Effects of nitrogen application rate on dry matter accumulation, nitrogen efficiency, and potassium and sodium uptake of sweet potato (Ipomoea batatas) in coastal North Jiangsu Province
氮肥用量对滨海滩涂区甘薯干物质积累、 氮素效率和钾钠吸收的影响

Sweet potato (Ipomoea batatas) is a high energy crop with great potentials in the coastal areas in China. In order to determine optimum nitrogen (N) application rate (NAR) in sweet potato production, a field experiment was conducted in coastal North Jiangsu Province. Survival rate (SR), commodity rate (CR), dry weight vine-tuber ratio (V/T), dry matter accumulation (DMA), N accumulation (NAV), N use efficiency (NUE), N harvest index (NHI), and potassium (K) and sodium (Na) uptakes of sweet potato were investigated under six N levels (N0~N5). The N levels were 0 kg(N)·hm-2(N0), 60 kg(N)·hm-2 (N1), 120 kg(N)·hm-2 (N2), 180 kg(N)·hm-2 (N3), 240 kg(N)·hm-2 (N4), and 300 kg(N)·hm-2 (N5), respectively. The results were summarized as follows: (1) A sig-nificant positive correlation was noted between NAR and aboveground DMA or NAV at P < 0.01, but no significant correlation ex-isted between NAR and root NAV at P > 0.05. (2). Compared with N0, N1 treatment had no significant effects on sweet potato V/T, SR, NUE and NHI. (3) Sweet potato CR, root and tuber DMA as well as theoretical yield (TY=NAV×NUE×NHI) were highest under N1 treatment. When sweet potato NARs were 60~300 kg(N)·hm-2 , significant positive correlation existed between NAR and V/T at P < 0.01. However, significant negative correlation was noted among SR, CR, NUE, NHI, root and tuber DMA of sweet potato at P < 0.01. (4) There was significant positive correlation between K and Na uptake at P < 0.01; both of which increased with increasing NARs. K and Na contents of aboveground tissues of sweet potato under N1 treatment were significantly higher than those under other treatments. However, K/Na ratio for the whole plant was not different among treatments. The study suggested that the optimum NAR in sweet potato fields in coastal North Jiangsu Province was 60 kg(N)·hm-2.