Tillage, Green Manure And Residue Retention Improve Aggregate-Associated Phosphorus Fractions Under Rice-Wheat Cropping

Abstract

The sustainability of rice-wheat system (RWS) in north-western India 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. 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. In rice, the main plot treatments were combinations of wheat straw and Sesbania green manure (GM) management: (1) puddled transplanted rice (PTR) with no wheat straw (PTRW0), (2) PTR with 25% wheat stubbles (12-15 cm long) retained (PTRW25), (3) PTR without wheat straw and GM (PTRW0+GM), and (4) PTR with wheat stubbles (25%) and GM (PTRW25+GM). Three sub-plots treatments in the successive wheat crop were (1) conventional tillage with rice straw removed (CTWR0), (2) zero tillage (ZT) with rice straw removed (ZTWR0) and (3) ZT with 100% rice straw retained as surface mulch (ZTWR100). Results of the present study revealed that all phosphorus fractions were significantly higher in PTRW25+GM followed by ZTWR100 compared with PTRW0/CTWR0 treatment within both macro- and micro-aggregates. The total phosphorus (P), available P, alkaline phosphatase and phytin-P were significantly higher under ZTWR100 than CTWR0. Principal component analysis identified NaOH-Po, NaHCO3-Pi and HCl-P as the dominant and reliable indicators for evaluating P transformation within aggregates under conservation agriculture based practices.