Crop Coefficient for Estimates of Daily Crop Evapotranspiration

Wright, James L. (1981) Crop Coefficient for Estimates of Daily Crop Evapotranspiration. pp. 18-26. In: Proc. Am. Soc. Agric. Engrs., Irrig. Scheduling Conf. 1981/12.

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Abstract

Crop coefficients are used with values of reference evapotranspiration (ET)
to estimate water use of a crop. Since the direct measurement of reference
ET is expensive, time consuming, and laborious, it is usually preferable to
calculate it tram more easily obtainable climatic data. Extensive research
on reference ET methods and Improved crop coefficients has been conducted
because of their application in irrigation scheduling and other aspects of
water resources allocation. management and planning.

Various procedures have been used to obtain the necessary experimental crop
and reference ET data, and several types of crop coefficient curves have been
published during the past ten years (Jensen 1974, Doorenbos and Pruitt 1977,
Burmas et al. 1980, Wright 1979, 1981). Crop coefficients must be matched
with the appropriate reference ET. The climatic adequacy of the methods, the
necessary input data, and the time scale all need to be understood and carefully
applied if accurate estimates of crop water requirements are to he
obtained for either irrigation scheduling or water resources planning. The
available methods for estimating reference ET and improved crop curves, when
properly applied, permit estimates of crop ET which are within the accuracy
of most field irrigation systems to deliver water (Jensen et al. 1971, Jensen
and Wright 1978, Wright and Jensen 1978).

This discussion briefly reviews the nature and origin of commonly used coefficients
and outlines the conditions under which they can be appropriately
applied. The application of recent "basal" crop coefficients (Wright 1981)
is discussed and "mean" crop coefficients recently developed from ET data obtained
with weighing lysimeters in Southern Idaho are also presented.

Item Type:	Conference or Workshop Item (Paper)
NWISRL Publication Number:	0470
Subjects:	Water > Evapotranspiration Research methodology Mass Import - autoclassified (may be erroneous)
Depositing User:	Dan Stieneke
Date Deposited:	20 Nov 2010 21:57
Last Modified:	19 Jan 2017 19:00
Item ID:	1023
URI:	https://eprints.nwisrl.ars.usda.gov/id/eprint/1023