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Crop Coefficients for Colorado: The Rocky Ford Lysimeters

Crop Coefficients for Colorado: The Rocky Ford Lysimeters. Allan Andales Assistant Professor and Extension Specialist Soil and Crop Sciences Department Colorado State University. Estimation of crop evapotranspiration ( ET c ). ET c = ET rs x K cr. where

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Crop Coefficients for Colorado: The Rocky Ford Lysimeters

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  1. Crop Coefficients for Colorado: The Rocky Ford Lysimeters Allan Andales Assistant Professor and Extension Specialist Soil and Crop Sciences Department Colorado State University

  2. Estimation of crop evapotranspiration (ETc) ETc = ETrs x Kcr where ETrs = reference crop ET (tall reference like alfalfa) = the ET rate from a uniform surface of dense, actively growing vegetation (hypothetical crop) having specified height (50 cm or 20 inches for alfalfa) and surface resistance (to vapor transport), not short of soil water, and representing an expanse of at least 100 m (328 ft) of the same or similar vegetation (ASCE-Standardized Reference ET equation) Kcr = crop coefficient based on tall reference

  3. Crop lysimeter and instrumentation Precipitation Radiation (Rs, Rn, PAR) Temperature (air, canopy, soil) Wind (speed, direction) Humidity (ea) Atmospheric pressure Soil water content (Neutron probe) Soil heat flux ET(atmometer)

  4. Lysimeter project at Rocky Ford • One reference lysimeter (1.5 m x 1.5 m x 2.4 m) to measure ETr(completed in 2009) • One crop lysimeter (3.0 m x 3.0 m x 2.4 m) to measure ETc(completed in 2006) • Network of 12 weather stations along the Arkansas Valley (part of COAgMet) • Lysimeters located at CSU-Arkansas Valley Research Center (AVRC), Rocky Ford, Colorado 1,274 m (4179 ft) above MSL 300 mm (11.8 in) avg. annual precip. Rocky Ford clay loam soil

  5. Example lysimeter load cell output June 7, 2008

  6. Alfalfa hay raw Kcr curve in 2008(cutting cycles 2, 3, and 4) Evaporation from surface wetted by rainfall

  7. Alfalfa hay raw Kcr curve in 2009(4 cutting cycles)

  8. Fitted Kcr curve for 2nd alfalfa cutting in 2008

  9. ETrs x Kcr = ETc

  10. Acknowledgements • Funding provided by the Colorado Water Conservation Board, the Colorado Agricultural Experiment Station, Colorado Water Institute, and the Colorado Division of Water Resources • Technical assistance provided by USDA-ARS (Fort Collins, CO and Bushland, TX) • Collaborators: Lane Simmons1, Mike Bartolo1, Dale Straw2, Tom Ley2, Abdel Berrada1, Lee Sommers1, Reagan Waskom1, Frank Johnson1, Hamdan Al Wahaibi1, José Chávez1, Tom Trout3 • 1Colorado State University • 2Colorado Division of Water Resources • 3USDA-ARS

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