Long-term impact of legume-inclusive diversification and nutrient management practices on phosphorus dynamics in...

An insight into the dynamics of soil phosphorus (P) pools with long-term cropping/management practices would help in designing efficient and sustainable management module(s). The study aimed to investigate the long-term impact of diversified rice-based rotations and variable nutrient management practices on the dynamic composition of P pools and their influence on systems' base-crop productivity in an alkaline soil of Indo-Gangetic plain (Fluvisol). Treatments consisted of four rotations [rice-wheat (R-W), rice-wheat-mungbean (R-W-Mb), rice-wheat-rice-chickpea (R-W-R-C), rice-chickpea (R-C)] each with three nutrient treatments [control (CT), integrated nutrient management (INM), sole-chemical fertilizers (CF)]. Notably, R-C exhibited higher levels of bioavailable-P (soluble-P, Ca₂-P, labile-Po), particularly in subsurface soil depth (0.2-0.4 m) compared to other rotations. Likewise, the inclusion of chickpea every alternate year (R-W-R-C) resulted in higher Ca₂-P (40%), labile-Pi (15%), labile-Po (11%), and moderately labile Po (8%) compared to R-W rotation demonstrating an increased significance of chickpea in maintaining a favorable soil P regime in alkaline soil. Both R-C and R-W-R-C reduced the surface-to-subsurface depth ratio (SSBR) of soluble-P and Ca₂-P while increasing the ratio for microbial biomass P. Even with a suboptimal fertilizer-P rate, INM significantly increased soluble-P (4-33%), labile-Po (13-17%), microbial biomass P (10-26%), moderately labile-Po (4-17%) compared to CF and exhibited higher SSBR values. Correlation analysis demonstrated the substantial influence of very-labile carbon, microbial and phosphatase activities on P availability. The treatment-induced changes in labile-P pools significantly influenced rice (base-crop) yields. In conclusion, chickpea-inclusive diversification and INM could be a sustainable approach to enhance P bioavailability and crop productivity in tropical rice soils.