Effects Of Different Nitrogen Levels On Soil Nitrogen Leaching Accumulation And Crop Yield In The Yellow River Irrigation Area

Adequate nitrogen supply is a necessary condition for high yield of crops.Excessive nitrogen application not only causes resource waste,but also causes soil and groundwater environmental pollution.Reasonable water and nitrogen management measures have an important guiding role in the protection of farmland ecological environment safety.In order to clarify the effects of different nitrogen application levels on soil nitrogen leaching accumulation rules and crop yields in the irrigation area of the Yellow River,this experiment selected the farmland of Xijinglin village,Linqing city,the downstream of the irrigation area of the Yellow River as the research object.,to study the dynamic changes of soil water and nitrogen,crop growth and yield,water and nitrogen use efficiency and nitrogen accumulation at different nitrogen levels.The winter wheat experiment set 4 nitrogen application levels,respectively 0（CK）,80（N1）,160（N2）,240 kg ha^-1（N3）;summer maize experiment set 4 nitrogen application levels,respectively 0（CK）,120（N1）,180（N2）,270 kg ha^-1（N3）,2 irrigation levels 132 mm（I1）,166 mm（I2）.The 15N tracer technology was used to study the absorption and distribution of fertilizer nitrogen and soil nitrogen by various organs of different water and fertilizer treatments during the maturity period of maize.At the same time,the excitation law of fertilizer nitrogen on soil nitrogen,the residual and loss of fertilizer nitrogen in the soil of each treatment were studied.The Root Zone Water Quality Model（RZWQM）was used to simulate the process of crop yield,soil water and nitrogen utilization and nitrate nitrogen leaching under different water and nitrogen conditions.The main conclusions are as follows:（1）The distribution pattern of NO₃^--N in soil profile under different nitrogen treatments is similar.The content of NO₃^--N increases with the increase of nitrogen application,nitrogen application has little effect on soil NH₄⁺-N.After harvesting winter wheat and summer maize,the cumulative amount of NO₃^--N in the 0～200 cm soil layer is shown as:N3>N2>N1>CK,the more nitrogen is applied,the greater the cumulative amount.After the harvest of summer maize in I2,NO₃^--N loss in the 0～200 cm soil layer was greater than that of I1.Irrigation increased the NO₃^--N leaching loss.Reasonable water and fertilizer management can reduce the accumulation of nitrogen leaching.The soil moisture content of the 0～80 cm soil layer in the summer maize changed greatly in 2019,0～120 cm soil layer in the winter wheat season changed greatly.The change trend of the soil moisture content of each soil layer was basically the same under different nitrogen levels.（2）Increasing the amount of nitrogen application can increase the yield of winter wheat and summer maize,but the yield of crops with excessive nitrogen application decreases.The water use efficiency of winter wheat-summer maize in 2019 increased first and then decreased with the increase of nitrogen application,and the range of variation was 29.2～45.3 kg ha^-1 mm^-1,14.2～16.1 kg ha^-1 mm^-1,and the moisture of summer maize in 2020 utilization efficiency increases with the increase of nitrogen application rates.Appropriate increase in irrigation amount can improve water use efficiency,and its variation range is 9.7～13.0 kg ha^-1 mm^-1.The NUE and PFP of winter wheat decreased with the increase of nitrogen application rates,and the ANUE first increased and then decreased with the increase of nitrogen application rates.The PFP in summer maize decreases with the increase of nitrogen application rates.Increasing irrigation can increase the PFP of summer maize.（3）The absorption of fertilizer nitrogen by summer maize accounts for 19.43%～28.62%of the TN absorption,and the absorption of nitrogen in the soil accounts for 71.38%～80.57%of the TN absorption.The competitive ability of the various organs of summer maize to fertilizer nitrogen is the grain,stalk,and leaves from large to small.The excitation of soil nitrogen is a positive excitation effect,and the excitation rate is 114.92%～166.33%.Fertilizer nitrogen absorption rate,soil residual rate and loss rate after summer maize harvest were29.41%～50.75%,20.45%～31.41%,and 24.67%～41.26%,respectively.The N2I2 treatment summer maize had the largest fertilizer nitrogen absorption rate,which was 50.75%,the appropriate ratio of water and fertilizer is conducive to the plant to make full use of water and fertilizer and reduce the loss of water and fertilizer.（4）The RZWQM model can better simulate soil water and nitrogen migration and crop yield.It is proposed based on the simulation research on the effects of NO₃^--N leaching,crop yield,water and nitrogen utilization under different water and nitrogen conditions.Taking into account economic and environmental benefits,a set of better summer maize water and nitrogen management mode,that is,the irrigation amount is 166 mm,and the nitrogen application rate is 180 kg ha^-1.