The findings, published in the journal Agricultural Water Management by researchers Xufeng Li, Lijian Zheng, and Juanjuan Ma, highlight a significant breakthrough in sustainable facility agriculture. Greenhouse farming often suffers from the over-application of fertilizers and pesticides, which destroys soil structure and reduces how much water the ground can hold. By introducing biochar—a porous, carbon-rich material—into the soil, the researchers demonstrated that it is possible to repair this damage and create a more harmonious relationship between the dirt, the water within it, and the roots of the tomato plants. This balanced state, referred to as the coupling coordination degree, proved to be the most critical factor in determining whether a tomato crop would thrive.

The results of the two-year greenhouse experiment showed that biochar significantly altered the physical makeup of the soil. It increased the presence of healthy soil aggregates by nearly twenty-three percent, making the ground more porous and better aerated. This structural change allowed the soil to act much more efficiently as a reservoir. Specifically, the soil’s available water content—the portion of moisture that plants can actually use—jumped by nearly thirty-six percent. Because biochar is less dense than traditional soil, it also reduced the overall soil bulk density by up to twelve percent, meaning the roots had to fight through less mechanical resistance as they grew.

This improved underground environment had a direct and positive impact on tomato root morphology. In biochar-treated plots, the tomato roots became significantly thinner and longer. This change is beneficial because thinner roots have a higher surface area density, allowing them to explore more of the soil to find nutrients and moisture. The study found that root surface area density and volume density both saw massive increases, sometimes more than seventy percent higher than in soil without biochar. These “hungry” roots were better equipped to transport water to the rest of the plant, which is why the researchers observed a noticeable increase in the total dry matter of the tomatoes.

When these factors—soil structure, water availability, and root growth—were analyzed together, the researchers found that biochar increased their coordination degree by as much as eighty-six percent. This synergy was the engine behind the increased yields. Tomato harvests were up to thirty-three percent higher in treated plots, primarily because each individual fruit grew heavier rather than the plants simply producing a higher number of small fruits. Water use efficiency also improved by nearly thirty percent, suggesting that farmers could grow more food while using less of a precious resource. Interestingly, the second year of biochar application showed even better results for tomato yield than the first, indicating a lasting “legacy effect” of the soil amendmentA soil amendment is any material added to the soil to enhance its physical or chemical properties, improving its suitability for plant growth. Biochar is considered a soil amendment as it can improve soil structure, water retention, nutrient availability, and microbial activity.   More.

However, the study also provided a warning about excessive use. While applying more biochar generally led to better soil structure and higher water content, it did not always lead to higher yields. At the highest application rate of sixty metric tons per hectare, tomato yields actually began to decline compared to more moderate doses. This happens because too much biochar can lead to nutrient fixation, essentially “locking up” the food that plants need, or causing the plant to put too much energy into early leaves and not enough into later fruit ripening. By using a comprehensive evaluation model, the team identified thirty metric tons per hectare as the absolute best rate for balancing soil health with maximum fruit production. This research offers a clear roadmap for greenhouse managers to improve their sustainability and profits simultaneously.

Source: Li, X., Zheng, L., & Ma, J. (2026). Improving the yield of greenhouse tomato by adjusting the coupling coordination degree of soil-water-root system using a biochar. Agricultural Water Management, 329, 110354.