Ind-uced defoliation. The plants will generally use all available 

 moisture within the root zone. The amount of use is a function 

 of the amount of moisture available. This is to say that the avail 

 ability of soil moisture is often the limiting factor in the late- 

 season evapo transpiration. This also may account^ in part, for the 

 August-September coefficients being lower than the July coefficieni 



Early- or late-season precipitation, although a part of 

 evapotranspiration and reflected in the pan and atmometer coeffic- 

 ients, is, quite often, not a beneficial source of moisture to the 

 plants. Early-season precipitation is evaporated from the soil su: 

 face with little gainful effect upon plant grov/th. Late-season 

 precipitation is either evaporated from the soil or vegetative sup- 

 face, and/or transpired by the plant without contributing substanti,, 

 ly to the plant cultural requirements. Thus, pan and atmometer 

 coefficients for early and late season must be applied with cautic: 

 and only after a thorough evaluation of rainfall amount, frequency 

 and pattern, as well as knowledge of the late- season availability 

 of soil moisture. 



Based on the information summarized in Table 5^ monthly 

 pan and atmometer coefficients for the two years of record have 

 been determined, and are shown on Figures A and B on Plate b. 

 There is, in general, rather close agreement between the monthly 

 pan or atmometer coefficients for both 1959 and i960. There are 

 also several indications that evapotranspiration for cotton some- 

 times exceeds evaporation from pans. The July pan coefficients 

 for 1959 and i960 were respectively I.07 and I.08, which indicates 

 that evapotranspiration exceeds evaporation from the free-water 



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