measured periods are not biased, and the seasonal coefficients 

 appear to be reasonable. Curves of seasonal accumulated evapo- 

 transplratlon versus evaporation are shovm on Plate 5, Figures C 

 and D. As noted previously, each curve on Plate ^j is plotted for 

 an individual year, with separate zero lines for indication of 

 evapotranspiration. Evaporation from pan and atmometers was plotted, 

 using the date of June 30 as the common point on all curves. 



The pan and atmometer coefficients derived after com- 

 bining the two years of record at the Pittville AA plot are shown 

 in Table 7 , and are compared with coefficients derived in the same 

 manner at the Arvin CC plot. For purposes of comparison, average 

 coefficients were determined not only for the period of record, 

 but also for the growing season, as shown in Bulletin No. 2. 



By any method of determining seasonal coefficients, the 

 Pittville pan coefficient is approximately 17 percent higher than 

 the Ai'-vin coefficient, and the Pittville atmometer coefficient is 

 approximately 27 percent higher than the Arvin coefficient. Whether 

 the difference is due primarily to basic climatic differences be- 

 tween the two areas, v/hlch affect different plant and evaporation 

 response, or due to experimental error, is not knovm at this time. 



Cotton Coefficients 



Pan and atmometer coefficients for cotton for each period 

 of measurement during 1939 and 196O are shown in Figures J and K 

 of Plate 4. Also shov/n are estimates of the percent of ground 

 cover, available moisture, and other factors affecting plant growth 

 and water use. There is a rather close agreement betv/een the two years 



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