SAVING WATER BY CULTIVATION 47 



The nature of the soil is of considerable importance. 

 The finer the texture of the soil, the more rapidly does 

 the water move upward to be changed into vapor. The 

 darker the color of the soil, the more rapid the evapora- 

 tion; for dark-colored soils absorb the heat of the sun- 

 shine much more quickly than do lighter-colored ones 

 such as characterize the arid region. The richer the soil 

 is in soluble salts, the slower is the evaporation of water 

 / rato-%he airT^-For that reason, evaporation from alkali 

 lands is slow. The rate of evaporation is more rapid 

 from a deep than from a shallow soil, for a given loss of 

 water does not so greatly reduce the percentage of mois- 

 ture in a deep as in a shallow soil. 



Meteorological conditions determine very largely 

 the rate of evaporation of water from soils. Of these, 

 temperature is most important. The higher the tempera- 

 ture, the more rapid is the conversion of water into water 

 vapor. Of almost equal importance is the intensity and 

 quantity of sunshine. Much more water is lost from a 

 wet soil on a sunny day than on a cloudy one. Shade is 

 extremely effective in checking evaporation. In the Utah 

 work, a saving of 25 per cent of the water evaporated 

 was effected when the soil was shaded; and, in all proba- 

 bility, as the temperature is very much lower in the 

 shade, an even higher degree of saving may be effected. 

 Frequently, a high temperature and much sunshine go 

 together, so that their effects are felt at the same time. 

 The drier the air, the more rapidly will the air take up 

 water vapor. In the arid region, the relative humidity 

 of the air is low, and evaporation goes on, as has been 

 shown, much more rapidly than in humid sections. 

 Winds, likewise, exert a strong drying effect on soils, 

 especially in districts where the air is relatively dry. The 



