Submitted to: International Evapotranspiration Irrigation Scheduling Conference
Publication Type: Proceedings
Publication Acceptance Date: August 8, 1996
Publication Date: N/A
Interpretive Summary: Determining when to water crops and how much water to apply is a difficult decision for farm managers. Some farmers make such decisions by computing how much water is lost (evaporated) each day based on meteorological conditions (air temperature, wind speed, humidity, and precipitation amounts) and knowledge of "ideal" plant growth. Since most crops are not "ideal," the farmers using this technique may be over- or under-irrigating, resulting in high costs for water as well as low crop yields. A new technique was tested in which images acquired from airborne cameras were used to assess crop variability, and this information was combined with meteorological measurements to determine the "actual" crop water loss. Results for a farm in Arizona showed that water savings could be achieved with remotely-sensed information using this new technique. This information will be useful for farmers, researchers, and ultimately, the public through water savings and increased food and fiber production.
Remote sensing techniques provide an effective method for estimating crop evapotranspiration over large areas. This paper addresses the use of multi-temporal airborne digital multispectral video imagery acquired over a cotton crop througthout a growing season to obtain reflectance-based crop coefficients. A water balance was maintained in the root zone of the cotton crop in three fields with actual evapotranspiration estimates based on crop coeffecients using the spectral methodology as well as the FAO crop curves. Results indicate that the reflectance- based crop coefficients followed the actual field cotton growth and could have provided up to a 12% savings in water based on a simulated schedule. The FAO crop coefficients underestimated the actual ET during the vegetative stage of growth and overestimated towards the latter portions of the season.