Effects of biochar amendment with phosphorus fertilizer on organic phosphorus transformation and soybean phosphorus uptake in red soil

Objective To investigate the effect of biochar addition at different phosphorus (P) levels on P transformation and crop P uptake in red soil, as well as the underlying processes and mechanisms, and provide a scientific basis for the application of biochar in reducing P input and increasing efficiency, as well as promoting soybean P uptake.

Method An acidic red soil was used as the test soil to explore the effects of 4%(w) rice straw biochar under four phosphate fertilizer levels (0, 30, 60 and 90 kg·hm⁻²) on contents of soil components, phosphatase activity, microbial biomass P content and soybean P uptake and their correlations.

Result P level, biochar and their interaction had significantl effects on soybean P absorption, soil P composition and turnover. The biochar addition promoted soybean P uptake and P use efficiency, with a more significant effect at 30 kg·hm⁻² P treatment. Biochar application at different P levels increased soil inorganic P content, especially the NH₄F-Pi, HCl-Pi. Without phosphate fertilizer, adding biochar reduced NaOH-extractable organic P by 48.5%. Furthermore, adding biochar with 0 and 30 kg·hm⁻² P treatment increased soil alkaline phosphatase activity by 71.7% and 46.0% respectively, and soil microbial biomass P content by 458.3% and 84.0% respectively.

Conclusion Biochar addition under low P conditions significantly promotes plant P uptake and P use efficiency, while also enhancing the biological transformation of soil labile organic P.