| The waste of crop straw resources and the farmland nitrogen loss have become the urgent problems that need to be solved urgently in the development of agriculture in China.Excessive application of nitrogen fertilizer will not only reduce the nitrogen use efficiency of crops,but also lead to the increase of nitrogen residue and various nitrogen-containing gas emissions in farmland,resulting in environmental pollution.Therefore,this paper took summer maize in Guanzhong area of Shaanxi as the research object,and investigated the effects of nitrogen application on summer maize growth,yield,nitrogen absorption and utilization,soil NO3--N residues,and ammonia volatilization in farmland under different straw returning modes through field experiments.The experiment adopted a completely randomized block design,and set up two factors:nitrogen application measures and straw returning modes.Four nitrogen application measures included no fertilizer F0,slow release fertilizer rate F1(180 kg·ha-1),urea reduction nitrogen application rate F2(180 kg·ha-1),and farmer urea traditional nitrogen application rate F3(270 kg·ha-1);the straw returning modes had 2 levels,namely,no-straw returning（N）and straw returning（S）.There were 8treatments were established.The main research results are as follows:（1）Both straw returned to the field and nitrogen application could promote the growth and yield of summer maize;nitrogen application could significantly increase the above-ground biomass,yield and components of summer maize at maturity.Compared with the traditional nitrogen application of farmers,reducing the application of available nitrogen fertilizer and the application of slow-release fertilizers would not reduce the yield of summer maize,and F1 slow-release fertilizer treatment had the largest yield.（2）Under different straw returning modes（N and S）,nitrogen application could significantly increase nitrogen accumulation of summer maize.And compared with farmer urea traditional nitrogen application rate F3,the application of slow-release fertilizer and urea reduction would not reduce the nitrogen accumulation of summer maize.The effect of straw returning on nitrogen accumulation of summer maize was not obvious.Straw returning combined with nitrogen fertilizer could increase nitrogen use efficiency and partial productivity of nitrogen fertilizer of summer maize.（3）The maximum emission peak of ammonia volatilization in summer maize farmland usually occurred 1-2 days after fertilization.The ammonia emission rate remained at a high level within one week after fertilization,and then entered low emission state.After 7 days of fertilization,there was basically no significant difference in ammonia volatilization rate of each treatment.The cumulative amount of ammonia volatilization within one week after fertilization accounted for more than 80%of the total ammonia emissions during the ammonia volatilization monitoring period.Under different straw returning modes（N and S）,the maximum rate of ammonia volatilization and the cumulative amount of ammonia volatilization of each nitrogen application treatment were F3>F2>F1>F0.Under the conventional urea treatments（F2 and F3）,the ammonia emissions of S treatment were higher than that of the N treatment.Both slow-release nitrogen fertilizer and reducing available nitrogen fertilizer rate could reduce the loss of soil ammonia volatilization.The ammonia emission of summer maize in topdressing stage was much larger than that in basal fertilizer stage.（4）During the whole growth period of summer maize,under different straw returning modes（N and S）,the nitrate nitrogen content in 0-100 cm soil of each nitrogen application treatment showed F3>F2>F1.Under different nitrogen application levels（F1,F2 and F3）,the nitrate nitrogen accumulation of 0-100 cm soil in the different growth periods of S treatment was lower than that of N treatment by 8.21%～39.63%,0.73%～59.15%and7.55%～56.23%,respectively,indicating that straw returning could reduce the NO3--N residue in 0-100 cm soil layer.The soil NO3--N accumulation in different growth stages of straw returning（S）treatment showed a decreasing trend,while the straw not to returned the field（N）treatment showed a trend of first increasing and then decreasing.In conclusion,straw returning+slow-release nitrogen fertilizer treatment could reduce the amount of ammonia volatilization loss in farmland soil,and increase maize yield and nitrogen absorption and utilization efficiency to a certain extent,and achieve a good effect of ensuring crop yield and reducing nitrogen loss in farmland.Therefore,straw returning+slow-release nitrogen fertilizer treatment（SF1）was the best experimental treatment combination for stable production and emission reduction of summer maize in this study area. |
