Responses of nitrogen supply forms on leaf photosynthetic characteristics and root characters of sweetpotato

In order to study the effect of different nitrogen supply forms on leaf photosynthetic characteristics, root yield and quality of sweetpotato, a pot experiment was conducted with three nitrogen forms, NH+4-N［(NH4)2SO4)］, NO-3-N(NaNO3) and CONH4-N(urea) using sweetpotato cv. Xushu18. The results showed the chlorophyll contents(CCI) with CONH4-N were the highest after 30 d and 50 d of planting, while CCI with the NH+4-N was the highest in 70 d. The photosynthetic rate and photosynthetically active radiation(PAR) under the NH+4-N treatment are the highest. TheNO-3-N treatment could promote more photosynthesis of sweetpotato leaves, and the yield under the NH+4-N treatment is higher than those of the NO-3-N and CONH4-N treatments, increased by 10.6% and 17.2%, respectively. There are significant differences(P0.05) between the NH+4-N treatment and other treatments. Meanwhile, the starch content and protein content of sweetpotato roots under theNH+4-N treatment are the highest, while the soluble sugar content and reducing sugar content under the CONH+4-N treatment are the highest. The NH+4-N treatment promotes the values of peak viscosity, breakdown and consistence of sweetpotato starch, and theNO-3-N treatment promotes the values of through viscosity and final viscosity.