| Summary: | Previous work suggests that some sweet potato (Ipomoea batatas, L.) cultivars can produce high storage root yields on soils without fertilizer N addition. This study was conducted to compare storage root yields, total biomass, N uptake and fibrous root weights of sweet potato cultivars grown on low N level soils with and without N addition. In 1987 and 1988, improved sweet potato cultivars developed at International Institute of Tropical Agriculture (IITA), Ibadan, Nigeria were grown with and without 50 kg N ha−1 in Oxic Paleustalfs with low N and C concentrations. Yields of 21 to 38 Mg ha−1 were produced for four of the five improved cultivars grown in soil without N addition. Total biomass, foliage, fibrous root and storage root weights and N concentration in leaves were not influenced by fertilizer N addition. Up to 158 and 89 kg N ha−1 uptake in total biomass occurred with the +N and −N treatments, respectively. Indigenous soil N levels and fibrous root weights for − N vs. +N treatments could not account for the total N uptake and biomass produced on soils without N addition.
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