Effects Of Nitrogen Management On Nitrogen Distribution,Utilization In Orchard And Apple Tree Physiology Under Water Storage Pit Irrigation

The efficient utilization of water and fertilizer is an important content of the sustainable development of agricultural production.The coupling effect of water and fertilizer under different irrigation methods will have an impact on the utilization law and efficiency of water and fertilizer.With the popularization and application of reservoir irrigation technology,it is of great significance to explore the distribution law of water and nitrogen,reveal the utilization mechanism of apple tree nitrogen fertilizer.Based on the results of previous studies on the optimum irrigation water limits,the distribution of soil ammonium nitrogen and nitrate nitrogen,the response of root system,canopy leaf,stem flow and apple yield and quality of fruit trees and the utilization efficiency of water and nitrogen at different scales were systematically analyzed in this study.And,by using¹⁵N stable isotope tracer technique,the distribution of fertilizer nitrogen in soil and apple trees and utilization of fertilizer nitrogen at different time scales were studied.In addition,apple tree root growth prediction model and leaf photosynthetic rate model based on typical artificial neural network（BP）and PSO improved artificial neural network（PSO-BP）were established,and the models under different algorithms were compared.The main findings are as follows:（1）Compared with surface irrigation,under the same nitrogen fertilizer management system,water storage pit irrigation can effectively promote the accumulation of ammonium nitrogen and nitrate nitrogen in the middle layer of soil（20-80 cm）,reduce the accumulation of ammonium nitrogen surface layer and deep nitrate state in soil,improve the hydrolysis rate of urea and reduce the hydrolysis time of urea.As the amount of nitrogen applied increased,the mean amount of ammonium nitrogen in soil increased significantly,while the mean amount of nitrate nitrogen in soil increased first and then decreased with the increase of nitrogen application.High nitrogen application did not continuously increase soil nitrate content.The absolute content of ammonium nitrogen and nitrate nitrogen in soil was significantly affected by fertilization period,and the absolute content of ammonium nitrogen and nitrate nitrogen in soil was significantly increased by fertilization in fruit expansion period.Compared with one fertilization,two fertilization can increase the absolute content of ammonium nitrogen and nitrate nitrogen in soil,but the difference is not significant.（2）Changes of irrigation and fertilization patterns can cause that of the growth of apple trees.Compared with surface irrigation,water storage pit irrigation can promote the growth of apple tree root,canopy and leaf under the same fertilization management mode.The response of root system to fertilization is faster and the overall level is kept at a higher level.under the WSPI,the diurnal variation of stem flow has a significant peak phenomenon,and the peak value is significantly higher.All the indexes of root,canopy and leaf,as well as the stem flow value increased first and then decreased with the increase of total fertilization,except chlorophyll.In this experiment,low fertilization amount（300 kg N/hm²）was the optimum fertilization amount for root system and canopy leaf growth.During different fertilization periods,the emphasis of fruit tree growth was slightly different.Compared with the expansion period fertilization,the canopy and leaf index values,as well as the stem flow rate of trunk were larger,while theΔRLD andΔRSAD was smaller.Under the same total amount of fertilizer,the canopy and leaf of apple tree increased slightly in the split fertilization treatments,while the RLD,RSAD and stem flow increased significantly.（3）Using the stable isotope tracer technique of ¹⁵N,it was found that WSPI can effectively promote fertilizer nitrogen to go deep into the middle layer of soil（40-100 cm）and reduce the accumulation of nitrogen in surface and deep soil layers.The fertilizer nitrogen was mainly concentrated in the middle layer of soil under the condition of low nitrogen application,compared with that under the condition of high nitrogen application.The distribution of fertilizer nitrogen under each treatment was similar,mainly concentrated in the shallow middle layer of soil.Under the condition of fertilization during fruit expansion,the nitrogen content of fertilizer in soil is relatively high.And,under different fertilization management,the distribution of fertilizer nitrogen in the following year was significantly different.In general,soil fertilizer nitrogen remained the most in the second year under the split fertilization with high fertilizer application,while the residue of fertilizer nitrogen in soil was the smallest under the split fertilization with low fertilizer application and low fertilizer application in late flowering period.In addition,under the experimental conditions,apple leaves and apple fruits mainly used fertilizer nitrogen from the previous year,while the fertilizer nitrogen mainly used by apple tree roots was related to the fertilization period and fertilization amount.Early fertilization and low fertilization were beneficial to the absorption of fertilizer nitrogen by roots.The absorption degree of leaf fertilizer increased month by month,while that of fertilizer nitrogen in the previous year was the opposite.The distribution order of fertilizer nitrogen among apple organs was root>fruit>leaf,while that of fertilizer nitrogen in last year was fruit>root>leaf.In the whole treatment,two fertilizations can promote the distribution of fertilizer nitrogen to each organ more evenly.（4）In the study of water and fertilizer utilization efficiency,it was found that under the same fertilization conditions,WSPI significantly improved the instantaneous water use efficiency of leaves,water use efficiency of yield level and nitrogen agronomic use efficiency.the instantaneous water use efficiency and nitrogen agronomic use efficiency of leaves were higher under low fertilization,but the change of fertilization amount had no significant effect on the water use efficiency of yield level.in addition,split fertilization methods could significantly improve the instantaneous water use efficiency of leaves,water use efficiency of yield level and nitrogen agronomic use efficiency.（5）The model simulation of root length growth and leaf photosynthetic rate shows that compared with the typical artificial neural network model（BP）,the artificial neural network model improved by particle swarm optimization（PSO-BP）can effectively improve the simulation accuracy and reduce the simulation error.The MAPE and RMSE of the PSO-BP model were reduced by 34 percentage points and 22.51 in the root growth model,and the MAPE and RMSE of the leaf photosynthetic rate model were reduced by 1.6 percentage points and0.268,respectively.