Effect Of Nitrogen Base Topdressing Ratio Of Three Kinds Of Soil Texture On Dynamic Distribution Of Water And Nitrogen In Wheat And Maize And Simulation Of Water Transport In HYDRUS Model In Heilonggang Area

Wheat-corn rotation is the main farming system in North China,and the two crops play an important role in grain production in China.Water and nitrogen is an important factor affecting crop growth,and its distribution in soil is closely related to texture.Therefore,studying the dynamic distribution and utilization efficiency of water and nitrogen in different texture soils and optimizing the fertilization management system are of great significance to improve crop yield,nitrogen use efficiency and reduce nitrogen pollution to the environment.This paper was conducted in Baimu Village,Jiajiakou Town,Ningjin County,Hebei Province.Wheat and maize were taken as the research objects.No nitrogen fertilizer was applied on sandy soil,light soil and clay soil,and the base-topdressing ratio of nitrogen fertilizer was treated at 3:7,4:6,5:5,6:4 and 7:3 to study the yield and water and nitrogen use efficiency of winter wheat and summer maize,and the dynamic changes of soil water content,water storage,NH4+-N and NO3--N during crop growth.At the same time,using HYDRUS model to simulate the dynamic distribution of soil moisture and long-term monitoring of the dynamic changes of soil moisture in three kinds of soil verify each other.The results can provide a scientific basis for the rational application of nitrogen fertilizer to wheat with different soil texture in this area.The main results are as follows:1.In wheat season,in sandy soil,light soil and clayey soil,the nitrogen base topdressing ratio was 3:7,4:6 and 5:5,respectively.Wheat yield,water use efficiency and nitrogen production efficiency were the highest.The vertical distribution of soil water content of sandy loam wheat varied greatly at different growth stages,and the 40-60cm of sandy loam soil water content remained at a high level.Although the water content increased rapidly after irrigation,it decreased rapidly,which was not conducive to the absorption and utilization of wheat.The soil water content of light loam and clay loam was higher in the whole growth stage,and the soil water content of light loam was 9.3%-26.2%,while that of clay loam was 9.7%-27.6%.The soil water storage capacity of clay loam>light loam>sandy loam,indicating that the sandy loam soil with large particles is easy to seep,and it is necessary to prolong the sprinkler irrigation time during irrigation.The contents of NH4+-N and NO3--N in the soil mainly varied in the soil tillage layer(0-40 cm),and were greatly affected by the amount of nitrogen applied.The more nitrogen was applied in the topsoil,the higher the content of NH4+-N and NO3--N in the soil,and the content of NH4+-N and NO3--N decreased with the deepening of the soil layer.Under the influence of precipitation,NH4+-N and NO3--N in light loam soil were easier to leach to the depth of soil layer,and the contents of NH4+-N and NO3--N in clay loam soil were higher than those in light loam and sandy loam soil at maturity,indicating that the water and nitrogen conservation capacity of clayey soil was stronger than that of light loam and sandy soil,and the topdressing ratio of nitrogen fertilizer could be appropriately enlarged.2.In the corn season,we mainly studied the effects of the same water and fertilizer treatment on the water and nitrogen distribution and yield of maize in the wheat season with different nitrogen base topdressing ratio.The results showed that in the plot with more nitrogen fertilizer in the wheat season,there was a higher value of water,water storage,NH4+-N and NO3--N in the 0-200 cm soil in the corn season,and the yield was also higher than that of other treatments,and the proportion of nitrogen application was adjusted in the wheat season.It can increase the yield of corn.However,due to the rainy summer and frequent irrigation,NH4+-N and NO3--N will move to the depth of the soil layer with water,especially the NO3--N is still high in the soil depth.With the extension,of time,it is easy to make the leaching of NO3--N in the soil,and even cause the pollution of groundwater environment.In different texture soil,different nitrogen base and topdressing ratio of wheat in the previous crop had little effect on the yield of maize in the following crop.3.The comparative analysis of the simulated and measured values of soil water content of three kinds of soil texture by HYDRUS-1D model showed that the simulation accuracy R2 of wheat and corn were 0.63-0.82 and 0.74-0.94,respectively,and the Nash efficiency coefficients were 0.51-0.77 and 0.52-0.91,respectively.The results show that the simulated values fit well with the measured values,which can well reflect the dynamic changes of soil moisture in three kinds of soil texture,so as to grasp the dynamic distribution of soil moisture and provide theoretical support for wheat and corn to establish a reasonable irrigation system.