Nitrogen Use Efficiency In Grain Sorghum Genotypes.

Grain sorghum is an important crop in the semi-arid regions. 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 N use efficiency (NUE) is limited. Objectives of this research were to (a) determine the response of sorghum genotypes (hybrids and inbred lines) to N; and (b) quantify genotypic differences in nitrogen use efficiency. Field experiments were conducted at three locations (Hays, Ottawa and Manhattan, Kansas) in 2010. Six hybrids and six inbred lines were grown at three N regimes; 0, 45 and 90 kg N ha^-1. Experimental design was a split-plot design with N as main plots and genotypes as sub-plots, with four replications. Planting was done in May and June across all the locations, and N fertilizer (Urea, 46%N) was applied at emergence. Data on biomass was measured at vegetative, flowering and maturity, and grain yield at maturity. Concentrations of N in the grain and components of NUE were determined for Ottawa. There were significant effects (P<0.05) of genotypes and N on biomass and grain yield across all locations. Hybrids was generally superior to inbred of all traits. 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.There were significant differences among genotypes for all NUE traits at 45 and 90 kg N ha^-1. Across genotypes N uptake efficiency ranged from 17 to 50, utilization efficiency from 64 to 90, recovery from 3 to 30 and total NUE from 13 to 42. This data suggest that there were significant differences for NUE traits in sorghum hybrids and inbred lines.