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.
In Objective 1A (Little bluestem improvement), the evaluation of these 21 Little bluestem lines is complete and are in the process for the being released to the public. The public release ‘Arhing’ Little bluestem will provide a tallgrass plant to grassland managers that establishes more quickly and more resilience to climate change and drought. In Objective 1B (Low-nitrate Sudangrass), 100 seeds from 5 accessions of Sudangrass (PI 658662, PI 658665, PI 660661, PI 521355, PI 660662) were acquired from the germplasm resource and information network (GRIN) system, and 80 seeds from each population have been planted in the greenhouse. Plants from each population are grown in their own bay of the greenhouse to prevent cross-pollination between populations and will be allowed to open pollinate. Once seed from each population is mature, it will be harvested and bulked according to population. This seed will be grown under high-nitrate conditions and tested for nitrate accumulation. Those plants exhibiting low nitrate accumulation will be self-pollinated and the seeds from each plant kept separate. A second cycle of selection will be conducted using seed acquired from the first cycle. In Objective 2A (Patch burn vs. Broadcast burn study), ARS scientists have conducted all the burning events required for the experiment. These burning events were all very near the end of the projects allowable burn window because of a new and unforeseen step requirement in the Area’s controlled burning approvals process necessitated by federal law. ARS scientists have learned from this new approval requirement and should not have the issue again in future years. The cattle are currently grazing the pastures for the growing season grazing period and will complete this grazing period near the end of July. We do not anticipate any further issues with this experiment this coming winter grazing period. Some preliminary analysis has been completed relative to animal performance Objective 2B (Weather and Climate Tool Applications) and is mostly on track with the milestones outlined in the project. Working in collaboration ARS scientists from Boise, Idaho, and others in the long-term agroecosystem research network, this year we have developed a website that produces climate data in a format that is readily usable in agricultural models and other applications (https://webapps.jornada.nmsu.edu/weather/; Note: This website is in beta version and should not be used other than to see the status of this effort) allowing recommendation to be adjusted to climate change. The website utilizes a high-quality public data product (gridMET) that provides many agriculturally important weather attributes across the contiguous United States on a ~4-km grid daily from January 1, 1979 to current (data within the last 60 days is preliminary and subject to change) as it source of data. This data source while high quality, is inaccessible to the typical agricultural model user and the real benefit to our tool will be to convert attributes to the required units and transform the data into a format that is readily usable by modelers and model users. With respect to the grazing/forage production tool development, the datasets needed are still being compiled and methods developed. Tools to compare cumulative precipitation and accumulated growing degree days (GDD) for a particular year with the climatology of those attributes are available online (GDD and Precipitation; these too should be considered beta), but the satellite and grazing use data still need to be integrated into a system. In Objective 3A (Switchgrass fertility and soil OC), the 3 start-year blocks of switchgrass are now established, and initial soil samples have been collected from all 4 start-year blocks. Further, the 4th start-year block was planted in early July 2021. All treatments and harvests have been completed on time and very preliminary results produced, but the long-term nature of some treatments (e.g., fertilizer applications every 3rd year) will make any interpretation of any preliminary results premature. In Objective 4A, the field research is being completed and indirect calorimetry is being evaluated. Because this project is one year delayed due to the COVID-19 shutdown, sample and data analysis is delayed by one year. In Objective 4B, the field research is still being completed and indirect calorimetry is being evaluated. Further, heifers have been bred and their offspring will be completed in the next year. Because this project is one year delayed due to the COVID-19 shutdown, next year will be the first evaluation of offspring from the maiden heifers.
1. Preference of a grass fly for native grasses. The grass fly, Conioscinella nuda (Adams), feeds on developing seeds of native grasses reducing their seed yield potential. An ARS researcher in Woodward, Oklahoma, collected the grass fly in the field plots of big bluestem, indiangrass, little bluestem, and sand bluestem. The mean number of insects collected varied from 9.7 to 27.0 adults per 15 plants, and the order of preference for this fly among the native grasses was big bluestem, little bluestem, sand bluestem, and indiangrass. The observed differences among the species may be related to seed hairs. The seeds of big bluestem and little bluestem are mostly smooth compared to those of sand bluestem and indiangrass which are covered with hairs. Breeding plants with seed hairs may reduce the damage produced by this insect.
2. Effect of nitrogen fertilization on biomass yield of sand bluestem. Sand bluestem is one of the most productive native grasses on sandy soils in the Great Plains making it a good candidate for use as renewable energy; however, very little information is available for its biomass production under high nitrogen fertilization rates. An ARS researcher at Woodward, Oklahoma, in a six-year study, that included two drought years, fertilized plots of sand bluestem annually at four rates with urea nitrogen (0, 35, 70, and 105 pounds of nitrogen (N)/acre) to determine the effects of fertilization on biomass yield and nitrogen use efficiency (the pounds of harvested biomass per pound of applied N). Unfertilized plots of sand bluestem averaged 1.3 tons/acre of biomass compared with 3.7 tons/acre of biomass for plots fertilized with 105 pounds N/acre. In addition, drought significantly impacted the biomass yield of sand bluestem; however, at high fertilization rates and certain environmental conditions, sand bluestem can produce biomass yields greater than 6 tons/acre.
3. Plant population density affects the biomass of Ravenna grass. Ravenna grass is known to produce an abundance of biomass, but it is unknown how plant population density affects its biomass potential or other plant traits. An ARS scientist at Woodward, Oklahoma, studied the effects of plant population density on biomass yield; plant growth traits; nitrogen removal; and sucrose concentration in leaves and culms. Biomass yield of Ravenna grass was affected by plant population density in at least four ways. First, biomass yield increased as plant population increased, and the biomass yield reached a maximum of 16.2 megagrams per hectare at a plant population density of 10,640 plants per hectare. Second, plant population density effected the number of reproductive stalks per plant where low plant densities produced a greater number of reproductive stalks per plant. Third, sucrose concentration was affected by plant density, where low plant density produced higher concentrations of sucrose, and where stalks of larger diameters tended to produce higher concentrations of sucrose. And forth, plant density effected the amount of nitrogen removed with biomass. As biomass yield increased with plant density the removal of nitrogen also increased. The data suggest that further research was needed to determine the optimum nutrient requirement for Ravenna grass to sustain high biomass yields at a density of 10,000 plants per hectare.
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