Enhancing soil health and phosphorus use efficiency with modified biochar amendment

Phosphorus (P) is essential for plants, but its low solubility in soils limits bioavailability, requiring excess P application for successful crop production. Biochar is often applied to enhance nutrient retention in the soil. Metal-coated (modified) biochar is gaining popularity to further improve these effects. However, P uptake and utilization in plants after pristine and modified biochar applications have not yet been quantified. This study investigated soil health, sorghum biomass and grain yield, P uptake, and plant P utilization efficiency (PUE) using sorghum (Sorghum bicolor (L.) Moench) as a test crop. Treatments compared were three biochar types [iron-modified biochar (FeB),magnesium-modified biochar (MgB), and unmodified pristine biochar (PrB)] and a no-biochar control (CK). Biochar additions increased sorghum grain (10-27 %) and biomass (5-15 %) yields compared to CK, with the highest increase in grain yield observed with FeB. Specifically, modified biochars (FeB and MgB) decreased P concentration in leaves, roots, and shoots, resulting in an average increase in PUE by 61 % and 34 %, respectively, compared to PrB and CK. P uptake in the seed was significantly higher in FeB than in PrB. Leachate analysis showed that FeB and MgB retained more P, S, and Cu, while increasing the availability of cations (Ca, Mg, Mn, Na, and Zn) in the leachate. The mechanism of P utilization varied among P modifiers; Mg-modified biochar enhanced crop production by increasing plant photosynthesis, while Fe-modified biochar regulated P bioavailability and crop production by affecting soil pH and nutrient availability. Nevertheless, modified biochar amendment could enhance agronomic and environmental sustainability of crop production by increasing crop yield, PUE, and soil biological activity while mitigating P loss through leaching.