Suitable nitrogen application reducing N2O emission and improving grain yield in wheat-maize crop rotation system in Beijing suburb

Abstract: Nitrous oxide (N2O) has been recognized as one of the most important trace gases in the atmosphere that causes global warming and stratospheric ozone depletion. Nitrogen (N) fertilizer is considered as the primary source of N2O emissions from agricultural soils. N2O production and emission processes are influenced by a number of soil and environmental variables, interacting of soil water and N processes, crop uptake and management practices. As a large agricultural country, China consumes the greatest amount of synthetic N fertilizer which accounts for 30% of the world consumption. Therefore, quantifying N2O emissions from agricultural soils and seeking suitable mitigation measures have become a relatively hot issue in international global climate change studies. It is a great challenge to guarantee high crop yields while reducing N2O emissions under high input of N fertilizers (e. g., N fertilizer application rate can be as high as 600 kg/hm2 in the North China Plain). However, few field data sets are available for the exploration of the effects of fertilizer N regimes on soil N2O emission in Beijing suburb, one of the regions with the most intensive agriculture in North China Plain. The main objectives of this research were to identify the characteristics of N2O emission from winter wheat - summer maize rotation land in Beijing suburb, and to seek a way that could decrease N2O emission and increase or keep crop yield. N2O exchange fluxes from the intensively cultivated winter wheat - summer maize rotation system in Beijing suburb, Fangshan District, were measured by the static chamber technique under 8 levels of N treatments from October 13, 2012 to September 28, 2013. Eight treatments with 3 replications (each micro-plot was 80 cm in diameter and 0.5 m2 in area) were contained in the experiment: N0 (0 kg/hm2), N1 (50 kg/hm2), N2 (100 kg/hm2), N3 (150 kg/hm2), N4 (200 kg/hm2), N5 (250 kg/hm2), N6 (300 kg/hm2), and N7 (400 kg/hm2) respectively for each crop field. The results indicated that the cumulative emissions of N2O from 8 levels of N treatments were 0.08-0.52 kg/hm2 (winter wheat) and 0.26-3.70 kg/hm2 (summer maize), respectively. The N2O emission during the wheat growing season from 8 levels of N fertilization treatments accounted for 0.05%-0.13% of the total N loss, and during the maize growing season were 0.78%-1.02%, which indicated that the emission of N2O mainly occurred during the maize growing season. It was obvious that the application of existing chemical fertilizers showed significantly seasonal and diurnal variation on the N2O emissions in wheat-maize rotation system in the suburbs of Beijing. Considering fertilizer rates, N2O emission and crop yield, it was concluded that the fertilization rate of N4 (200 kg/hm2) for each crop was very reasonable, which could provide the basis for applying fertilizer rationally, reducing farm production costs, estimating greenhouse gas emissions from cropland and compiling national greenhouse gases emission inventory.