Soil N₂O emission in contour hedgerow/crop intercropping system in subtropical China

Nitrous oxide (N₂O) is one of the important greenhouse gases with a very strong global warming effect. Emissions of N₂O resulting from anthropogenic activities and agricultural management practices have gained international significance in the combating climate change. A field experiment was conducted from Nov. 2008 to Oct. 2009 to evaluate N₂O emissions in the crop rotation system of winter wheat and summer maize with contour Amorpha fruticosa hedge in subtropical China using static chamber gas chromatograph technique. Four treatments - compound planting of crop and hedgerow without return of hedgerow plant branches and leaves (AR), compound planting of crop and hedgerow with incorporation of hedgerow plant branches and leaves (AI), compound planting of crop and hedgerow with hedgerow plant branches and leaves mulching (AC) and monocropped crop (CK) - were used in the experiment. Results from the field observations suggested that the trends in emitted N₂O fluxes under AR, AI, AC and CK were similar. Total N₂O emissions from the four treatments during the whole growing season of winter wheat/summer maize rotation system were respectively 127.62 mg·m^-2, 209.66 mg·m^-2, 208.73 mg·m^-2 and 77.52 mg·m^-2. The order of N₂O emission at different growth of winter wheat was: flowering-ripening stage > elongation-flowering stage > seeding emergence-elongation stage. The corresponding order of N₂O emission at different growth stages of maize was: elongation-tasseling stage > seeding-elongation stage > tasseling-ripening stage. Furthermore, seasonal variation in N2O emission was regulated by soil temperature in winter wheat season and by water-filled soil pore space in summer maize season. Contour hedgerow intercropping and returning of hedge plant branches and leaves markedly enhanced soil N₂O emission in complex agro-ecosystems. Compared with hedge plant branches and leaves mulching, incorporation of branches and leaves promoted N₂O emission.