Study On The Difference Of Apple Growth And Fruit Quality Under Different Water-Nitrogen Coupling Conditions

The Loess plateau has unique geographical conditions for the development of high-quality apple industry.Irrigation and fertilization have been the two key factors limiting the development of apple.In order to explore the optimal water-nitrogen coupling combination model for apple tree planting on the Loess plateau,the experiment took six-year-old Fuji as the experimental material and set three different nitrogen application levels(pure nitrogen)in combination with water-fertilizer integration technology:N1(0.3kg/tree),N2(0.2 kg/tree),N3(0.1 kg/tree).Three irrigation levels were:W1(75%～85%field capacity),W2(65%～75%field capacity)and W3(55%～65%field ca Pacity).A completely random design was adopted to study the effects of different water and nitrogen coupling on physiological growth,quality and yield of apple trees.The main research results are as follows:1.Shoot length and leaf area increased with the increase of water and nitrogen supply level.Irrigation and nitrogen application had significant effects on shoot length and leaf area(P<0.01),but coupling effects of water and nitrogen had no significant effects on shoot length and leaf area(P>0.05).The maximum shoot length and leaf area appeared in N1W1treatment,while the minimum was N3W3 treatment.The shoot length in water-nitrogen coupling treatment was lower than that in CK treatment.2.Nitrogen and irrigation had significant effects on chlorophyll content,net Photosynthetic rate(Pn),transpiration rate(Tr),stomatal conductance(Gs)and water use efficiency(WUE).Under the same nitrogen application level,chlorophyll content increased with the increase of water supply,that is,W1>W2>W3.Under the same water supply condition(except W3),chlorophyll content first increased and then decreased with the increase of nitrogen application,that is,N2>N1>N3.Under the same nitrogen application and water supply conditions,the net photosynthetic rate,transpiration rate,stomatal conductance and water use efficiency of leaves under N1W1 treatment were higher than those under flood irrigation at different periods.During the growth period,leaf Pn,Tr and Gs increased first and then decreased,and reached the maximum value in August.Under the coupling condition of water and nitrogen,the maximum value of Pn,Tr and Gs of leaves in May and September was N1W1,and in July and August,the maximum value of Pn,Tr and Gs of leaves was N2W1.Under the same nitrogen application level,leaf Pn,Tr and Gs increased with the increase of water supply,that is,W1>W2>W3.Under the same water supply condition,leaf Pn,Tr and Gs increased with the increase of nitrogen application rate in different growth periods.In May and September,leaf Pn,Tr and Gs increased with the increase of nitrogen application rate.N1>N2>N3;In July and August,leaf Pn,Tr and Gs showed a trend of first increasing and then decreasing with the increase of nitrogen application rate,that is,N2>N1>N3.3.The contents of nitrogen,phosphorus and potassium in leaves were significantly affected by irrigation(P<0.01).Under the same nitrogen application level,the contents of nitrogen,phosphorus and potassium in leaves increased with the increase of water supply,that is,W1>W2>W3.Nitrogen application had a significant effect on leaf nitrogen content,but had no significant effect on leaf phosphorus and potassium content.In2021 and 2022,nitrogen,phosphorus and potassium in leaves treated with N1W1 and N2W1 were higher than those treated with CK.4.Different water and nitrogen treatments had significant effects on fruit quality and yield.Fruit weight per fruit increased with the increase of water and nitrogen supply level.Nitrogen application and irrigation had significant effects on fruit diameter(P<0.01).Under the same nitrogen application condition,soluble solid,soluble sugar and ascorbic acid increased with the increase of irrigation amount.Under the same water supply condition,soluble solid,soluble sugar and ascorbic acid increased first and then decreased with the increase of nitrogen application rate,that is,N2>N1>N3.Titrable acid increased with the increase of water and nitrogen supply level.The solid acid ratio decreased with the increase of irrigation amount,and increased first and then decreased with the increase of nitrogen application rate.Both irrigation and nitrogen application had significant effects on fruit coloring(P<0.01).Increasing water supply and nitrogen application could significantly improve fruit brightness value.Nitrogen application had significant effect on peel hardness(P<0.01).Water had a significant effect on the ductility of pericarp(P<0.01).The pulp hardness decreased with the increase of irrigation amount.pulp crispness increased with the increase of water.Irrigation had significant effects on the contents of nitrogen,phosphorus and potassium(P<0.01),nitrogen application had significant effects on the contents of nitrogen(P<0.05),but had no significant effects on the contents of phosphorus and potassium(P>0.05).In 2021,the apple yield increased with the increase of water and nitrogen supply level,that is,the yield of N1W1 treatment increased with the increase of1573 kg/hm~2compared with CK;in 2022,the apple yield increased with the increase of irrigation amount,but decreased with the increase of nitrogen application level,that is,the yield of N2W1 increased with the increase of 2167 kg/hm~2compared with CK.5.Comprehensive evaluation of different water-nitrogen coupling was carried out by principal component analysis.The results showed that the optimal water-nitrogen combination model could improve the physiological growth,quality and yield of apple trees by keeping soil water content at 75%～85%of field water capacity and applying 0.2 kg nitrogen per tree.