Nitrogen cycling enhanced by conservation agriculture in a rice-based cropping system of the eastern Indo-Gangetic Plain

Changes in soil tillage and residue retention after introducing conservation agriculture practices in intensive rice-based cropping systems in Bangladesh may alter nitrogen (N) cycling and N fertilizer requirements. An experiment was established on a farmer’s field, with a legume dominated-rotation (lentil-mungbean-monsoon rice), two types of tillage – strip planting (SP) and conventional tillage (CT); and two levels of residue retention – high residue (HR) and low residue (LR). A total seven crops were studied in the 2.5 year periods (2010-13). Soil total N concentration (TN), soil N-stocks after Crop 7 and the annual N accumulation rates at 0-15 cm soil depth for 2010-13 are presented. At the end of Crop 7 (after 2.5 years), SP treatment increased the TN concentrations and N-stocks by 11 % compared to CT at 0-15 cm soil depth. The annual soil N accumulation rates were 66 kg/ha with SP while N losses were 20 kg/ha under CT during 2010-13. The N accumulation rate was 3.3 times higher with HR than LR. From 2010 to 2013, the N balance calculation indicated an estimated N gain of 51 kg/ha in SPHR but a loss in CT which ranged from 9 kg/ha in CTHR to 319 kg/ha in CTLR at 0-15 cm soil depth. The N uptake was also 14 % higher from grain and straw under SP than CT. Both SP and HR increased TN, N-stocks and N accumulation by contrast with N loss under CT. However, the turnover of TN in SPHR needs longer investigation because of likely effects on N fertiliser requirements