Abstract
The objective of this study was to determine the accuracy and reliability of 2 optical chlorophyll meters: FieldScout CM 1,000 NDVI and Yara N-Tester, in predicting neutral detergent fibre (NDF), acid detergent fibre (ADF), acid detergent lignin (ADL), acid detergent insoluble nitrogen (ADIN) and in vitro ruminal organic matter degradability (IVOMD) of 3 tropical grasses. Optical chlorophyll measurements were taken at 3 stages (4, 8 and 12 weeks) of regrowth in Brachiaria hybrid, and Megathyrsus maximus and at 6 and 12 weeks of regrowth in Paspalum atratum (cv. Ubon). Optical chlorophyll measurements showed the highest correlation (r = 0.57 to 0.85) with NDF concentration. The FieldScout CM 1,000 NDVI was better than the Yara N-Tester in predicting NDF (R(2) = 0.70) and ADF (R(2) = 0.79) concentrations in Brachiaria hybrid and NDF (R(2) = 0.79) in M. maximus. Similarly, FieldScout CM 1,000 NDVI produced better estimates of 24 h IVOMD (IVOMD(24h)) in Brachiaria hybrid (R(2) = 0.81) and IVOMD(48h) in Brachiaria hybrid (R(2) = 0.65) and M. maximus (R(2) = 0.75). However, these prediction models had relatively low concordance correlation coefficients, i.e., CCC >0.90, but random errors were the main source of bias. It was, therefore, concluded that both optical chlorophyll meters were poor and unreliable predictors of ADIN and ADL concentrations. Overall, the FieldScout CM 1,000 NDVI shows potential to produce useful estimates of IVOMD(24h) and ADF in Brachiaria hybrid and IVOMD(48h) and NDF concentrations in M. maximus.