Greenhouse gas emissions from soil under maize-soybean intercrop in the North China Plain

Intercrop systems can exhibit unique soil properties compared to monocultures, which influences the microbially-mediated processes leading to greenhouse gas emissions. Fertilized intercrops and monocultures produce different amounts of N2O, CO2 and CH4 depending on their nutrient and water use efficiencies. The objective of this study was to compare the fluxes and seasonal emissions of N2O, CO2, and CH4 from a maize-soybean intercrop compared to maize and soybean monocultures, in relation to crop effects on soil properties. The experiment was conducted during 2012, 2013 and 2014 at the WuQiao Experimental Station in the North China Plain. All cropping systems received urea-N fertilizer (240 kg N ha(-1) applied in two split applications). The cropping systems were a net source of CO2 and a net sink of CH4, with significantly (P < 0.05 in 2012) and numerically (2013 and 2014) lower N2O flux and smaller seasonal N2O emissions from the maize-soybean intercrop than the maize monoculture. The proportion of urea-N lost as N2O was lower in the maize-soybean intercrop (1.6% during the 3-year study) and soybean monoculture (1.7%), compared to maize monoculture (2.3%). Soybean reduced the soil NO3 (-)-N concentration and created a cooler, drier environment that was less favorable for denitrification, although we cannot rule out the possibility of N2O reduction to N-2 and other N compounds by soybean and its associated N-2-fixing prokaryotes. We conclude that maize-soybean intercrop has potential to reduce N2O emissions in fertilized agroecosystems and should be considered in developing climate-smart cropping systems in the North China Plain.