The Threshold Of Optima N Rate Of Winter Wheat Based On Yield,Economic Efficiency And Environmental Impact In Dryland

The Loess Plateau has a vast area and is one of the main areas of grain production in China.Winter wheat as the main food crop species in dryland is of key significance for agricultural production activities in the region.Based on the rapid growth of China’s population,the core of solving food security problems is to ensure the steady growth of crop yields in the field,but this also leads to the problem of excessive nitrogen application.This status quo not only reduces the nitrogen use efficiency,but also leads to a series of problems such as excessive nitrogen fertilizer application,soil non-point source pollution and the decline of land cultivation quality.In order to ensure the sustainable development of agriculture and green development,the current research hotspot has changed from the basic requirements of high crop yield to the rational regulation of environmentally friendly nitrogen fertilizer.However,the research on the nitrogen fertilizer threshold of winter wheat in the dryland of the Loess Plateau is still lacking.Therefore,this study took the field experiment in the Yangling Cao Xinzhuang experimental farm of Northwest A&F University in the wheat growing season of 2017-2018,explore the high-yield,high-efficiency and environmentally friendly nitrogen fertilizer threshold for winter wheat fields.A total of five nitrogen levels were set in this study:No nitrogen treatment（N0）,75kg of pure nitrogen per hectare（N75）,150 kg of pure nitrogen per hectare（N150）,225kg of pure nitrogen per hectare（N225）and 300 kg of pure nitrogen per hectare（N300）.Wheat plants and soil samples were collected at various stages of winter wheat growth and development in dryland,the nitrogen uptake and soil mineral nitrogen content of different growth stages were measured,the yield and composition of different treatments were determined after wheat harvest.The fertilizer yield effect curve,economic benefit curve and environmental effect（soil mineral nitrogen residue）curve are configured,the model uses the model to simulate the optimal yield,best economics,and minimum environmental effects of nitrogen fertilizer use and threshold.The main results of the final study are as follows:（1）Nitrogen application significantly increased wheat grain yield,grain storage capacity,1000-grain weight,kernel number per panicle,number of ears per hectare,and grain storage capacity（P<0.1）.These indicators increased with the increase in nitrogen fertilizer application,then peaked and then began to show a downward trend.The maximum grain yield of wheat is N225,which is 8113 kg·ha^-1.Excessive nitrogen can not only increase or even reduce wheat yield.The effect of nitrogen application on wheat harvest index was not significant.（2）Nitrogen treatment significantly increased nitrogen uptake（P<0.1）and increased33.48-82.97 kg N·ha^-1 compared with no fertilization control.The nitrogen uptake of wheat was positively correlated with the amount of nitrogen applied.Apparent use of nitrogen fertilizer in wheat showed a decreasing trend with increasing nitrogen application,showing a negative correlation.（3）The leaves of the various organs of wheat were the most transported to the grain,followed by the stalk and the hull.Nitrogen application significantly increased nitrogen transport in wheat stems and leaves（P<0.1）.Nitrogen transport in wheat stalks and leaves increased first and then decreased with the increase of nitrogen application rate,and the maximum value was treated in N225.Nitrogen application could not significantly affect the nitrogen transport efficiency of wheat hulls,stems and leaves.Nitrogen application significantly increased the nitrogen contribution rate of wheat stalks and leaves（P<0.1）.（4）The nitrate content of soil in wheat field was 0-20cm,and the nitrate content in soil profile was higher,then decreased,and the nitrate content in 60-200cm soil layer increased to some extent.The overall performance of soil nitrate nitrogen content increased with the increase of nitrogen fertilizer application.The law between ammonium nitrogen and nitrogen application rate is not prominent,but the ammonium nitrogen content of nitrogen treatment is higher than that of no nitrogen treatment.（5）The net income of wheat is:N150(5067.58￥·ha^-1)>N225(5001.99￥·ha^-1)>N75(4727.43￥·ha^-1)>N0(4548.65￥·ha^-1)>N300(4377.05￥·ha^-1).There is a negative correlation between the ratio of production to investment and the amount of nitrogen applied.（6）After considering the yield,economic and environmental factors of wheat production activities,the optimal nitrogen application threshold for winter wheat planting in dryland in the Loess Plateau is 126.33-147.36 kg·ha-1.