Study On The Nitrogen Fertilizer Application Mode Of Apple Trees Under The Condition Of Integrated Water And Fertilizer

Apple tree is one of the four major fruit tree crops.Compared with the traditional fertilization method used in apple orchards,drip irrigation fertilization technology has significant water-saving and fertilizer saving effects,and is suitable for fruit tree production.Therefore,how to achieve high-quality and efficient apple production through optimizing nitrogen fertilizer management under drip irrigation conditions is an urgent problem that modern orchards need to solve.This study takes the Fuji"Yanchang Red"apple tree as the research object.Field experiments were conducted under drip irrigation conditions in Luochuan County,Shaanxi Province from October 2020 to October 2022,including fertilization amount,nitrogen fertilizer type,nitrogen fertilizer distribution ratio,and different drip irrigation technical parameters.The fertilization experiment was conducted with two treatments:constant(300 kg N hm^-2,187.5 kg P hm^-2,375kg K hm^-2)and reduced（80%constant fertilization）;The experiment set up F and CK for the distribution ratio of nitrogen fertilizer topdressing（F relatively increased the proportion of nitrogen fertilizer during the germination stage）;The nitrogen fertilizer type experiment used three different nitrogen fertilizer types:urea,urea ammonium nitrate,and urea ammonium nitrate calcium;The experiment on drip irrigation technical parameters was conducted using a complete combination of three factors:one row,one tube,and two tubes（P1,P2）,with a spacing of 30cm and 50 cm between drip heads（D1,D2）,and a fertilization cycle of 15 and 30 days（T1,T2）.The effects of different nitrogen fertilizer application modes on apple tree growth,mineral nutrition,yield and fruit quality,as well as the distribution and residual amount of soil nitrate nitrogen were analyzed under drip irrigation conditions.A comprehensive evaluation was conducted based on the effects of yield,quality,and environmental benefits on different nitrogen fertilizer types,and the combination of drip irrigation technical parameters was optimized.The main results are as follows:（1）The research on fertilization experiments shows that reduced fertilization can reduce the leaf area index and fruit nitrogen,phosphorus,and potassium content compared to constant fertilization,and has a decreasing trend in the cumulative growth of new shoots and leaf nitrogen,phosphorus,and potassium content;The yield and VC content of reduced fertilization increased by 10.45%and 13.46%compared to constant fertilization;The content of nitrate and titratable acid decreased by 20%and 8.94%respectively;The residual nitrate nitrogen in 0-80cm soil decreased by 36.97%,while the residual nitrate nitrogen in 80-200cm soil decreased by 23.35%.Therefore,reducing fertilization can increase yield,improve quality,and reduce soil nitrate nitrogen residue.（2）The experimental research on different nitrogen fertilizer allocation ratios shows that increasing the germination stage and reducing the nitrogen fertilizer ratio from new shoots to young fruits can reduce the leaf area index,cumulative growth of new shoots,and nitrogen,phosphorus,and potassium content of fruits;Increasing the germination stage and reducing the nitrogen fertilizer ratio from new shoots to young fruits increased the hardness and sugar acid ratio by 3.31%and 19.03%respectively compared to CK treatment.The nitrogen,phosphorus,and potassium content in fruits decreased by 15.16%,16.31%,and 16.94%,respectively.In 2021,the soluble sugar content and nitrate content increased by 12.2%and8.31%,respectively.Therefore,increasing the germination stage and reducing the nitrogen fertilizer ratio from new shoots to young fruits will not affect yield and soil nitrate nitrogen residue,but can improve fruit hardness and sugar acid ratio.（3）Experimental studies on nitrogen fertilizer types have shown that urea ammonium nitrate solution reduces the cumulative growth of new shoots in apple trees during the young fruit and fruit expansion stages,as well as the leaf area index during the flowering and fruiting stages and the flourishing period of new shoots,compared to urea.The yield,soluble solids,and soluble sugar content of apple treated with urea and ammonium nitrate increased by18.33%,15.47%,and 27.52%respectively compared to urea,showing a decreasing trend in nitrate content and an increasing trend in sugar acid ratio;The yield and soluble solid content of apple treated with urea ammonium nitrate calcium increased by 27.49%and 17.33%compared to urea,while the residual nitrate nitrogen in 0-80cm soil decreased by 22%.The multi-objective comprehensive evaluation of apple production based on apple yield,quality,and soil environmental effects shows that using urea+ammonium nitrate calcium as nitrogen fertilizer under drip irrigation can increase apple yield,improve quality,and reduce soil nitrate nitrogen residue.（4）The experimental study on drip irrigation technical parameters showed that one row,one tube,spacing between drip heads of 30cm,and fertilization period of 30 days showed an increasing trend in the cumulative growth of new shoots and leaf area index of fruit trees.The spacing between two drippers in a row of 30cm is greater than the spacing between drippers in a row of 50cm.The fruit shape index,VC content,soluble sugar content and titratable acid content increased with two tubes per row compared with one tube per row;The distance between emitters of 30cm can increase the weight,hardness and sugar acid ratio of single fruit,reduce the content of titratable acid and nitrate,and increase the soluble sugar;The content of VC and titratable acid increased in 15 days of fertilization cycle compared with 30 days of fertilization cycle.The top three treatment combinations in TOPSIS comprehensive evaluation are one row and two tubes,with a spacing of 30cm between drip heads and a fertilization cycle of 30 days;One row with two tubes,with a spacing of 30cm between the drip heads,and a fertilization cycle of 15 days;One row and one tube,with a spacing of 30cm between drip heads,and a fertilization cycle of 30 days.Through the above research,it was found that in the apple production in the Loess Plateau region of Shaanxi Province,under the conditions of one row and two pipes,a distance of 30cm between the drip heads,and a fertilization cycle of 30 days,reduced fertilization was carried out.Applying urea+ammonium nitrate calcium fertilizer and increasing the ratio of nitrogen fertilizer during the sprouting stage to reduce the proportion of nitrogen fertilizer during the shoot young fruit stage can increase apple yield,improve fruit quality,and reduce soil nitrate nitrogen residue.