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Title: PRODUCTIVITY AND FORAGE QUALITY OF WARM SEASON GRASS PASTURES IN RELATION TO CANOPY REFLECTANCE IN ASTER WAVEBANDS

Author
item Starks, Patrick
item Zhao, Duli
item Phillips, William
item Brown, Michael
item Coleman, Samuel

Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 10/1/2005
Publication Date: 11/1/2005
Citation: Starks, P.J., Zhao, D., Phillips, W.A., Brown, M.A., Coleman, S.W. 2005. Productivity and forage quality of warm season grass pastures in relation to canopy reflectance in aster wavebands. 20th Biennial Workshop on Aerial Photography, Videography, and High Resolution Digital Imagery for Resource Assessment, October 4-6, 2005, Weslaco, Texas. 2005 CDROM.

Interpretive Summary: Estimation of forage biomass production and quality variables during the growing season is important for adjusting stocking rate and making pasture management decisions. Remote sensing instrumentation on board current satellites may be the only practical means of estimating these plant variables over large expanses of land. Past research has shown that the amount of “light” (ultraviolet through the shortwave infrared wavelengths) reflected from a plant community is an indicator of plant health, stress, leaf area and the amount of nitrogen in the plant. An experiment was conducted to determine the feasibility of measuring biomass and selected plant quality variables using the Advanced Spaceborne Thermal Emission and Reflectance Radiometer (ASTER) sensor on board the TERRA satellite. A hand-held hyperspectral radiometer was used to measure the amount of light reflected in 256 wavebands from five bermudagrass pastures, located at the Grazinglands Research Laboratory in El Reno, Oklahoma, during the 2002 and 2003 growing seasons. Selected data from the hand-held instrument were used to mimic the amount of radiation reflected by the bermudagrass pastures as seen by seven wide wavebands of ASTER. The reflected light measured within these seven wavebands, as well as all possible combinations of waveband ratios, were statistically related to aboveground biomass, neutral detergent fiber (NDF), acid detergent fiber (ADF), crude protein (CP) concentration, and CP availability. Samples of vegetation were collected from the bermudagrass pastures and concentrations of NDF, ADF, and CP were determined using standard laboratory chemical methods. Overall, CP content highly and linearly correlated with the shortwave infrared (1600-1700 nm) / Red (630-690 nm) waveband ratio with a correlation coefficient of 0.554 (sample size of 414). Using single wavebands or waveband ratios explained 26, 55, and 51% of the variability in the laboratory data, for aboveground biomass, CP concentration, and CP availability, respectively. Bermudagrass NDF and ADF had poor correlation with reflected light measured in the ASTER wavebands compared to either CP or biomass. Our preliminary results suggest that ASTER may be used to measure CP concentration and biomass production for large expanses of warm season grass pastures.

Technical Abstract: Estimation of forage biomass production and quality parameters during the growing season is important for adjusting stocking rate and making pasture management decisions. We hypothesized that remotely sensed data collected from satellite platforms may be used to estimate rangeland productivity and forage quality. Data collected during the 2002 and 2003 growing seasons were used to determine the relationships between aboveground biomass, neutral detergent fiber (NDF), acid detergent fiber (ADF), crude protein (CP) concentration, and CP availability of five bermudagrass pastures with canopy reflectance or reflectance ratios in wide wavebands. Canopy reflectance was measured throughout the growing seasons using a portable, hyperspectral radiometer and converted to seven wide wavebands based on spectral ranges of the Advanced Spaceborne Thermal Emission and Reflectance Radiometer (ASTER) on board the TERRA satellite. Forage NDF, ADF, and CP concentrations were quantified using standard laboratory chemical methods. Overall, CP content highly and linearly correlated with the ratio of reflectance in the shortwave infrared (1600-1700 nm) to Red (630-690 nm) with a correlation coefficient of 0.554 (sample size of 414). Use of canopy reflectance or reflectance ratios in given wavebands explained 26, 55, and 51% of variances, respectively, for aboveground biomass, CP concentration, and CP availability. Pasture NDF and ADF had poor correlation with canopy reflectance compared to either CP or biomass. Our preliminary results suggest that remote sensing of canopy reflectance can be used for in-situ and nondestructive prediction of CP concentration and biomass production in warm season grass pastures. The information from this study may also be useful for large scale monitoring of rangeland quality based on ASTER data.