Development of a municipal sludge-based water-retaining material for soil improvement and plant growth

Dispersed information on water retention and availability in soils may be compiled in databases to generate pedotransfer functions. The objectives of this study were: to generate pedotransfer functions to estimate soil water retention based on easily measurable soil properties; to evaluate the efficiency of existing pedotransfer functions for different geographical regions for the estimation of water retention in soils of Rio Grande do Sul (RS); and to estimate plant-available water capacity based on soil particle-size distribution. Two databases were set up for soil properties, including water retention: one based on literature data (725 entries) and the other with soil data from an irrigation scheduling and management system (239 entries). From the literature database, pedotransfer functions were generated, nine pedofunctions available in the literature were evaluated and the plant-available water capacity was calculated. The coefficient of determination of some pedotransfer functions ranged from 0.56 to 0.66. Pedotransfer functions generated based on soils from other regions were not appropriate for estimating the water retention for RS soils. The plant-available water content varied with soil texture classes, from 0.089 kg kg-1 for the sand class to 0.191 kg kg-1 for the silty clay class. These variations were more related to sand and silt than to clay content. The soils with a greater silt/clay ratio, which were less weathered and with a greater quantity of smectite clay minerals, had high water retention and plant-available water capacity.

Poly‐γ‐glutamic acid (γ‐PGA) has been demonstrated to exhibit a soil water retention effect; however, the agricultural irrigation practices induce a cyclic pattern of wetting and drying in the soil, and its synergistic interaction with γ‐PGA remains unclear. To explore the amendment effects of γ‐PGA on pores structure, aggregates distribution, and soil water retention characteristics under dry‐wet cycles, an experiment was established with the number of dry‐wet cycles (0, 2, 4, and 8 times; a single dry‐wet cycle involved reducing soil water content from 80% to 40% of field water capacity) and γ‐PGA addition rates (0%, 4%, and 8%, represented by P0, P4, and P8, respectively). The results indicated that γ‐PGA enhanced the structure of soil pores and distribution of aggregates; especially, P8 exhibited a remarkable increase in pore number by 91.68% and mean weight diameter of aggregates by 17.17%, compared to P0. Additionally, the soil enhanced by γ‐PGA exhibited higher water retention capacity, with P4 and P8 showing average increases of 4.26% and 12.58% in saturated water content compared to P0. Notably, the effect of γ‐PGA on pores structure, aggregates distribution, and water retention characteristics was regulated by dry‐wet cycles. The γ‐PGA had the most significant improvement effect on soil structure under 8 times dry‐wet cycles, the optimal development on water retention characteristics under four times dry‐wet cycles. Therefore, these findings suggest that the optimal approach to enhance soil structure and water retention capacity is by incorporating γ‐PGA at a concentration of 0.8% in conjunction with 4–8 dry‐wet cycles.

This study investigates the effects of variations in volume density and blotong application on the physical properties of Ultisol soil and the growth of sweet potato plants. The main objectives of the research are to assess how different levels of volume density and blotong application affect soil characteristics and plant growth. The study employs a qualitative approach, incorporating literature review and library research to explore existing knowledge and methodologies related to soil physics and plant physiology. The research involves conducting experiments where Ultisol soil samples with varying volume densities are treated with different levels of blotong application. Parameters such as soil bulk density, porosity, water retention capacity, and sweet potato plant growth parameters are measured and analyzed. The results reveal significant correlations between volume density, blotong application, and soil physical properties. Higher volume density generally leads to decreased soil porosity and water retention capacity, while blotong application demonstrates a positive impact on soil structure and plant growth. The findings highlight the importance of optimizing soil volume density and implementing blotong application techniques to enhance soil fertility and support healthy plant growth, particularly in Ultisol soil conditions. In conclusion, this research contributes valuable insights into sustainable agricultural practices for improving soil quality and crop productivity, emphasizing the significance of tailored management strategies for different soil types and crops.

Efficient water management is vital for sustaining agricultural productivity and ensuring food security. Recently, super absorbent polymers (SAPs) have emerged as valuable soil amendments due to their ability to conserve water by stabilizing soil structure and enhancing soil quality. However, many commonly used SAPs are not readily biodegradable, which can result in long-term environmental pollution. This study aimed to assess the effectiveness of biodegradable SAPs as soil conditioners for addressing water scarcity in subtropical regions. Five concentrations of biodegradable Fasal Amrit polymer (EFP) (P1: 0, P2: 0.02%, P3: 0.04%, P4: 0.08%, and P5: 0.12%) were tested to evaluate their impact on soil hydraulic properties. Soil water retention curves (SWRCs) were generated, and water capacity indicators were derived using the van Genuchten model. The SWRCs showed that EFP-treated soils enhanced water retention capacity compared to the control. With increasing EFP concentrations, the infiltration rate consistently declined, from the highest in P1 to the lowest in P5. Moreover, EFP-treated soils exhibited lower hydraulic conductivity than the control. Soil aggregate stability significantly improved (p lessthan 0.05) with higher EFP concentrations, as the polymer promoted better soil aggregation. These results demonstrate that EFPs can improve water retention and availability for crops by enhancing soil hydrological properties, making them a promising solution for mitigating water scarcity as effective soil conditioners. Keywords: biodegradable, soil hydrological properties, super absorbent polymer, water retention, water scarcity

Effect of soil organic carbon on soil water retention

Performance of herbaceous Evolvulus pilosus on urban green roof in relation to substrate and irrigation

The water retention capacity of soils characterizes a quasiequilibrium between the forces retaining and removing the soil water. It has been studied under field and laboratory conditions. It is shown that the gravity factor, as well as the soil particle-size distribution and structure, has an important role in determining the soil water capacity after the outflow of gravitational water. Our study enlarges the traditional notion about the nature of the field water capacity and capillary water capacity. Physically substantiated methods for determining these constants from the soil water retention curves are suggested. The assessment of the amount of perched water in the layers with broken capillary systems, such as in the layered soils and in the artificial soil-like bodies created upon the construction of soil drainage systems, is of particular importance. Regularities of the water retention capacity in such layered soils of different textures with inclusions of gravelly and peat layers have been analyzed. It is shown that the creation of layered soils with gravelly and peat layers may be an efficient method to rise the soil water retention capacity and protect the soil from secondary salinization.

Eichhornia crassipes also known as water hyacinth (WH) is listed among world's most invasive weed species. In tropical regions, green infrastructures have to undergo multiple drought cycles, which induces desiccation cracks and also lead to water-stressed condition of plants. The use of organic materials is advocated in green infrastructure for increasing water retention and ground-covering ability of vegetation. The main objective of this paper is to explore the influence of inclusion of waste WH fibres on hydraulic characteristics (water retention and cracking) of vegetated soils. Three soil series including bare (without vegetation) soil (BS), soil + grass (SG) and soil + grass + WH-fibre (SGWH) were tested for 73 days. The grass parameters stomatal conductance (SC), evapotranspiration (Etr), grass density (GD), shoot length (SL) and soil parameters (i.e. suction (ψ), volumetric moisture content (θ), crack intensity factor (CIF), evaporation (Er)) were monitored for all series. SGWH decreases the CIF potential of soil by 55·5 and 25% for BS and SG respectively. The inclusion of WH fibres increases the GD and SL as compared with SG. Furthermore, WH-fibre inclusion increased the soils’ water-retention capacity throughout the suction range due to its hydrophilic nature. The higher hemicellulose content and porous surface morphology of WH fibre, naturally improves soil's ability to retain water which is conducive to vegetation even under drought conditions.

In the rhizosphere, all transport processes considered fundamental in regulating resource availability and accessibility for plants and microorganisms are controlled by water retention and its temporal dynamics in the soil pore space, the rhizosphere liquid architecture (RLA). As the soil dries, root water and nutrient uptake becomes increasingly limited as the cross-sectional area and connectivity of the pore water declines. At the same time, diffusive transport ceases, negatively affecting root exudate transport and limiting microbial activity as enzyme diffusion and activity drop. The extent to which soil structural and biological processes influence local water retention and, in turn, related transport processes in the rhizosphere remains a challenging task. This study aimed to elucidate the effect of root growth and extracellular polymeric substances (EPS) on soil water retention in the rhizosphere of maize. High-resolution X-ray tomography was used to capture gradients in water distribution as a function of rhizosphere age and distance from the root surface. This combination of techniques allows distinguishing between soil structure versus primarily biologically induced modification. This study is a step toward a better understanding of the feedbacks between plants, microorganisms, and soil in controlling rhizosphere transport properties in this complex process aimed at optimizing resource availability and acquisition.

Sludge biodrying coupled with photocatalysis improves the degradation of extracellular polymeric substances

Effects of nonylphenols on soil microbial activity and water retention

Purpose: This paper focuses on the problems of soil water depletion and greenhouse gas emissions caused by improper soil management practices in arable lands. The results of previous studies were analyzed and the effects of deep ploughing on highly and less compacted soil were discussed. In addition, the effect of organic matter incorporation on soil water retention, and greenhouse gas emissions was evaluated.Research Method: To assess the impact of deep ploughing on soil moisture, two soil series (Andigama and Madampe) were selected. Moisture content was measured in ploughed and un-ploughed soil over a year using a neutron moisture meter. Coconut cultivations interplanted with nitrogen-fixing trees for eight years were used to assess soil improvement of the unproductive Andigama series. Soil compaction and water retention were measured using a cone penetrometer and neutron scattering technique in dry and rainy seasons. Palm oil sludge was mixed with sandy loam soil in various ratios and incubated for three months. Greenhouse gas emission was then analyzed using gas chromatography.Findings and Values: The results indicated that deep ploughing significantly (p < 0.05) improved soil water retention during both rainy and dry periods in compacted soils but had no significant (p > 0.05) effect in less compacted soils due to disruption of natural pore structure. Alternatively, agroforestry systems with nitrogen-fixing trees enhanced the soil water retention in degraded lands. Furthermore, an optimal ratio (15%) of palm oil sludge incorporation into the soil under optimal water conditions reduced the emissions of greenhouse gases such as CH₄ and N₂O. Overall, the findings demonstrate that incorporating organic matter and adopting appropriate land management practices minimizes the emission of greenhouse gases, which is essential to reducing global warming and mitigating climate change impacts.

Enhancing the sludge dewaterability by electrolysis/electrocoagulation combined with zero-valent iron activated persulfate process

Biochar is a porous and carbon-rich material produced through biomass pyrolysis. It has in the past two decades received unpreceded research attention and continues as studies reveal various and multifunctional potential to ameliorate both soil quality and crop productivity (Xu et al., 2025).Biochar's porous structure, high surface area and chemical stability enable improved soil nutrient retention, water holding capacity and microbial habitat environment. Consequently, biochar is increasingly recognized as a key tool for enhancing agroecosystem resilience, particularly under conditions of environmental stress such as acidic, degraded, saline or heavy-metal polluted soils, as well as soils prone to drought (Liu et al., 2025;Liu et al., 2024;Liu, Ma, et al., 2022;Liu, Manevski, et al., 2022). The Carbon Removal and Carbon Farming Directive of the European Union includes biochar (including soil applications) as one of the permanent carbon removal activities with technological maturity and deemed robust scientific understanding (EC, 2024). Yet, many effects of biochar and rates of application on soil processes and crop growth remain insufficiently understood across different soil types and depts, plants species and functional categories, precipitation regimes and irrigation managements; further research is essential to reveal its mechanisms of action from cell to plant and agroecosystem level, interactions with other soil amendments and to also support evidence-based government policy recommendations to ensure its safe and sustainable agricultural use.In that regard, several Research Topics of Frontiers have been launched involving biochar applications in soils and beyond, including environmental purposes of soil nutrition, water and wastewater treatment and biomethane production (Sánchez, 2024), research revealing plant physiological response to abiotic stress (Zhang et al., 2025), and how agroecosystems thrive on biochar-amended soils for their resilience. It is this latter Research Topic 'Biochar Role in Enhancing Agro-ecosystem Resilience' providing new evidence on biochar contribution to crops and vegetables productivity and nutrition, soil carbon stabilization, and sustainable agricultural management even on a medium-to long time scale (Gao et al., 2025;Upadhyay et al., 2025;Xu et al., 2025). These studies collectively highlight the positive role of biochar in supporting sustainable intensification while simultaneously addressing soil degradation and climate-related challenges.Studies within this Research Topic demonstrate that biochar as soil amendment significantly improves crop growth, biomass production, and yield stability. Biochar has been shown to mitigate abiotic stress effects, including ozone-induced oxidative damage, resulting in improved photosynthetic performance, antioxidant activity, and crop yield (Upadhyay et al., 2025). Biochar thus could enhance plant physiological resilience by concurrently reducing oxidative stress and improving nutrient availability. In addition, an extensive scientific literature review clearly reveals improved nutrient uptake efficiency in vegetables grown on biochar-amended soil through enhanced cation exchange capacity and soil nutrient retention; the porous structure of biochar facilitates adsorption of essential macronutrients such as nitrogen and phosphorus, and likely micronutrients which are especially important for vegetables growth, also reducing leaching losses and increasing plant availability (Xu et al., 2025). This improved nutrient availability at agroecosystem level translates into enhanced plant biomass accumulation and productivity. Machado et al. (2026) focused on integrated soil management systems and further demonstrated the potential of biochar combined with organic amendments such as compost to enhance plant growth and improve crop nutritional quality compared to conventional fertilization alone. Such synergistic effects are yet to be fully revealed but so far can be attributed to improved soil fertility, increased microbial activity, and enhanced nutrient cycling. Overall, the studies in this Research Topic confirm that biochar improves plant performance through multiple mechanisms, including improved nutrient retention, enhanced stress tolerance, and optimized soil physical properties, ultimately contributing to improved crop productivity and agro-ecosystem resilience.Beyond its direct effects on crop growth, biochar plays a critical role in improving soil carbon storage and soil health. Due to its highly aromatic and stable carbon structure, biochar resists microbial decomposition, allowing carbon to remain stored in soil for extended periods. Mediumto long-term (10-years) field experiments reported in this Research Topic demonstrate significant increases in soil organic carbon following one-time biochar application, regardless of application rate, confirming its role as an effective carbon sequestration strategy (Gao et al., 2025). Biochar also improves soil physical properties, including soil aggregation, porosity and water retention capacity, which enhance overall soil function and resilience. Improvements in soil structure promote root growth and microbial activity, further enhancing nutrient cycling and soil fertility (Liu, Ma, et al., 2022). In addition, biochar increases soil pH in acidic soils and improves cation exchange capacity, contributing to improved nutrient retention and reduced nutrient losses.Importantly, biochar application contributes to long-term stabilization of organic carbon by promoting interactions between biochar particles and native soil organic matter, resulting in enhanced carbon persistence and reduced greenhouse gas emissions (Xu et al., 2025;Machado et al., 2026). These findings highlight biochar's potential to simultaneously enhance soil fertility and contribute to climate change mitigation.

At present time exists a lot of soil tillage practices with different effects on soil productivity, therefore the effects of two tillage systems (conventional: CT, and miminum: MT) and two different soil types (Chernozem and Mollic Fluvisol) on soil physical quality indicators and water availability were evaluated in an on-farm study in the Krakovany (Danube Lowland, Slovakia). We evaluated pore-size distributions and selected hydro-physical properties (capillary rise, maximum capillary water capacity and retention water capacity). The total porosity (P) on average by 23% and by 14%, non-capillary pores (Pn) by 271% and by 114% and semicapillary pores by 102% and by 192% were significantly greater for CT than MT in Chernozem and in Mollic Fluvisol, respectively. The content of capillary pores (Pc) was significantly greater for MT than CT on average by 13% and 8% in Chernozem and in Mollic Fluvisol, respectively. The average content of capillary rise (ΘCR), maximum capillary water capacity (ΘMCWC) and retention water capacity (ΘRWC) were higher by 6, 10 and 13% under MT than CT in soil profile of Chernozem. The same effect of soil tillage systems in Mollic Fluvisol was not observed. In Chernozem under MT with increased P, ΘCR significantly increased, however, under CT, the ΘCR significantly decreased. At the same time we determined negative correlations between Pn and soil water retention characteristics under CT. Higher content of Pc resulted in higher values of capillary rise, maximum capillary water capacity and retention water capacity in both soil types under both tillage systems.