The role of maize plants in regulating soil profile dynamics and surface emissions of nitrous oxide in a semiarid environment

To study the effects of maize plants on nitrous oxide (N2O) fluxes from a dryland experimental farm, in situ soil profiles of N2O concentrations and surface emissions were investigated in a field experiment from 2014 to 2015 in the semiarid areas of northwestern China. The experiment included four treatments: unplanted and N-unfertilized soil (C0), unplanted soil fertilized with 225 kg N ha(-1) (CN), maize-planted and N-unfertilized soil (P0), and maize-planted soil fertilized with 225 kg N ha(-1) (PN). Surface N2O emissions and soil N2O concentrations at depths of 0, 10, 20, 30, 40, and 50 cm were measured weekly. Nitrogen fertilization significantly increased the soil N2O concentrations and surface emissions. Compared to the unplanted soil, the presence of maize plants significantly decreased the N2O concentrations at depths of 10-40 cm during the maize growing season. The modeled N2O fluxes at a depth of 10 cm presented a similar pattern to the chamber measurements. However, there was a discrepancy between the concentration gradient and chamber methods when the fluxes were high, mainly because the gradient method could not detect N2O production and consumption process above the uppermost gas sampler (0-10 cm). Soil moisture and temperature were critical factors affecting the N2O concentrations and surface emissions. The respective cumulative surface emissions and effluxes at a depth of 10 cm during the maize growing season (PN treatment) were decreased by 8.9 and 17.9% in 2014 and by 14.7 and 17.5% in 2015 compared to values of the CN treatment. This was mainly due to the decrease in soil moisture caused by the growth of the maize plants, which resulted in a soil condition less suitable for N2O production