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ARS Home » Northeast Area » University Park, Pennsylvania » Pasture Systems & Watershed Management Research » Research » Publications at this Location » Publication #240374
Title: Estimating carbon fluxes on small rotationally grazed pastures

Author
item Skinner, Robert
item WYLIE, BRUCE - Us Geological Survey (USGS)
item GILMANOV, TAQIR - South Dakota State University

Submitted to: American Forage and Grassland Council Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 5/13/2009
Publication Date: 6/21/2009
Citation: Skinner, R.H., Wylie, B.K., Gilmanov, T.G. 2009. Estimating carbon fluxes on small rotationally grazed pastures [abstract]. In: American Forage and Grassland Council Conference Proceedings. p. 1. CDROM

Interpretive Summary: An interpretive summary is not required.

Technical Abstract: Satellite-based Normalized Difference Vegetation Index (NDVI) data have been extensively used for estimating gross primary productivity (GPP) and yield of grazing lands throughout the world. Large-scale estimates of GPP are a necessary component of efforts to monitor the soil carbon balance of grazing lands and other agricultural systems. However, the usefulness of satellite-based images for monitoring rotationally grazed pastures in the northeastern US might be limited because paddock size is often smaller than the resolution limits of the satellite image. The purpose of this research was to compare NDVI data from satellite images with data obtained using a ground based hand-held system capable of fine-scale (sub-meter) NDVI measurements. Gross primary productivity was measured by eddy covariance systems that have continuously collected net ecosystem exchange (NEE) data on two pastures in central Pennsylvania since January 2003. Light curve analysis and relationships between nighttime temperature and flux were used to partition NEE into GPP and ecosystem respiration. Weekly 250 m resolution satellite NDVI estimates were obtained for each pasture from the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite beginning in 2003. Hand-held NDVI data were collected in 2006, 2007 and 2008 from one of the two pastures. The effect of moisture stress on GPP was estimated by regressing mid-day GPP vs. soil water content, and correction factors were developed to adjust NDVI-derived estimates of GPP during times when moisture was limiting. Satellite and hand-held NDVI-estimated GPP were compared with daily measured GPP from the eddy covariance systems, and with weekly averages of GPP. Weekly averages provided better correlations between NDVI and GPP than did daily values. Including a correction factor for moisture stress improved correlations slightly, but only if unique factors were used for each year. This presentation will compare results from the satellite and hand-held NDVI data to determine if data at the 250 m resolution provided by MODIS are capable of adequately predicting seasonal trends in GPP as well as short-term changes due to harvests by grazing animals or machinery. We will also discuss the potential for remotely-sensed NDVI to provide a useful tool for extrapolating eddy covariance measurements from individual pastures to whole-farm and larger scales.