|| Guretzky, J. A., Cook, B. J., Biermacher, J. T., Reuter, R. R., Mosali, J., Kering, M.
||Switchgrass (Panicum virgatum L.) may transform agriculture as a dedicated energy crop grown, harvested, and converted to biofuels at industrial refining facilities. In the near and intermediate terms, information is needed on whether switchgrass can be integrated into, rather than require displacement of, present agricultural production situations. Stocker cattle production, which involves the placement of young, lightweight cattle on high quality pastures before finishing on high grain diets, is a viable economic enterprise where switchgrass may have value because of its early spring availability and wide adaptability.
Our objectives were to determine: (1) stocker cattle gain, number of grazing days supported, herbage mass, and herbage nutritional value following early-season grazing of switchgrass; (2) end-of-year biomass yields after grazing cessation; and (3) the economics of retained stocker cattle ownership on switchgrass.
A 9.72 ha field of ‘Alamo’ switchgrass was established successfully in May 2007 at the Noble Foundation Red River Farm near Burneyville, OK. Twelve, 0.81-ha paddocks were created within this tract to evaluate effects of early-season stocking density (0, 2, 4, and 6 steers per paddock, grazing from mid April to mid June). Commercial stocker steers were purchased in October, preconditioned, and placed on winter rye pasture to uniformly prepare them to graze switchgrass after winter pasture termination. Animals weighing approximately 306 kg were removed from the winter pasture, shrunk overnight without feed or water, weighed individually, implanted with a growth implant, and randomly assigned to the switchgrass treatments. Herbage mass and nutrient composition were monitored at biweekly intervals during the grazing period and once at the end of the growing season.
Stocking density affected herbage mass and the number of grazing days supported. At the start of grazing, herbage mass and nutrient composition were similar among treatments, ranging from 1500 to 2000 kg DM ha-1, 14% crude protein, and 62% total digestible nutrients. Thereafter, herbage mass increased rapidly in the zero- and two-steer per paddock treatments, with growth rates averaging 113 and 45 kg ha-1 d-1 between 17 April and 6 June for these treatments, respectively. Herbage mass in the four- and six-steer per paddock treatments remained fairly steady from 17 April to 6 June, ranging from 1500 to 2500 kg ha-1. By 6 June, herbage mass averaged 7200 kg ha-1 in the zero-steer, 4200 kg ha-1 in the two-steer, 2200 kg ha-1 in the four-steer, and 2500 kg ha-1 in the six-steer per paddock treatments. The switchgrass paddocks supported 20 days of grazing in the six-steer, 30 days of grazing in the four-steer, and > 60 days of grazing in the two-steer per paddock treatments.
Information on animal daily gain, end-of-season biomass yields, and production economics will be reported as these data become available and should improve understanding of the value of switchgrass as a dual-purpose forage and bioenergy crop and possibly identify an economically viable use of switchgrass today and vehicle for jump-starting the cellulosic industry tomorrow.