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Title: ESTIMATION OF FORAGE NITROGEN CONCENTRATION AND IN VITRO DRY MATTER DIGESTIBILITY OF GRASS PASTURES USING PLANT CANOPY HYPERSPECTRAL REFLECTANCE

Author
item Starks, Patrick
item Zhao, Duli
item Brown, Michael
item Coleman, Samuel

Submitted to: ASA-CSSA-SSSA Annual Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 9/15/2006
Publication Date: 11/12/2006
Citation: Starks, P.J., Zhao, D., Brown, M.A., Coleman, S.W. 2006. Estimation of forage nitrogen concentration and in vitro dry matter digestibility of grass pastures using plant canopy hyperspectral reflectance [abstract]. ASA-CSSA-SSSA Annual Meeting Abstracts, November 12-16, 2006, Indianapolis, IN. p. 266.

Interpretive Summary: ABSTRACT ONLY.

Technical Abstract: Timely assessment of forage nitrogen (N) concentration and in vitro dry matter digestibility (IVDMD) during the growing season can help livestock managers make decisions for adjusting stocking rate and managing pastures. Nondestructive measurements of pasture canopy hyperspectral reflectance may provide a rapid and inexpensive means for estimating these two nutritive variables. An experiment was conducted in the 2002 and 2003 growing seasons at the USDA-ARS, Grazinglands Research Laboratory to determine relationships between forage N and IVDMD and canopy reflectance of warm season grass pastures. Canopy reflectance from eight bermudagrass pastures was measured using a portable spectroradiometer. Laboratory chemical methods were used to determine forage N concentration and IVDMD. The reflectance data were used to develop and validate algorithms for estimation of forage N and IVDMD. Forage N concentration linearly correlated (r = 0.82, P < 0.0001) with a ratio of reflectance at 705 and 1685nm wavebands (R705/R1685) and IVDMD correlated with R705/R535 (r = 0.71, P < 0.0001). Multiple regression, band-depth analysis with stepwise regression, and partial least squares regression techniques enhanced the relationships between N and IVDMD and canopy reflectance values (0.81 |r| 0.90, P < 0.0001). However, validation of these equations indicated only slightly improved model efficiency for predicting the two forage nutritive values. Our results suggest that forage N concentration and IVDMD of bermudagrass pastures can be rapidly and nondestructively estimated during the growing season using canopy reflectance in a few narrow wavebands.