Studies on Agronomic Measures for High Yield Virus-free Sweet Potato "Longyan 7-3"

To study the effects of NPK fertilizer and planting density on potato yield,virus-free sweet potato "Longyan 7-3" was cultured with 4 factors ×5 levels quadratic general rotational design. A high yield mathematical model was built by computer simulation to obtain the optimum agronomic measures. The results showed that: (1) the optimal combination of 4 factors for yield over 45.0 t·hm-2 was: applying urea between 163.05-191.55 kg·hm-2, crude calcium 546.6-653.4 kg·hm-2, potassium sulphate 510.3-614.55 kg·hm-2, and planting density at 5.45×104-5.80×104 plants per ha; (2) the effect of 4 factors on potato yield was in order of K＞planting density＞N＞P fertilizer; (3) the interaction effects on the yield were observed among the factors; (4) increase of K and N fertilizers were conducive to the yield enhancement of Longyan 7-3; and (5) the suitable planting density resulted the high proportion of large and medium size tuber.