Retention of Crop Residue Increases Crop Productivity and Maintains Positive Sulfur Balance in Intensive Rice-Based Cropping Systems

Conservation Agriculture (CA) is promoted as a novel practice for high yielding, rice-based crop rotations but there has been limited study of its effects on sulfur (S) balance. In an annual rice-rice-wheat cropping pattern, common in the Eastern Gangetic Plain (EGP), we evaluated S balance and crop productivity after 24 consecutive crops with minimum soil disturbance and increased crop residue retention treatments relative to conventional practice on a sulfur-deficient silt clay loam soil. The experiment was sampled after 8 continuous years (i.e., 24 crops) of (A) minimum soil disturbance (strip planting=SP) versus conventional tillage (CT) and (B) low crop residue retention (LR=current practice) or high residue retention (HR). Thereafter, during crops 25-30, the plots were split between the current recommended dose of S (CD) and 150% of CD (HD) to assess effects on partial S balance. Soils were re-sampled after crop 30. High residue retention and HD produced a positive S balance (9-10 kg ha(-1) yr(-1)). The component crop yields and rice+rice+wheat yield were also significantly higher in HR with HD than other treatments. Soil organic carbon, total nitrogen and S content were significantly higher in SP coupled with HR. In both tillage systems, the current practice of LR with CD resulted in a small negative S balance (1-2 kg ha(-1) yr(-1)). The intensive rice-rice-wheat cropping patterns of the EGP involve high grain yield and significant crop residue removal, but with CA there is an opportunity to reverse the current negative S balance and improve soil health while increasing crop yield.