Location: Natural Resource Management Research2013 Annual Report
1a. Objectives (from AD-416):
Specific objectives of this research include: Objective 1. Provide management guidelines to improve the conservation and enhancement of agroecosystem function and structure in grasslands of the NGP. Objective 2. Improve the viability of cattle production on the NGP by providing management strategies that increase the efficiency of forage utilization. Objective 3. Develop methods to alter the composition of beef so that it better meets the emerging market demand for healthier beef.
1b. Approach (from AD-416):
An automated rainout shelter will be used to simulate drought conditions and test if early-season water stress and (or) defoliation following water stress will have greater impact on productivity of switchgrass or western wheatgrass or on mixtures of western wheatgrass and alfalfa. The influence of soil attributes on growth characteristics of perennial grasses will be determined with greenhouse evaluations using soil collected under native vegetation and under severely weed invaded plant communities at four sites between Mandan, ND and Pierre, SD. Field-based estimates of the greenhouse gases carbon dioxide and nitrous oxide will be used to determine if soil emissions of nitrous oxide offset carbon uptake by moderately grazed mixed-grass prairie. Satellite-based estimates of plant canopy carbon:nitrogen ratio will be determined for five native rangeland pastures and these estimates will be used to determine if they can be used to estimate forage quality for pastures on the northern Great Plains. Trials with cattle will be conducted to determine if grazing higher quality forages with supplemental flaxseed and (or) forages containing condensed tannin will result in reduced methane emissions per unit of beef produced and greater economic returns. Other trials with cattle will be conducted to determine if omega-3 fatty acid levels in beef can be raised substantially if fattening yearlings are fed flaxseed or flaxseed oil that is treated to protect the alpha-linolenic acid in it from hydrogenation by ruminal microbes.
3. Progress Report:
Objective 1 of this project was to provide management guidelines to improve the conservation and enhancement of agroecosystem function and structure in grasslands of the northern Great Plains. Under this objective, research was completed for sub-objectives 1.1, 1.2 and 1.3 and manuscripts and outreach material were published. Objective 2 of this project was to improve the viability of cattle production on the northern Great Plains by providing management strategies that increase the efficiency of forage utilization. Within this objective, research was conducted for sub-objective 2.3 and a manuscript was submitted for publication and accepted. Lastly, Objective 3 was to develop methods to alter the composition of beef so that it better meets the emerging market demand for healthier beef, and within this objective, sub-objective 3.1 was completed and a manuscript was published.
1. Switchgrass water use efficiency. Agricultural use of water has become a great concern in western parts of the Great Plains, especially regarding effects of bioenergy crop production on water quality and quantity. ARS scientists at Mandan, ND compared the water use efficiency and soil water deficits for switchgrass (a bioenergy grass), western wheatgrass and a western wheatgrass-alfalfa mixture (two common forage crops). Water use efficiency was strongly influenced by biomass production and the high productivity of switchgrass resulted in the highest water use efficiency. The water use efficiency of switchgrass was nearly 4 to 5 times that of western wheatgrass, which had water use efficiency that was much more variable. Although switchgrass had the highest water use efficiency, it also had the greatest soil water deficit. This research suggests that switchgrass is a productive bioenergy crop for the drier areas of the northern Great Plains but its greater depletion of soil water may be an issue in a multi-year drought or if switchgrass is used in annual crop rotation.
2. Weather, but not stocking rate, affects carbon dioxide emissions from grassland. Grasslands represent the largest land resource in the world, yet little is known about how their management affects the carbon cycle. To help address this knowledge gap, ARS scientists at Mandan, ND measured carbon dioxide flux from native vegetation and crested wheatgrass pastures over three years. More carbon dioxide was emitted from soil of the crested wheatgrass pasture compared to a native vegetation pasture under heavy grazing; however there was no difference in carbon dioxide emission between heavy and light grazing for native vegetation. Soil temperature and moisture status were strongly associated with carbon dioxide emissions, though associations were seasonally dependent with temperature most relevant during spring and fall and moisture status most important in summer. Accordingly, weather conditions have a strong influence on grassland carbon dioxide emissions, and as a result, long-term monitoring is necessary to confidently discern management effects on the carbon cycle.
3. Airborne images useful for predicting rangeland vegetation characteristics. The quantity and quality of rangeland vegetation varies significantly throughout a growing season, yet there are limited tools available to predict these characteristics on large scales. The recent availability of high resolution aerial imagery offers a new approach to landscape scale monitoring of vegetation. Using aerial imagery and field data from Grand River National Grassland near Lemmon, SD, ARS scientists at Mandan, ND developed two new models to predict vegetation characteristics at the end of the growing season. The models used a combination of landscape attributes, vegetation data, and hyperspectral images for describing rangeland vegetation characteristics. The new models will inform land managers where conservation efforts may be required across complex grassland landscapes.
4. Formulating optimum grass-legume mixtures. Knowledge of how the proportions of grasses and legumes in a forage seed mixture affect production and resistance to weed invasion is needed to guide the formulation of forage seed mixtures for farmers. ARS scientists at Mandan, ND, Madison, WI, and University Park, PA evaluated 30 different mixtures of grasses and legumes to determine how mixture proportions affected yield and weed invasion resistance. Grass-legume mixtures had less weed invasion than grass or legume monocultures. Mixtures also produced as much as or more forage than nitrogen-fertilized grass monocultures. Optimal legume proportions of 30 to 40% were achieved with a wide range of seed mixtures containing different grass and legume proportions. This indicates that farmers have wide flexibility in formulating seed mixtures for specific locations and to achieve specific functions in their forage operations.
Liebig, M.A., Kronberg, S.L., Hendrickson, J.R., Doug, X., Gross, J.R. 2012. Carbon dioxide efflux from long-term grazing management systems in a semiarid region. Agriculture Ecosystems and the Environment. 164:137-144.