Non-destructive foliar chlorophyll measurement has the potential to predict crude protein concentration and in vitro ruminal organic matter digestibility in Bracharia decumbens herbage

Abstract

Quick and accurate estimation of crude protein (CP) concentration and in vitro ruminal organic matter digestibility (IVOMD) of tropical pastures is critical to determine possible nutrient deficits prior to herbage utilization. We, therefore, investigated the potential of a non-destructive hand-held chlorophyll gun (FieldScout CM 1000 NDVI Meter) to predict lignin (sa), acid detergent fiber (ADF), CP concentration and IVOMD of growing Bracharia decumbens Cv. Basilik herbage. The average of five (5) foliar chlorophyll index measurements obtained by a “point and shoot” action from an approximate 40–45° vertical angle prior to harvesting from each sampling unit was recorded. After chlorophyll measurements, herbage samples were cut according to a stratified random sampling design from four differently managed B. decumbens Cv. Basilik pastures to leave an 11cm stubble height. Herbage sampling was synchronized with existing grazing patterns used at the study sites. The respective pastures were sampled at 14 (Brac-14), 28 (Brac-28), 11 (Brac-11) and 13 (Brac-13) days post-grazing. Relationships between chlorophyll indices (CI), pasture CP concentration and IVOMD were best described by simple linear and polynomial models, respectively. Correlation coefficients (r2) between CI and CP and IVOMD ranged from 0.70 to 0.95 and 0.69–0.85, respectively. Chlorophyll index gave the best estimates for CP concentration and IVOMD in Brac-14 and Brac-13 where CCC and R2 was high, and rMSPE and model related errors were very low. Chlorophyll gun indices accounted for 68–90% and 64–78% variance of CP and IVOMD (P<0.05), respectively, in Brac-14 and Brac-13 herbage. Prediction models for lignin (sa) and ADF were inaccurate and unreliable. We conclude that CI measurements have the potential to predict CP content and IVOMD of B. decumbens pastures. However, further calibration studies are needed to test the sensitivity of the chlorophyll gun under different growing conditions and also with pasture herbage that is sufficiently heterogeneous in chemical composition.