Biochar particle size plays a decisive role in boosting tomato yields under salty soils
image: Interaction between biochar particle size and soil salinity levels on soil properties and tomato yield
Credit: Zhuqing Wu, Yaqiong Fan, Zhengquan Zhou, Xinmei Hao & Shaozhong Kang
A new study reveals that not all biochar works the same way in agriculture. The size of biochar particles can significantly influence how well crops grow, especially in salt-affected soils that challenge global food production.
“Biochar is widely recognized as a promising soil amendment, but our findings show that its particle size can completely change its effects,” said the study’s corresponding author. “Choosing the right biochar form is just as important as choosing the right fertilizer.”
Soil salinity is a growing global problem that reduces crop yields by limiting plants’ ability to absorb water and nutrients. Biochar, a carbon-rich material produced from biomass, has been widely studied for its potential to improve soil health. However, until now, little was known about how biochar particle size interacts with soil salinity to affect crop performance.
In this study, researchers conducted controlled greenhouse experiments using tomatoes grown under different salt conditions and treated with either large-particle or small-particle biochar. The results revealed a striking contrast in how biochar size influenced plant growth and yield.
Under saline conditions, large-particle biochar significantly improved tomato yields. Compared to untreated soils, yields increased by up to 36.5 percent under moderate salinity. This improvement was linked to better soil structure and enhanced salt leaching, which reduced harmful salt accumulation around plant roots.
In contrast, small-particle biochar had the opposite effect under the same saline conditions. Yields dropped by as much as 44.2 percent in highly saline soils. Researchers found that smaller particles increased soil microporosity, trapping salts in the root zone and intensifying stress on plants.
Interestingly, the situation reversed in non-saline soils. When no salt stress was present, small-particle biochar delivered the best performance, boosting tomato yield by about 51 percent compared to untreated soil. This was attributed to improved water retention and nutrient availability, which supported plant growth in otherwise favorable conditions.
Beyond yield, biochar also influenced key soil properties. The study showed that biochar application increased soil pH and total nitrogen content while reducing calcium levels due to selective adsorption. These changes can affect nutrient cycling and plant uptake, further shaping crop outcomes.
The researchers also observed strong links between soil conditions and plant performance. Higher yields were associated with better soil water content and balanced pH, while excessive salt ions such as sodium and calcium were negatively correlated with productivity.
Overall, the findings highlight that biochar is not a one-size-fits-all solution. Instead, its effectiveness depends on matching the right particle size to specific soil conditions.
For farmers and land managers, the implications are clear. Large-particle biochar is better suited for reclaiming saline soils and improving crop productivity under salt stress. Meanwhile, small-particle biochar may be more effective in non-saline environments where water retention is the priority.
The study provides practical guidance for optimizing biochar use in agriculture and underscores the importance of tailoring soil amendments to local conditions.
As soil salinization continues to threaten food security worldwide, such targeted strategies could help farmers make better use of sustainable materials like biochar to maintain and even increase crop yields.
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Journal Reference: Wu, Z., Fan, Y., Zhou, Z. et al. Interaction between biochar particle size and soil salinity levels on soil properties and tomato yield. Biochar 7, 30 (2025).
https://doi.org/10.1007/s42773-024-00417-z
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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.