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Title: Calibration and use of plate meter regressions for pasture mass estimation in an Appalachian silvopasture

Author
item DOUGHERTY, MARK - Auburn University
item BURGER, JAMES - Virginia Polytechnic Institution & State University
item Feldhake, Charles
item ABDELGADIR, A - Auburn University

Submitted to: Archives of Agronomy and Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/12/2011
Publication Date: N/A
Citation: N/A

Interpretive Summary: Producers raising livestock need information on forage availability to accurately schedule grazing systems. Complex forage production systems such as silvopastures where solar radiation interception in non uniform, and in complex topography such as in Appalachia where soil water availability is variable, present challenges for producers to accurately assess forage mass. A standardized plate meter for measuring pasture mass was calibrated by allowing it to rest on the forage canopy and measuring the height to which it was supported. The area was then clipped, dried, and weighed to allow calibration of plate height to forage mass. Using the calibration regression it was possible to rapidly estimate forage mass at numerous sites within the silvopasture to give a spatial pattern of forage availability. This work is useful to the scientists developing better management tools for forage systems and for producers coordinating animal grazing with forage availability. It will benefit our economy by helping American farmers more efficiently utilize grazing lands and increase income which contributes to strengthening rural communities.

Technical Abstract: A standardized plate meter for measuring pasture mass was calibrated at the Agroforestry Research and Demonstration Site in Blacksburg, VA, using six ungrazed plots of established tall fescue (Festuca arundinaceae) overseeded with orchardgrass (Dactylis glomerata). Each plot was interplanted with bare root honeylocust (Gleditsia triacanthos) and black walnut (Juglans nigra) seedlings spaced along a gradient ranging from 1.8m to 11.0m. Plate height (PH) of forage between trees was measured by placing a 46cm x 46cm x 5.6 mm-thick acrylic plastic plate meter on pasture canopy at six random locations four times from May to July. Plate height was measured between the ground and the plate as it rested on the pasture canopy. To calibrate the plate meter against a known dry matter yield, 50cm x 50cm clip plots followed each PH measurement. The resulting calibration regression slope was 421 kg (ha cm)-1, with an r2 of 0.86. A unique research application investigating the response of forage mass to site elevation is presented using the developed equation. The field calibrated regression slope of ruler height (RH) to PH was 1.71cm cm-1, with an r2 of 0.87, showing good correlation between RH and PH. The comparable regional regression equation of Rayburn et al. (2007) was found to adequately predict independent calibration clip plot data reported at this site. These results support the application of regional regression equations for estimating pasture mass in areas having similar climates and pasture composition. However, in regions having different pasture composition or climate, site-specific calibration of plate meters and ruler heights should follow methodologies described in this paper.