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Crop Science Abstract -

Analysis of Cell-Wall Carbohydrates and Starch in Alfalfa by near Infrared Reflectance Spectroscopy1


This article in CS

  1. Vol. 27 No. 3, p. 586-588
    Received: June 12, 1986

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  1. K. A. Albrecht,
  2. G. C. Marten,
  3. J. L. Halgerson and
  4. 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.

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