130 Kansas Academy of Science. 



If the evaporation from the open pan actually represented water loss 

 from the soil, Kansas long ago would have been a hopeless desert, for 

 the evaporation measured in this way will always be greatly in excess of 

 precipitation. The season's evaporation would amount to almost 6,400 

 tons of water per acre, or for the whole state approximately 350 billion 

 tons — enough to produce nearly a billion tons of dry forage, if it could 

 all be evaporated through the leaves of plants. 



It is not to be supposed, of course, that the data obtained enable us 

 even to guess at the actual loss of water from the soil, for as soon as 

 the top layer of the soil becomes dry it forms a protecting blanket 

 against the effects of the dry atmosphere, especially if it is kept loose- 

 textured and well-tilled. But we can, after a fashion, grasp the sig- 

 nificance of the intense evaporating power of the air to the living plant. 

 The leaves of plants contain a high percentage of water, and they are 

 exposed freely to the drying power of the air, which is believed to be 

 equivalent on an ordinary dry day to nearly a thousand atmospheres of 

 force. That is, when an object is becoming air dry, the molecules of 

 water are extracted from the substance at least with a force of about 

 fourteen thousand pounds per square inch. All of the moisture lost by 

 the plant under the influence of these tremendous atmospheric forces 

 must be made good by the actively absorbing roots, and if they fail to 

 keep up with the drying process, wilting must occur. If the failure is 

 by a narrow margin, wilting is only temporary, but even this greatly 

 reduces plant production, while if the failure is severe, permanent 

 wilting and death ensue. 



One of the most imp6rtant problems just ahead, therefore, is to 

 determine the relation of evaporation from the standard pan to evapora- 

 tion from the soil. On a day when the evaporation from the pan reaches 

 .5 inch, how much drier does the soil become at a depth of six inches, or 

 eighteen inches, where the mass of plant roots are located? And when we 

 have a whole month of dry weather, how rapidly is the soil water de- 

 pleted? What influence has soil type on the rate of water loss? What 

 difference is there in the rate of water loss from fields of corn, wheat, etc., 

 and on fallow land? These problems involve many complex factors, and 

 may be very difficult to solve. But during the coming season it is hoped 

 that a study can be made of several selected localities in Douglas county, 

 with the purpose of determining the relation of atmospheric evaporation 

 intensity, as measured by the Standard Class A Evaporation station, to 

 the rate of disappearance of water from the soil itself. Such a study, 

 aside from its scientific interest, should be of considerable practical im- 

 portance. 



