Comparing Biomass Yields of Low-Input High-Diversity Communities with Managed Monocultures Across the Central United States

Abstract

Biofuel cropping expansion is increasing pressure on food, grazing, and conservation lands. Debate over the efficacy of converting diverse native plant communities to managed monocultures prompted us to explore the extensive crop and ecological site productivity databases maintained by US Department of Agriculture-Natural Resources Conservation Service. We compared annual net primary productivity (ANPP) of diverse native plant communities to ANPP of alfalfa (Medicago sativa L.) in Nebraska, Kansas, and Oklahoma; to coastal bermudagrass (Cynodon dactylon [L.] Pers.) in northern and central Texas; and to buffelgrass (Pennisetum ciliare [L.] Link.) in extreme southern Texas. In only 21% of the 1,238 sites in Nebraska, Kansas, and Oklahoma did native communities produce more or equivalent ANPP compared with managed alfalfa or coastal bermudagrass. In contrast, southern Texas native communities had greater ANPP than did buffelgrass at 81% of the sites. Regression analyses based on these results suggested that managed switchgrass (Panicum virgatum L.) ANPP would consistently exceed native community ANPP. We identified the type of sites that could remain in diverse communities or be converted to diverse communities and have productivity as great as or greater than highly managed monocultures of alfalfa, coastal bermudagrass, or buffelgrass. However, because of the low ANPP on these sites, biomass production may not be the optimal use of such sites. These lands may be better suited to providing other ecosystem services.

Appendix 1

To illustrate how this meta-analysis was conducted, we felt it would be appropriate to demonstrate how data were collected for a representative soil in a representative county. First, the Web Soil Survey was accessed (http://websoilsurvey.nrcs.usda.gov) and initiated by clicking the green “START WSS” button on the homepage. Under the “Quick Navigation Navigate By...” toolbar on the left side of the page, click the “Soil Survey Area” tab to expand it. Select the appropriate State and County from the drop down menus. For example, choose Oklahoma and Woodward County from the list. The Soil Survey Area is now “Woodward County, Oklahoma.” Click the “Set AOI” button in the upper right corner of the Soil Survey Area box. It may take a moment while the program clips the soils needed for your area of interest (AOI). The “Area of Interest Properties” will expand once the soils are clipped. It contains a “Soil Data Available from Web Soil Survey” tab, which should be expanded by default. This contains data about when the Soils Maps and Soil Data were updated for this county; in this case, Soil Maps are Version 1, March 30, 2004, and Soil Data are Version 6, September 16, 2008. The AOI is mapped on the right side of the page, with crosshatches delineating its area.

To determine yields on the soils in this AOI, click on the “Soil Data Explorer” tab at the top of the page. The default setting should have the “Suitabilities and Limitations for Use” menu already expanded. From the dropdown list, choose “Vegetative Productivity,” which will expand that category. In this example, to find alfalfa yield data, click “Yields of Non-Irrigated Crops (Component),” which will open a drop down box. In this box, choose “Alfalfa hay” as the crop in the “Basic Options” dropdown. Click the “View Rating” button in the corner of the box. This will produce a table titled “Tables—Yields of Non-Irrigated Crops (Component): Alfalfa hay (Tons)—Summary By Map Unit.” When alfalfa hay production is reported for a given soil series, the average tonnage is listed in the “Rating” column. At the time of this publication, there was no reported alfalfa hay production for Delwin fine sand with 1% to 3% slopes, so this soil in this county was excluded from our comparative analysis. The next soil on the list reports alfalfa hay yields: the Carey silt loam with 1% to 3% slopes (CaB) averages 2.38 tons of alfalfa acre^-1.

To see the native community productivity data reported for CaB in this county, select the “Soils Reports” tab at the top of the page. On the left hand side of the page, click on the “Vegetative Productivity” tab. It will open up a dropdown menu. Choose “Rangeland Productivity and Plant Composition” from the list and click the “View Soil Report” button. This will create a table under the map titled “Report—Rangeland Productivity and Plant Composition” detailing range yields on favorable, normal, and unfavorable years. It also gives information on the ecological site description and dominant plant species. The CaB soils support loamy prairie, and miscellaneous perennial grasses make up 35% of the rangeland plants, followed by little bluestem (15%), sideoats grama (10%), and others.