Effects Of Continuous Decrement Of Nitrogen And Phosphorus And Combined With Zinc Fertilizer On Fruit Yield,Quality And Phosphorus,Zinc Use Of Guanxi Pomelo

To solve the problem of excessive application of fertilizer,especially phosphorus(P),in pomelo production area of Guanxi Pomelo in Pinghe County,Fujian Province,China,we conducted a field experiment to carry out nitrogen(N)and P reduction fertilization test using Guanxi Pomelo in Pinghe County,Fujian Province in 2016.In the previous studies,it was found that excessive P reduced the availability of zinc(Zn)in soil and caused Zn deficiency in trees.Therefore,an experiment of P reduction combined with Zn fertilizer was started in 2018.To further explore the effects of N and P reduction potential and combined application of Zn fertilizer on the yield,quality and nutrient utilization of pomelo,we continued the experiment.The results not only provide theoretical basis and technical support for rational and efficient fertilization,but also contribute the reduction of fertilizer loss and control of non-point source pollution in Guanxi pomelo orchard.The main results obtained are as follows:(1)The reduction of P fertilizer and its combined application of Zn fertilizer increased the fruit yield of pomelo,and P fertilizer could still be reduced.In the fifth and sixth years,the fruit yield of pomelo was declined at the treatments of 30% and 60%reduction of N fertilizer,while 70%(P1)reduction of P fertilizer increased the yield in the sixth year,indicating the P fertilizer had the potential of reduction.In the third and fourth years,P fertilizer reduction and combined with Zn fertilizer increased the fruit yield of pomelo,and the effects of 35% P fertilizer reduction(P2)combined with Zn spraying was the best treatment.(2)The fruit quality were improved by reduction of N and P fertilizer and combined application of Zn fertilizer.In the fifth and sixth years,N and P reduction in Guanxi pomelo,the fruit juice rate,edible rate,soluble solids,titratable acid and vitamin C content were improved,but the fruit weight and peel thickness were decreased.Principal component analysis showed that the fruit quality of N1P2 and N1P1 was better treatments.In the third and fourth years,P reduction combined with foliar Zn application also improved fruit quality,P reduction reduced fruit weight and skin thickness,but increased juice yield,vitamin C content,soluble solid and titratable acid contents.Zn application increased fruit weight,water content and soluble solid contents,but decreased titratable acid contents.Principal component analysis showed that 70% of P reduction combined with Zn fertilizer had better fruit quality.(3)The effects of N and P reduction fertilization on leaf N and P contents were different in different periods,and the contents of all elements were within the appropriate range.Zn application significantly increased leaf Zn concentration and low P level was beneficial to leaf Zn accumulation.N and P reduction fertilization had little effects on total N and P contents in fruit skins;N reduction decreased total P in fruit flesh,P reduction increased total P in fruit flesh.Spraying Zn fertilizer significantly increased the contents of Zn in leaf,pericarp and flesh,while reduction of P fertilizer significantly affected the contents of total P in pericarp and flesh and Zn contents in leaf,pericarp and flesh.(4)The pH,organic matter,alkali-hydrolyzable N and available Zn in subsurface soil of each treatment were all lower than those in surface soil,and all were in the appropriate range.However,the contents of available P and available potassium in surface and subsurface soil were higher,and far exceeded the standard upper limit.Moderate N and P reduction fertilization and P reduction combined with Zn fertilizer can alleviate soil acidification and increase soil organic matter content.In conclusion,60% of N fertilizer reduction and 70% of P fertilizer reduction had the better effects at 5th and 6th by the analysis of yield,quality of fruit and the nutrients of tree and soil.It was recommended that the amount of N,P and Zn were 0.64 kg,0.39 kg and 40 g/(plant·a)in Guanxi Pomelo.