适宜施氮量降低京郊小麦-玉米农田N2O排放系数增加产量

为明确京郊地区小麦-玉米轮作农田的N_2O排放特征,寻求既能减少N_2O排放又保证粮食产量的切实有效措施,以京郊地区冬小麦-夏玉米轮作农田为研究对象,运用静态箱法对8个施氮水平的农田N_2O交换通量进行了连续一年对比研究,每季作物施肥量分别为N0(0 kg/hm~2),N1(50 kg/hm~2),N2(100 kg/hm~2),N3(150 kg/hm~2),N4(200 kg/hm~2),N5(250 kg/hm~2),N6(300 kg/hm~2),和N7(400 kg/hm~2)。在N0-N7施氮量条件下冬小麦季N_2O排放量为0.08~0.52 kg/hm~2;夏玉米季0.26~3.70 kg/hm~2。整个轮作周期,小麦季各处理N_2O排放损失率为0.05%~0.13%;玉米季0.78%~1.02%。在京郊地区冬小麦-夏玉米轮作体系中夏玉米季氮肥施入农田土壤后,土壤N_2O排放通量高于小麦季。京郊农田土壤N_2O排放通量表现出明显的季节性和日变化规律。综合考虑本试验条件下施肥量、N_2O排放量和京郊地区潮土农田小麦-玉米产量,研究认为该轮作体系中每季作物的施肥量为N4(200 kg/hm~2)比较合理,可为合理施肥及估算中国农田温室气体排放量提供参考。

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.