CHAPTER IV. CORRELATION OF EVAPOTRANSPIRATION 

 DATA WITH AGROCLIMATIC DATA 



To attempt concurrently to measure evapotransplration 

 of the many species of Irrigated crops presently grovm In Cali- 

 fornia is impractical because of financial and manpower require- 

 ments. Likewise impractical is the measurement of evapotransplration 

 of a single crop at more than a few locations. 



The most promising approach at this time appears to be 

 to determine the important and measurable parameters affecting 

 evapotransplration rates, and to correlate actual measurements of 

 evapotransplration with those parameters . Three Important para- 

 meters which appear independently to affect evapotransplration are 

 climate, plant conditions, including physiological factors, and 

 soil moisture availability. Differences in the physical and chemical 

 properties of soils and soil fertility are not considered to directly 

 affect evapotransplration, even though they may have indirect effects, 



This chapter discusses the relationship of each of those 

 parameters of evapotransplration, and summarizes the analysis of 

 data collected through 1960. In this regard, basic research on 

 factors affecting evapotransplration is being conducted by the Uni- 

 versity of California, as an integral part of the Vegetative Water 

 Use Program. The Agricultural Research Service is also conducting 

 basic research in this field. The results of these research pro- 

 grams have affected, and shall continue to Influence, the course 

 of these studies. 



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