286 Irrigation and Drainage 



KINDS OF SOIL WHICH SOONEST DEVELOP ALKALI 



Where alkali waters are used for purposes of irri- 

 gation, and where sweet waters are being used under 

 conditions of little or no drainage, the clayey soils 

 are the ones which soonest begin to show the bad 

 effects of concentrated salts. This is so for many 

 reasons. 



In the first place, the soils of clayey texture, as has 

 been established by experiments recorded on page 201, 

 are not as effective mulches as the sandy soils, hence, 

 even where thorough tillage and shade are resorted 

 to, there must necessarily be a larger rise of salt- 

 bearing water to the surface to produce accumulation 

 than is the case with the coarse, sandy soils. 



In the second place, when water is applied to a 

 sandy soil, not nearly as much remains adhering to 

 the surface of the soil grains and entangled between 

 them, so that it quickly spreads downward farther 

 below the surface than is the case with the clay. This 

 being true, it takes less water to produce effective 

 drainage, and the roots of the crop spreading farther 

 in the sands, the salts cannot become concentrated as 

 they may in the clays. 



In the third place, since more water is held in 

 contact with the soil grains of the clays, and since 

 the total surface for chemical action to take place upon 

 is very much larger in the claye} r soils than in the 

 sands, it is plain that soluble salts, including alkalies, 

 may form more rapidly in one case than in the other, 

 hence, that the open, sandy soils cannot become 



