Crop Science Journal of Natural Resources and Life Sciences Education
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Published in Crop Sci 27:586-588 (1987)
© 1987 Crop Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
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Analysis of Cell-Wall Carbohydrates and Starch in Alfalfa by near Infrared Reflectance Spectroscopy1

K. A. Albrecht, G. C. Marten, J. L. Halgerson and W. F. Wedin2

Analysis of the structural and nonstructural polysaccharide composition of herbage by conventional techniques is time consuming and difficult to perform on large numbers of samples. This study was conducted to evaluate the utility of near infrared reflectance spectroscopy (NIRS) for analysis of cell-wall carbohydrates and starch in alfalfa (Medicago sativa L.). The leaves and stems of two alfalfa cultivars grown in two environments and ranging in maturity from vegetative to early seed pod were assayed by conventional means for concentrations of six cell-wall sugars and starch. Calibration equations were obtained by multiple linear regression of conventional laboratory assay values on NIR spectra from 150 randomly selected samples using a scanning monochromator NIR spectro-computer system. Calibration equations were verified with 30 additional samples from the original population of 180. From six to nine wavelengths were required to develop the best equations for the various carbohydrate components. The squared coefficients of multiple determination (R2) of the calibration equations ranged from 0.83 to 0.99. The lowest R2 values were associated with cell-wall sugars having concentrations < 30 g kg-1 dry weight and small ranges in concentration. With these equations, standard errors of analysis of carbohydrates by NIRS were (in g kg"') 8.5 for total structural carbohydrates, 6.6 for glucose, 3.0 for xylose, 1.2 for arabinose, 0.7 for galactose, 1.3 for mannose, and 4.3 for starch. We conclude that NIRS is a rapid and precise means to analyze cell-wall carbohydrates and starch in alfalfa.

Key Words: Medicago sativa L. • Polysaccharides • Glucose • Xylose • Arabinose • Galactose • Mannose • Starch

1 Contribution of the Agronomy Dep., Univ. of Florida; the USDA-ARS and Univ. of Minnesota; and Iowa State Univ. Florida Agric. Exp. Stn. Journal Series no. 7349 and Minnesota Agric. Exp. Stn. Scientific Journal Series Paper no. 14935.

2 Former assistant professor, Agronomy Dep., Univ. of Florida, Gainesville, FL 32611 (currently, assistant professor, Univ. of Wisconsin, Madison, WI 53706); research agronomist, USDA-ARS and professor, Agronomy Dep., Univ. of Minnesota; scientist, Univ. of Minnesota; and professor, Agronomy Dep., Iowa State Univ.

Received for publication June 12, 1986.




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Copyright © 1987 by the Crop Science Society of America.