Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 4, 2010
Publication Date: October 7, 2010
Citation: Coblentz, W.K., Jokela, W.E., Hoffman, P.C., Bertram, M.G. 2010. Unique Dairy Applications for Eastern Gamagrass in Central Wisconsin: I. Yield Potential. Agronomy Journal. 102:1710-1719. Interpretive Summary: When replacement dairy heifers are offered diets comprised largely of corn silage or other high-energy (high-starch) forages, they often become overweight, which may damage their future performance as lactating cows. Blending corn silage with a high-fiber grass to dilute the energy content of dairy-heifer or dry-cow diets is one potential management option for overcoming this problem. Our research objective was to assess the yield potential of one such grass, eastern gamagrass, which is a perennial warm-season grass that could be used for this purpose. Based on our evaluation of agronomic traits, eastern gamagrass will likely survive indefinitely under the climatic conditions of central Wisconsin. Based on past work, two-cut harvest systems provide better forage quality characteristics than single-cut harvest systems, but our yields from two-cut systems did not compete with one-time harvests timed during early- or mid-August. Yields of dry matter from one-cut systems increased through mid-August, and this suggests that yields may be further improved by delaying a single harvest until even later in the summer. Because poorer forage quality is desirable for these unique applications (heifer and dry-cow diets), this approach for increasing yields may be viable and needs to be evaluated critically. Our study also indicates that producers should expect a clear benefit from a one-time application of nitrogen (N) fertilizer at rates ranging from 50 to 100 lbs N/acre, but diminishing returns are likely at higher application rates. This work is important because it provides commercial heifer-raising operations a potential option for diluting the energy content of corn silage in heifer diets.
Technical Abstract: Replacement dairy heifers offered diets comprised largely of corn (Zea mays L.) silage or other high-energy forages often become overconditioned, which may damage their future performance as lactating cows. Our objective was to assess the yield potential of a perennial C4 grass, eastern gamagrass [Tripsacum dactyloides (L.) L.], for incorporation into fiber demanding dairy-heifer or dry-cow diets. Replicated field plots of ‘Pete’ eastern gamagrass were evaluated within nine harvest systems and four N fertilization regimes. Across the 3-yr trial (2007-2009), harvest system interacted with production year (P < 0.001). For one-cut harvest systems, yields of DM increased across harvest dates, reaching numerical maximums of 7192, 9764, and 7554 kg ha-1 by mid-August of 2007, 2008, and 2009, respectively. During each year, there was a strong linear (P < 0.001) effect of harvest date; however, higher-ordered effects varied within year. Relatively large yield increases (= 1812 kg ha-1) between early and mid-August during 2008 and 2009 suggest that better yields could be achieved by delaying one-cut harvests of eastern gamagrass beyond mid-August. Yields of DM from two-cut harvest systems were not competitive with one-cut harvest systems timed in mid-August. Nitrogen fertilization increased (P < 0.001) yields of DM, exhibiting both linear (P < 0.001) and quadratic (P = 0.027) effects of application rate. However, efficiency of N usage was reduced as fertilization rates increased.