This paper seeks to discuss irrigation water requirement estimates in the
light of current practice, important developments during the 1970's, significant
research and future research and applications of that research. Each of
these are elaborated in more detail in the text of this paper.
A major addition to the science and art of estimating irrigation water requirements
has been to replace the often ambiguous "potential evapotranspiration"
with "reference crop evapotranspiration". In the past decade a series of experiments
relating irrigation water applications to crop yield now permit a
much better economic analysis of the use of water for irrigation. The estimation
of monthly irrigation water requirements was facilitated, particularly
for varying climatic conditions with the United Nations publication "Crop
Water Requirements" by Doorenbos and Pruitt (1977).
Estimation of daily water requirements for purposes of irrigation scheduling
has been refined by the development of an albedo model and a wind function
for the Penman method, that is variable throughout the season, Wright (1981).
Several western states are experiencing lawsuits or other legal deliberations
involving seasonal irrigation water requirements because of conflicts between
groups of water users or water right transfers from agriculture to industry
or municipal use. Irrigation scheduling continues to be refined from the
standpoints of predicting ET, verifying yield conditions and other factors
like production and peak pumping power reduction. Future research probably
will include emphasis on breeding crops that require less water, refinements
on the relationships between yields and water consumption, refinements in
methods of estimating irrigation water requirements, and the development of
irrigation schemes that minimize water and energy requirements.
For other methods and more detail the reader is referred to sources such as
Doorenbos and Pruitt (1977), Jensen (1974), Barman. et al. (1981)
