Influence of Nitrogen Fertilizer on Growth and Yield of Grain Sorghum Hybrids and Inbred Lines

Grain sorghum (Sorghum bicolor (L.) Mocnch] is an important crop in semiarid regions of the world because of its drought tolerance. Nitrogen is one of the most limiting nutrients in crop production due to low availability and loss. We hypothesize that there are differences in physiological and yield traits among grain sorghum genotypes in response to N. The objectives of this study were to determine the responses of sorghum genotypes (hybrids and inbred lines) to N fertilizer and the relationship between their physiological and yield traits. Field experiments were conducted at two locations in Kansas for two seasons (2010 and 2011). Genotype x N regimes and year x genotype interactions were significant for leaf chlorophyll, aboveground biomass, grain yield, and seed number. Overall, the hybrids were superior to inbred lines for grain yield and total aboveground biomass, but grain yields of inbred lines TX2783 and T X7000 were comparable to hybrids. Maximum total aboveground biomass, leaf chlorophyll index, and grain yield were obtained at 90 kg N ha(-1). Across years, application of 45 and 90 kg N ha-1 resulted in an increase in yield of 13 and 48% over (1 kg N ha(-1), respectively. No strong relationship was detected between genotypes and leaf chlorophyll index or chlorophyll a fluorescence and grain yield, but there was a strong relationship between seed number and total aboveground biomass and grain yield. Leaf chlorophyll index and chlorophyll a fluorescence did not provide physiological basis for differences in N response among the genotypes for grain yield.