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The Use of Near-Infrared Reflectance Spectroscopy to Predict Species Composition of Forage Mixtures¹

Assessment of species composition of hay, pasture, and range samples is an important but laborious factor in forage quality evaluation. Near-infrared reflectance spectroscopy (NIRS) was evaluated as a rapid technique for prediction of the species composition of hay and pasture forages and weeds. In Exp. 1, 97 mixtures were formed using eight species. Each species varied from 0 to 100% in each mixture. Each mixture of dried, ground material was scanned with monochromatic light from 1100 to 2500 nm at 2-nm intervals, and the reflected energy was recorded. Percentage of each species was then regressed on the spectra using a modified stepwise regression procedure. Calibration equations with coefficients of determination (R²) from 0.94 to 0.99 and standard errors of difference (SED) from 1.9 to 6.8% were obtained using five to seven equation terms. Johnsongrass [Sorghum halepense (L.) Pers.] could not be predicted (SED = 6.8%) as precisely as the others, whereas blue panicgrass (Panicum antidotale Retz.) and sunflower (Helianthus annuus L.) were precisely predicted (SED < 2%). One to three harvest dates of seven species of hay were used in a second experiment to determine if variability within a species resulted in additional imprecision. In general, SED were higher; however, all but ‘Midland’ bermudagrass [Cynodon dactylon (L.) Pers.] gave SED of 10 or less, and the R² of the calibration data set ranged from 0.84 to 0.98. Bermudagrass predictions were more precise if samples containing eastern gamagrass [Tripsacum dactyloides (L.) L.] cut at boot were removed from the data set. With proper calibration, NIRS could save much time normally used to separate species in hand-clipped samples. The number of samples that can be analyzed in an experiment could be increased, and hence the accuracy of determination of species composition in a given pasture should be improved.

Key Words: NIRS • Species composition • Prediction • Hay

² Research animal nutritionist, Livestock and Forage Res. Lab., USDA-ARS, P.O. Box 1199, El Reno, OK 73036; research chemist, Richard B. Russell Research Center, USDA-ARS, Athens, GA 30603; and chemist, Livestock and Forage Res. Lab., USDA-ARS, P.O. Box 1199, El Reno, OK 73036.

Received for publication July 9, 1984.

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