Tillage, green manure and residue retention improves aggregate-associated phosphorus fractions under rice–wheat cropping

The sustainability of the rice–wheat system is threatened due to the deterioration of soil health and emergence of new challenges of climate change caused by low nutrient use efficiency and large scale burning of crop residues. The conservation agriculture based on tillage intensity, crop residue retention and raising green manuring (GM) crops during the intervening period between wheat harvest and rice establishment offers opportunities for restoration of phosphorus (P) dynamics and stimulate phosphatase activities within the macro-and micro-aggregates. Phosphorus and phosphatase activities in the soil aggregates affected by different residue management practices remain poorly understood. Thus, soil samples were obtained after a five-year field experiment to identify the effect of tillage, green manure and residue management on aggregate-associated phosphorus fractions. Four main plot treatments in rice included combination of wheat straw and GM were conventional till puddled transplanted rice (PTR) with no wheat straw (PTR W0 ), PTR with 25% wheat stubbles retained (PTR W25 ), PTR without wheat straw and GM (PTR W0 + GM), and PTR with wheat stubbles and GM (PTR W25 + GM). Three sub-plots treatments in the successive wheat crop were conventional tillage (CT) with rice straw removed (CTW R0 ), zero tillage (ZT) with rice straw removed (ZTW R0 ) and ZT with rice straw retained as surface mulch (ZTW R100 ). Results of the present study revealed significantly higher phosphorus fractions (HCl-P, NaHCO 3 -P i and NaOH-P o ) in treatment PTRW 25 + GM and ZTW R100 compared with PTRW 0 /CTW R0 within both macro- and micro-aggregates. The total phosphorus (P), available P, alkaline phosphatase and phytin-P were significantly higher under ZTW R100 than CTW R0 . The principal component analysis identified NaOH-P o , NaHCO 3 -P i and HCl-P as the dominant and reliable indicators for evaluating P transformation within aggregates under conservation agriculture-based practices.