Feeding a growing population requires a lot of water, and modern agriculture faces two related problems: it consumes massive amounts of freshwater, and it often leaches expensive fertilizers (nitrates and phosphates) into the environment, causing pollution. This challenge is even more complex when using recycled municipal wastewater for irrigation, which can also carry high nutrient loads. A new study in Iran Agricultural Research by lead author Tohid Balouchi Anaraki, corresponding author Mohammd Shayannejad, and their colleagues at the Isfahan University of Technology demonstrates a powerful, two-part solution that grows more food with less water and less pollution.

The researchers tested a combination of smart water management and soil enhancement. The first part involved “controlled drainage” (CD), a technique that adjusts the subsurface drainage system to keep more water in the field when the crop needs it, rather than letting it all flow away freely, as in “free drainage” (FD). The second part involved amending the soil with two levels of raw sugarcane bagasse (a fibrous waste product) and two levels of biochar made from that same bagasse. Biochar is a stable, carbon-rich charcoal made by heating biomassBiomass is a complex biological organic or non-organic solid product derived from living or recently living organism and available naturally. Various types of wastes such as animal manure, waste paper, sludge and many industrial wastes are also treated as biomass because like natural biomass these More in a low-oxygen environment. This greenhouse study used municipal wastewater to irrigate field peas (Pisum sativum L.) under these different conditions.

The results for water conservation were immediate and clear. The controlled drainage (CD) system, by holding water in the root zone, reduced total water consumption by 22% compared to the free drainage (FD) system. The soil additives acted like a sponge, helping the soil hold onto that water. The 1.32% biochar (BIC1.32%) treatment was the most effective, increasing the soil’s water holding capacity by 43.3% compared to the control soil. Even the 2% raw bagasse (BA2%) provided a significant 24.3% boost. This combination meant less irrigation water was needed, and the water that was applied stayed available to the plants for longer.

This approach also solved the nutrient-leaching problem. By preventing excess water from draining away, the CD system slashed nutrient losses. It decreased nitrate leaching by 19.73% and phosphate leaching by 24.23%. Those nutrients did not just disappear; they stayed in the soil. Compared to free drainage, controlled drainage increased the amount of nitrate in the soil by 44.25% and phosphate by 28.78%.

With more water and more nutrients available, the field peas thrived. The plants in the CD system were able to absorb 75% more nitrate and 13.3% more phosphate than the plants in the FD system. This translated directly into bigger plants and higher yields. The combination of controlled drainage and the 1.32% biochar additive increased the final plant dry weight by 26.2% compared to the same additive in the free drainage system. The 2% bagasse treatment was nearly identical, boosting dry weight by 26%.

The most important finding for farmers, especially in water-scarce regions, is the improvement in water productivity—the “crop per drop.” By growing significantly more plant biomass with less water, the controlled drainage system made the irrigation water 1.8 times more productive than the free drainage system. This study provides a practical blueprint for a more sustainable farming system: using an agricultural waste product (bagasse) to create biochar, amending the soil to hold water, and using a smart drainage system to keep both water and nutrients in the field where they belong.

Source :Anaraki, T. B., Shayannejad, M., Khozani, A. R. M., Gheysari, M., & Eshghizadeh, H. R. (2025). Effects of bagasse and its biochar on the leaching of solutes and water uptake by field pea (Pisum sativum L.) under controlled and free drainage conditions and irrigation with municipal wastewater. Iran Agricultural Research, 44(2), 41–52.