Effects of Nitrogen Fertilization on Forage Sorghum Nutrient Composition

Whole plant nutrient composition was investigated as forage sorghum (Sorghum bicolor (L) Moench) nitrogen (N) fertilization regimes were changed for Virginia production systems. Five N rates were applied to forage sorghum plots using a randomized complete block design with four replications. Total digestible nutrients (TDN), crude protein (CP) concentrations, neutral detergent fiber (NDF) and acid detergent fiber (ADF) were analyzed from two harvests, 40 days post emergence and 45 days after first cutting, using near infrared spectroscopy. No significance for TDN, CP, ADF or NDF across N rates was found for either cutting. Means for TDN were 57.0% and 59.0% for the first and second cutting and means for CP concentrations where 9.0% and 10.4 %, respectively. Plant height and normal difference vegetative index readings were taken twice for each harvest period and were not significant across N rates. Dairy manure had been applied in previous years which could have led to higher plant available N rates. Lower than average rainfall may have limited growth for the second growth period.