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United States Department of Agriculture

Agricultural Research Service

Title: Combining Remotely-Sensed Crop Coefficients with the Fao-56 Procedures

Authors
item HUNSAKER, DOUGLAS
item Barnes, Edward
item Clarke, Thomas
item KIMBALL, BRUCE
item Fitzgerald, Glenn
item Silvertooth, J - UNIV OF ARIZONA
item Hagler, J - USDA-ARS, PHOENIX
item Pinter Jr, Paul

Submitted to: Agronomy Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: November 13, 2002
Publication Date: November 26, 2002
Citation: Hunsaker, D.J., Barnes, E.M., Clarke, T.R., Kimball, B.A., Fitzgerald, G.J., Silvertooth, J.C., Hagler, J., Pinter Jr, P.J. 2002. Combining remotely-sensed crop coefficients with the FAO-56 procedures. Agronomy Abstracts, CD Rom (A03-Hunsaker 205300-P).

Technical Abstract: A field plot experiment was conducted in 2002 at The University of Arizona, Maricopa Agricultural Center to evaluate whether the normalized-difference vegetation index (NDVI) could provide estimates of crop coefficients for use in scheduling irrigations of cotton. Treatment variables included two irrigation scheduling approaches that were based on methodology outlined in the Food and Agricultural OrganizationÂżs Paper No. 56 (FAO-56). The first scheduling approach calculated daily crop evapotranspiration (ETc) from a locally-derived, basal crop coefficient (Kcb) curve developed using FAO-56 guidelines. The second scheduling approach used Kcb that were based on frequent ground-based measurements of NDVI and a previously derived relationship between NDVI and cotton water use. Reference evapotranspiration (ETo) for both irrigation treatments was calculated per FAO-56 methods using daily local weather-station data. Additional experimental variables (three plant densities and two N fertilization levels) created conditions that were expected to alter crop water use yet are not commonly nor easily accounted for in a typical implementation of FAO-56 procedures. Supporting measurements included biweekly overflights with a precision 3 CCD imaging system and thermal scanner and frequent observations of soil water contents, midday canopy temperatures, stem flow, crop growth and yield. Results are expected to reveal the potential for using NDVI to provide near-real time feedback when adjusting Kcb based on crop response to spatial variation in cultural and edaphic conditions. This approach is expected to result in more efficient use of irrigation water.

Last Modified: 9/29/2014
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