The vision of this research is to increase the ecological and economic sustainability of forage based livestock production systems associated with the Southern Plains mixed grass prairie. Our strategy is to minimize environmental impacts and increase the efficiency of plant and animal resources while addressing the production and conservation goals for mixed grass prairie. Over the next 5 years, we will focus on these following objectives: Objective 1: Improve native and introduced warm-season grass establishment and resilience to biotic and abiotic stressors. Subobjective 1A: Evaluate 21 germplasm lines of little bluestem for establishment and adaptation at 3 sites. Subobjective 1B: Select and breed Sudan grass with reduced ability to accumulate excess nitrate from the soil with a goal of releasing a new cultivar for use in the southern Great Plains. Objective 2: Evaluate the potential for using patch-burning and weather assessment tools on rangelands to improve the productivity of stocker cattle, while enhancing other ecological services. Subobjective 2A: Evaluate the potential for using patch-burning on rangelands to improve the productivity of stocker cattle while enhancing other ecological services. Subobjective 2B: Contribute and utilize weather and climate tool applications through the Long-term Agroecosystem Research (LTAR) Climate Group for national and regional LTAR agricultural and natural resource modeling programs in grazing management, ecosystem monitoring and remote sensing, soil productivity, hydrology and erosion and evaluate, develop and implement landscape-scale applications for weather and climate related rangeland planning and management needs. Objective 3: Determine the effects of weather, timing, and the amount of nitrogen (N) fertilization applied to forage grasses either through inorganic or organic N sources and their effect on ecological services. Subobjective 3A: Determine the effects of the amount and timing of N fertilizer application on dormant season harvested switchgrass biomass production and changes in soil organic carbon stocks. Subobjective 3B: Determine the utility value of underseeding red clover as an N fixer for winter-wheat pasture production to replace inorganic N from fertilizer. Objective 4: Determine genetic, annual and seasonal effects on methane emission by grazing stocker cattle. Subobjective 4A: Evaluation of new technologies in indirect calorimetry for grazing beef cattle. Subobjective 4B: Gas flux by calves from dams identified as either high or low methane emitters.
The research described herein provides essential knowledge to enhance the production and conservation goals for Southern Plains agroecosystems. The Southern Plains mixed-grass prairie is one of the United States' most important crop and livestock-producing regions that supports many rural communities and provides habitat for a host of plants and animals. The region’s agricultural enterprises are challenged with uncertainties in profitability, reliance on unsustainable land use practices, and an ever-increasing concern for the environment. Specifically, this project will 1) improve native and introduced warm-season grass establishment and resilience to biotic and abiotic stressors, 2) evaluate the potential for using patch-burning and weather assessment tools on rangelands to improve the productivity of stocker cattle, while enhancing other ecosystem services, 3) determine the effects of weather, timing, and the amount of nitrogen fertilization when applied to cool-season annual or warm-season perennial forage grasses either through inorganic or organic nitrogen sources and their effect on ecological services, and 4) determine genetic, seasonal and annual effects on methane emission by grazing stocker cattle. Experiments will concentrate on breeding and selecting new perennial forages and the effects of livestock grazing, prescribed fire, and soil disturbances on vegetation composition, diversity, production, and vegetation heterogeneity and animal body weight (BW) gains. Coordinated experimentation will leverage interdisciplinary work of 4 scientists to address integration of forage-livestock systems through new forages, use of patch burning and livestock grazing management to support sustainable and economically viable agricultural enterprises.
Objective 4 of our project was to determine genetic, annual and seasonal effects on methane emission by grazing stocker cattle. In the first subobjective (4A), researchers at Woodward, Oklahoma, are evaluating new technologies that were originally designed to monitor the methane emissions by grazing cattle and recently transformed this technology to a calorimeter by adding the ability to measure oxygen consumption. This transformation enables the technology to measure the basal metabolic rate of grazing cattle in their productive environment. This goal’s significance is that until this technology is fully developed, the energy efficiency of cattle can only be measured in confinement where behavior is altered from their native environments. With the development of this technology, cattle can be studied on the landscape where they are grazing, and the greenhouse gas emission and oxygen consumption estimates are not altered by the removal of the animal from their native environment. To better understand the relationship between herbage intake and energy efficiency, we compared two methods for estimating parameters important for understanding the digestion processes in grazing ruminants such as rate of passage, fecal output, and gastrointestinal fill. The difference between these two methods is the software used to model indigestible marker concentration in feces following a pulse dose of an external and indigestible marker. One method used a program for a proprietary software with a long history of use in ruminant digestion research and the other was a novel program from an open source software. What was unique about this work was that a synthetic dataset was used where hypothetical animals defined a known marker concentration profile and then these profiles were sampled several nominal times with different sources of error in both sample time and measured concentration. These samples were then fit with each software and the results were compared between results for both the mathematical model parameters and the derived biological parameters. The novel software produced results that are very similar to the proprietary software and for a few parameters the repeatability of the results obtained with the novel software was greater. This validation of software programs will increase the availability of digesta kinetics results that are used in commercial software by consulting nutritionist to formulate diets for ruminant animals. Objective 1 of our project was to improve native and introduced warm-season grass establishment and resilience to biotic and abiotic stressors. The first subobjective (1A) was to evaluate 21 germplasm lines of little bluestem for establishment and adaptation at 3 sites. Novel little bluestem (Schizachyrium scoparium) lines are being evaluated in three regional trials over a three-year period evaluating seedling emergence and forage production. In general, lines recurrently selected for improved germination in a simulated dry condition emerged better and had greater stand development than non-selected lines in the three sites differing in rainfall and soil types (Enid, Oklahoma; Woodward, Oklahoma; and Knox City, Texas). In collaboration with an ARS scientist from Stillwater, Oklahoma, we developed a bioassay to select winter barley (Hordeum vulgare) experimental lines for rapid seed germination in simulated dry conditions, because rapid seed germination is an important trait enhancing stand establishment under moisture-limited environments. Suitable selection pressure and selection intensity were determined for use in in vitro recurrent selection experiments of winter barley to improved germination and seedling vigor. Cycle 1 of selection of two winter barley lines were completed at ARS Woodward, Oklahoma. Cycle 1 seedlings were transferred to ARS Stillwater, Oklahoma for crossing of superior lines in greenhouse conditions. Once these seeds are harvested, we will begin the in vitro Cycle 2 selection process. The second subobjective (1B) was to select and breed Sudan grass with reduced ability to accumulate excess nitrate from the soil with a goal of releasing a new cultivar for use in the southern Great Plains. We have not been able to make seed increases of Sudan grass (Sorghum bicolor ssp. drummondii) breeding lines in the greenhouse due to COVID-19 pandemic, however, with the limited seed of breeding lines we planted a small plot for a field evaluation at Woodward, Oklahoma, and in collaboration with an ARS scientist at Stillwater, Oklahoma, have screened the plant materials for resistance to the sugarcane aphid (Melanaphis sacchari). Both experiments are in the preliminary stages.
1. Plants with rapid root and shoot development have better performance and persistence when establishing in dry soil conditions. Plant materials with rapid root and shoot development will lead to better performance and persistence during drought stress periods. Scientists in Woodward, Oklahoma, evaluated the variation of root and shoot development among three little bluestem (Schizachyrium scoparium) parental lines and their three generations of selection. Selection for increased seed germination of little bluestem in simulated dry conditions resulted in little bluestem populations with longer roots, taller shoots, and greater root and shoot biomass. Seedling root and shoot lengths increased for every selection generation. Such plant materials have the potential to be developed into superior cultivars useful for biomass production, livestock grazing, and/or conservation planting which will result in enhanced ecosystem services.
2. Ravenna grass can produce biomass for bioenergy production. Ravenna grass (Tripidium ravennae) is known to produce an abundance of biomass, but it is unknown how plant population density affects its biomass potential or other plant traits when grown for bioenergy production. A scientist in Woodward, Oklahoma, studied the effects of plant population density on biomass yield; plant growth traits; nitrogen removal; and sucrose concentration in leaves and culms. It was found that the biomass yield of Ravenna grass was affected by plant population density in at least four ways. First, biomass yield increased as plant population increased. The biomass yield reached a maximum of 14.5 tons per acre. Plant population density affected the number of reproductive stalks per plant where low plant densities produced a greater number of stalks. Low-plant densities produced higher concentrations of sucrose, and plant density affected the amount of nitrogen removed from the soil. Biomass yield increased with plant density, but also increased the removal of soil nitrogen. Based on this research, Ravenna grass can be produced as a feedstock to biofuel production companies without the need for nitrogen fertilizer inputs.
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Flynn, C.K., Zhou, Y., Gowda, P.H., Moffet, C., Wagle, P., Kakani, V.G. 2019. Burning and climate interactions determine impacts of grazing on tallgrass prairie systems. Rangeland Ecology and Management. 73(1):104-118. https://doi.org/10.1016/j.rama.2019.10.002.
Gunter, S.A. 2019. Effects of stocking and supplementation rates on the performance of steers grazing mixed-grass prairie during the winter. Applied Animal Science. 35:641-651. https://doi.org/10.15232/aas.2019-01864.
Thompson, L.R., Beck, M.A., Gunter, S.A., Williams, G.D., Place, S.E., Reuter, R.R. 2019. An energy and monensin supplement reduces methane emission intensity of stocker cattle grazing winter wheat. Applied Animal Science. 35:433-440. https://doi.org/10.15232/aas.2018-01841.
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Steiner, J., Springer, T.L. 2020. Seed production. In K.J. Moore, M. Collins, C.J. Nelson and D.D. Redfearn editors. Forages-The science of grassland agriculture, II. 7th edition. Chichester, West Sussex England, UK: John Wiley & Sons Ltd. p. 581-592. https://doi.org/10.1002/9781119436669.ch32.
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