Phosphorus (P) is an essential macronutrient for plant growth, but its limited availability in most soils due to insoluble precipitates poses a significant challenge to agriculture. To address this, 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 has emerged as an eco-friendly 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. A comprehensive review published in Soil Ecology Letters by Radwa Fathy, Wagdi Elagroudi, Ahmed A. Taha, and Ahmed Mosa, explores the various ways biochar influences phosphorus dynamics in soil, aiming to unlock soil P reserves and enhance its phytoavailability.

The review highlights that the inherent phosphorus content of biochar is highly dependent on both the feedstockFeedstock refers to the raw organic material used to produce biochar. This can include a wide range of materials, such as wood chips, agricultural residues, and animal manure. More material and the pyrolysisPyrolysis is a thermochemical process that converts waste biomass into bio-char, bio-oil, and pyro-gas. It offers significant advantages in waste valorization, turning low-value materials into economically valuable resources. Its versatility allows for tailored products based on operational conditions, presenting itself as a cost-effective and efficient More temperature. For instance, biochar derived from bones, and subjected to pyrolysis temperatures above 600∘C, exhibited the highest P concentrations, reaching up to 124,216 mg kg−1 and 31,160 mg kg−1 respectively. This is significantly higher than P concentrations in biochar from woody wastes (1410 mg kg−1) or crop residues (4701 mg kg−1).

Beyond its direct P contribution, biochar plays a crucial role in indirectly modulating P dynamics by influencing soil physicochemical characteristics and stimulating beneficial microorganisms. The review emphasizes biochar’s pivotal role in encouraging the colonization of microorganisms that mediate P phytoavailability, such as vesicular arbuscular mycorrhizae (AM) and phosphate-solubilizing bacteria (PSB). For example, AM fungi can exploit biochar as a physical growth medium and a source of nutrition, improving P translocation into plant roots by about six times in some cases. Similarly, rice husk and rice straw biochars have been shown to act as bacterial shelters, improving P solubilization by up to 43.9% through enhanced secretion of polysaccharides, organic acids, and phosphatase activity by PSB.

Biochar’s ability to minimize P losses through surface runoff and percolation into groundwater was also highlighted. Its high porosityPorosity of biochar is a key factor in its effectiveness as a soil amendment and its ability to retain water and nutrients. Biochar’s porosity is influenced by feedstock type and pyrolysis temperature, and it plays a crucial role in microbial activity and overall soil health. Biochar More and water sorption capacity contribute to reducing runoff and soil losses, leading to improved P retention in the soil matrix. Studies have shown that biochar application can reduce total and dissolved reactive P losses from paddy fields by 6.77%-17.62% and 6.22%-10.28%, respectively. Furthermore, biochar application generally leads to a considerable increase in phosphorus use efficiency (PUE) in plants, averaging 43.36% compared to 20.26% in unamended soils. The PUE varied significantly based on biochar’s feedstock (29.1%-38.5%), pyrolysis temperature (9.4%-60.1%), and application rate (29.9%-88.1%).

While biochar offers numerous benefits, the review also notes contradictory results, with significant effects observed in lab investigations but only minimal effects in field-scale experiments. This disparity underscores the need for further research to contextualize lab-scale data with real-world field findings. Future prospects include tailoring functionalized biochar for specific soil types, developing biochar as a carrier for P-solubilizing microorganisms to maintain their viability, and further investigating the kinetic mobility of orthophosphate ions in the charosphere.

Source: Fathy, R., Elagroudi, W., Taha, A. A., & Mosa, A. (2025). Modulating effects of biochar on phosphorus dynamics in soil-biota-plant system: a comprehensive review.