Genotypic Differences in Yield and Nitrogen Use Efficiency Traits in Grain Sorghum.

Grain sorghum is an important crop in the semi-arid regions of Africa, Asia and United States. Productivity of grain sorghum is limited by soil fertility, especially nitrogen (N). Sorghum genotypes are known to vary in their response to nitrogen, however, the information on nitrogen use efficiency is limited. The objectives of this research were to (a) determine the response of sorghum genotypes (hybrids and inbred lines) to nitrogen fertilizer; and (b) quantify genotypic differences in nitrogen use efficiency (NUE). Field experiments were conducted at three locations (Hays, Ottawa and Manhattan in; Kansas) in 2010 and 2011. Six hybrids and six inbred lines of grain sorghum were grown with 0N, 45N and 90 kg N ha^-1. The experimental design was a split-plot design with nitrogen regimes as main plots and genotypes as sub-plot, with four replications. Planting was done in May and June across all the locations, and nitrogen fertilizer (Urea, 46% N) was applied at emergence. Nitrogen concentrations in the grain and component of NUE were determined for Ottawa and Manhattan. There were significant effects of genotypes (P<0.05) and nitrogen (P<0.05) on biomass and grain yield across all locations. Sorghum hybrid 99480 produced maximum grain yield across all locations. While, inbred SC35 had the lowest grain yield. Maximum biomass and grain yield was obtained at 90 kg N ha^-1, followed 45 kg N ha^-1, and lowest in 0N kg ha^-1. Across genotypes, total NUE ranged from 17.2 to 42.6 kg kg^-1, utilization efficiency from 24.9 to 60.2 kg kg^-1, N uptake efficiency from 56.1 to 82.5%, , recovery from 2 to 52%, and NHI from 43.6 to 81.3%. Overall, our data suggest that there were significant differences for NUE traits in sorghum hybrids and inbred lines. There are opportunities to breed for higher NUE in grain sorghum.