Rice-wheat cropping system: tillage, mulch, and nitrogen effects on soil carbon sequestration and crop productivity

Maintenance of organic carbon in soil (SOC) is critically important for sustained agricultural productivity and environmental quality. This paper presents SOC resulting from differences in tillage types and demonstrates how mulch and nitrogen (N) application can mediate the tillage functions on SOC and crop productivities. The results are derived from a 4-year field-scale study carried out in a low-land under sub-tropical hot and humid environment of Nepal. It compared eight treatment combinations, viz., tillage (no-tillage and conventional tillage), mulch (no-mulch and 12 Mg ha(-1) year(-1) of mulch), and N application (recommended versus leaf color chart method) under rice-wheat cropping system. Seasonal grain and biomass yields of these crops were recorded and at the end of the 4-year study, quantified the organic carbon stock of soil; Within 15 cm of surface soil, SOC stock (Mg C ha(-1)) was statistically (p < 0.05) higher on no-tillage plots (11.2-11.8) than on conventional tillage plots (9.2-10.5). The treatment effect was more pronounced on winter wheat productivity where conventional tillage combined with straw-mulch exceled the performance of no-tillage. Clearly, no-tillage had the environmental benefit, and conventional tillage had the crop productivity benefit.