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-yrold 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. Research QuestionCorn silage production can result in considerable soil erosion on marginal and sloping cropland. To create more sustainable silage production systems and help reduce soil erosion, high yielding, high quality perennial grass silages are needed as alternatives to corn for silage production on erosive cropland. Eastern gamagrass is a high quality, native perennial warm-season grass with forage dry matter yields that compare favorably with corn silage. However, before eastern gamagrass can be recommended as an alternative to corn for silage production on erosive cropland, the fermentation characteristics and quality of eastern gamagrass silage must be evaluated under different N rates. The objective of this research was to evaluate the fermentation characteristics and quality of first cut and regrowth eastern gamagrass silage under different N rates and compare these characteristics to corn silage. Literature SummaryDry matter yields of eastern gamagrass range from 2.2 to 9.8 ton/acre, which compare favorably with corn silage dry matter yields. Forage quality of eastern gamagrass is excellent if harvested at the proper stage of maturity. Although concentrations of acid detergent fiber (ADF) and neutral detergent fiber (NDF) are generally greater in eastern gamagrass than in cool-season grasses and legumes, the apparent digestion coefficients of these fiber components are greater in eastern gamagrass. Since eastern gamagrass is a perennial, annual input costs for establishment and maintenance would be less than corn silage, and it could help reduce soil erosion. Study DescriptionThe research was conducted using a 5-yr-old stand of ‘PMK-24’ eastern gamagrass established on a Piopolis silty clay loam soil, near Clifton Hill, in north central Missouri. The eastern gamagrass stand was divided into 15 plots and ammonium nitrate was applied in the spring at three rates equivalent to 0, 100, and 200 lb N/acre. In 1992 corn was grown adjacent to the eastern gamagrass stand for comparison, using standard corn production practices, and N was applied in the spring at 150 lb/acre. The first eastern gamagrass harvest was taken at the seed development stage in 1991 and the inflorescence emergence stage in 1992. Regrowth harvests were taken at the vegetative stage both years. Corn was harvested for ensiling at the early dent stage of maturity. The harvested forage was hand packed (direct cut) and ensiled in mini-silos. Applied QuestionDoes eastern gamagrass make high quality silage for use as an alternative to corn silage on erosive cropland? Eastern gamagrass silage harvested at inflorescence emergence or vegetative stages had greater concentrations of crude protein (2.6 to 4.2 percentage units), lactic and acetic acid (1.4 to 5.9 fold), and greater pH (0.4 to 0.8 units) than corn silage (Table 1). However, eastern gamagrass silage also had greater concentration of ADF (11.5 to 15.3 percentage units), NDF (8.0 to 15.5 percentage units), and lignin (1.8 to 6.1 percentage units, and lower in vitro digestibility (10.9 to 21.3 percentage units) than corn silage (Table 1). Greater concentrations of ADF, NDF, lignin and lower in vitro digestibility suggest that eastern gamagrass will not provide comparable levels of energy as corn silage. Eastern gamagrass harvested at the inflorescence emergence or vegetative stages had greater concentrations of crude protein (2.0 to 3.5 percentage units), greater in vitro digestibility (7.7 to 11.0 percentage units), and lower concentrations of ADF (3.2 to 7.5 percentage units), NDF (2.3 to 17.0 percentage units), and lignin (6.9 to 8.3 percentage units) than eastern gamagrass harvested at the seed development stage (Table 1). Increasing the N rate increased eastern gamagrass silage crude protein 1.6 to 3.0 percentage units and tended to decrease concentrations of ADF and NDF. If harvested at the vegetative or inflorescence emergence growth stages and proper moisture content, eastern gamagrass makes good quality silage that could be used for backgrounding and maintenance of beef cattle, but due to its lower in vitro digestibility it is not recommended for high producing dairy cattle. RecommendationsEastern gamagrass can be used to produce high quality grass silage and help reduce soil erosion on marginal and sloping cropland vulnerable to excessive soil erosion. However, care should be taken to ensure the first harvest is taken at either vegetative or inflorescence emergence growth stages. Delaying the first harvest to a more advanced growth stage resulted in material that was lower in quality and hard to pack. Following sufficient rest period, eastern gamagrass will produce good, leafy regrowth from which a second silage cutting can be taken. If the first harvest or regrowth forage has a moisture content > 80%, the forage should be wilted prior to ensiling. Eastern gamagrass silage could be used for backgrounding and maintenance of beef cattle, but due to its lower in vitro digestibility it is not recommended for use with high producing dairy cattle. Producers interested in using eastern gamagrass in place of corn for silage production on marginal and erosive cropland should weigh the potential benefits of reduced annual input costs and reduced soil erosion against reduced forage quality. Table 1Percentage moisture in the fresh forage and fermentation and quality characteristics of eastern gamagrass and corn silage under different rates of N (lb N/acre) in 1991 and 1992. First harvestRegrowth harvest01002000100200Corn1991Silage pH4.444.654.384.614.654.42--Lactic acid, %1.381.222.951.922.042.01--Acetic acid, %2.272.762.131.411.832.21--Butyric acid, %0.981.370.290.000.080.19--NH₃-N, % of total N6.410.48.55.14.78.1--Crude protein, %6.48.89.49.911.911.5--ADF, %48.547.146.444.043.643.2--NDF, %82.272.373.965.265.766.0--Lignin, %19.218.721.118.821.419.0--IVDMD, %48.246.948.856.652.755.2--1992Silage pH4.414.564.404.344.384.333.89Lactic acid, %0.120.080.112.621.102.240.50Acetic acid, %3.964.395.201.222.673.030.85Butyric acid, %0.030.160.050.000.180.020.00NH₃-N, % of total N7.510.010.55.47.16.95.8Cruie protein, %9.110.711.88.510.211.47.6ADF, %41.342.740.742.140.238.927.4NDF, %71.263.868.871.370.068.455.8Lignin, %12.211.812.814.713.716.110.0IVDMD, %58.554.659.849.451.650.670.7