1109
Fall Harvest Management of Eastern Gamagrass
Recent research has suggested that eastern gamagrass (EGG) may be an effective alternative to chopped straw in the blended diets of dairy heifers and cows. Most extension materials discussing appropriate fall management of EGG recommend avoiding harvest within about 6 weeks of first frost. Using this guideline for central Wisconsin, a final harvest of EGG would need to occur before August 15; however, previous research has shown that single-harvest yields of DM are not maximized by that date because of inadequate accumulation of growing degree days. Our objectives were to evaluate yields of DM, plant persistence, and nutritive value for EGG harvested at 15-d intervals between August 1 and November 1. Residual forage growth was burned each May, and all forages were fertilized with 84 kg N/ha annually. Data collected from 2010 through 2013 indicated that yields of DM increased with linear (P < 0.01) and quadratic (P < 0.01) effects over harvest dates, peaking at > 7400 kg/ha on both the September 15 and October 1 harvest dates. Overall DM yields varied with year, but were greatest (P < 0.01) during the final year (2013) of the trial (7967 kg/ha), thereby suggesting stands were not damaged by fall harvests. Percentage of continuous row coverage also was assessed, but was not affected by harvest date (P ≥ 0.22). Concentrations of NDF increased from 75.8 to 82.0% across harvest dates, exhibiting both linear and quadratic (P < 0.01) effects. Similarly, acid-detergent lignin increased from 4.07 to 5.12% between August 1 and November 1, exhibiting only a linear (P < 0.01) effect of harvest date. Crude protein declined linearly (P < 0.01) across harvest dates, ranging from 7.69 to 3.67%. Energy density also declined linearly (P < 0.01) over harvest dates, ranging from 53.2% TDN on August 1 down to 43.9% TDN on November 1. One-time harvests of EGG during fall allowed for improved yields of DM through October 1, and did not affect stand persistence. For harvests timed between August 1 and November 1, EGG will likely range between 75.0 and 82.0 % NDF, and exhibit an energy density of approximately 50% TDN. These characteristics, coupled with the consistent observation that EGG haylage is not sortable by dairy heifers or cows, make EGG a potentially attractive alternative to chopped straw.
Keywords: eastern gamagrass, fall harvest management, DM yield