Herbage mass, nutritive value and canopy spectral reflectance of bermudagrass pastures

Timely and accurate detection of above-ground herbage mass and the nutritive value of pastures can help the more efficient adjustment of stocking rate and determine the timing of protein supplements to be fed to livestock grazing these pastures. The objectives of this study were to determine seasonal variation in herbage mass, neutral-detergent fibre (NDF), acid-detergent fibre (ADF) and crude protein (CP) concentrations of herbage and canopy reflectance of pastures of genotypes of bermudagrass (Cynodon dactylon L.), and to analyse the relationships between these descriptors of nutritive value of herbage and canopy reflectance in broad spectral wavebands. Three bermudagrass pastures of varieties Midland and Ozarka, and an experimental hybrid, 74 x 12-12, were established in 1991 and had received the same field management and stocking rate. Canopy reflectance, above-ground herbage mass of DM and CP, and NDF, ADF and CP concentrations of herbage were measured in the growing seasons of 2002 and 2003. Year, genotype and sampling date significantly (P < 0.05) affected most measured variables. Ratios of canopy reflectance in blue to red (R-(blue)/R-(red)) and in near infrared to red (R-(NIR)/R-(red)) wavebands were highly correlated with concentrations of CP in herbage and herbage mass of CP but the relationships between reflectance ratios and NDF and ADF concentrations of herbage were relatively low. It is concluded that the CP concentration of herbage and herbage mass of CP of pastures can be estimated throughout the growing season using remote sensing of canopy reflectance and the information may be used for pasture and livestock management.