Mechanism Study On Ammonia Volatilization And Notrogen Use Efficicency Under Different Water And Nitrogen Management Practice

The lack of agricultural water resources and the low nitrogen?N?use efficiency have become a common problem in China.With the increase in food demand,this concern has become increasingly serious.Guanzhong Plain is main wheat producing area in Shaanxi province,and its wheat production accounts for about 60%of the province's total production.In wheat production,the inappropriate N fertilizer management irrigation and practices have also become increasingly prominent.Based on the Guanzhong Plain area,this study set up irrigation and non-irrigation cultivation treatments,combined with different N management practices with various N application rates and application time.The dynamics changes of ammonia volatilization,the N utilization,and crop growth and grain yield of winter wheat were studied.Meanwhile,root growth as affected by the ammonia volatilization,and underlying mechanisms were also studied.It provides a theoretical basis for water and N management for wheat production in the Guanzhong plain area,China.The main conclusions of this study are as follows:?1?Supplementary irrigation significantly increased grain yield and its yield components;the increased ratios were near 50%-60%in drought years?2015-2016?.Meanwhile,supplemental irrigation significantly increased wheat plant height,leaf area index and aboveground biomass production.N application rate also showed a significant effect on grain yield and yield components,both of which increased with increasing N application rates from0 to 240 kg N hm^-2.However,the yield and yield components were even reduced when N application rate was increased from 240 to 360 kg N hm^-2.All wheat morphological parameters including plant height,leaf area index and biomass,etc.,illustrated the same trend as grain yield against various N application rates.?2?Split N application can increase the plant height,leaf area index and aboveground biomass of winter wheat,compared with basal N application practice.The difference of grain yield was significant between different N levels,and the highest yield was achieved under N application rate of 240 kg N hm^-2.At the same level of N application rate of 240 kg N/hm²,the grain yield and spike number were 8.6%and 5.7%higher,respectively,in split N application than basal N application method.?3?The N content was higher under supplemental irrigation than that of rain-fed treatment,andtheNcontentofvariousorgansfollowedtheorder:Grain>Leaf>Spike+glume>Stem+Leaf Sheath.Significant differences of N accumulation and distribution ratios among different organs between different treatments were found.The amount of N accumulation increased first and then decreased with the increase of N application rate.The N accumulation under supplemental irrigation treatment was higher than that of rain treatment,irrespective of N level.The order of N accumulation in different organs was grain>Stem+Leaf sheath>Spike+glume>Leaf.Under the same irrigation management practice,the partial factor productivity of applied N,N recovery efficiency,N physiological efficiency,and N agronomic efficiency of winter wheat were significantly reduced with increasing N application rate.But the differences between different irrigation practices were not significant.?4?Under the same N application rate,the ammonia volatilization flux and accumulation differed significantly between different N application methods.The ammonia volatilization flux was lower under split N application than that of basal N application practice.Soil moisture and soil ammonium nitrate concentration of 0-40cm significantly affected the ammonia volatilization,and there was a significant positive correlation between soil water content and ammonia volatilization.The significant and positive correlation of soil ammonium N concentration with ammonia volatilization was also identified.With increasing N application rate,the N accumulation in various organs also increased.N accumulation was higher under basal N application than that of split N application,regardless of N application level.TheorderofNaccumulationindifferentorganswas grain>stem+sheath>spike+glume>leaf.With the increase of N application rate,N recovery efficiency,N agronomic efficiency,and N physiological efficiency decreased significantly.?5?Ammonia volatilization from urea application significantly inhibited seed germination and early seedling growth in the control experiment.As the amount of urea increased,ammonia toxicity became even worse.Roots were more sensitive to ammonia toxicity than shoots.The variation in the response of genotypes to ammonia toxicity was distinguishing.This study emphasized the potential of the selection of varieties with high tolerance to ammonia toxicity in improving seed germination and uniform seedling establishment through a breeding programme.The physiological mechanisms of seed germination responsible for high tolerance to ammonia toxicity are rapid root hair formation and the possible synergistic effects between several endogenous plant hormones.In conclusion,the highest yield of winter wheat was achieved under the N rate of 240 kg N hm^-2,and the supplemental irrigation and appropriate N management practice were more conducive to achieve the high-yield and high N use efficiency in wheat production.