Scope of Present Program and Report 



To accomplish the foregoing objectives. It Is necessary 

 to measure evapotransplratlon for various crops within the major 

 agricultural zones of the State, and to measure various climatic, 

 plant, and soil factors which Influence evapotransplratlon. To 

 date, accurate measurements of evaporation have been made of only 

 a few crops within certain of the major agricultural service areas 

 of the State, because of financial and personnel limitations. Ad- 

 ditional installations will be required to provide complete evalua- 

 tion of all major agricultural zones and the principal crops grown 

 within California. 



In order to maximize the utility of the data provided by 

 the relatively few evapotransplratlon measurement stations, a cor- 

 relative program has been carried on to relate evapotransplratlon 

 to evaporation indices. Theoretically, coefficients derived by 

 comparing evapotransplratlon to evaporation from pans or atmometers 

 can be used to make reliable estimates of evapotransplratlon within 

 any agrocllmatic zone where evaporation data are available. Basic 

 research on such relationships is being conducted by the University 

 of California as a part of the vegetative water use program. 



The agrocllmatic monitoring program, described fully in 

 Chapter II, is designed to collect the basic agrocllmatic data 

 necessary to make reliable estimates of evapotransplratlon within 

 each agrocllmatic zone. Chapter III discusses evapotransplratlon 

 measurements and the collection of data relative to plant condi- 

 tions, soil moisture, and other factors which may affect evapo- 

 transplratlon rates. The criteria, methods, and Instrumentation 



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