274 Irrigation and Drainage 



had been taken up along the underground path 

 to accumulate over the low-lying lands, and since 

 the evaporation of 12 inches of salt -laden water may 

 produce more deposits than the same depth of rain 

 would be sure to remove in leaching downward, the 

 chances are favorable to accumulation. 



INTENSIVE FARMING MAY TEND TO THE ACCUMU- 

 LATION OF ALKALIES 



It has already been pointed out that during the 

 growing season, after vegetation has come into full 

 action, nearly all of the rains which fall in humid 

 climates are retained near the surface until they are 

 evaporated, either through the growing crop or from 

 the soil, and since these waters tend to form salts 

 when they are in contact with the soil grains, they 

 must tend to increase the salt content near the surface. 

 It is plain, too, that the heavier the crops produced 

 and the greater the number of them in the season, the 

 less is likely to be the loss of any water from the field 

 by under -drainage ; hence the greater the tendency 

 for soluble salts to accumulate. Then, if during the 

 winter season of a country the rainfall is deficient, so 

 that little leaching can take place, conditions become 

 still more favorable for the accumulation of alkalies. 



Further than this, if irrigation is practiced during 

 the growing season only, and this water also is 

 evaporated from the soil in addition to the natural 

 rainfall, it is plain that the amount of soluble salts 

 in the soil must increase, both on account of that 

 which may have been in the water applied, and that 



