| Wheat and maize rotation is the main approach to plant crops in north China. Currently due to the pursuit of high yield and high profits in agricultural production activity, there is a big blindness and randomness of nitrogen fertilizer. However, excessive application of N fertilizers will decrease crop yields and waste fertilizer,and also lead to soil,water and atmosphere polluted. Research on the effects of different N fertilizer management practices on crops and N2 O emissions will assist the selection of effective N management measures which enable achieving high crop yields and nitrogen utilization while reducing N2 O emissions.The paper selected wheat-maize rotation system as the research object, and combined field experiment with indoor analysis method. We conducted field trials setting up 7 treatments of no N fertilizer(CK), farmers common N rate(AN), optimal N rate(ON), 20% reduction in optimal rate + Dicyandiamide(ON80% + DCD), controlled release fertilizer in optimal rate(ON-SR), controlled release fertilizer 20% reduction in optimal rate,20% reduction in optimal rate + Nano-carbon(ON80% + NC). The static closed chamber was adopted to collect gas during crop growth, and study seasonal change of N2 O emission flux.Biological character, yield, nitrogen absorption and utilization,and space-time dynamic change of soil nitrogen and nitrogen balance were researched in wheat-maize rotation system. Finally, the treatment which gets the best economic benefits and reduce effectively environmental pollution of nitrogen fertilizer was determined through the comprehensive analysis of crop yields, economic benefits, effect of mitigating N2 O emissions and soil nitrogen apparent loss. The main conclusions of this study were as following:1. There were obvious seasonal characteristics of N2 O emissions under different nitrogen fertilizer management practices and N2 O emissions were mainly concentrated in the sowing-greening stage of wheat and sowing-jointing stage of maize, accounting for 54.6%-68.2 % and 55.45%-76.85% of the overall emissions respectively. 23.81%-39.69% of N2 O emissions was from the whole stages of wheat during the two wheat-maize rotation system, and maize accounting for 60.31%-76.19%. Considering the total rotation system, compared with AN, N2 O emissions were decreased by 25.70%, 53.35%, 20.10%, 40.61%, and 39.92% respectively under ON, ON80%+DCD, ON-SR, ON80%-SR and ON80%+NC, and emission factors were declined by 0.02-0.23 percentage points.The effect of N2 O emission reduction of the ON80%+DCD treatment is better than the two treatments of ON80%-SR and ON80%+NC.We therefore recommend reasonable adjustment of basal/topdressing ratios of N fertilizers to be adopted based on periodic characteristics of soil moisture and N2 O emissions.2. Reasonable application of nitrogen fertilizer is favorable for improving crop yields and its components. Compared with AN, nitrogen fertilizer production efficiency of wheat and maize under other nitrogen treatments were improved by 20.15%-79.53% and 28.68%-74.74%,respectively,nitrogen agronomic efficiency improved by 38.28%-108.18% and 14.82%-143.03%, and nitrogen harvest index increased by 1.91-12.78 and 2.21-6.35 percentage points.Compared with AN, the grain yield of the first and second crop rotation system were increased by 2.74%-13.50% and 0.31%-9.88%,and the ON80%+DCD treatment get the biggest increase and its net benefits were improved by 32.15% and 22.99%.3. The temporal-spatial distribution discipline of soil nitrate nitrogen in wheat-maize rotation system.was definited. The content of nitrate nitrogen reduced with the extension of the growth period of wheat or maize, and the soil depth deepen.Except CK, nitrogen apparent loss from wheat and maize was decreased with nitrogen application rate reduced.Thus we should control nitrogen fertilizer scientifically and reduce nitrogen loss such as leaching into groundwater, atmospheric volatilization.The results showed that crop yields and economic benefit is better from the ON80%+DCD treatment with least amount of N2 O emissions and soil nitrogen apparent loss less.The nitrogen fertilizer management ensure a stable high yield, and effectively reduce the risk of environmental pollution. The ON80%+DCD treatment can be a fertilization method as recommended for farmers. |
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