obtained during any one period of depletion is expressed In Table A-6 

 under the heading "Twice the Standard Error," 



The effects of percent ground cover and, possibly, of 

 stage of crop maturity and available soil moisture, are illustrated 

 in Plate 3, which compares accumulated evapotransplration of dif- 

 ferent crops. These measurements were made in the Arvln area under 

 similar climatic conditions and on the same soil series. Differences 

 in percent ground cover d.nd possibly crop maturity and available 

 soil moisture cause differences in slopes of the curves shown in 

 Plate 3. Defoliation caused the abrupt changes in evapotransplration 

 rates reflected in the curves on cotton and plums. Alfalfa remains 

 green at this location throughout the year, and shows little seasonal 

 slope changes. It is of interest to note the much higher July and 

 August rates of evapotransplration by cotton, as compared to alfalfa 

 and plums in both 1959 and 1960. A complete explanation for this 

 cannot be presented; however, certain of the factors affecting evapo- 

 transplration are discussed in the following chapter. 



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