Effects Of Decrement Application Of Nitro Gen And Phosphorus Fertilizer With Zinc Foliage Dressing On Fruit Yield,Quality,and Nutrient Use Of Guanxi Pomelo

Excessive application of chemical nitrogen and phosphorus fertilizer results in excessive nitrogen and phosphorus concentrations in soil and available zinc deficience in trees and soil of Guanxi pomelo orchard in Pinghe County,Fujian Province.Field experiment was established from March,2016,with 27-year-old acid pomelo rootstock white pulp Guanxi pomelo as the test material,treatments were designed as continuous decrement application of nitrogen and phosphorus fertilizer from 2016 and decrement application of phosphorus fertilizer with foliar zinc application from 2018.The fruit yield and quality,soil nutrient availability,and tree nutrient accumulation and efficiency were analysized,with the aim at decrement application of chemical fertilizer,improvement of fruit quality and production efficiency,sustainable and high-quality development of Guanxi pomelo industry.The main results are as follows:?1?The decrement application of 60%nitrogen and 70%phosphorus led to no significant decline in fruit yield of Guanxi pomelo from the third year or 2018,while decrement 30%nitrogen and 35%phosphorus did continue to increase some fruit yield until the fourth year or 2019.Particularly combining decrement 35%phosphorus with foliar application of zinc fertilizer significantly increased fruit yield,and even decrement70%phosphorus combined with foliar application of zinc fertilizer could also raised fruit yield certainly.?2?Appropriate decrement of nitrogen fertilizer significantly reduced fruit weight,but increased fruit solid acid ratio and soluble solids content;moderate decrement of phosphorus fertilizer significantly reduced fruit peel thickness,titratable acid content,and increased vitamin C content;therefore,the best quality of fruit was inevitably displayed under medium decrement application of nitrogen and phosphorus fertilizer.Decrement application of phosphorus fertilizer combined with foliar application of zinc fertilizer significantly reduced peel thickness and titrable acid content,but increased edible rate,juice yield,soluble solids,solid acid ratio,particularly the best fruit quality presented under the medium decrement of phosphorus with zinc application.?3?Decrement fertilization of nitrogen and phosphorus had less effect on the contents of nitrogen and phosphorus in fruit pulp and peel of Guanxi pomelo,while the zinc concentrations in fruit peel and pulp were increased by application of zinc fertilizer significantly especially raised more under medium decrement phosphorus fertilization.The phosphorus and zinc contents in fruit pulp were higher than peel of Guanxi pomelo,but the nitrogen concentration in fruit pulp was nearly the same as peel.?4?The nitrogen and phosphorus concentrations of Guanxi pomelo leaves were all within appropriate range and varied with one accord annually.The leaves nitrogen content exhibited the highest in May,decreased from July to September,and kept no more change in November;while the leaves phosphorus content was higher in May,decreased in July,increased in September,and also kept no more change in November.The leaves zinc concentration was raised by foliar application of zinc fertilizer,resulted in appropriate leaves zinc concentration of trees with zinc treatment,but dificient leaves zinc concentration of trees without zinc treatment,also resulted in higher leaf zinc content of zinc treated plant in 2019 than 2018 with continuous foliar application of zinc fertilizer.?5?The foliar application of zinc fertilizer significantly increased the zinc contents in leaves,fruit peels and flesh of Guanxi pomelo,reduced phosphorus content of the tree,and improved fruit yield and quality of Guanxi pomelo.?6?The soil p H and the concentrations of soil organic matter,available N,available P,avaiable K and available Zn in the surface soil of all treatment Guanxi pomelo orchard were higher than subsoil,especially the soil available phosphorus content was excessive,the soil available potassium content was rich.Decrement applicatio of nitrogen and phosphorus and combination with zinc foliar application alleviated soil acidification,and increased soil organic matter and available Zn content.?7?Based on results of fruit yield and quality,tree nutrients use,soil nutrient availabilty,the optimal decrement application of nitrogen and phosphorus fertilizer was recommended:30%decrement of nitrogen fertilizer and 35%decrement of phosphate fertilizer as 1.12 N kg/?plant·a?,0.85 P₂O₅kg/?plant·a?,two times 0.2%foliar application of 40 g ZnSO₄·7H₂O/?plant·a?.