Effects of Biochar on Rhizosphere Phosphorus Fraction, Phosphatase Activity and Phosphorus Uptake of Soybean at Different Growth Stages

Objective This study investigated the effect of biochar application on rhizosphere phosphorus (P) dynamics, P uptake, and transport of soybean at different growth stages in lateritic red soil.

Method A pot experiment was conducted with four treatments including CK (control), P (addition of 13 mg kg⁻¹ P), BC (addition of 4% rice straw biochar), and BP (addition of 13 mg kg⁻¹ P and 4% rice stalk biochar). Using methods such as sequential P fractionation, soil enzymology and real-time quantitative PCR to explore the effects of biochar combined with low P fertilizer on P fraction, phosphatase activity and microbial biomass P, plant P uptake and P transport gene expression at soybean seeding stage, podding stage and harvesting stage.

Result Compared with CK and P treatments, BC and BP treatments significantly increased soil pH, salt base saturation, Bray-P, inorganic P, organic P and residual P at the seeding stage, podding stage and harvesting stage. They also increased inorganic P proportion while reducing organic P and residual P proportion and the expression of soybean P transporter genes, resulting in promoted soybean P uptake. The alkaline phosphatase activity and microbial biomass P content of BC and BP treatments reached the highest peak at the podding stage. Compared with the non-biochar addition treatments (CK and P), biochar addition (BC and BP) increased alkaline phosphatase activities by 43%, 67% and 48% at the seeding, podding and harvesting stages, respectively. Compared with CK, the microbial biomass P content in the BC treatment increased by 50%, 83% and 43% at the seeding, podding and harvesting stages, respectively. Similarly, the BP treatment showed increases of 69%, 76% and 77% in microbial biomass P content at the seedling, podding and harvesting stages compared to CK.

Conclusion Biochar application, either alone or combined with low P fertilizer, significantly increased soil P availability and soybean P uptake in latosolic red soil. This effect was associated with increased alkaline phosphatase activity and microbial biomass P, with the greatest enhancement observed during the soybean podding stage, indicating a notable promotion of enzymatic organic P mineralization at the soybean podding stage.