Scientists have uncovered how different types of biochar influence the movement of water in agricultural soils that contain excessive phosphorus, offering new insights into how farmers can reduce nutrient loss and protect surrounding water bodies.
In a new study, researchers investigated how two widely available agricultural biochars affect water infiltration and leakage in phosphorus enriched vegetable soils. The findings suggest that biochar made from rice husks can significantly slow water movement through soil, potentially reducing the risk of phosphorus leaching and improving water retention for crops.
Vegetable production systems often rely on heavy irrigation and frequent fertilization. Over time, these practices can lead to large accumulations of nutrients in the soil, particularly phosphorus. When rainfall or irrigation water moves quickly through such soils, dissolved nutrients can be carried downward or washed away, contributing to water pollution in nearby ecosystems.
"Excess phosphorus in vegetable soils has become a widespread environmental concern," said one of the study's authors. "Understanding how soil amendments influence water movement is critical for preventing nutrient losses and improving the sustainability of vegetable production."
Biochar is a carbon rich material produced by heating biomass such as crop residues or agricultural waste in low oxygen conditions. Because of its porous structure and chemical properties, biochar is increasingly used to improve soil fertility, retain nutrients, and enhance water holding capacity.
In this study, the research team compared two types of biochar derived from agricultural residues that are common in southern China: rice husk biochar and palm silk biochar. The scientists incorporated these materials into sandy loam vegetable soil at two application rates and then conducted controlled soil column experiments to track how water infiltrated and moved through the soil profile.
The experiments revealed clear differences between the two biochar types. Rice husk biochar was more effective at slowing water infiltration through the soil surface layer. At higher application rates, it increased the soil's saturated water content while reducing hydraulic conductivity, meaning that water was retained longer in the soil instead of moving quickly downward.
Palm silk biochar behaved somewhat differently. Its pore structure helped delay water release and enhance water retention, but it did not suppress infiltration as strongly as rice husk biochar.
Despite these differences, both biochar types significantly reduced water leakage from the soil. The researchers found that biochar amendments decreased cumulative water leakage by roughly twenty to forty percent compared with untreated soil.
The team also identified key soil properties that control these hydrological processes. Structural equation modeling showed that total organic carbon played an important role by increasing the soil's ability to hold water, while changes in soil pH helped reduce the speed at which water moves through the soil.
"Biochar does not simply act as a physical sponge," the researchers explained. "It changes the chemical and structural properties of soil in ways that collectively regulate water movement."
While a higher application rate of biochar produced the strongest hydrological effects, the researchers suggest that a moderate rate may offer a better balance between environmental benefits and practical costs for farmers.
Overall, the study highlights how selecting the appropriate biochar feedstock can help manage water and nutrient dynamics in intensive vegetable production systems. By slowing water movement and reducing phosphorus losses, biochar amendments may contribute to more sustainable agriculture while protecting surrounding water resources.
The findings provide new mechanistic insights into how biochar properties interact with soil characteristics to shape hydrological processes, helping guide future strategies for managing nutrient rich agricultural soils.
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Journal Reference: Yu, X., Wang, R., Guo, Y. et al. Contrasting effects of rice husk and palm silk biochars on water infiltration and leakage in a phosphorus-enriched sandy-loam vegetable soil. Biochar 8, 26 (2026).
https://doi.org/10.1007/s42773-025-00543-2
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About Biochar
Biochar (e-ISSN: 2524-7867) is the first journal dedicated exclusively to biochar research, spanning agronomy, environmental science, and materials science. It publishes original studies on biochar production, processing, and applications—such as bioenergy, environmental remediation, soil enhancement, climate mitigation, water treatment, and sustainability analysis. The journal serves as an innovative and professional platform for global researchers to share advances in this rapidly expanding field.
