A new study published in Biochar shows that combining green manure with biochar can help farmers reduce nitrogen fertilizer use while improving soil health, water retention, carbon storage, nutrient supply, and microbial activity.
The research, titled "Synergistic effects of green manure and biochar for a win-win in nitrogen reduction and soil health: insights from multiple assessment frameworks," was conducted by Lianhao Zhao and colleagues through a three-period field experiment from 2021 to 2024 in a maize cropping system on the North China Plain. The team tested winter fallow, green manure, and green manure plus biochar under conventional fertilization and different levels of controlled-release fertilizer reduction.
Modern crop production has often relied on heavy fertilizer inputs to secure yields, but excessive nitrogen use can worsen soil acidification, disrupt nutrient balance, reduce biological activity, and increase environmental losses. The new study points to a more balanced path: moderate nitrogen reduction combined with organic field practices that restore the soil's natural functions.
"Our results show that nitrogen reduction does not have to come at the cost of soil health or crop productivity," said corresponding author Wen Yin. "When green manure and biochar were used together, they created a stronger and more resilient soil system, especially under moderate controlled-release fertilizer reduction."
The strongest performance was found when green manure and biochar were combined under a 30% reduction in controlled-release fertilizer. Under this treatment, the soil showed the greatest improvements in water retention, carbon sequestration, nitrogen fixation, nutrient supply, microbial diversity, and overall soil quality. The study also found that maize yield could be maintained under this moderate fertilizer reduction, while nitrogen fertilizer productivity increased.
In contrast, a 45% fertilizer reduction created risks of excessive nitrogen cutback, lowering key nutrient functions and reducing yield. This finding suggests that fertilizer reduction should be carefully calibrated rather than applied as a simple across-the-board cut.
A key innovation of the study was its use of multiple soil quality assessment frameworks. The researchers measured 22 soil indicators, including physical, chemical, and biological properties, and built a soil function-based evaluation system covering five core functions: water retention, carbon sequestration, nitrogen fixation, nutrient supply, and microbial diversity provision. They also compared this approach with two minimum dataset methods based on principal component analysis and network analysis.
The soil function-based framework provided the highest accuracy, while the principal component-based minimum dataset offered the best balance between efficiency and accuracy. The network-based method maintained reasonable accuracy using only four indicators, making it promising for rapid screening across larger areas.
One of the most important findings was that soil microbial diversity emerged as a central driver of improved soil quality. Green manure and biochar appeared to work mainly by strengthening microbial diversity and water retention, which then indirectly supported carbon sequestration and nutrient supply.
"Healthy soil is not only about adding nutrients," said corresponding author Qiu Zhao. "It is about restoring the biological and physical processes that allow soil to store water, cycle nutrients, protect carbon, and support stable crop production."
The study provides a practical framework for designing sustainable maize systems in the North China Plain and similar agricultural regions. By integrating green manure, biochar, and moderate controlled-release fertilizer reduction, farmers may be able to reduce fertilizer inputs, maintain yield, and rebuild degraded soils at the same time.
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Journal Reference: Zhao, L., Zhang, X., Ning, X. et al. Synergistic effects of green manure and biochar for a win-win in nitrogen reduction and soil health: insights from multiple assessment frameworks. Biochar 8, 123 (2026).
https://doi.org/10.1007/s42773-026-00638-4
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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.
