the capillary rise data.\u003c/p\u003e\n \u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\n \u003cdiv class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\u003cimg 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width=\"492\" height=\"59\"\u003e\u003c/div\u003e\n \u003c/div\u003e\n \u003cp\u003ewhere, H\u003csub\u003emax\u003c/sub\u003e is the maximum capillary rise height in cm, W\u003csub\u003eUR\u003c/sub\u003e is the rate of water uptake in cm s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and t is the total sub irrigation time in seconds. The mean and standard error of these two fitting parameters is reported.\u003c/p\u003e\n \u003cp\u003eAirflow through the foam was calculated according to ASTM D3574-11 test G (ASTM Standard D3574-11, \u003cspan class=\"CitationRef\"\u003e2012\u003c/span\u003e), whereby airflow (in L min\u003csup\u003e-1\u003c/sup\u003e) was measured through the sample at a standard pressure difference (125 Pa). A calibration curve was generated for determining the linear relationship between airflow and open cell content (Yasunaga et al., \u003cspan class=\"CitationRef\"\u003e1996\u003c/span\u003e) and the effective open cell fraction is reported. Analysis was done in triplicate and the mean and standard error are reported.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\n \u003ch2\u003e2.4. Germination / Growth Trials\u003c/h2\u003e\n \u003cp\u003eThe two germination trials and two vegetative yield trials were performed in a temperature-controlled greenhouse at the Arthur Willis Environmental Centre (AWEC) at the University of Sheffield with a day/night regime of 12 h at 20\u0026deg;C/12 h at 15\u0026deg;C. Germination Trial 1 (GT1) was conducted between 2023/02/15 and 2023/02/22. Vegetative yield trial 1 (VYT1) was conducted between 2023/02/22 and 2023/03/29, using seedlings from GT1. Germination trial (GT2) was conducted between 2023/05/17 and 2023/05/25, Vegetative yield Trial 2 (VYT2) was conducted between 2023/05/25 and 2023/06/19 using seedlings from GT2. Tomato \u0026ldquo;Moneymaker\u0026rdquo; (\u003cem\u003eSolanum lycopersicum\u003c/em\u003e), lettuce \u0026ldquo;little gem\u0026rdquo; (\u003cem\u003eLactuca sativa\u003c/em\u003e) and pak choi (\u003cem\u003eBrassica rapa\u003c/em\u003e var \u003cem\u003echinensis\u003c/em\u003e) seeds were purchased from Suttons seeds (Devon, UK).\u003c/p\u003e\n \u003cp\u003eVitalink Hydromax SW two-part hydroponic nutrient was used for all germination and vegetative yield trials. For germination trials, media plugs were soaked in 4 mL L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e nutrient solution (2 mL L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e part A and 2 mL L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e part B) for 5 minutes before planting. For all vegetative yield trials, the nutrient concentration was 8 mL L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (4 mL L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e part A and 4 mL L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e part B). All experiments were maintained at pH 6 using dilute phosphoric acid.\u003c/p\u003e\n \u003cp\u003eFor GT1 and GT2 20 seeds of each crop were germinated in individual growing media starter cubes of size 25 mm \u0026times; 25 mm \u0026times; 40 mm. Two separate hydroponic systems were used in VYT1 and VYT2, a recirculating hydroponic nutrient film technique (NFT) system, for lettuce and pak choi and a dripper fed open system for tomato. Drippers were pressure compensated 2 L h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e drippers used to provide irrigation for 5 equally spaced one-minute intervals in the daytime. For the dripper trial, tomato seedlings were transferred into larger media blocks of size 100 mm \u0026times; 100 mm \u0026times; 65 mm. For NFT crops, seedlings were transferred into the channels in their starter media blocks. For VYT1 four replicates were used for the tomato vegetative yield trial and seven replicates for the lettuce trial, the number of replicates was dictated by the maximum number of samples that could be run in the system. The reduced number of media in VYT2 meant more replicates could be completed. For this trial eight replicates were used in the tomato trial and ten replicates were used in the lettuce and pak choi trial. For germination and vegetative yield trials, days after planting is reported (DAP) as the number of days since seeds were sown in the media.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\n \u003ch2\u003e2.5. \u003cem\u003ePythium\u003c/em\u003e Infection Trial\u003c/h2\u003e\n \u003cp\u003e\u003cem\u003ePythium\u003c/em\u003e sp. isolates 2021\u0026thinsp;\u0026minus;\u0026thinsp;110 and 2021\u0026thinsp;\u0026minus;\u0026thinsp;116 were sourced from the Norwegian Institute of Bioeconomy Research (NIBIO) fungal culture collection. Both strains were isolated in 2012 from a tomato greenhouse. Isolates were confirmed as \u003cem\u003ePythium\u003c/em\u003e sp. by sequencing internal transcribed spacer 1, 5.8S ribosomal RNA gene, and internal transcribed spacer 2 using the ITS1oo (Riit et al., \u003cspan class=\"CitationRef\"\u003e2016\u003c/span\u003e) and ITS4 (White et al., \u003cspan class=\"CitationRef\"\u003e1990\u003c/span\u003e) primers, producing consensus sequences and searching for alignments in GenBank using BLASTN (Benson et al., \u003cspan class=\"CitationRef\"\u003e2012\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003e\u003cem\u003ePythium\u003c/em\u003e sp. isolates were cultured for 7 days at 25\u0026deg;C in the dark and without shaking (Postma et al., \u003cspan class=\"CitationRef\"\u003e2005\u003c/span\u003e). Cultures consisted of a glycerol stock (1 mL 15% glycerol and plug of V8 juice agar covered in mycelium), revived from storage at -70\u0026deg;C, in V8 juice media which contained 4 mL V8 Juice (Campbell Soup Co., Camden, NJ, USA), 16 mL deionised H\u003csub\u003e2\u003c/sub\u003eO (dH\u003csub\u003e2\u003c/sub\u003eO) and 60 mg CaCO\u003csub\u003e3\u003c/sub\u003e. Inoculums were prepared by washing mycelial mats three or four times in dH\u003csub\u003e2\u003c/sub\u003eO, weighing mats to determine inoculum dose, blitzing for 30 s at low speed with a D-8 homogeniser (MICCRA, Buggingen, Germany) in 50\u0026ndash;100 mL dH\u003csub\u003e2\u003c/sub\u003e0 and topping up to a final volume of 200\u0026ndash;330 mL with dH\u003csub\u003e2\u003c/sub\u003eO. The final \u003cem\u003ePythium\u003c/em\u003e inoculum contained 5.5\u0026ndash;9.5 g of mycelial mat per L per isolate. Seeds of tomato, lettuce, and pak choi were sown in individual growing media starter cubes (25 mm \u0026times; 25 mm \u0026times; 40 mm) pre-soaked in 4 ml per L of PlantStart propagation feed (Vitalink, Coventry, UK). For each crop and medium combination, 24 seeds were sown. Following sowing, starter plugs were inoculated with 1 mL of \u003cem\u003ePythium\u003c/em\u003e inoculum or 1 mL of dH\u003csub\u003e2\u003c/sub\u003eO as a control. In repeat three, 1 mL of \u003cem\u003ePythium\u003c/em\u003e inoculum or 1 mL of dH\u003csub\u003e2\u003c/sub\u003eO were added again at 2 days post sowing. Plugs were maintained for 14 days post sowing at the Arthur Willis Environmental Centre (AWEC), University of Sheffield, under a 12 h day/12 h night regime (20\u0026deg;C/15\u0026deg;C) within propagators at 100% relative humidity (RH). Germination was recorded every day and at 14 days post sowing (DAP) fresh weight of above ground tissue was measured.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\n \u003ch2\u003e2.6. Statistics\u003c/h2\u003e\n \u003cp\u003eFor the analysis of the physical properties of the foams, the mean and standard error were reported. Germination trials, GT1 and GT2, were evaluated using Kaplan-Meier survival analyses for germination and cotyledon expansion, generated with the Lifelines package in Python (Davidson-Pilon, \u003cspan class=\"CitationRef\"\u003e2019\u003c/span\u003e). These survival curves were compared using pairwise log-rank tests, and media that exhibited significant differences from the mineral wool control were reported. For vegetative yield trials, VYT1 and VYT2, shoot fresh mass (SFM) and shoot dry mass (SDM) were analysed using a one-way ANOVA with growing media as the factor. These analyses were performed with the Statsmodels package in Python (Seabold and Perktold, \u003cspan class=\"CitationRef\"\u003e2010\u003c/span\u003e). When the ANOVA indicated significant differences between means, post hoc Tukey HSD tests were conducted using the SciPy stats package (Virtanen et al., \u003cspan class=\"CitationRef\"\u003e2020\u003c/span\u003e). Python 3.12.4 was used for all analyses and figure generation.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"3. Results","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\n \u003ch2\u003e3.1. PUF Physical Properties\u003c/h2\u003e\n \u003cp\u003eThe density of the foams showed minimal variation, ranging from 24 to 29 kg m\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e, classifying them as low-density foams. This limited density variation was expected, as only surfactant quantities were altered, which have a minimal impact on foam density (Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eA). Foam density decreased with increasing S2 concentration, reaching a minimum when S2 was 1 PPHP. Cell diameters ranged from 600 \u0026micro;m to 800 \u0026micro;m, typical for polyether flexible foams. Cell diameter decreased with increasing concentrations of either surfactant, reaching a minimum of approximately 600 \u0026micro;m (Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eB). The ten foams exhibited a uniform distribution of cell diameters, providing a spectrum suitable for testing. Effective open cell content ranged from 0.13 to 1 (zero indicates every cell is closed, and one that every cell is fully open), with several foams exhibiting fully open cells and others nearly completely closed cells (Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eC). Prior to this research (Wright et al., \u003cspan class=\"CitationRef\"\u003e2022b\u003c/span\u003e) we have demonstrated that these properties are predictive of polyurethane foam hydrodynamic behaviour, a critical factor influencing plant growth (Wright et al., \u003cspan class=\"CitationRef\"\u003e2021a\u003c/span\u003e). Consequently, the primary objective of the formulation was to generate foams with a wide range of cell structures. This variation in cell properties resulted in foams with diverse water uptake capacities, with fully closed cell foams exhibiting minimal water uptake (\u0026lt;\u0026thinsp;0.5 cm) and partially or fully open cell foams, particularly those with smaller cells, absorbing up to 3 cm of water (Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eD). Similarly, a broad range of water uptake rates (WUR) was achieved. WUR varied from near zero (~\u0026thinsp;0 cm s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), particularly in samples with low effective open cell content due to restricted water ingress, with majority of samples having rates around 1 cm s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and a few with the lowest surfactant loadings having rates nearing 0.15 cm s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eE). Physical properties for each formulation are summarised in Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e\n \u003ctable id=\"Tab2\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003ePhysical properties of PUF formulations\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003ePUF Formulation\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u0026rho; / kg m\u003csup\u003e-3\u003c/sup\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003ed /\u0026micro;m\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eP\u003csub\u003eeff\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eH\u003csub\u003emax\u003c/sub\u003e / cm\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eW\u003csub\u003eUR\u003c/sub\u003e / cm s\u003csup\u003e-1\u003c/sup\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eF01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e27.4\u0026thinsp;\u0026plusmn;\u0026thinsp;0.20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e784\u0026thinsp;\u0026plusmn;\u0026thinsp;29\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.90\u0026thinsp;\u0026plusmn;\u0026thinsp;0.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.129\u0026thinsp;\u0026plusmn;\u0026thinsp;0.003\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eF02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e26.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e718\u0026thinsp;\u0026plusmn;\u0026thinsp;21\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.76\u0026thinsp;\u0026plusmn;\u0026thinsp;0.06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.135\u0026thinsp;\u0026plusmn;\u0026thinsp;0.016\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eF03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e24.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.05\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e679\u0026thinsp;\u0026plusmn;\u0026thinsp;18\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.84\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.074\u0026thinsp;\u0026plusmn;\u0026thinsp;0.003\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eF04 (*)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e24.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e669\u0026thinsp;\u0026plusmn;\u0026thinsp;17\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.694\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.94\u0026thinsp;\u0026plusmn;\u0026thinsp;0.14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.023\u0026thinsp;\u0026plusmn;\u0026thinsp;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eF05\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e23.7\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e611\u0026thinsp;\u0026plusmn;\u0026thinsp;13\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.373\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.63\u0026thinsp;\u0026plusmn;\u0026thinsp;0.21\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.010\u0026thinsp;\u0026plusmn;\u0026thinsp;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eF06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e28.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.33\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e801\u0026thinsp;\u0026plusmn;\u0026thinsp;28\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.85\u0026thinsp;\u0026plusmn;\u0026thinsp;0.06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.134\u0026thinsp;\u0026plusmn;\u0026thinsp;0.018\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eF07 (**)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e27.0\u0026thinsp;\u0026plusmn;\u0026thinsp;0.14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e683\u0026thinsp;\u0026plusmn;\u0026thinsp;26\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.897\u0026thinsp;\u0026plusmn;\u0026thinsp;0.07\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.07\u0026thinsp;\u0026plusmn;\u0026thinsp;0.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.055\u0026thinsp;\u0026plusmn;\u0026thinsp;0.003\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eF08 (*)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e26.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e624\u0026thinsp;\u0026plusmn;\u0026thinsp;15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.380\u0026thinsp;\u0026plusmn;\u0026thinsp;0.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.35\u0026thinsp;\u0026plusmn;\u0026thinsp;0.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.012\u0026thinsp;\u0026plusmn;\u0026thinsp;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eF09\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e26.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.13\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e569\u0026thinsp;\u0026plusmn;\u0026thinsp;12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.135\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.397\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.033\u0026thinsp;\u0026plusmn;\u0026thinsp;0.003\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eF10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e25.1\u0026thinsp;\u0026plusmn;\u0026thinsp;0.09\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e594\u0026thinsp;\u0026plusmn;\u0026thinsp;13\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.180\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.613\u0026thinsp;\u0026plusmn;\u0026thinsp;0.11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.015\u0026thinsp;\u0026plusmn;\u0026thinsp;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003e\u003csub\u003e*Indicates the two best performing foams in VYT2 for drip fed tomatoes; **indicates the best performing foam in VYT2 for lettuce in NFT systems\u003c/sub\u003e.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\n \u003ch2\u003e3.2. Germination Trial (GT1)\u003c/h2\u003e\n \u003cp\u003eGermination fraction (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e) for the mineral wool control (MW) were 75% for tomato, and 70% for lettuce seeds germinating within 8 days. Germination fraction and Kaplan-Meier survivability curves for tomato and lettuce in foams F02 - F05, F07 and F08 were not significantly different from MW controls. Germination was notably reduced in four polyurethane foam (PUF) formulations: F01, F06, F09, and F10. This reduction was observed for both tomatoes (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eA and B) and lettuce (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eC and D) with all four Kaplan-Meier curves exhibiting significant deviations from the MW curve (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;.05, pairwise log-rank test). Consequently, vegetative yield trial 1 (VYT1) proceeded with seedlings from the MW control and the six foam formulations (F02-F05, F07, and F08) where the Kaplan-Meier curves did not differ significantly from the MW curve.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\n \u003ch2\u003e3.3. Vegetative Yield Trial (VYT1)\u003c/h2\u003e\n \u003cp\u003eSeedlings from GT1 were transferred into an NFT hydroponic system (lettuce) and a dripper fed hydroponic system (tomato) for vegetative yield trial (VYT1). Lettuce was grown to yield, and tomatoes were grown until flowering began. The shoot fresh mass (SFM) and shoot dry mass (SDM) was measured for both lettuce and tomato. One way ANOVA indicated that there was no significant effect of media on the SFM or SDM for either of the crops (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e and Table \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e\n \u003ctable id=\"Tab3\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eANOVA table for VYT1.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCrop\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMass\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSum Sq\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003ed.f.\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eF value\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003ep\u003c/em\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTomato\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSFM\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4043\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6,21\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e.434\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTomato\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSDM\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e31.13\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6,21\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e.321\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eLettuce\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSFM\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6681\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6,24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.22\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e.314\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eLettuce\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSDM\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7.107\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6,42\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.905\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e.500\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003eFollowing the first vegetative yield trial (VYT1) the number of growing media formulations was reduced. This step was required to increase the number of replicates for the remaining candidates, thereby enhancing the statistical power of the experiment. However, due to limitations in the number of plants that could be accommodated in each system, increasing the number of replicates necessitated a reduction in the number of growing media tested. The two best performing foam media (based on mean shoot fresh mass) for each crop were carried forward to GT2 and VYT2. The best performing foam media were F07 and F08 for tomato, and F04 and F07 for lettuce with MW as a control as shown by the purple asterisk in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e. Therefore, three foams were taken forward into GT2 and VYT2: F04, F07 and F08.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\n \u003ch2\u003e3.4. Multicrop/system Trial\u003c/h2\u003e\n \u003cdiv id=\"Sec14\" class=\"Section3\"\u003e\n \u003ch2\u003e3.4.1. Germination Trial (GT2)\u003c/h2\u003e\n \u003cp\u003eGermination rates in mineral wool (MW) control were \u0026gt;\u0026thinsp;0.85 for all three crops. All three foams matched the performance of MW for each crop. Kaplan-Meier survival analysis, followed by pairwise Log-rank tests, showed no significant differences in germination timing or rates between the foams the MW control in any of the crops (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e). This result was consistent with findings from GT1 and confirms that the foam media also supported pak choi germination comparably to the MW control.\u003c/p\u003e\n \u003cp\u003eHowever, pak choi cotyledon emergence differed in the foam media compared to MW. Pak choi seedlings in foam opened their cotyledons under the media surface, likely due to light penetration through the foam structure (Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e). This caused a slight initial lag in growth of pak choi grown in foams compared to MW. Further studies into optimal planting depth in foam, as well as the option of germinating seedlings in the dark, should be explored to mitigate this effect.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec15\" class=\"Section3\"\u003e\n \u003ch2\u003e3.4.2. Vegetative yield Trial (VYT2)\u003c/h2\u003e\n \u003cp\u003eSeedlings from GT2 were transferred into an NFT hydroponic system (lettuce and pak choi) and a dripper fed hydroponic system (tomato) for the vegetative yield trial (VYT2). Lettuce and pak choi were grown to a harvestable stage, while tomatoes were grown until the onset of flowering. Shoot fresh mass (SFM) and shoot dry mass (SDM) were measured for both lettuce and tomato (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eGrowing media significantly affected SFM (ANOVA; F[3,28]\u0026thinsp;=\u0026thinsp;5.38, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;.0047) and SDM (ANOVA; F[3,28]\u0026thinsp;=\u0026thinsp;8.22, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;.0044) in the dripper fed tomato growth trial. Post-hoc analysis revealed that two foam based media (F04 and F08) yielded significantly higher SFM and SDM than the MW control (Tukey HSD test; \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;.05). In contrast, F07 did not perform significantly differently from the MW control in VYT2, this is consistent with the results from VYT01. Consequently, two of the three foam media tested (F04 and F08) resulted in tomato growth that met or exceeded that observed in the MW control within this dripper fed system. Furthermore, the variation in both SFM and SDM for the tomato crops grown in the foams was similar to that of the MW crops. Notably, F04 produced the highest mean biomass (mean SFM and mean SDM). F08 yielded the second highest mean SFM and SDM, performing consistently with performance in VYT1.\u003c/p\u003e\n \u003cp\u003eFor the NFT system, growing media significantly affected the SFM (ANOVA; F[3,36]\u0026thinsp;=\u0026thinsp;3.38, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;.029) and the SDM (ANOVA; F[3,36]\u0026thinsp;=\u0026thinsp;6.81, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001) of the lettuce crop in VYT2. Post-hoc analysis showed that all three-foam media yielded similar SFM compared to the MW control; however, F08 showed slightly suppressed SFM, with two replicates having particularly low values. Post-hoc analysis of SDM indicated that F08 produced significantly lower SDM than the other two foam samples (F04, F07) and the MW control. The results of the VYT2 lettuce trial showed good agreement with VYT1 results compared to the tomato trial, particularly as F04 and F07 were the best performing media in terms of mean biomass in both VYT1 and VYT2. Consistent with this, F08, which was the fourth best performing medium in VYT1, was the lowest performing of the foam media in the VYT2 lettuce trial and was only selected for this trial due to performing well in tomato growth trials.\u003c/p\u003e\n \u003cp\u003eFor pak choi NFT trials, growing media did not significantly affect SFM (ANOVA; F[3,36]\u0026thinsp;=\u0026thinsp;2.12, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;.115). However, growing media significantly affected SDM (ANOVA; F[3,36]\u0026thinsp;=\u0026thinsp;3.17, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;.0357). Further post-hoc analysis on SDM indicated that there were no statistically significant differences between any two groups. All three-foam media exhibited a marginal decrease in total biomass (mean SFM and mean SDM) when compared to mineral wool. This reduction was likely a combination of suppressed early growth due to cotyledon emergence below the surface of the foam media and the pak choi exhibiting a preference for the root zone conditions provided by mineral wool, potentially due to differences in aeration or moisture retention.\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec16\" class=\"Section2\"\u003e\n \u003ch2\u003e3.5. \u003cem\u003ePythium\u003c/em\u003e infection trial\u003c/h2\u003e\n \u003cp\u003eDamping off, caused by oomycete pathogens of the genus \u003cem\u003ePythium\u003c/em\u003e is a problematic disease in hydroponic horticulture, particularly for young plants (Amrhein et al., \u003cspan class=\"CitationRef\"\u003e2025\u003c/span\u003e). To evaluate whether the physical properties of soilless growing media influences disease susceptibility in hydroponic systems, we inoculated plants grown in MW, F04, F07 or F08 with \u003cem\u003ePythium\u003c/em\u003e. As these \u003cem\u003ePythium\u003c/em\u003e isolates were sourced from a tomato greenhouse, only tomato was focused on for the disease assays.\u003c/p\u003e\n \u003cp\u003eIn tomato, \u003cem\u003ePythium sp.\u003c/em\u003e can cause seed decay along with pre- and post-emergence damping off (Gravel et al., \u003cspan class=\"CitationRef\"\u003e2005\u003c/span\u003e) Thus, we monitored germination and cotyledon emergence along with post emergence growth. In media inoculated with \u003cem\u003ePythium\u003c/em\u003e, the total fraction and timing of cotyledon emergence showed little change for the three-foam media (F04, F07, F08) compared to their respective controls. However, a marked decrease in cotyledon emergence was observed in mineral wool (MW), dropping from 0.95 (control) to 0.33 when challenged with \u003cem\u003ePythium\u003c/em\u003e. Pairwise Log-rank tests comparing the \u003cem\u003ePythium\u003c/em\u003e challenged groups indicated that the Kaplan-Meier survival curve for MW differed significantly from those for F07 and F08. No significant difference was found between the curves for the \u003cem\u003ePythium\u003c/em\u003e challenged F04 and MW media (Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003eA-D).\u003c/p\u003e\n \u003cp\u003eAfter 14 days, plants which had emerged were harvested, and weighted, shoot fresh mass (SFM) exhibited high variance across all samples, and mean SFM was comparable across all media types and treatments (\u003cem\u003ePythium\u003c/em\u003e vs. control) for the surviving plants (Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003eE). The reduced germination in MW but comparable SFM values among surviving plants across treatments (Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003eD \u0026amp; E) suggests that pathogen induced mortality primarily occurred pre-emergence (damping off or seed decay), with minimal effects attributable to post-emergence damping off in this experiment.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"4. Discussion","content":"\u003cp\u003eTo investigate the potential of polyurethane foams (PUF) as customisable hydroponic growing media, a set of ten foams exhibiting a range of physical properties was synthesised. The objective was to determine if optimising these properties could benefit specific crops or hydroponic systems compared to a 'one size fits all' growing media such as mineral wool. Formulation and synthesis were successful in generating variation among the ten foams regarding key target properties: open cell fraction, cell size, water uptake rate (W\u003csub\u003eUR\u003c/sub\u003e), and maximum water uptake (H\u003csub\u003emax\u003c/sub\u003e). These foams subsequently underwent two germination and two vegetative yield trials to evaluate their performance against a standard mineral wool (MW) control.\u003c/p\u003e \u003cp\u003eFollowing the initial germination trial, four foam formulations were excluded from further testing due to significantly lower germination and/or germination rates compared to the MW control. Examination of the normalised physical properties of these four unsuccessful formulations provides insight into potential reasons for their poor performance. Analysis revealed that these four foams had properties at the extremes of the range. They included the two formulations with the largest and the two with the smallest cell sizes as well as those with the highest and lowest effective open cell fractions (Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). As previously demonstrated (Wright et al., \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2022b\u003c/span\u003e) cell size and open cell fraction strongly influence water uptake characteristics. Correspondingly, these four foams exhibited the lowest H\u003csub\u003emax\u003c/sub\u003e values among all ten formulations. Furthermore, PCA analysis (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e) revealed that this group was made up of two subgroups, each consisting of two foams (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e; pink dots). These two groups different along axis that correlated with the vectors W\u003csub\u003eur\u003c/sub\u003e and p\u003csub\u003eeff\u003c/sub\u003e. Two had very high-water uptake rates, and two had low water uptake rates. These findings suggest two distinct failure modes related to inadequate water management within the root zone. Firstly, the two foams characterised by small, predominantly closed cells likely impeded capillary action, resulting in both slow water uptake rates and low maximum capillary rise. (H\u003csub\u003emax\u003c/sub\u003e). Secondly, the two foams with large, mostly open cells, while potentially allowing rapid initial water uptake, likely also exhibited excessive drainage, ultimately leading to similarly low H\u003csub\u003emax\u003c/sub\u003e values. In both scenarios, the resulting suboptimal water availability (either too little retention or too rapid drainage) likely contributed directly to the observed poor germination rates.\u003c/p\u003e \u003cp\u003eThe poor performance of these four formulations provides important insights into the boundary conditions for designing effective PUF based growing media. Notably, these results suggest that successful PUF media require a sufficient minimum water retention (H\u003csub\u003emax\u003c/sub\u003e). Achieving this appears dependent on attaining a balanced pore structure, likely characterised by partially interconnected pores (avoiding extremes of fully open or closed structures) and moderate cell sizes.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn the initial vegetative yield trial (VYT1), tomato and lettuce yields were comparable across the tested media. Based on performance in the initial germination (GT1) and vegetative yield (VYT1) trials, the three most promising foam formulations (F04, F07, and F08) were selected for further evaluation. In subsequent germination tests (GT2), these three selected foams demonstrated germination and rates comparable to MW for all three tested crops: tomato, lettuce, and pak choi.\u003c/p\u003e \u003cp\u003eA second vegetative yield trial (VYT2) directly compared these three selected foams against MW using two distinct hydroponic systems tailored to different crops: a dripper fed system for tomatoes and a nutrient film technique (NFT) system for lettuce and pak choi. In the dripper system used for tomatoes, foams F04 and F08 produced significantly higher vegetative yields than MW, whilst F07 yielded comparably to the MW control. Conversely, in the NFT system used for lettuce, foams F04 and F07 produced yields comparable to MW, whereas F08 performed significantly worse (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;.05). Between the two foams matching MW performance in the lettuce/NFT trial, F07 achieved the higher mean vegetative yield. Yield in the pak choi trial was similar between the three-foam media and the MW control, with all three foams performing slightly worse than the MW control, likely due to crops germinating below the surface of the foam, hampering early growth.\u003c/p\u003e \u003cp\u003eAnalysis of the relationship between hydroponic performance and material properties provides insights into optimisation for specific systems. Examination of the hydrodynamic properties associated with the highest yielding foams in the tomato/dripper system (F04 and F08; Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e ; purple triangles and asterisks in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) reveals relatively slow water uptake rates coupled with high maximum capillary rise. These characteristics are advantageous for an intermittent dripper system, as slower water uptake and potentially slower release (implied by high capillary retention) help maintain media moisture and nutrient availability between irrigation events. Structurally, these foams (F04, F08) possessed moderate cell sizes and effective open cell contents relative to the full range synthesised.\u003c/p\u003e \u003cp\u003eIn contrast, the best performing foam for lettuce in the NFT system (F07) exhibited faster water uptake rates compared to F04/F08, slightly higher maximum capillary rise, a more open cell structure (higher open cell content), but similarly moderate cell sizes (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e ; yellow inverted triangle and asterisks in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). This more open structure is likely advantageous in an NFT system, where the media's role in water retention is less critical due to continuous nutrient solution flow. Furthermore, the open cells may facilitate easier root anchorage and subsequent penetration through the media into the NFT channel.\u003c/p\u003e \u003cp\u003eThese initial trials indicate that a \u0026ldquo;one size fits all\u0026rdquo; approach to growing media is unlikely to produce media that is crop and system optimised and furthermore that PUF media can be used as a platform to determine growing media physical property \u0026ldquo;recipes\u0026rdquo;, that are both crop and system optimised. Finally, these media were also subjected to a pathogen screen to determine whether PUF influences the biological facet of growing media use. PUF appeared to reduce the effect of a \u003cem\u003ePythium\u003c/em\u003e pathogen on germination of tomato plants. Compared to the MW medium, the reduced early mortality observed in two of the foam media (F07 and F08) under \u003cem\u003ePythium\u003c/em\u003e challenge was an unexpected finding, suggesting that these foam media may possess disease suppressive properties against this pathogen. Potential explanations warrant investigation: the physical properties of the foam surface may be less conducive to \u003cem\u003ePythium\u003c/em\u003e proliferation compared to MW; a chemical component or property of the foam might possess antimicrobial activity effective against the oomycete pathogen, or the foams alter root properties or induce resistance mechanisms in the host. Further investigation of the mechanism of this disease suppression is required to understand how microbes interact with the foam media before utilising these foams as model growing platforms in experiments involving biological factors, such as pathogen screening or the application of beneficial plant health or growth promoting microorganisms.\u003c/p\u003e \u003cp\u003eIn conclusion, this study demonstrates that a single 'one size fits all' growing media formulation is not optimal for different crops and hydroponic systems. Furthermore, it demonstrates the potential of PUFs as a versatile platform for developing tailored growing media recipes, allowing for the identification of physical property attributes optimal for a given crop and system requirements.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthors Contributions\u003c/h2\u003e \u003cp\u003eConceptualisation: HCW, AJR, SWW, SAR; Methodology: HCW, SWW; Software: HCW; Validation: HCW, SWW; Investigation: HCW, SWW; Data Curation: HCW, SWW; Formal Analysis: HCW, SWW; Writing \u0026ndash; Original Draft: HCW; Writing Review and Editing: HCW, SAR, DDC, AJR, SWW; Visualization: HCW; Supervision: DDC, AJR, SAR; Funding Acquisition: DDC, AJR, SAR, HCW.\u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003eThe authors would like to acknowledge the contributions of Caleb Morgan who conducted ITS sequencing of the \u003cem\u003ePythium\u003c/em\u003e strains. This work is supported by the \u0026lsquo;Transforming UK food systems\u0026rsquo; research programme via UKRI\u0026rsquo;s Strategic Priorities Fund (BB/V004719/1) as well as BBSRC Protected and Controlled Environment horticulture research programme (BB/Z514433/1).\u003c/p\u003e\u003ch2\u003eData availability statement.\u003c/h2\u003e \u003cp\u003eThe data that support the findings of this study are openly available at : \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.15131/shef.data.29314193\u003c/span\u003e\u003cspan address=\"10.15131/shef.data.29314193\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eAl Meselmani, M. A., Wright, H. C., Cameron, D. D., and Ryan, A. J. (2020). How scientists and refugees brought green to the Desert Garden. \u003cem\u003eNat. Rev. 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S., Garcia-Garcia, A. L., Ventura-Zapata, E., Barceinas-Sanchez, J. D. O., and Sosa-Savedra, J. C. (2022). A Review on Hydroponics and the Technologies Associated for Medium-and Small-Scale Operations. \u003cem\u003eAgric.\u003c/em\u003e 12, 1\u0026ndash;21. doi: 10.3390/agriculture12050646\u003c/li\u003e\n \u003cli\u003eVirtanen, P., Gommers, R., Oliphant, T. E., Haberland, M., Reddy, T., Cournapeau, D., et al. (2020). SciPy 1.0: fundamental algorithms for scientific computing in Python. \u003cem\u003eNat. Methods\u003c/em\u003e 17, 261\u0026ndash;272. doi: 10.1038/s41592-019-0686-2\u003c/li\u003e\n \u003cli\u003eWhite, T. J., Bruns, T., Lee, S., and Taylor, J. (1990). \u0026ldquo;AMPLIFICATION AND DIRECT SEQUENCING OF FUNGAL RIBOSOMAL RNA GENES FOR PHYLOGENETICS,\u0026rdquo; in \u003cem\u003ePCR Protocols\u003c/em\u003e, (Elsevier), 315\u0026ndash;322. doi: 10.1016/B978-0-12-372180-8.50042-1\u003c/li\u003e\n \u003cli\u003eWright, H. C., Cameron, D. D., and Ryan, A. J. (2021a). 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Flexible polyurethane foam with sodium bentonite: improving the properties of foams for use as a synthetic growing media. \u003cem\u003eActa Hortic.\u003c/em\u003e, 47\u0026ndash;54. doi: 10.17660/ActaHortic.2021.1305.7\u003c/li\u003e\n \u003cli\u003eYasunaga, K., Neff, R. A., Zhang, X. D., and Macosko, C. W. (1996). Study of Cell Opening in Flexible Polyurethane Foam. \u003cem\u003eJ. Cell. Plast.\u003c/em\u003e 32, 427\u0026ndash;448. doi: 10.1177/0021955X9603200502\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[{"identity":"55aa9de3-e93b-4625-b949-7f64c477676f","identifier":"10.13039/501100000268","name":"Biotechnology and Biological Sciences Research Council","awardNumber":"BB/Z514433/1","order_by":0},{"identity":"4135e974-3053-4494-86d4-e7fd0fd8d7e0","identifier":"10.13039/100014013","name":"UK Research and Innovation","awardNumber":"BB/V004719/1","order_by":1}],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"University of Sheffield","isAcceptedByJournal":true,"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":"growing media, horticulture, hydroponic, mineral wool, polyurethane foam, soilless","lastPublishedDoi":"10.21203/rs.3.rs-6890616/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6890616/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe increasing adoption of hydroponics and soilless cultivation techniques in food production has increased the demand for novel soilless growing media, presenting a unique opportunity for the development of customised media. Given the wide variety of crops and cultivation techniques used in soilless systems, optimising the physical properties of novel media for specific crops and systems presents both a challenge and an opportunity, as many growing media components provide only a single set of physical properties to work with. Polyurethane foams (PUFs), a promising soilless growing media, offer flexibility, as their formulation chemistry can be adjusted to produce foams with a diverse range of physical properties. This adaptability enables the tailoring of foams for specific crops and systems, providing valuable insights into optimised growing media \u0026ldquo;recipes\u0026rdquo; for various conditions. In this study, we examined 10 distinct PUF formulations with a range of physical properties through germination and growth trials. A preliminary investigation into whether physical or chemical characteristics of these media influence disease susceptibility was conducted by inoculating tomato plants with \u003cem\u003ePythium sp\u003c/em\u003e. An initial germination trial using lettuce and tomato identified four PUF formulations as unsuitable. A subsequent small scale growth trial demonstrated that the remaining six formulations performed comparably to mineral wool (MW) in terms of yield. Three of these formulations, which showed the highest yields, were then tested in yield trials for lettuce and pak choi in a nutrient film technique (NFT) system and for tomato using a dripper-fed system. Results indicated that two PUF formulations surpassed MW in vegetative yield in tomato trials, while two PUF formulations matched MW in lettuce yield in NFT trials. However, pak choi plants grown in foam displayed slightly lower yields than those in MW, although differences were not significant. All foam samples suppressed \u003cem\u003ePythium\u003c/em\u003e, as evidenced by no observed reductions in germination rates or seedling mass when compared to the uninfected samples, warranting further investigation into disease suppression potential. Overall, these yield results underscore that a \u0026ldquo;one size fits all\u0026rdquo; approach to soilless media formulation is inappropriate; rather, media should be optimised according to both hydroponic technique and crop type to maximise yields and other benefits. This study demonstrates that PUFs offer a valuable platform for developing tailored growing media \"recipes\" aligned with specific crop and system requirements.\u003c/p\u003e","manuscriptTitle":"Polyurethane Foam as a model platform for evaluating properties of soilless growing media","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-06-19 08:23:05","doi":"10.21203/rs.3.rs-6890616/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":"caaaf361-d658-46c0-af68-c2981fa91d84","owner":[],"postedDate":"June 19th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":50031629,"name":"Horticulture"},{"id":50031630,"name":"Polymer Science"}],"tags":[],"updatedAt":"2025-10-16T14:24:14+00:00","versionOfRecord":{"articleIdentity":"rs-6890616","link":"https://doi.org/10.3389/fhort.2025.1646783","journal":{"identity":"frontiers-in-horticulture","isVorOnly":true,"title":"Frontiers in Horticulture"},"publishedOn":"2025-10-15 00:00:00","publishedOnDateReadable":"October 15th, 2025"},"versionCreatedAt":"2025-06-19 08:23:05","video":"","vorDoi":"10.3389/fhort.2025.1646783","vorDoiUrl":"https://doi.org/10.3389/fhort.2025.1646783","workflowStages":[]},"version":"v1","identity":"rs-6890616","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6890616","identity":"rs-6890616","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}