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Development of Near Infrared Reflectance Spectroscopy Calibrations to Estimate Legume Content of Multispecies Legume–Grass Mixtures

Dep. of Plant Sci., Technische Universität München, D-85350 Freising, Germany

View larger version (30K): [in a new window]   Fig. 1. Near infrared spectra of a legume sample (solid line) and a grass sample (dotted line) harvested in May 1999: (A) original absorbance spectra and (B) vector normalized first derivative spectra. The first derivative describes the slope of the original spectrum at a certain wave number. Therefore, the unit of the y axis in Fig. 1B is absorbance units per wave number.

View larger version (55K): [in a new window]   Fig. 2. Flow chart for the development of the different calibration algorithms for the determination of the legume content in multispecies mixtures. Strategy A results in calibrations derived only from grass mixtures (0%) and legume mixtures (100%). For Strategy B, artificially mixed standards were added. RMSECV, root mean square error of cross-validation; RMSEP, root mean square error of prediction (test-set validation).

View larger version (21K): [in a new window]   Fig. 3. Near infrared reflectance spectroscopy (NIRS) prediction of the legume content of artificially mixed samples using Model A1 (q.v. Fig. 2), which was developed based on an end-points calibration.

View larger version (22K): [in a new window]   Fig. 4. Comparison of the predicted legume content of duplicate legume–grass mixtures where one replicate was prepared from fresh material, dried, and ground as a mixture and the other mixed from dry, ground material according to the standard procedure. For both sample sets, legume content was predicted using Model A1 (q.v. Fig. 2).