Effects Of Nitrogen Fertilizer Reduction On Water And Nitrogen Distribution In Soil Profile And Growth Of Summer Maize

The formula fertilization technology of reasonable nitrogen reduction can further promote the reduction and efficiency of chemical fertilizers and reduce the risk of environmental pollution.From June to September 2021,a field experiment was conducted in the experimental field of Handan City,Hebei Province.Four nitrogen application treatments were designed to study the effects of N0 formula nitrogen-free（N₀PK）,N1 formula low nitrogen（N₁PK）,N2 formula high nitrogen（N₂PK）and N3conventional fertilization（N₃PK）on soil profile water and nitrogen distribution,summer maize growth,yield and water and nitrogen use efficiency.HYDRUS-1D model was established to simulate the process of water and nitrogen transport in soil profile,and verified with the measured values.The results of this study can provide scientific basis for reasonable nitrogen application of summer maize in this area.The main findings are as follows:（1）Nitrogen fertilizer reduction could reduce nitrogen content and leaching loss in soil profile.Nitrogen application had no significant effect on water content of soil profile,and water content decreased first and then increased in vertical direction.The application of nitrogen fertilizer increased the nitrate nitrogen content in the soil profile,and the peak value of nitrate nitrogen content continued to move down with the growth period.Compared with N3 treatment,the average nitrate nitrogen content in soil profile of N2 and N1 treatment decreased by 5.74%～18.65%and 26.09%～38.81%,and the accumulation of nitrate nitrogen in mature period decreased by 6.08%and 29.61%.Ammonium nitrogen was less affected by nitrogen application rate and water movement.During the growth period,ammonium nitrogen was mainly distributed in the 0～40cm soil layer.Compared with N3 treatment,the average ammonium nitrogen content of N2and N1 treatments decreased by 4.14%～13.70%and 4.11%～16.51%,and the accumulation of ammonium nitrogen at maturity decreased by 5.39%and 10.16%.（2）Reasonable nitrogen application rate can promote the growth and development of summer maize.The plant height of summer maize increased by 1.39%～3.75%with nitrogen fertilizer.Stem diameter and leaf area index increased by 6.86%-15.78%and9.31%-24.21%respectively.Compared with N0,the stem diameter and leaf area index of N2 and N3 treatments increased by 11.61%～15.78%,11.90%～13.33%and15.77%～20.64%,13.39%～24.21%,respectively.The increase of N1 treatment was6.86%～8.49%and 9.31%～10.95%.（3）Reasonable nitrogen application rate can improve summer maize yield and water and nitrogen use efficiency.Compared with N0 treatment,N2 and N3 treatments increased yield by 38.19%and 37.66%,and N1 treatment increased yield by 29.78%.The water use efficiency of each nitrogen treatment was not significantly different from that of N0 treatment by 28.91%-38.73%.The highest nitrogen use efficiency was41.30%in N2 treatment and the lowest was 33.50%in N3 treatment.In summary,under the premise of ensuring higher yield and water and nitrogen use efficiency and lower nitrogen accumulation and leaching loss,N2 treatment is to reduce nitrogen fertilizer on the basis of N3 conventional fertilization,and nitrogen fertilizer application rate 225kg/hm2 is the best nitrogen application rate in summer maize season in southern Hebei.（4）Based on HYDRUS-1D,the simulated and measured values of water and nitrogen content in soil profile of summer maize with different nitrogen application rates were compared and analyzed.The results showed that the variation range of Nash efficiency coefficient of water and nitrate nitrogen in soil profile was 0.64～0.98 and0.71～0.99,and the variation range of determination coefficient R² was 0.87～0.99 and0.64～0.98.It shows that the simulated value and the measured value are well fitted,which can well reflect the dynamic changes of soil water and nitrogen under different nitrogen application rates,so as to grasp the dynamic distribution of soil water and nitrogen,which can provide theoretical support for the formulation of reasonable fertilizer application rate.