Effect of phosphorus on yield and nutrient absorption and utilization in starch-type sweet potato

【Objectives】 In order to provide theoretical basis for scientific and rational application of phosphate fertilizer in high yield sweet potato, different phosphor application amounts on the nutrient uptake, distribution and yield, and the phosphorus nutrition effect of starch-type sweet potato were studied. 【Methods】 A starch-type sweet potato,Yushu 17 with starch content of 24.06 %, was used as material. A field experiment with randomized block design was conducted with seven treatments(application amounts of P2O5 0, 0, 37.5, 75, 112.5, 150, 300 kg/hm2, respectively). For the treatment of P2O5 0, no N and K2O was applied neither. For the others, N 90 kg/hm2 and K2O 150 kg/hm2 were basal applied. The fresh weight, dry weight and total N, P and K contents in the leaves, vines and roots were measured every 30 d, and a total of five samplings were taken since transplanting. The fresh yield, vines yield were weighed, the harvest index(HI), P agronomic efficiency(PAE), P apparent utilization efficiency(PAUE), P harvest index(PHI), P physiological utilization efficiency(PPUE), P partial factor productivity of applied(PFPP)and P increase rate(PIR)were calculated at harvest. The absorption of N, P and K were evaluated at harvest. 【Results】 1)Proper P2O5 application amount are capable of improve the biomass and yield, and thus a high agronomic efficiency. Treatments of P2O5 112.5 and 150 kg/hm2 led to the economic yield increase of 19.4% and 21.06%. 2)The contents of N and P in different parts were all in order of leaves vines roots, and that for K content in order of vines leaves roots at the 60, 90 and 150 days after transplanting. The content ratio of N in leaves: vines: roots was 4.08∶1.62∶1 on the 60 day, the P content ratio was 2∶1.35∶1 on the 90 day, and that of K was 2∶1.8∶1 on the 150 day after transplanting. 3)Application of P increase the absorption of N, P and K in the leaves, vines and roots, and the absorptive amount was in order of KNP. The increasing rate of the absorptive amounts of N, P and K were 23.9% to 66.6%, 29.6% to 58.5% and 41.3% to 73.7% with application of P. The absorptive amounts of P and K were in order of rootsvinesleaves, while that of N was rootsleavesvines. 4)Under different P application amounts, the K2O requirement was from 6.94 g to 11.48 g, N from 4.24 g to 6.61 g and P2O5 from 1.93 g to 2.84 g for every 500 kg fresh tubers. The highest nutrient requirement for every 500 kg fresh tubers was in the treatment of P2O5 112.5 kg/hm2, with requirement of N 6.61 g, P2O5 2.84 g and K2O 11.08 g. 5)The obtained highest PAUE and PFPP were 16.6% and 343.0 kg/kg, respectively under the treatment of P2O5 37.5 kg/hm2, the highest PAE, PPUE and PHI were 136.7 kg/kg, 777.9 kg/kg and 65.9%, respectively, with P2O5 112.5 kg/hm2. 6)The absorptive amounts of N, P and K were significantly or very significantly and positively correlated with each other, and also positive correlatied to the yield at harvest. 【Conclusions】The application of P fertilizer could increase the yield of sweet potato, but decrease P2O5 efficiency. Under the experimental condition, the most appropriate amount of P2O5 was 112.5 kg/hm2 at N 90 kg/hm2 and K2O 150 kg/hm2 for high yield in sweet potato.