Transfer of a calibration model from a benchtop to a handheld NIR spectrometer to predict nitrogen content of warm-season forage

Abstract

<b><sc>Abstract.</sc></b> <b>With increasing availability of portable or handheld near infrared (NIR) spectrometers, it would be beneficial if an existing calibration model for a benchtop instrument can be transferred to a handheld instrument with minimal loss in prediction performance. In this study, a partial least squares (PLS) regression model developed to calibrate a benchtop NIR (B1) to estimate nitrogen content (N) of forage was transferred to another benchtop (B2) and two handheld NIR spectrometers (H1 and H2). B1, B2, and H1 had similar specifications, while H2 had a shorter spectral range, with a wider interval. After each transfer, changes in the model‘s performance were evaluated in terms of model parameters, including coefficient of determination of validation (</b><b> = 0.894 and RPD = 3.13). The transferred model, however, was still useful for research and quality control applications based on r² and RPD. The predicted N values were compared before and after calibration transfer using the Bland-Altman plot analysis. This analysis revealed a large bias (9.97 g kg^-1) between B1 and H2 that could be corrected.</b>