Absorption and utilization of different nitrogen forms for sweet potato

The objective of this study was to determine effects of nitrogen forms on nitrogen absorption and utilization, and nitrogen efficiency for storage root production in sweet potato．Three nitrogen forms CONH4-N（urea），NH+4-N（NH4HCO3） and NO-3-N（CaNO3）, were applied in the field culture experiments, respectively. The changes of absorptive root activity and nitrogen absorption during sweet potato development, accumulation and distribution of nitrogen at the harvest，and yield of storage root were studied．The results show that absorptive roots are more vigorous in NH+4-N or NO-3-N vs. CONH+4-N treatment．Plants subjected to NH+4-N or NO-3-N have a higher level of initial nitrogen, accumulate more nitrogen, and exhibit a higher level of nitrogen fertilizer use efficiency and15N production efficiency (i.e. storage root weight per unit fertilizer-nitrogen)．Plants treated with NH+4-N or NO-3-N have 16.37% or 10.52% higher storage root yield compared to CONH+4-N treated plants. Plants subjected to NH+4-N accumulate lower nitrogen, and exhibit a higher level of15N distribution in storage roots．Plants treated with NH+4-N exhibit 5.30% higher storage root yield, 13.28% higher nitrogen production efficiency (i.e. storage root weight per unit nitrogen) and 5.29% higher15N production efficiency compared to NO-3-N treated plants．NH+4-N is most suitable for obtaining high yield and high efficiency in sweet potato．