Submitted to: Agricultural Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/19/2016
Publication Date: 10/26/2016
Publication URL: http://handle.nal.usda.gov/10113/63275
Citation: Springer, T.L., Gunter, S.A., Goldman, J.J., Moffet, C. 2016. Optimizing eastern gamagrass forage harvests using growing degree days. Agricultural Sciences. 7:710-715.

Interpretive Summary: Scientists at the Southern Plains Range Research Station, Woodward, Oklahoma calculated growing degree days for 10 years of eastern gamagrass (Tripsacum dactyloides) harvest data from three separate experiments (1978-1982), (2001-2003), and (2008-2009). Three harvests were made in each year of the experiments, and plants were harvested in the boot stage of growth at each harvest. On average, each harvest interval requires approximately 672 ± 15 cumulative growing degree days (GDD). This value should be useful anywhere eastern gamagrass is grown because plant development depends on the accumulation of specific quantities of heat. Therefore, it is possible to predict when growth events should occur during a growing season regardless of differences in temperatures from year to year. This would place the first, second, and third harvests on or near 30 May, 16 July, and 30 August each year, respectively at Woodward, Oklahoma. In theory, 2 to 5 harvests are possible depending upon location in the USA. Accessing GDDs is another useful tool that forage producer can use in the production and management of eastern gamagrass.

Technical Abstract: Tripsacum dactyloides (L.) L., commonly known as eastern gamagrass is useful for grazing, stored forage, soil amelioration and conservation, and potentially as a biofuel feedstock. Our goal was to calculate accumulated growing degree days (GDD) from existing datasets collected for eastern gamagrass forage production experiments in northwestern Oklahoma, and discuss the use of GDD, instead of calendar harvest dates, in the production of eastern gamagrass forage. Growing degree days were calculated from 1 January each year using the 'optimum day method.' For 10 harvest years, the first eastern gamagrass harvest required 692 ± 26 cumulative GDD. Based on long-term weather data from Woodward, Oklahoma this would place the first harvest on or near 1 June. The second harvest required 635 ± 27 cumulative GDD which would place the second harvest on or near 15 July and the third harvest required 690 ± 23 cumulative GDD placing it on or near 30 August. Averaging the 30 harvest, each harvest required an average of 672 ± 15 cumulative GDD. Using GDD to predict harvest events is a useful tool that forage producer can use in the production of eastern gamagrass forage in the USA.