Net global warming potential and greenhouse gas intensity in a double-cropping cereal rotation as affected by nitrogen and straw management

The effects of nitrogen and straw management on global warming potential (GWP) and greenhouse gas intensity (GHGI) in a winter wheat-summer maize double-cropping system on the North China Plain were investigated. We measured nitrous oxide (N2O) emissions and studied net GWP (NGWP) and GHGI by calculating the net exchange of CO2 equivalent (CO2-eq) from greenhouse gas emissions, agricultural inputs and management practices, as well as changes in soil organic carbon (SOC), based on a long-term field experiment established in 2006. The field experiment includes six treatments with three fertilizer N levels (zero N (control), optimum and conventional N) and straw removal (i.e. N-0 N-opt and N-con) or return (i.e. SN0, SNopt and SNcon). Optimum N management (N-opt, SNopt) saved roughly half of the fertilizer N compared to conventional agricultural practice (N-con, SNcon), with no significant effect on grain yields. Annual mean N2O emissions reached 3.90 kg N2O-N ha(-1) in N-con and SNcon, and N2O emissions were reduced by 46.9% by optimizing N management of N-opt and SNopt. Straw return increased annual mean N2O emissions by 27.9 %. Annual SOC sequestration was 0.40-1.44Mg C ha(-1) yr(-1) in plots with N application and/or straw return. Compared to the conventional N treatments the optimum N treatments reduced NGWP by 51 %, comprising 25% from decreasing N2O emissions and 75% from reducing N fertilizer application rates. Straw return treatments reduced NGWP by 30% compared to no straw return because the GWP from increments of SOC offset the GWP from higher emissions of N2O, N fertilizer and fuel after straw return. The GHGI trends from the different nitrogen and straw management practices were similar to the NGWP. In conclusion, optimum N and straw return significantly reduced NGWP and GHGI and concomitantly achieved relatively high grain yields in this important winter wheat-summer maize double-cropping system.