A Comparison of Methods for Moisture Determination of Forages for near Infrared Reflectance Spectroscopy Calibration and Validation1
- W. R. Windham,
- J. A. Robertson and
- R. G. Leffler2
Near infrared reflectance spectroscopy (NIRS) has gained widespread acceptance for the determination of nutritional quality in forages. However, little attention has been given to investigating its use in the analysis of moisture content of forages. Our objectives were to assess the use of Karl Fischer (KF) titration for the determination of the water content of forages and to compare this method with oven methods for use in NIRS calibration and validation. In the first experiment we assayed 68 samples of eight bermudagrass [Cynodon dactylon (L.) Pers.] cultivars. The methods of moisture analysis used were KF, forced-air (FA) oven at 135 and 105°C for 2 and 24 h, respectively, and vacuum oven (VO) at 100°C for 24 h at 4 kPa laboratory vacuum. Moisture contents measured with the FA 105°C and VO methods were comparable but lower (P<0.05) than those obtained with the FA 135°C and KF methods, which were similar. The NIRS calibrations were developed within moisture methods from 48 bermudagrass samples and the remaining 20 samples used for validation. Calibrations within methods predicted the validation samples with a standard error of analysis (SEA) of 2.8 for FA 135°C, 3.2 for FA 105°C, 3.8 for VO, and 2.6 g kg-1 for KF. In the second experiment, KF and FA 135°C based calibrations were tested on 30 samples composed of six different types of bermudagrasses, temperate grasses, legumes, silages, and silage-based dairy cattle (Bos taurus) rations. Analysis with an FA 135°C calibration and validation with FA 135°C values resulted in large negative biases due to a loss of C-containing substances as well as water, especially from the fermented materials. However, analysis with KF calibration and validation with KF values resulted in no bias and acceptable SEAs. The ability of the KF-based calibration to accurately assess water content in more diverse populations is due to the specificity of KF for water and the very strong absorbance of water at 1930 nm regardless of the sample type.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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