Long-Term Impact of Crop Diversification and Nutrient Management on Soil Phosphorus Pools in Indo-Gangetic Plain

Understanding the dynamics of soil phosphorus (P) over extended periods of soil and crop management practices is essential for sustainable P management. This study assessed the impact of four crop rotations [maize-wheat (M-W), maize-wheat-mungbean (M-W-Mb), maize-wheat-maize-chickpea (M-W-M-C), and pigeonpea-wheat (P-W)] each with three levels of nutrient management [control (CT), integrated nutrient management (suboptimal fertilizer+ farmyard manure + crop residue + bio-fertilizers; INM), and sole-chemical fertilizers (CF)] on soil inorganic and organic P (Pi and Po) pools and crop-soil relationships at the end of 15-year cropping. Legume-inclusive rotations resulted in higher labile-P pools, being higher with M-W-M-C and P-W. M-W-M-C rotation had higher moderately labile organic P (Po) in both surface (+23%) and subsurface (+18%) depths over M-W. Di-calcium P (Ca2-P) (+6%) and microbial biomass P (MBP) (+46%) increased in M-W-Mb over M-W, while iron-P (Fe-P) was reduced (-12%) in subsurface soil. INM enhanced bioavailable-P [soluble-P (+17%), labile-Pi (+15%) labile-Po (+12%), MBP (+96%), moderately labile-Po (+22%)] over CF in surface soil, while CF had a higher Fe-P (+16%). Legumes in rotation caused notable changes in the surface-to-subsurface ratio (SSBR) of Ca2-P (1.18-1.50) and occluded-P (1.64-2.78). INM had a higher SSBR of labile-P pools but had a lower SSBR of occluded-P facilitating mobilization of the later in the surface. Hence, in tropical soils, legume-inclusive diversification (particularly with chickpea) and INM involving crop residue recycling could be a sustainable option to improve P use efficiency, crop productivity, and save fertilizer resources.