Effect of Nitrogen and Phosphorus on Growth and Yield of Sweet Potato in Potassium-rich Soil

Field experiments were conducted to study the nitrogen and phosphorus fertilization on growth dynamics and tube production of sweet potato. The nitrogen test showed that fresh weight of tuber and aboveground parts reached the maximum in the plants treated with 75 kg/hm2nitrogen, and the fresh potato yield was 51 519.25 kg/hm2. In addition, the tuber number per plant was 5.0,commodity potato proportion was 89.43%, and the average weight of tuber per plant was 1 084.71 g. Further studies showed that the total biomass, increased as the nitrogen level rising under low fertilization rate(nitrogen≤75 kg/hm2), sharply decreased under high fertilization rate(nitrogen≥75 kg/hm2). The other fertilization experiment revealed that the maximum of potato production was 46 802.35 kg/hm2 at the level of 135.0 kg/hm2phosphate. And the number of tubers per plant was 4.65, commodity potato proportion was 91.0%, the weight of tubers per plant was 978.0 g. Under low phosphorus rate(≤135.0 kg/hm2), tuber yield increased as the application of phosphate.However, the production was significantly declined if the dosage of phosphorus was more than 135.0 kg/hm2. This study suggested that, for optimum sweet potato yield and income, rational fertilization of nitrogen and phosphorus was very important.