Effect of reduced N application and soybean intercropping on soil N₂O emission in sweet corn fields in South China

Intercropping systems have been proved to be sustainable, boosted crop productivity and increased resource utilization. However, little has been known about the effect of intercropping on greenhouse gas emissions in field soils. Intensive mono-cropping of sweet corn along with N fertilizer overuse induces nitrous non-point pollution in South China. Cereal-legume intercropping can reduce N application while maintaining crop yield. The objective of this study was to determine the effect of sweet corn and soybean intercropping under reduced N fertilizer on soil N₂O emission and crop yield. A field experiment was conducted in South China Agriculture University during three seasons (autumn of 2013, spring of 2014 and autumn of 2014), two N fertilizer levels (N0: 300 kg·hm^-2 and N1: 360 kg·hm^-2) and three planting patterns sweet corn||soybean intercropping system with line ratios of sweet corn to soybean of 2︰3 (S2B3) and 2︰4 (S2B4), sole sweet corn (SS) were used. N₂O emission in the field was determined using the static chamber/gas chromatographic technique. Results showed that reduced N application significantly decreased Global Warming Potential of N₂O (GWPN₂O, kg·hm^-2), with treatment of S2B4-N0 producing the lowest GWPN₂O, respectively 66.31%, 84.08% and 51.31% less than S2B4-N1 during the three seasons. However, no significant difference in GWPN₂O was noted among different planting patterns. In addition, reduced N application did not reduce crop yield and land equivalent ratio (LER) was greater than one in every intercropping systems. As the yield of intercropping system was higher than that of mono- cropping of sweet corn and reduced N application decreased soil N₂O emission, intercropping and reduced N application significantly decreased Greenhouse Gas Intensity of N₂O (GHGIN₂O = GWPN₂O/yield, kg·t^-1). The lowest GHGIN₂O was observed under S2B4-N0 treatment. During the three seasons, the average GHGIN₂O under S2B4-N0 treatment dropped by 71.60% and 71.21% compared with that under SS-N0 and S2B4-N1 treatments, respectively. The study demonstrated that intercropping with reduced N application was an efficient strategy for maintaining crop yield, increasing land use rate and reducing N₂O emissions. The S2B4-N0 had the best effect.