Effect Of Management Practices On N₂O Emissions And Soil Organic Carbon From The Typical Winter Wheat-summer Maize Cropland In North China Plain

Global warming is one of the most serious global environmental problems for human beings, and agricultural activities are the important anthropogenic emission sources of greenhouse gases（GHGs）, especially non-CO2 greenhouse gases. The measures for slowing the climate change in agricultural production include two aspects-mitigating greenhouse gas emissions and increasing sinks of GHGs. The soil carbon pool is 3 times and 4 times of the atmospheric carbon pool and the vegetation carbon pool, respectively. A variety of farming activities can enhance agricultural soil carbon sink to slow down the increasing rate of GHG concentration in the atmosphere with low-cost. In this study, a long-term field experiment was conducted in a winter wheat- summer maize field on the North China Plain. Six different management practices were set as treatments in this study including :1)No fertilization + Plowing（CK）; 2)Conventional fertilization + Plowing（FS）; 3)Combination of manure with fertilizers+ Plowing（FM）;4)Conventional fertilization +Straw incorporation +Plowing（FST）; 5)Conventional fertilization +Straw incorporation+Rotary tillage（FSR）;6)Conventional fertilization +Straw mulch +no-tillage（FSN）. N₂ O emissions during three consecutive years were monitored and, and the changes of soil organic carbon（SOC） after 5 years conducting of different practices were measured to evaluate the effect of fertilization, tillage and straw incorporation on soil N₂ O emissions and SOC. And the contribution of various production means and production activities on the carbon footprint were evaluated to screen the best management practices from winter wheat-summer maize production system according to the life cycle method. This study could provide technical supports for the intensive farmland with stable high yield and low-carbon in the North China area. Following results were got in this study:1. The seasonal characteristics of N₂ O emission were similar under different management practices from the winter wheat- summer maize field: emission peaks usually occurred after fertilization and irrigation. N₂ O emissions during winter wheat growth period were affected by both temperature and soil moisture, while it was mostly affected by soil moisture during summer maize growth period.2. Applying 30% of total nitrogen from manure could decrease N₂ O emissions by 15.6%（average of two years）, and the N₂ O emission intensity per unit production also showed lower（0.16%）, indicating that it was the recommendable practicable with stable crop yield and low-carbon emissions.3. The carbon footprint was ranged between 1550.2 to 2025.8kgC-e/hm2/a in winter wheat-summer maize production system under different management practices（except for the no fertilization control with value of 811.0-828.8kgC-e/hm2/a）. The carbon footprint derived from chemical fertilizer producing contributed the highest share of total carbon footprint（42.9%-49.3%, specifically the share was 36.0-39.0% for the treatment applied with contributions of fertilizer and manure）, and other contribution sources followed were irrigation consumes（21.3%-27.8%）, the application of nitrogen fertilizer（16.0-24.3%）, agricultural machinery（8.0-10.8%） and the production of seeds（3.0%-3.9%） and pesticides（0.4%-0.5%）. Therefore, decreasing the carbon emissions from chemical fertilizer industry was important for the carbon footprint of agricultural product life cycle.4. The in situ straw incorporation experiment indicated that the decomposition rate under no-tillage was slower while the humification coefficient was relative higher compared with that under conventional plough tillage or rotary tillage.5. Five years long-term experiment showed that the changing rate of SOC was varied under different management practices. During 5 years period, the relative changing rate of SOC were treatment with combination of manure with fertilizers（2.66%/a） > no-tillage with straw incorporation（0.92%/a） > plough or rotary tillage with straw incorporation（0.74-0.78%/a） > only chemical fertilizer（0.30%/a）. The average annual decrease rate of SOC of control plot was 3.78% in no fertilization and plowing treatment during 5 years. Compared with conventional fertilization and without straw, combination of manure with chemical fertilizers could increase SOC, as well as straw mulch under no-tillage.6.The crop yields under different management practices were In this experiment, There were no significant differences on crop yields among the studied treatments, indicating that combined application of manure with chemical fertilizers together could make a markedly drop on carbon footprint（16.7%） in winter wheat-summer maize system. and the carbon footprint, to some extents, could be decreased by no-tillage with straw mulching. From economic aspect, straw incorporation the field would get better economic benefits with annual benefit of 20450.7 Yuan/hm2/a, and higher ration of output/input was 1.69.Considering multiple index of crop production, N₂ O emissions, lifecycle carbon footprint, carbon costs and output ratio, etc., combined application of organic manure with chemical fertilizer and straw incorporation were the recommended practices with stable crop yields and low-carbon emissions in winter wheat- summer maize production system.