Location: Rangeland and Pasture Research2011 Annual Report
1a. Objectives (from AD-416)
1) Develop management and monitoring tools based on improved estimates of carbon sequestration and loss potential of Southern Plains mixed-grass prairie under alternative grazing systems. 2) Determine the interactions of season and frequency of prescribed burning and livestock grazing on ecosystem function, vegetation heterogeneity, and animal responses in the southern mixed-grass prairie. 3) Determine the impact of plant diversity (including invasive weeds) on establishment, productivity, and stability of degraded cropland and arid pastures seeded with improved native and introduced germplasm. 3.1) Evaluate the herbage production and soil responses of grass monocultures and in 2-, 4-, 8-, and 16-way mixtures of native and introduced grasses and grass-forb mixtures in pasture plantings for revegetation of marginal crop land in the Southern Plains. 3.2) Evaluate the use of legumes as a nitrogen source for grass-legume mixtures for reclaiming marginal croplands in the Southern Plains. 3.3) Develop optimum methods and timing for winter seeding of eastern gamagrass (Tripsacum dactyloides) 3.4) Develop establishment and management practices to integrate Texas bluegrass (Poa arachnifera) into Southern Plains complementary grazing systems. 4) Develop decision support tools for planning and management of forage-based livestock systems for the southern mixed-grass prairie and its associated marginal crop lands to extend seasonal forage yields and produce acceptable livestock products across wider gradients of soils and environmental conditions.
1b. Approach (from AD-416)
Major red meat production assets of the Southern Plains include temperate winter weather and a high forage production potential from a combination of rangeland, perennials established on marginal farmland, and annuals on farmland. Major natural resource problems include drought, over-used rangeland, farmland highly susceptible to erosion, weeds, difficulty in grass and forb establishment, low fertility on farmland seeded to forages, and low forage quality from late summer through winter. The challenge is to develop economic, energy-efficient grazing systems for the area while maintaining or improving the plant, soil, water, wildlife, and aesthetic resources. The overall approach is to gather information on forage production and quality, and cattle gain on native rangelands, perennial forages growing in marginal farmlands, and annual farmed forages as affected by management, climate, and soils. The information will be used to develop and test forage and grazing management strategies for red meat production systems.
3. Progress Report
For the ongoing study of carbon sequestration by rangeland, the 10 years of data have been summarized and are being molded into a peer-reviewed article (Objective 1). In the patch burning study, all years of the study have been completed and the data is currently being analyzed and a manuscript for peer-review publication is being prepared (Objective 2). The data for the examination of mixtures of grass to stabilize marginal cropland was completely collected by FY2010 and an article was published in FY2011 in the Agronomy Journal (Objective 3.1). The evaluation of legumes as a nitrogen source study has been initiated and the four years of samples have been collected; samples for year four are currently being analyzed in the laboratory (Objective 3.2). All the data to examine the Great Plains Framework for Agricultural Resource Management model was transferred to cooperators in Fort Collins, CO, in FY2008. In FY11, the manuscript was published in the Rangeland Ecology and Management journal (Objective 4).
1. Grass canopy depletion in pastures affects foraging behavior. Forage intake is a key determinate of cattle performance in pasture-based production systems. Forage intake depends not only on the nutritive value of the grass, but also its accessibility. Accessibility is directly related to the pasture's previous grazing events. Wheat (Triticum aestivum L.) pastures were previously grazed to produce three different depletion levels: ungrazed (control), as well as medium and high levels of depletion. These grazing scenarios were then sampled for sward surface height and amount of green leaf and stem remaining. Pasture depletion resulted in cattle moving along the pasture more quickly as they grazed, covering a greater portion of the pasture and consuming less per feeding station. With this high-quality monoculture type pasture, cattle adapted their foraging behavior and were able to sustain a high-diet quality. These results imply that behavioral adaptations would make diet quality less sensitive to certain levels of pasture depletion, but energy expenditure would be increased because of the need to search for preferable forage.
Polley, H.W., Phillips, B.L., Frank, A.B., Bradford, J.A., Sims, P.L., Morgan, J.A., Kiniry, J.R. 2011. Variability in light-use efficiency for gross primary productivity on Great Plains grasslands. Ecosystems. 14:15-27.