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Near Infrared Reflectance Spectroscopy Analysis of Forage Quality in Four Legume Species¹

Near infrared reflectance Spectroscopy (NIRS) technology needs verification as to its utility for forages that represent diverse species, environments, and managements. Our objectives were to determine whether single NIRS calibration equations could reliably assess components of the feeding quality of alfalfa (Medicago saliva L.) grown to a range of maturities in several environments and whether single equations could be developed to simultaneously analyze components of the quality of total forage and plant parts of alfalfa, birdsfoot trefoil (Lotus cornieulattis L.), red clover (Trifolium pratense L.), and white clover (Trifolium repens L.). In the first experiment, we assayed four forage quality components in 234 alfalfa samples from eight cutting schedules of two cultivars grown in two locations in each of 2 years. In Exp. II, we assayed five quality components in 167 samples of total forage and plant parts selected from seven harvests from two growth periods of two cultivars of each of four perennial legume species. Calibration equations for in vitro digestible dry matter (IVDDM), crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), and acid detergent lignin (ADL) were obtained by multiple linear regression of known conventional laboratory assay values on NIR spectra from up to 204 samples using a scanning monochromator NIR spectre-computer system. Equations were validated with up to 49 additional samples that had been selected from the original populations. From three to nine wavelengths were required to develop the best calibration equations for the various quality components. The squared coefficients of determination (R¹) of these equations ranged from 0.93 to 0.99. These equations allowed NIRS analysis of quality values in verification samples within standard errors (dag/kg) of 1.56 to 2.06 for IVDDM, 0.42 to 1.0 for CP, 1.46 to 2.23 for NDF, 1.30 to 1.70 for ADF, and 0.63 for ADL. We concluded that our NIRS system can quickly evaluate the feeding quality of perennial legumes to a degree of accuracy similar to that of laborious conventional analyses and that several species can be evaluated simultaneously with single calibration equations nearly as well as can single species.

Key Words: Alfalfa • Medicago sativa L. • Birdsfoot trefoil • Lotus corniculatus L. • Red clover • Trifolium pratense L. • White clover • Trifolium repens L. • Protein • Neutral detergent fiber • Acid detergent fiber • In vitro digestible dry matter

² Research agronomist, USDA-ARS and professor of agronomy, Univ. of Minnesota; research assistant, Univ. of Minnesota; research plant physiologist, USDA-ARS and professor of agronomy, Iowa State Univ.; associate scientist, Univ. of Minnesota; and research associate, Iowa State Univ. Request reprints from senior author at Agronomy and Plant Genetics Dep. Univ. of Minnesota, 1509 Conner Ave., St. Paul, MN 55108.

Received for publication February 27, 1984.