EASTERN GAMAGRASS SILAGE FERMENTATION CHARACTERISTICS AND QUALITY UNDER DIFFERENT NITROGEN RATES

Perennial grass silages are needed as alternatives to corn (Zea mays L.) silage on erosive cropland. Eastern gamagrass [Tripsacum dactyloides (L.) L.] may offer an alternative to corn for silage production, but it's fermentation characteristics and quality under different rates of N have not been evaluated. A 5-yr-old stand of 'PMK-24' eastern gamagrass was treated in 1991 and 1992 with ammonium nitrate at 0, 100, and 200 lb N/acre and harvested for silage. Corn was grown adjacent to the eastern gamagrass stand in 1992 for comparison. First harvest eastern gamagrass forage was ensiled at the seed development stage in 1991 and inflorescence emergence stage in 1992, and regrowth forage at the vegetative stage both years. Eastern gamagrass silage pH was not influenced by stage of maturity or N rates, and averaged 0.4 to 0.8 pH units greater than corn silage. Concentrations of lactic and acetic acid in eastern gamagrass silage ranged from 1.1 to 3.0%, were not affected by N rates, and were greater than for corn silage. Eastern gamagrass silage had 2.6 to 4.2 percentage units greater crude protein (CP), 11.5 to 15.3 percentage units greater acid detergent fiber (ADF), 8.0 to 15.5 percentage units greater neutral detergent fiber (NDF), 1.8 to 6.1 percentage units greater lignin concentrations, and 10.9 to 21.3 percentage units lower in vitro dry matter digestibility (IVDMD) than corn silage. Eastern gamagrass harvested at inflorescence emergence or vegetative stages had 2.0 to 3.5 percentage units greater CP, 3.2 to 7.5 percentage units lower ADF, and 2.3 to 17.0 percentage units lower NDF concentrations than eastern gamagrass harvested at the seed development stage. Increased rates of N increased eastern gamagrass silage CP 1.6 to 3.0 percentage units, and tended to decrease ADF and NDF concentrations. If harvested at the vegetative or inflorescence emergence stage and proper moisture content, eastern gamagrass makes good quality silage, but of lower IVDMD than corn. Producers interested in using eastern gamagrass in place of corn for silage production on marginal and erosive cropland will have to weigh the potential benefits of reduced annual input costs and reduced soil erosion against reduced forage quality.