Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 1, 2005
Publication Date: February 24, 2006
Citation: Starks, P.J., Zhao, D., Phillips, W.A., Coleman, S.W. 2006. Development of canopy refletance algorithms for real-time prediction of bermudagrass pasture, biomass and nutritive values. Crop Science. 46:927-934. Interpretive Summary: Forage productivity and nutritive quality, such as aboveground biomass, crude protein (CP), neutral detergent fiber (NDF) and acid detergent fiber (ADF), are important indicators for pasture and livestock management. Both traditional chemical and near-infrared spectroscopy laboratory analyses of these parameters can be costly and time consuming. The objectives of this study were: (1) to develop linear relationships between selected quality variables of live bermudagrass pastures and canopy reflectance measured using a portable spectroradiometer in a few selected wavebands and (2) to compare the predicted values of these variables with measured values via laboratory chemical methods. Pasture CP concentration was predicted reasonably well using either the simple reflectance ratio of reflectance at 605nm to reflectance 515nm (R605/R515) or the first derivative of reflectance at 545 nm. Biomass production could be predicted using either the R915/R975 ratio or the first derivative of reflectance at 935 nm. Relationships between forage NDF or ADF and the reflectance ratios and the first derivatives of reflectance were poor. The simple two-waveband reflectance ratios or the first derivatives of canopy reflectance at given wavebands could be used for real-time and nondestructive prediction of CP concentration and biomass of bermudagrass pastures during the growing seasons.
Technical Abstract: Timely assessments of forage biomass production and quality variables during the growing season are useful to livestock managers for adjusting stocking rates and for pasture management. Remote sensing of plant canopy reflectance may provide a rapid and inexpensive means of estimating pasture nutritive values and biomass. An experiment was conducted in the 2002 and 2003 growing seasons to determine the relationships of neutral detergent fiber (NDF), acid detergent fiber (ADF), crude protein (CP) concentration, biomass, and CP availability of bermudagrass (Cynodon dactylon, L) pastures with canopy reflectance ratios and first derivatives of reflectance in narrow wavebands. Pasture CP concentration, biomass, and CP availability correlated closely and linearly with the reflectance ratios of R605/R515, R915/R975, and R875/R725 (r2 = 0.44~0.63***), as well as with the first derivatives of reflectance with wavebands centered at 545, 935, and 755 nm (r2 = 0.49~0.68***), respectively. Linear equations between each quality variable and the ratios and derivatives of reflectance were developed based on data pooled across years, plant genotypes, and sampling dates. Validation of developed equations indicated that CP concentration, biomass, and CP availability could be fairly well predicted using either the ratios or derivatives of the reflectance with root-mean-square errors (RMSE) of 1.5%, 1200 kg ha-1, and 95 kg ha-1, respectively. Pasture NDF and ADF had lower correlation with canopy reflectance than other measured quality variables. Our results suggest that the selected two-narrow-waveband reflectance ratios or the first derivatives can be used for real-time and nondestructive prediction of biomass production and CP concentration in bermudagrass pasture.