The Effect Of Nitrogen And Phosphorus Fertilizer Reduction On Yield,quality Of Guanxi Pomelo And Tree,soil Nutrient

In view of excess fertilization for Guanxi pomelo in Pinghe County,Fujian Province,reducing nitrogen（N）and phosphorus（P）application was studied for higher yield and better quality fruit.The field experiment was conducted with white pulp Guanxi pomelo trees.Based on previous questionnaire,the maximum amount of N and P fertilization were:N1.60 kg/（plant·year）,and P₂O₅ 1.30 kg/（plant·year）,which were set as the high level of N treatment（N1）and P treatment（P1）according to the local soil nutrients status and the characterization of nutrients demand of pomelo.And then,the middle level of N treatment（N2）and P treatment（P2）,low level of N（N3）and P（P3）treatments were set up with 30%gradient reducing of N fertilization and 35%gradient reducing of phosphate fertilization respectively.It is of great importance to promote local pomelo industry green and efficient development.The main conclusions of the study are summarized as follows:（1）In 2016,the yield of N and P reduced fertilization treatments increased by27.04%-58.93%compared with the highest amount of N and P fertilization treatment（N1P1）.In 2017,compared with the N1P1 treatment,the output of other treatments that reduced the amount of N and P fertilization performed different.The yield of N1P2,N1P3,N3P1 and N3P3 treatments decreased,and the N1P2 treatment decreased the most by20.11%.But the yield of N2P1,N2P2,N2P3 and N3P2 treatments increased,and the N2P3 treatment increased the most by 11.55%.Along with the decreased application of N fertilizer,the yield increased first and then decreased.Different to N fertilization,with the decrease of phosphate fertilizer application,the highest yield was achieved in the level of P3 in both 2016 and 2017.（2）According to the results of the internal and external fruit quality of Guanxi pomelo in both 2016 and 2017,reducing the amount of N and phosphate fertilizer increased the fruit juice yield,edible ratio,total soluble solids（TSS）,the ratio of TSS to titratable acid（TA）and vitamin C content in different degrees,and reduced aspect ratio,single fruit weight,peel thickness,TA content in different degrees.Compared with different the levels of N,P levels had little effect on fruit quality indexes of Guanxi pomelo.The results of variable effects showed that the effects of N and P levels and their interactions on quality indexes varied as the fruit developing.The results of principal component analysis and cluster analysis showed that the fruit quality of N2P2,N2P3 and N3P1 was relatively better than other treatments,and the comprehensive score of principal component analysis was the highest in N2P3,up to 1.65,and the fruit quality was relatively better.（3）The differences of P,K,Mg contens in pulp and P,Ca,Mg contens in peel were not significant among N levels.The differences of N,P,K,Ca,Mg contens in pulp and of N,P,K contens in peel were also not significant among P levels.Overall,reducing the amounts of N and P fertilization had little effect on the contents of N,P,K,Ca,Mg in both pulp and peel of Guanxi pomelo.In addition,the contents of Ca and Mg in peel were higher than that in pulp,but the content of P in pulp was higher than that in peel,and the contents of N and K in the pulp and the peel were almost equal,respectively.（4）According to the dynamic change of leaf N,P,K,Ca,Mg contents in May,July,September and November of both 2016 and 2017,the contents of N,P,K,and Mg in leaf of each treatment were relatively higher in May,then decreased in July and September,and were relatively stable or slightly increased in November.However,the contents of Ca in the leaf increased with leaf age.According to the diagnostic criteria of Guanxi pomelo leaf mineral nutrient content,the mean values of leaf N,P,K and Ca were sufficient,and the mean content of Mg was relatively low in both years.（5）The pH and contents of organic matter,available-N,available-P,available-K,available-Ca and available-Mg in the surface soil of both 2016 and 2017 were higher than the subsurface soil.The contents of available-P in the surface and subsurface soils were much higher enough for the environment pollution risk.The content of available-K in the surface and subsurface soil were rich with a risk of exceeding,while farmers should pay more attention to excess potassium fertilizer application.Reduced amounts of N and P fertilizer and mixed with Ca and Mg fertilizers can help to alleviate soil acidification caused by excessive fertilization and effectively supplement soil available-Ca and available-Mg content.（6）We concluded that the amounts of N fertilizer should be reduced 30%and phosphate fertilizer should be reduced 70%,specifically 1.12 kg N per plant per year and0.39 kg P₂O₅ per plant per year as optimum application rates.Besides,for the orchards with relatively lower P environment risk,the amounts of N fertilizer should be reduced30%and phosphate fertilizer should be decreased 35%were recommended,specifically1.12 kg N per plant per year and 0.85 kg P₂O₅ per plant per year.