Maize lowers the N2O emissions from maize/soybean intercropping

Abstract

Interspecific interactions between intercropped maize and soybean are expected to cycle soil nitrogen efficiently and avoid N₂O emissions. However, the unique interactions of maize and soybean with nitrogen cycling bacteria makes it hard to predict the crop-specific impact on soil N₂O production. We conducted a field microcosm experiment with root separation to simulate monoculture and intercropping with maize and soybean. Intercropped maize reduced the N₂O emissions by 16–41%, compared to monoculture maize. This was related to reduced nitrification by ammonia-oxidizing bacteria and denitrification reactions (as indicated by the abundance of nirS and nirK gene copies), as well as drier soil conditions and lower soil NO₃⁻-N levels. Soil N₂O emissions were the same in monoculture and intercropped soybean, suggesting stable denitrification (based on nirS, nirK and nosZ genes) with constant soil physicochemical conditions. As monoculture maize can stimulate soil N₂O emission through denitrification, this work justifies the adoption of maize-soybean intercropping as a low N₂O-emitting practice in sustainable agriculture, due to its beneficial effects on soil biology and biochemistry.