Estimating Crude Protein Concentration of Smooth Bromegrass Pasture Using NDVI Data.

Pasture forage mass (FM) is typically monitored in grazing situations, but its usefulness is limited without consideration of forage quality.  Crude protein (CP) measurement provides information to indicate adequacy for grazing livestock. Optical sensing devices have been used to remotely sense various crop characteristics, including normalized difference vegetation index (NDVI).  The latter have been related to chlorophyll content, which could also indicate sward CP.  We measured NDVI and estimated FM from compressed forage height in bromegrass pastures at approximately monthly intervals during 2008 to 2015 grazing seasons to relate them to CP of hand-grabbed samples.  Seven seasons’ data were included for calibration, using stepwise multiple regression with pasture CP as the dependent variable.  Earlier work with five years’ season-long data produced a correlation coefficient of only 0.67, so the additional data were added, and separated as to year and stage of pasture maturity to locate sources of error of prediction.