Effects Of Reduced Nitrogen Fertilization On Nitrogen Content,fruit Yield And Nitrogen Fertilizer Utilization Of Citrus Trees

The planting area and output of citrus production in China are increasing year by year,while the amount of nitrogen fertilizer application has also increased.The excessive area of nitrogen fertilizer used in the country exceeds half of the planted area,causing a large amount of nitrogen fertilizer loss,and excessive nitrogen will cause excessive growth of tree nutrients,reduce fruit quality,and affect fruit yield.Citrus trees use nitrogen fertilizer less efficiently.Appropriate application of nitrogen can promote the vegetative and reproductive growth of citrus trees.To this end,under the realistic conditions of generally excessive fertilizer application,explore the reduction of nitrogen fertilizer application on citrus trees.The influence of vegetative growth and yield is of great significance to guide the rational fertilization of citrus orchards and improve the utilization rate of nitrogen fertilizer.This study was carried out in the citrus planting area of Banyue Town,Dangyang City,Hubei Province.A plot experiment of"Reduced Nitrogen Fertilization on Citrus Tree Growth and Fruit Quality and Yield"and a micro-plot experiment of"¹⁵N Isotope Tracer of Citrus Trees on Nitrogen Fertilization".The plot experiment experiment set up four treatments,namely:?1?No nitrogen fertilizer?N0?;?2?Reduce nitrogen fertilizer by 30%relative to local conventional nitrogen application?N1?;?3?Reduce nitrogen fertilizer by 15%relative to local conventional nitrogen application?N2?;?4?Local conventional nitrogen application rate?N3?.In the micro-plot experiment,apply 3 atom%of ¹⁵N-urea according to the amount of nitrogen applied by N1 treatment,and set up two treatments,namely:?1?the base fertilizer is ¹⁵N-urea,top dressing is common urea;?2?the base fertilizer is common urea,top dressing ¹⁵N-urea.Both the plot experiment and the micro-plot experiment determine the nutrient content and leaf quality of the leaves,twigs,perennial leaves,and perennial branches of citrus trees at different growth stages,and the quality and yield of the fruit at the mature stage.In the micro-plot experiment,the proportion of nitrogen derived from fertilizer in each organ of the tree was also measured.The main findings are as follows:?1?Compared with N3 treatment,the nitrogen and phosphorus contents of citrus tree leaves and branches of N2 and N1 treatments were not significantly different;the nitrogen content of the current leaf increased in spring and then decreased,and the change trend of the phosphorus content of the current leaf was the opposite;The nitrogen content of perennial leaves also increased first and then decreased,and the trend of phosphorus content in perennial leaves was the same.?2?The fruit quality results from 2018 to 2019 show that,compared with N3 treatment,the fruit shape index of N2 treatment is better,and the peel thickness of N2 and N1 treatments is reduced by 1.50%to 10.52%;compared to N3 treatment,N2 and The soluble solids content of N1 treated fruits increased by 5.70%to 11.51%,the solid acid ratio increased by 6.13%to42.79%,the juice yield increased by 1.11%to 9.99%,and the edible rate increased by 0.41%to 5.44%,and The acidity of the fruit is reduced by 14.99%?21.17%,and the vitamin C content of the fruit is not affected,which means that reducing the amount of nitrogen fertilizer can improve the quality of the fruit.?3?From 2018 to 2019,compared with N3 treatment,the single fruit weight of N2 and N1 treatment decreased by 0.68%to 10.35%,fruit yield decreased by 0.99%to 3.52%,and nitrogen reduction within 30%did not significantly reduce fruit yield.And it can reduce the amount of nitrogen carried out by the fruit,so it is better to reduce the application of nitrogen fertilizer to less than 30%.?4?The results of ¹⁵N isotope tracing of fertilizer nitrogen showed that the absorption capacity of citrus tree to basic fertilizer nitrogen was significantly higher than that of top dressing nitrogen.From the germination stage to the young fruit stage,the new organs have a strong ability to absorb basal fertilizer nitrogen.The Ndff%of flowers,current leaves,current branches and young fruit is significantly higher than other organs;from the expansion stage to the mature stage,the basal fertilizer nitrogen of all organs Absorptive capacity is relatively strong,nitrogen fertilizer is mainly supplied to the fruit.?5?At the mature stage,the size of the ¹⁵N distribution rate of basal fertilizer in each organ is Fruit>Perennial leaves>Annual leaves>Annual branches>Perennial branches>dressing is Fruit>Perennial leaves>Annual leaves>Perennial branches>Main root>Annual branches>Stem>Lateral root>Fibrous root.?6?The utilization rate of citrus tree base fertilizer is 5.78%,of which the utilization rate of base fertilizer nitrogen for fruits,perennial leaves and current year leaves is 1.88%,1.33%and 1.13%respectively;the utilization rate for top dressing is only 0.62%,It is mainly used by fruits;it is recommended to reduce the application amount of top dressing and increase the application amount of basal fertilizer,and delay the application of top dressing nitrogen until fruit expansion.