Mapping Prairie Grass Protein, Yield and Carbon
By Don Comis
September 26, 2007
A study by the Agricultural
Research Service (ARS) and the
University of North Dakota lays a
foundation for eventually allowing ranchers to get Web-based information on the
quality and quantity of forage plants in their fields. Ranchers could use this
information to determine stocking rates, as well as how much carbon is stored
in their forage plants.
Phillips and Ofer Beeri have developed a way to measure rangeland forage
plant yields in pounds per acre, and their quality in percent of protein
content, over many acres. Theyre using commercial HyMap hyperspectral
imagery taken by airplane, which lets them capture images at more than 200
wavelengthsall of the light in the visible wavelength bands and invisible
near-infrared and short-wave infrared wavelength bands.
Phillips is a plant physiologist at the
Northern Great Plains Research Laboratory in Mandan, N.D. Beeri is an
assistant professor of space studies at the
John D. Odegard School of
Aerospace Sciences at the University of North Dakota in Grand Forks.
Phillips and Beeri used images of two 32,741-acre ecoregions on opposite
sides of the Missouri River near the center of North Dakota, representing the
Northwestern Glaciated Plains and the Northwestern Great Plains ecoregions.
Although the regions are markedly different, the technique's accuracy across
regions remained the same: 82 percent for yield predictions, and 92 percent for
The scientists were able to measure the quantity and protein content of both
live and dead plant material, which often cant be distinguished by
conventional remote sensing. Dead grass and other plants are important in this
part of the country, where cold weather hinders decomposition. Cattle get some
protein out of dead grasses as well as live ones.
Using the images, Phillips and Beeri developed mathematical equations to
estimate rangeland plant biomass. They also applied and validated a previously
published algorithm for computing plants' carbon-nitrogen ratio. By combining
the equations, they were able to compute and map the percent of protein in
plant leaves over entire pastures of northern prairie grasslands.
Further research is needed to determine if the results apply in other
regions of the country as well.
ARS is the U.S. Department of
Agriculture's chief scientific research agency.