Grass and Pasture CoelTlolents 



Pan and atmometer coerflclents have been determined 

 using data from gx^ass and grass-pasture evapotransplrometer tanks 

 located In the Sacramento River Basin mountain valleys, in the 

 Lassen-Alpine mountain area, and in the Sacramento Valley floor 

 (Alturas, Coleville, and Davis). 



Graphs of coefficients and percent of ground cover for 

 pasture and grass, plotted against time, are presented in Figures A 

 through E of Plate ^, entitled "Variation of Pan and Atmometer Co- 

 efficients for Individual Periods of Measurements." Percent of 

 ground cover is relatively constant for those crops, and wide varia- 

 tions of the coefficients occur less than with alfalfa and cotton. 

 During the growing period, the grass was at nearly 100 percent 

 grovind cover in all of the evapotransplrometer tanks, as mowings 

 did not clip the foliage short enough to cause large reductions 

 in ground cover. While the ground was alv;ays sod- covered, the 

 colder climate at the mountain sites caused dormancy to some de- 

 gree during late fall, V7inter, and early spring. Approximate 

 ground cover percentages indicated on Figures A, B, and E of 

 Plate 4 are for the green and actively growing fraction of the 

 foliage. At Davis, the climate is not cold enough to force the 

 grass completely into winter dormancy. Occasionally at the Davis 

 site, however, small areas of ground surface were exposed through- 

 out the year, as indicated on Plate 4, Figures C and D. 



High water table conditions, typical of the predominant 

 irrigation practice in the mountain valleys, were maintained in 

 the Alturas and Coleville tanks. There was, therefore, no 



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