Near-Infrared Reflectance Spectroscopy: Different Strategies for Local Calibrations in Analyses of Forage Quality

Abstract

This paper deals with the problem of how to utilize a large calibration set with 10 different analytes in order to make the best predictions possible on a routine basis. Ten different strategies of using the data set were studied with the use of numbers of principal components ranging from 4 to 12. We found positive effects of scatter correction for most of the analytes. On average, the local regression methods were superior to the others. The optimum number of samples for local regression seems to be between 50 and 100. The largest reduction in root mean square error of prediction (RMSEP), in comparison to results for the traditional method, was found on scatter-corrected spectra and a proposed local calibration with 50 calibration samples. The gain in RMSEP for neutral detergent fiber (NDF), acid detergent fiber (ADF), and crude fiber was about 25% and for protein and in vitro digestible dry matter digestibility (IVDMD) about 10%, compared to results for the traditional universal calibration method.

Global or Local? A Choice for NIR Calibrations in Analyses of Forage Quality

“…This type of calibration is often referred to as universal calibration 11 or global calibration. This concept is used in the routine analyses of forages and performs very well.…”

“…Methods such as stepwise multiple linear regression (SMLR), principal component regression (PCR) and partial least squares (PLS) regression have proved their practical usefulness. 11 Many studies have been carried out to improve the calibration procedures. Their goal was to improve linearity, optimise precision and eliminate or reduce nuisance effects such as light scatter variations.…”

“…Their goal was to improve linearity, optimise precision and eliminate or reduce nuisance effects such as light scatter variations. 11 Some studies [13][14][15] have also indicated the possibilities of using nonlinear regression.…”

“…16 The LR technique has already been applied to forage. 11,18 It was concluded that scatter correction and local calibration should be used in the prediction of forage quality.…”

Calibration of near infrared reflectance spectroscopy to estimate nitrogen concentration in potato tissues

“…NIR is a secondary technique relying on calibration against a reference analysis ( Sjoholm et al, 1993), and the quality of the calibration process is critical (Aastveit & Marum, 1993). We have used Dumas combustion as the reference method as it measures all the N within a sample unlike Kjeldahl digestion .…”