Sandy soils are among the most challenging environments for agriculture because water drains quickly and nutrients are easily lost. A new long-term field experiment shows that combining biochar with compost and sludge can dramatically improve how sandy soils retain water, offering a practical strategy for farming in drought-prone regions.
Researchers conducted a 441-day lysimeter study to examine how different organic amendments influence the water balance of sandy soil under realistic environmental conditions. The team compared single amendments and combinations of biochar, compost, and sludge, monitoring soil moisture, drainage, and evaporation over time. Their results show that while each material provides benefits, the strongest improvements occurred when they were used together.
The triple combination of biochar, sludge, and compost reduced cumulative drainage by more than forty percent compared with individual amendments. This indicates that more water remained in the soil rather than draining away, which can help plants access moisture for longer periods between rainfall or irrigation events.
"Our findings show that integrating different organic materials can create a more stable soil structure that retains water more effectively than any single amendment alone," said the study's lead author. "This kind of synergy is especially valuable for sandy soils that normally struggle to support crops."
Biochar, a carbon-rich material produced by heating biomass in low oxygen conditions, played a key role in improving soil porosity and water holding capacity. Compost and sludge contributed additional organic matter and fine particles, which helped stabilize soil structure and further enhanced water retention. Together, these materials formed a more balanced pore network that slowed water loss and stabilized soil moisture levels.
The long duration of the experiment allowed the researchers to capture seasonal fluctuations in rainfall and temperature, making the results more representative of real agricultural conditions than short laboratory studies. Continuous monitoring showed that soils treated with the combined amendments maintained higher average moisture content and more stable storage across wet and dry periods.
Improved water retention also influenced other aspects of the soil water balance. Treatments containing biochar generally showed lower drainage and higher evaporation from the soil surface, suggesting that more water remained available within the soil profile. Statistical analyses confirmed that differences in drainage and evaporation among treatments were significant, demonstrating that the amendments meaningfully altered soil hydraulic behavior.
The study highlights the importance of considering soil management strategies that use multiple organic inputs rather than relying on a single amendment. By tailoring combinations to local conditions, farmers may be able to increase water use efficiency, reduce irrigation needs, and improve resilience to drought.
"These results provide practical evidence that combining organic amendments can help transform marginal sandy soils into more productive and resilient systems," the authors noted. "Such approaches could support sustainable agriculture in regions facing increasing water scarcity."
Beyond agriculture, the findings may also contribute to climate adaptation strategies. Improved soil water retention can reduce irrigation demand, enhance plant growth, and stabilize soil ecosystems, all of which are increasingly important as climate change intensifies drought risks worldwide.
The researchers conclude that integrating biochar, compost, and sludge represents a promising pathway for enhancing soil function, conserving water, and supporting sustainable land management in vulnerable environments.
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Journal Reference: Tenodi, S., Maletić, S., Kragulj Isakovski, M. et al. Impact of biochar, compost, and sludge amendments on the soil water balance of a sandy soil. Biochar 8, 14 (2026).
https://doi.org/10.1007/s42773-025-00509-4
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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.
