Effects Of Nitrogen Application On Growth And Nitrogen Absorption,Distribution And Utilization Of Dwarf Self Rootstock Apple

Shaanxi Province is one of the main apple producing areas in China,the planting area and yield of apple in 2020 are the first in China.Weibei dryland is one of the best apple producing areas in the world,and the output and quality of apple is the leader and guide of the domestic apple industry.In recent years,great changes have taken place in apple cultivation mode all over the world,the low rootstock close planting mode of apple has become the development direction of apple cultivation in the world.The root distribution of dwarf apple trees is shallower than that of arborized apple trees,and dwarf apple has the advantages of early flowering and early fruit bearing.Therefore,dwarf apple has higher requirements for water and fertilizer.At present,apple growers often apply fertilizer based on experience,and the amount and period of fertilization are uncertain.The survey found that the average pure nitrogen consumption of fruit farmers in Weibei dryland reached671.71 kg/hm²,and 78.3%of orchards were over applied with nitrogen fertilizer.At the same time,fertilization is mainly based on base fertilizer,and the amount of nitrogen fertilizer is generally large.This experiment takes 4 years old‘azhen Fuji’/M9-T337 as the material,and four nitrogen application levels,two fertilization periods and two irrigation treatments were set in this experiment and ¹⁵N tracer technique was used.This experiment is based on the combination of nitrogen application level and fertilization period,nitrogen application level and irrigation amount to explore the effects of two factors on the growth and development,yield and quality,¹⁵N absorption,distribution and utilization of dwarf apple.To provide a theoretical basis for nitrogen application rate,nitrogen application period and irrigation amount of dwarf rootstock apple trees in Weibei dryland.The main results are as follows:1.T2N3 and W2N3 treatments could significantly increase the length and fresh weight of new shoots,and increase the contents of chlorophyll a,b and total amount of apple leaves,and improve the net photosynthetic rate,transpiration rate and stomatal conductance,and significantly promote the photosynthesis of apple plants.T2N3 and W2N3 treatments increased the nitrogen content in leaves and fruits,and maintained the stable change of leaf nitrogen content during the fruit development cycle.At the same time,T2N3 and W2N3treatments could significantly improve the fruit yield with the average yield per plant reaching 19.08kg and 17.80kg,and significantly higher than other treatments,and improve the internal quality of the fruit,and significantly improve the content of soluble solids,titratable acids and soluble sugars.The maximum soluble solids are 16.43%and 15.69%,and the maximum soluble sugars are 15.86%and 15.08%.2.T2N3 and W2N3 treatments significantly increased the biomass,nitrogen content of various organs and total nitrogen content of apple plants.The biomass of apple plants reached 7.31kg and 7.30kg respectively,and the total nitrogen content reached 52.86g and50.19g respectively;It significantly improved the absorption and regulation ability of ¹⁵N in various organs of the plant,and promoted the absorption of ¹⁵N,and the absorption amount of ¹⁵N was the largest,up to 1027.42mg and 910.51mg,and improved the utilization rate of ¹⁵N,up to 34.24%and 30.35%.At the fruit ripening stage,the ¹⁵N distribution rate of plants to various organs did not change with the increase of fertilization period,irrigation amount and nitrogen application level.The general performance is fruit>root>leaf>perennial Branch>annual branch>trunk.Moreover,under different fertilization periods and irrigation amounts,the ¹⁵N distribution rate of trunk,perennial branch and annual branch increased first and then decreased with the increase of nitrogen application level,while the leaf and root showed the trend of decreasing first and then increasing,and the ¹⁵N distribution rate of fruit increased with the increase of nitrogen application level.The results showed that under the low nitrogen application level,the nitrogen nutrition absorbed by the tree was preferentially used for the growth of vegetative organs（leaves and roots）to ensure the nutrient source needed for fruit growth and development;When nitrogen nutrition is sufficient,it would increase the absorption and utilization of nitrogen by storage organs（trunk and perennial branches）.The above results showed that under the nitrogen application level of N3（360 kg/hm²）,T2 fertilization period（30%base fertilizer in autumn,8%nitrogen fertilizer every 20 days from germination to fruit expansion period,and 30%fruit expansion period）,W2（85%FC）irrigation,the growth and development of trees and fruit quality can be significantly improved,nitrogen use efficiency can be improved,yield and economic benefits can be improved.