Phosphorus (P) is a vital nutrient for plant growth, but tropical soils often limit its availability due to high adsorption capacities. This leads to inefficient phosphate fertilization and necessitates heavy doses of phosphorus, increasing production costs and depleting finite phosphate rock resources. To combat this, researchers are developing “smart fertilizers” that slowly release P, reducing its interaction with soil components. A recent study published in ACS Agricultural Science & Technology by Ronaldo Willian da Silva, Renato Ribeiro Passos, and their colleagues, investigated the agronomic efficiency of biochar-based organophosphate fertilizers in maize cultivation under field conditions.

This research explored fertilizers created with biochars from coffee straw (CSB), poultry litter (PLB), and eucalyptus bark (EBB), prepared through either homogeneous mixture or coating methods, and compared them to triple superphosphate (TSP). The study found that biochar-based organophosphate fertilizers significantly improved agronomic efficiency by 10.8% and P recovery by 2.4% compared to TSP. Additionally, they led to an 11.6 mg/kg increase in P availability in the soil after harvest. These findings suggest that incorporating biocharBiochar is a carbon-rich material created from biomass decomposition in low-oxygen conditions. It has important applications in environmental remediation, soil improvement, agriculture, carbon sequestration, energy storage, and sustainable materials, promoting efficiency and reducing waste in various contexts while addressing climate change challenges. More into fertilizers can lead to more effective P utilization and sustained soil fertility.

Among the different biochar types, PLB-based fertilizers proved particularly effective, showing the highest agronomic efficiency means and P recovery. They also resulted in a 31.94% greater amount of available P in the soil after harvest. This enhanced performance is likely due to PLB’s higher concentrations of calcium, magnesium, and phosphorus, along with a higher pHpH is a measure of how acidic or alkaline a substance is. A pH of 7 is neutral, while lower pH values indicate acidity and higher values indicate alkalinity. Biochars are normally alkaline and can influence soil pH, often increasing it, which can be beneficial More , which can influence P solubility and release. The study also highlighted the importance of the fertilizer preparation method; coating the biochar promoted a 5.1% greater P availability in the soil compared to homogeneous mixtures. For EBB-based fertilizers, coating specifically led to higher means in agronomic efficiency (111.4%) and P recovery (29.8%).

The proportion of biochar to TSP also played a crucial role. The 30% biochar/TSP ratio was identified as most effective in enhancing soil P availability and plant uptake, while also extending the residual effect of P in the soil. This higher ratio likely promotes a thicker coating of the granules, creating a greater physical barrier to the contact of P with soil particles. For granular fertilizers in the mixture mode, the presence of biochar appears to influence the P solubility. The gradual release of P ensures that the nutrient is available during critical growth stages of maize, such as intense vegetative growth and ear formation, when demand is highest. This controlled release mechanism helps to minimize P fixation in the soil , a common issue in tropical soils with high iron and aluminum oxide content.

The increased P availability in the soil after cultivation with organophosphate fertilizers, showing concentrations of 25.4% (P-water) and 20.1% (P-Mehlich-1) higher than TSP treatments, further supports their long-term benefits. Unlike highly soluble TSP, which can rapidly release P that then becomes adsorbed by soil components before plants can fully utilize it , biochar-based fertilizers provide a more sustained supply. This sustained release is crucial for maximizing P uptake by plants and improving overall crop productivity. The higher pH values of organophosphate fertilizers in relation to TSP also reinforce the hypothesis that biochar increases the pH of the solution around the granules, thereby reducing P adsorption.

The mean P recovery of organophosphate fertilizers by maize was 29.6%. While this might seem modest, it is notable considering the high P-draining character of tropical soils. The superior efficiency of these protected fertilizers stems from both the physical protection promoted by the biochar in the fertilizer and the chemical mechanisms that lead to a more gradual P release. This research offers compelling evidence that biochar-based organophosphate fertilizers are a promising solution for improving nutrient management, crop yields, and soil fertility in challenging tropical environments.

Source: da Silva, R. W., Passos, R. R., Silva Loquez, M. H. R., Andrade, F. V., Santos, D. A., Rangel, O. J. P., & Mendonça, E. S. (2025). Agronomic Efficiency of Biochar-Based Organophosphate Fertilizers. ACS Agricultural Science & Technology.