Abstract: The NPK fertilizer response and its optimum application rate on sweet potatoes was studied by field experiments in Fujian.The results showed that on average,the application of N,P,and K on sweet potatoes increased yield by 27.2%,15.8%,and 26.4%,respectively.The rates of the increase were N KP.The weight ratio of big-medium to small sweet potato was 6.7 in a NPK balanced fertilization.It was significantly higher than the N,P or K deficient controls.The output/input ratio of N and K fertilizers was higher in the summer sweet potatoes than in the autumn crop.However,the P fertilizer’s ratio was higher in the autumn.The optimum application rate for N was 168 kg·hm-2,48 kg·hm-2 for P2O5,and 168 kg·hm-2 for K2O,in the ratio of 1:0.3:1.0 on summer sweet potatoes.For the autumn crop,the optimum application rate was 174 kg·hm-2 for N,57 kg·hm-2 for P2O5,and 200 kg·hm-2 for K2O,in the ratio of 1:0.3:1.2.But obviously,the optimum application rate depends largely on the soil type and its fertility.The NPK balanced fertilization increased yield by 14.9% and net income 3600 yuan per hectare over the traditional practice in a higher yield farmland,or increased yield by 12.0% and income by 2200 yuan per hectare in a medium-low yield farmland.