Study On Fertilization And Optimization Of Qualityand Efficiency Improvement Of Pummelo (Citrus Grandis) In Zitong County, Sichuan Province

Pummelo[Citrus grandis]belonging to the genus Citrus,family Rutaceae,is a commercially valuable fruit crop in China.There has a long cultivation history for pummelo in Zitong County,with over 100,000 mu of planting areas.The brand"Tianbao pummelo"has been approved by the GAQSIQ and become the National Geographical Symbol Product in 2015.In the"13^th five-year Plan",Zitong government pointed out that the planting areas of pummelo will increase to 200,000 mu to promote the formation of a circular agricultural industry chain.Nowadays,pummelo in Zitong is standing in a period of rapid development.However,due to the extensive nutrition management,there are many problems such as unreasonable fertilization,inappropriate proportion of chemical elements.This phenomenon resulted in the poor-quality and low-efficiency of pummelo production and low incomes for farmers,which severely hindered the further development of pummelo industry in Zitong County.In this study,we firstly investigated the status of fertilization for pummelo,and then collected the soil from the orchard to determine the basic chemical elements.Based on the survey data,we designed the optimized fertilizer to apply for pummelo and select the excellent fertilization proportion.The main results are listed as follows.（i）There are many problems in fertilization for pummelo in Zitong County,Sichuan province,such as the inappropriate proportion,unreasonable fertilization method,etc.For instance,majority farmers just used fertilization in the young fruits period,while only 13%of farmers simultaneously fertilized basic fertilizer in the infancy period.Farmers mainly used compound fertilizer rather than organic fertilizer in the orchard without appropriate proportion of N,P and K elements.In addition,they often spread fertilize over the ground under the tree so that fertilizer was easily washed away by rainfall.（ii）Based on detection,the pH of orchard soil is approximate 7.70 without enough soil organic matter in the majority of orchards,resulting in the poor soil fertility capacity and nutrition availability.The deficient proportion of N,P,Fe,Zn and Mg elements reached 93.48%,86.94%,95.35%,67.39%and 93.48%,respectively.（iii）We designed three fertilization treatments for pummelo.The proportion of N,P₂O₅,K₂O,MgO,FeO,ZnO is 22,9,9,1.3,0.1,0.1（A）,and 15,6,24,1.3,0.1,0.1（B）fertilized in the infancy and young fruits periods,respectively.The results showed that 0.5 kg of A plus 1.0kg of B,and 0.6 kg of A plus 1.2 kg of B had significant improvement effects on the peel thickness,the content of soluble sugar,soluble solid,and vitamin C and sugar-acid ratio of pummelo,while revealed no obvious increase for fruit shape index,organic acid and TSS-acid ratio.The treatment by 0.5 kg of A,1.0 kg of B,0.5 kg of compound fertilizer and 5 kg of commercial organic fertilizer reached the excellent effects on the improvement of fruit quality of pummelo.Taken the cost and effect into consideration,we suggested that the fertilization consisted of 0.6 kg of A plus 1.2 kg of B should be used in the production of pummelo in Zitong County.