Placement effects on rice residue decomposition and nutrient dynamics on two soil types during wheat cropping in rice-wheat system in northwestern India

Crop residues are important sources of organic matter and plant nutrients and known to affect soil quality. Tillage affects residue decomposition and nutrient cycling processes. A 2 year field study was aimed to investigate the decomposition and nutrient dynamics from surface-placed and incorporated rice (Oryza sativa L.) residue on two soil types using the nylon mesh bag technique over wheat cropping cycle in rice-wheat system in northwestern India. A single-pool first-order exponential decay function showed R (2) larger than 0.9. Over the wheat growing cycle about 20% of buried rice residue and 50% of surface-placed residue remained undecomposed. Nitrogen exponential decay models were significant at P < 0.01. At wheat boot stage (1,100 growing degree days, DGD) 12 kg N ha(-1) (27% of the initial N) was released from the buried residue losing 60-65% of its N at the end of decomposition cycle. Nitrogen in surface rice residue increased throughout the decomposition cycle due to microbiological immobilization. The change in P with time (DGD) was small and weakly defined by the exponential function. Nutrient dynamics of rice residue indicate that it is not a potential source of N and P for wheat over short-term. The change in K concentration was well described by exponential function (R (2) 0.73-0.86). Potassium in rice residue decreased at a fast rate during the initial 20 days (400 DGD) and > 80% was released by 40 days (680 DGD).