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 dactyloide s (L.) L.] may offer an alternative to corn for silage production, but it's fermentation characteristics and quality under different rates o f N have not been evaluated. A 5-yr-old stand of 'PMK-24' eastern gama grass was treated in 1991 and 1992 with ammonium nitrate at 0, 100, an d 200 lb N/acre and harvested for silage. Corn was grown adjacent to t he eastern gamagrass stand in 1992 for comparison. First harvest easte rn 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 influ enced by stage of maturity or N rates, and averaged 0.4 to 0.8 pH unit s greater than corn silage. Concentrations of lactic and acetic acid i n 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 s ilage 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 1 5.5 percentage units greater neutral detergent fiber (NDF), 1.8 to 6.1 percentage units greater lignin concentrations, and 10.9 to 21.3 perc entage units lower in vitro dry matter digestibility (IVDMD) than corn silage. Eastern gamagrass harvested at inflorescence emergence or veg etative 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 developme nt stage. Increased rates of N increased eastern gamagrass silage CP 1 .6 to 3.0 percentage units, and tended to decrease ADF and NDF concent rations. If harvested at the vegetative or inflorescence emergence sta ge and proper moisture content, eastern gamagrass makes good quality s ilage, but of lower IVDMD than corn. Producers interested in using eas tern 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 qua lity.