Nitrous oxide emissions from soils amended by cover-crops and under plastic film mulching: Fluxes, emission factors and yield-scaled emissions

Abstract

Assessment of nitrous oxide (N2O) emission factor (EF) for N2O emission inventory from arable crops fertilized with different nitrogen sources are under increased scrutiny because of discrepancies between the default IPCC EFs and low EFs reported by many researchers. Mixing ratio of leguminous and non-leguminous cover crop residues incorporation and plastic film mulching (PFM) in upland soil has been recommended as a vital agronomic practice to enhance yield and soil quality. However, how these practices together affect N2O emissions, yield-scaled emissions and the EFs remain uncertain. Field experiments spanning two consecutive years were conducted to evaluate the effects of PFM on N2O emissions, yield-scaled emissions and the seasonal EFs in cover crop residues amended soil during maize cultivation. The mixture of barley (Hordeum vulgare) and hairy vetch (Vicia villosa) seeds with 75% recommended dose (RD 140 kg ha−1) and 25% recommended dose (RD 90 kg ha−1), respectively, were broadcasted during the fallow period and 0, 25, 50 and 100% of the total aboveground harvested biomass that correspond to 0, 76, 152 and 304 kg N ha−1 were incorporated before maize transplanting. It was found that the mean seasonal EFs from cover crop residues amended soil under No-mulching (NM) and PFM were 1.13% (ranging from 0.81 to 1.23%) and 1.49% (ranging from 1.02 to 1.63%), respectively, which are comparable to the IPCC (2006) default EF (1%) for emission inventories of N2O from crop residues. The emission fluxes were greatly influenced by NH4+N, NO3−-N, DOC and DON contents of soil. The cumulative N2O emissions markedly increased with the increase in cover crop residues application rates and it was more prominent under PFM than under NM. However, the yield-scaled emissions markedly decreased under PFM compared to NM due to the improved yield. With relatively low yield-scaled N2O emissions, 25% biomass mixing ratio of barley and hairy vetch (76 kg N ha−1) under PFM could be recommended to enhance yield and to mitigate N2O emissions in an upland maize cropping system.