In Loess Hilly-gully Region Apple ‖ Soybean Intercropping System Change And The Kind Of Soil Water And Nitrate Nitrogen Transfer Between Experimental Research

Drought,water shortage and poor soil quality in the Loess Plateau have seriously restricted the high-quality development of the local apple industry.Intercropping soybean in orchards is a green way to improve soil N nutrition and an important strategy to achieve green agricultural development.However,the water-N effects and N transfer status of soybean intercropping in young orchards on the Loess Plateau are still unclear,as is the effect of intercropping density on them.Therefore,this research in loess hilly-gully region apple||soybean compound system as the research object,to young orchard intercropping soybean nitrogen on soil water and nitrogen transfer effect as the goal,set up two intercropping field experiment and pot experiment in density,soil moisture monitoring for two years of the composite system,nitrate nitrogen content,fruit trees changes in physiological indexes and the fruit tree leaf nitrogen content,The ¹⁵N isotope labeling method was used to detect and calculate the transfer of nitrogen fixation from soybean to fruit tree.The main research results are as follows:（1）The effects of soybean intercropping on soil water storage and root development in the orchard complex system in different periods were proved.Before the flowering stage of soybean,medium density intercropping could increase soil water by 5.4%-17.6%,while high density intercropping could decrease soil water by 2.4%-5.9%.Soil water storage was deficient at flowering stage,podding stage and harvest stage,with a maximum deficit of 0.213,except for the increase of water storage at seedling stage in medium density intercropping.Medium and high intercropping increased fine root length density of fruit trees in 0-50 cm soil layer by 59.61%and 41.20%,and inhibited fine root development of fruit trees in 50-120 cm soil layer by 44.68%and 35.86%,respectively.（2）The effects of soybean intercropping on soil nitrate accumulation and crop growth in orchard complex system were clarified.In the drought year of 2021,the average nitrate accumulation in orchard soil was 14.56 kg/hm² during the 0-120 cm growth period,which decreased by 53.50%and 32.81%in medium and high density intercropping,respectively.The relative accumulation of nitrate nitrogen showed a trend of gradually decreasing and the proportion distribution of soil layers was gradually balanced.In 2022,soil nitrate accumulation was 14.64 kg/hm²,which decreased by 35.92%in medium density intercropping and increased by 50.98%in high density intercropping.The change pattern of relative nitrate accumulation in high density intercropping was basically the same,while the relative nitrate accumulation in medium density intercropping showed a sudden increase.Intercropping can effectively increase leaf area index of fruit trees,and the improvement ratio of medium and high density intercropping can reach 104.15%and 26.05%.（3）The relationship between nitrogen fixation transfer efficiency and intercropping density of soybean intercropping in orchard complex system was clarified.Intercropping could improve the transfer efficiency of nitrogen fixation and was affected by density.The nitrogen fixation efficiency of medium density intercropping was only 1.04%-1.52%,while that of high density intercropping was 35.25%-36.11%.The increase of density would improve the transfer efficiency of nitrogen fixation of legumes.The growth and development of leguminous crops would affect the proportion of nitrogen fixation transfer,and the proportion of nitrogen fixation transfer decreased from 53.03%to 34.53%after high density intercropping from flowering stage to pod-setting stage.The nitrogen content of fruit tree leaves can be effectively increased during the whole growth period of soybean in orchard intercropping,and the effect of increasing nitrogen content of fruit tree leaves in medium density intercropping is efficient and stable than that in high density intercropping.In conclusion,intercropping soybean orchard is a good orchard agricultural management measure,which can improve soil water status,promote soil nitrate nitrogen consumption,increase leaf nitrogen content of fruit trees and increase fruit tree crown width while nitrogen fixation transfer occurs.Therefore,intercropping soybean orchard in rain-fed Loess Plateau can achieve the maximum utilization of land resources,which is conducive to the efficient development of water and soil resources.