Sweet potato root and biomass production with and without nitrogen fertilization

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