At the Arvln and Glenburn sites, three sets of nev; at- 

 mometers were Installed at the berlnning of each season, and each 

 month one pair was replaced with a new pair. At Arvln, three pans 

 were operated, and the evaporation, which v;as nearly the same, was 

 avera,";ed. 



Data on percent of r;round cover were collected to deter- 

 mine effects of varying cover on evapotranspiratlon rates. The 

 term "percent ground cover," as used in this report, refers to the 

 percentage of ground surface covered by a canopy of living foliage 

 as viewed looking downward from directly above the crop. During 

 the first years, 1955-1937, few records were kept of percent ground 

 cover. However, from 1958 through 1960 it was standard procedure 

 to measure crop height, estimate percent ground cover, and record 

 both. 



When most of the moisture which plants can readily ex- 

 tract from within the root zone has been used, crop growth is 

 slowed and evapotranspiratlon rates may also be correspondingly 

 affected. To estimate available soil moisture at the test plots, 

 samples were taken and laboratory measurements of the moisture 

 content of the soil were made, utilizing the pressure plate mem- 

 brane technique with pressures varying from 0.1 to 15 atmospheres. 

 T ensiometers, instruments ^^^hich can be used to measure availability 

 of soil moisture for crop utilization, were installed at some plots. 

 Calculations of available soil moisture in the root zone were based 

 on the difference between moisture profiles determined from field 

 measurements and moisture profiles representing the moisture level 

 below which crops cannot readily extract moisture. 



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