Abstract:Phosphorus(P) and Potassium(K) are major important factors affecting citrus growth,yield and quality.Although the effects of P and K nutrition have well been documented for citrus trees in terms of fruit growth and yield,the influence of these two macronutrients on quality and storability of citrus fruits has not been fully elucidated.In the present study,a long-term field experiment was carried out for four years on Ponkan(Citrus reticulata Blanco var.Ponkan) in order to determine the effects of P and K application on fruit yield,quality and storability of citrus grown in a red-soil(orchard) with low P and K concentrations.The experiment was set up in a incomplete factorial design with 7 treatments,with three yearly rates of P(P 0,125 and 250 kg/ha) and K(K 0,250 and 500 kg/ha).The results showed that P or K,especially combined application of P and K greatly increased single fruit weight(62.93 to 114.11 g/fruit),fruit yield(19923 to 48234 kg/ha),content of soluble solids(12.2% to 13.3%) and soluble sugars(2.58% to 3.72%),(reducing) sugar content(4.51% to 6.16%),brixacid ratio(2.84 to 5.15)and vitamin C content(37.52 to 44.91(mg/100g FW)) of citrus fruits,and decreased titratable acidity(1.59% to 1.19%) of citrus fruits.Furthermore,P and K supply(effectively) reduced weight loss of fruit,rate of fruit decay,and modified the decrease of sugar content,acidity and Vc of fruit during storage of citrus fruits.It suggests that applying P and K could increase yield and quality of citrus fruit and improve sensory and nutritive quality and storability of fruit during storage.