Studies On The Influences Of Water And Nitrogen Coupling On Water And Nitrogen Use Efficiency And Crop Yield Sat A Typical Region In North China Plain

North China Plain is one of the major grain producing areas in China.Over-fertilizing nitrogen and over-irrigation are common in this region,which results in a low resource use efficiency and thus the great waste of water and fertilizer resources.Water crisis was aggravated and the crisis of grounder water population increased in this region.To improve water and fertilizer use efficiency is one of the fundamental solutions to the resource and environment problems of the North China Plain.Based on the long-term experiments made in typical area of the North China Plain,systematical researches on a wheat-corn rotation system were conducted on the influence of water and nitrogen fertilizer applications on soil nitrate nitrogen dynamic change,nitrogen absorption and utilization rate by winter wheat as well as grain yields.The main results are as follows:(1)Water and nitrogen coupling has obvious influence on the variations of soil nitrate nitrogen concentration on profiles.Fertilizing nitrogen can significantly increase the nitrate nitrogen concentration in soil solution.During the growing season of wheat,soil is dry and few precipitations is available under which irrigation after fertilizing can make nitrogen quickly move into soils to hamper the loss of nitrogen for volatilization and facilitate the storage of nitrogen for the use by crop at the late stage of development.During the growing season of maize,sufficient rainfall induced the transfer of nitrate nitrogen to deep soil layers and even out of the available zone for root absorption.(2)Soil nitrate nitrogen dynamic changes reflected climate,crop growth,roots activities and soil water movement during the growing season of wheat.At seeding stage,wheat utilize few nitrogen and irrigation after fertilizing transfers nitrogen to deep soils for the crop use at the late stage of development.Before green-turning stage,surface coverage was low and evaporation was strong,which resulted in concentrated nitrate nitrogen at soil surface layers prone to volatilize.After that,wheat roots have greatly developed,surface coverage also got higher,evaporation decreased and water and nitrogen absorption by roots increased.As a result,soil nitrate nitrogen concentration dropped as soil surface layer but increased at next layers.Thus,the key to improve nitrogen use efficiency is to limit the movement of nitrogen in the region of maximum root zone by irrigation and other field management measures.(3)Appropriate nitrogen inputs could increase the total nitrogen contents in grain and straw as well as winter wheat yields and nitrogen utilization rate,but excessive nitrogen fertilizer inputs could cause a fall in winter wheat yields and nitrogen utilization rate.For the research site,the critical nitrogen fertilizer application was between 190-230 kg·hm-2.The impacts of irrigation on total nitrogen content in plant,nitrogen utilization rate and winter wheat yields were found closely related to characteristics of rainfalls.The lack of rainfall in key growth periods could lead to great decrease in the winter wheat yield.Appropriate irrigation could increase winter wheat yields,but too much irrigation also did not help to further increase the crop yields.Irrigation exerted few influence on plant nitrogen content in the case of sufficient precipitations.When little rainfall was available,increasing irrigation hampered the nitrogen transfer from straw to grain.Thus,to maximize the benefits of the coupling effects of water and nitrogen in crop production,it is necessary to design appropriate irrigation and fertilization regime according to the water and nitrogen requirements of winter wheat and the rainfall during same periods.