Sick Soils not Influenced by Parasites 37 



rates, leaving a deposit of salts. This then is one way 

 in which alkali spots are formed. Another source of 

 alkali formation is through the decomposition of 

 volcanic rocks. This condition is found in some parts 

 of New Mexico. Another, and by far the most im- 

 portant, source of alkali formation is through capil- 

 larity and evaporation. This occurs when the water 

 accumulated in the soil is insufficient to raise the 

 water table high enough to permit evaporation. The 

 condition which most favors such an accumulation 

 of water is a bed or layer of a clayey character which 

 prevents the percolation of water downwards, below 

 a soil which does not have sufficient lateral drainage. 

 The source of the water may be springs, or the perco- 

 lation of surface rainwater, and in irrigated regions, 

 leaky canals or over-irrigation. The depth of the 

 water table, where capillarity becomes a source of 

 trouble, is about three feet. As all soil water contains 

 diluted salts, continual evaporation will leave alkali 

 spots or beds. To realize further what the alkali 

 accumulation means, Tinsley 1 has worked out some 

 interesting figures. 



"Suppose an acre of land, with the water table 

 within less than two feet of surface, and that the 

 amount of water evaporated from the surface in a 

 year was enough to cover the acre to a depth of one 

 foot, which the writer considers a low estimate for a 

 bare soil. Suppose further that when it reached the 

 surface, the water carried 100 parts of soluble matter 

 in 100,000 parts of water, which is about the salt 



. * Tinsley, J. D., New Mexico Agr. Expt. Sta. Bui. 42 : 3-31, 1902. 



