Nitrogen Impacts On the Yield and Cell Wall Composition of Contrasting Sorghum Lines Used for Biomass.

Nitrogen (N) fertilization improves yield of biomass crops like sorghum (Sorghum bicolor (L.) Moench), but impact of N on N use efficiency (NUE) and fiber composition are not understood.  Our objective was to determine how biomass yield, composition and NUE were influenced by N rate and sorghum genotype. Four N application rates (0, 67, 135, and 202 kg/ha) were applied to nine different sorghum lines and a maize (Zea mays L.) hybrid that was included as a control. Sorghum lines included grain, forage, high sugar, and photoperiod-sensitivity cultivars. Biomass and grain were hand-harvested and stover was analyzed for total N, neutral detergent fiber, acid detergent fiber, and acid detergent lignin, and cellulose, hemicellulose and lignin concentrations were calculated. A balanced ANOVA was used to determine the impact of sorghum genotype and N-application rate and yield and fiber composition. The photoperiod-sensitive sorghum, IS777, had the highest biomass stover yield and no grain yield, while maize had higher grain yields than sorghum. Sweet sorghum had low hemicellulose, cellulose and lignin concentrations, while maize stover had the highest concentrations of these cell wall constituents. As expected the brown-mid rib (BMR) sorghum lines had the lowest lignin concentrations, but one BMR line had the highest hemicellulose concentrations among all the sorghum lines. IS777, the only genotype with a significant difference in lignin concentration across N rates, exhibited an increase in lignin percentage with an increase in N-rate. N rate also significantly impacted the hemicellulose and cellulose percentages of various lines, including corn. Fiber composition was influenced by N rate and sorghum line, and therefore these factors need to be considered in the determination of optimum N applied to fields for sorghum production as a biofuel feedstock.