Objectives In this study, we analyzed the effects of N, P and K application rates and methods on yield, nutrient accumulation and utilization efficiency of yam (Dioscorea oppositifolia L.), to propose the optimal nutrient management pattern of yam.

Methods Two field experiments were conducted in the Suidong and Ximengchang Village, Baoding City, Hebei Province. ‘Bangyao’, a main extended yam cultivar in the central Hebei Plain, was used as the study materials. At Suidong Village, the four N levels were 0, 150, 225, 300 kg/hm² with the base to topdressing application ratio of 3∶7; the four P₂O₅ levels were 0, 75, 150, 300 kg/hm², which were applied as basic fertilizer; and the four K₂O levels were 0, 150, 225, 300 kg/hm² with the base to topdressing application ratio of 4∶6. The yield and N, P and K accumulations in aboveground and underground parts of yam were measured at different growth stages. In the experiment at Ximengchang Village, the four basic N levels were 0, 60, 90, 120 kg/hm² and the topdressing N levels were 240 kg/hm²; the four P₂O₅ levels were 0, 150, 225, 300 kg/hm² and applied as basic fertilizer; the K₂O 270 kg/hm² were applied in four ratios of base to topdressing application with 0∶0∶0, 5∶2∶2, 5∶4∶0 and 9∶0∶0. The yield and N, P and K accumulations in stem, leaf, bulbil and rhizome of yam were evaluated at harvest.

Results 1) The yield and N accumulation of yam in N rate of 300 kg/hm² were significantly higher than those in N rate of 225 kg/hm²; Under the same base to topdressing application ratio of N fertilizer, the apparent recovery efficiency (ARE), agronomic efficiency (AE) and partial fertilizer productivity (PFP) of N fertilizer in treatment with N 300 kg/hm² were significantly higher than those with N 450 kg/hm². At the same amount of N topdressing, there were no significant difference in yam yield among different N basal application rates, but the N and K accumulation in treatment at N 90 kg/hm² showed a significant increase compared to those at 60 kg/hm². 2) The yield and NPK accumulation of yam at P₂O₅ 150 kg/hm² were significantly higher than those at P₂O₅ 75 kg/hm², and the yield increase was up to 7.9%. When the P₂O₅ rate was beyond 150 kg/hm², the effect of yam increasing became not significant, but the aboveground N and K accumulation and the whole plant N accumulation at P₂O₅ 225 kg/hm² were significantly higher than those at P₂O₅ 150 kg/hm², and there was no significant difference in ARE between the two treatments. 3) The yield and NPK accumulation of yam at K₂O rate of 300 kg/hm² were significantly higher than those at K₂O 225 kg/hm². The ARE, AE and PFP of K at K₂O 300 kg/hm² were significantly higher than those at K₂O 450 kg/hm². When the total amount of K₂O was 270 kg/hm², splitting application had better effect on yield, NPK accumulation and ARE of yam than the one-time basal application.

Conclusions Appropriate supply of N, P and K fertilizer is beneficial to increase yam yield and nutrient accumulation. Excessive application would not increase yield, and influences the nutrient utilization efficiency adversely. The optimum NPK nutrient management pattern for yam cultivation to high yield and nutrient use efficiency are as follows: basal applying N 60–90 kg/hm², and topdressing N 210–270 kg/hm² at the yam seedling and early and full rhizome expansion stage, respectively; one-time basal applying P₂O₅ 150–225 kg/hm²; applying K₂O of 270–300 kg/hm² half as basal and half as topdressing, and the topdressing can be applied either once in the early rhizome expansion period or twice applied in early and full rhizome expansion, respectively.