| Three factor five level quadratic regression was used to study the effects of different ratios of N, P and K fertilizers on the yield and quality of fifteen year old F uji apple trees in south Xinjiang. The results showed that the order of effects on yield were potassium> nitrogen> phosphorus and they were all positive. N and P，P and K were positively interacted, while N and K were negatively interacted. With apple production 4 325.18 kg/667m2 as the goal, the opti-mal combination of N, P and K were respectively 27.06 kg/ 667m2，17.80 kg/ 667m2 and 2.06 kg/ 667m2. The influ-ence on quality showed that high N can increase fruit weight but can not either improve its shape or enhance the accumu-lation of content in fruit. Appropriate P and K can improve fruit color, while too high or too low N can not improve fruit hardness. N and K can promote significantly sugar accumulation in fruit. Controlling P and N supplying can reduce the fruit acidity to some extent. High K treatment produce high Vc content. |