Experimental warming-driven soil drying reduced N2O emissions from fertilized crop rotations of winter wheat-soybean/fallow, 2009-2014

Nitrous oxide (N2O) emissions from agricultural soils play an important role in the global greenhouse gas budget. However, the response of N2O emissions from nitrogen fertilized agricultural soils to climate warming is not yet well understood. A field experiment with simulated warming (T) using infrared heaters and its control (C) combined with a nitrogen (N1) fertilization treatment (315 kg N ha−1 y−1) and no nitrogen treatment (N0) was conducted over five years at an agricultural research station in the North China Plain in a winter wheat-soybean double cropping system. N2O fluxes were measured using static chambers about once every week during July 2009-June 2014. In the N1 treatment, warming decreased the soil moisture and N2O emissions in spring, autumn and winter and the annual cumulative emissions. Across all years, N2O fluxes were positively correlated with soil temperature and soil moisture. The effect of lower soil moisture on N2O fluxes exceeded that of higher temperature, leading to less N2O being released by the drier soils under warming. Nitrogen fertilizer increased N2O emissions without warming, but did not routinely increase N2O emissions under warming treatment. In the N0 treatment, warming neither decreased soil water content nor N2O emissions. Temperature and nitrogen input had significant direct and antagonistic effects on cumulative N2O flux in the N1 treatment. The decrease in N2O emissions from N1T was due to the significant decrease of soil water content, soil total nitrogen and organic matter, which consequently accelerated N cycle dynamics and advanced wheat growth.