moisture shortage at the::e sites. The cvapotranspirometer tanks 

 and ryegrass rield at Davis were frequently Irrigated, and it is 

 probable thiat soil moisture was not limiting there. Availability 

 of soil moisture Is assumed to have had little effect on evapo- 

 transpiratlon rates and coefficients at any of the three sites. 



Seasonal accumulated evapotransplratlon plotted against 

 accumulated pan evaporation and, except for Davis, accumulated 

 atmometer evaporation are shown on Plate ^, entitled "Comparison 

 of Pan and Atmometer Coefficients for Cotton, Alfalfa, and Grass,' 

 Figures E and F. Each curve is for an individual year, and has 

 separate zero lines for plotting evapotransplratlon. Evaporation 

 from pans or atmometers vras plotted using the date of June 30 as 

 the common point on all curves. Coefficients for the period of 

 record for both years were consistently similar for Alturas for 

 both pan and atmometer. The pan coefficient for the period of 

 record at Davis was likewise similar. 



Coefficients from three seasons of record in the mounta: 

 areas, combining Alturas and Coleville, are compared with coeffic:i 

 from Davis in Table 6. Coefficients are shown for both the growii 

 seasons assumed in Bulletin No. 2 and for the longer period for 

 v;hlch data were obtained. The reason for the differences between 

 the valley and mountain coefficients has not been ascertained. 



Alfalfa Coefficients 



Pan and atmometer coefficients have been determined froi 

 an alfalfa plot located near Pittville in the Sacramento River Ba;t! 

 mountain valleys, and from an alfalfa plot near Arvin in the Tula:! 

 Lake Basin Valley floor at the southern end of the Central Valley 



•58- 



