Effect Of Nitrogen Application On Carbon And Nitrogen Nutrition And Yield Of Korla Fragrant Pear

At present,the planting process of Korla Fragrant Pear in Xinjiang is facing many problems,such as nutrient imbalance,unstable yield and low nitrogen utilization rate caused by improper fertilization.Therefore,in this study,6-7 years old Korla Fragrant Pear were used as the test material,¹⁵N isotope tracing technology and ¹³C pulse labeling technology and data model analysis were used to study the characteristics of the accumulation and distribution of carbon and nitrogen in different organs of the Korla Fragrant Pear tree under different nitrogen levels（respectively 0、150、300、450 N·kg/hm²,equivalent to N₀N₁,N₂,and N₃）.Clarify the correlation between carbon and nitrogen nutrition and yield,establish a carbon and nitrogen coupling relationship with yield as the target,and propose the best nitrogen application rate.In order to coordinate the vegetative growth and reproductive growth of the tree through the amount of nitrogen fertilizer,so as to provide reference basis and technical support for the optimized fertilization of the pear orchard,promote the improvement of the nitrogen absorption and utilization efficiency of the Korla Fragrant Pear trees,and the high-quality and efficient development of the Korla Fragrant Pear industry.The results showed that:1.Under different nitrogen application treatments,the nitrogen absorption and regulation ability（Ndff value）of various organs of Korla Fragrant Pear tree showed N₃>N₂>N₁.The transport of ¹⁵N in the tree at different growth stages varies with the change of growth center.The Ndff values and ¹⁵N absorption of leaves and roots were higher at new shoot growing stage.When the fruit swelling stage,the new aboveground organs grew vigorously,there was a multi-source competition between one-year branches,leaves and fruits,the Ndff value and ¹⁵N absorption of the new organs increased significantly.At fruit maturity stage,the fruit became the growth center of the tree,had the highest Ndff value,and its ¹⁵N absorption was the highest under N₂ treatment（0.48 g）.The ¹⁵N distribution rate of various organs under different nitrogen treatments was also different.The ¹⁵N distribution rate of root system was the highest under N₂ treatment,the ¹⁵N distribution rate of leaves was the highest under N₃ treatment,and the ¹⁵N distribution rate of fruit was the highest under N₂ treatment,reaching 31.79%at fruit maturity stage.The¹⁵N utilization rate of Korla Fragrant Pear tree increased significantly with the development of growth period,and ¹⁵N utilization rates showed N₂（20.19%）>N₁（16.86%）>N₃（15.58%）at fruit maturity stage under different nitrogen application levels.2.The carbon accumulation in various organs of Korla Fragrant Pear was different under different nitrogen treatments.The carbon accumulation of the root system was N₂>N₃>N₁,and the carbon accumulation of one-year branches and leaves was N₃>N₂>N₁,the carbon accumulation of fruit was the largest under N₂ treatment at the swelling stage and maturity stage.The ¹³C content and distribution rate of each organ of the tree changed dynamically along with development of growth stages and increase of nitrogen application.At the new shoot growing stage,leaves and roots had stronger competitive abilities for photosynthate,and ¹³C distribution rates were the highest under N₁ treatment.During fruit swelling and mature stages,leaves and fruits had stronger competitive abilities,while ¹³C content and distribution rate in leaves were the highest under N₃ treatment.However,both content and distribution rate of ¹³C in fruits were the highest under N₂ treatment.3.The contents of total carbon and nitrogen in other organs except the trunk and fruit of Korla Fragrant Pear increased with the increase of nitrogen application rate,while the C/N ratio in various organs decreased gradually.The yield of Korla Fragrant Pear under different nitrogen application treatments was N₂>N₃>N₁>N₀.At the fruit maturity stage,the yield of Korla Fragrant Pear under N₂ treatment was was15915.25 kg/hm².Correlation analysis showed that in different growth stages,the total carbon and total nitrogen content of various organs were positively correlated with yield,while the C/N value was negatively correlated with the yield.In the yield effect model,through effect equation of nitrogen application and yield Y=-0.0704 X²+50.045 X+5483（R²=0.8711）（0≤X≤450）,the theoretical optimal nitrogen application rate was 355 kg/hm²;The yield of Korla Fragrant Pear and the C/N value of above-ground new organs and nitrogen application rate were regression analysis,and found that the C/N of middle and lower leaves could well fit the relationship between carbon and nitrogen nutrition and yield in tree.Therefore,it was determined that the C/N value range of the middle and lower leaves of the new organs was 17.8-20.8,and the theoretical nitrogen application rate was 300-323 kg/hm².To sum up,according to the experimental results and model analysis,on the premise of ensuring a higher nitrogen utilization rate and the coordination of carbon and nitrogen nutrients in the tree,the Korla Fragrant Pear yield is 11100-16500 kg/hm² as the economic target,and the appropriate nitrogen application range for 6-7 years old Korla Fragrant Pear is recommended to be 300-355 kg/hm².