Objective  NPK fertilization and utilization of manure for partial replacement in sweet potato farming were optimized for the agriculture in Fujian.

  Method   Based on field experiments, sweet potato growing fields in the province were classified. A ternary non-structural fertilization response model was constructed for each class to optimize the fertilization. Field tests and demonstrations were conducted to scrutinize and promote the recommended program.

  Result  The 4 classes of sweet potato fields in the province included (1) high yield paddy, (2) medium yield paddy, (3) medium-to-low yield field, and (4) low yield field. The sweet potato plants were highly responsive to N fertilizer application on the fields of higher yield, but P or K tended to benefit more the plants grown on lands of lower yields. According to the fertilization response models, the economic applications averaged 160 kg·hm⁻² on N, 62 kg·hm⁻² on P₂O₅, and 212 kg·hm⁻² on K₂O in the ratio of 1:0.4:1.3. However, the recommendation for different classes of field differed significantly. By replacing 25% NPK in the recommended fertilizations (RF) with manure, on average a 13.0% increase on tuber yield and 1 802 yuan·hm⁻² increase on net revenue over RF were realized. In the 79 field demonstrations with RF, the application of N was reduced by 16.7% and P₂O₅ by 47.41% while K₂O increased by 79.3% which resulted in 7.9% rise on yield and 3 394 yuan·hm⁻² more on net revenue over what practiced by the farmers (FP). On the other hand, in the 16 field tests where 25% NPK fertilizers was replaced with manure, the average yield rose by 11.0% with 4 192 yuan·hm⁻² higher in revenue.

  Conclusion  Although either RF or 25% NPK replaced by organic manure could significantly improve the sweet potato productivity and profitability, the use of organic manure to partially substitute chemical fertilizer was deemed superior for the farming in the province.