108 DRY LAND FARMING 



tivation ; (3) by keeping down weed growth, and (4) by 

 shading the soil, as in the process of mulching. In humid 

 areas these preventive measures call for but little consid- 

 eration. 



Where the precipitation is not more than 15 inches 

 in a year, the unbroken soil is usually so firm and dense 

 that rains seldom penetrate it to the depth of more than 

 a few feet, usually not more than 2 to 4, and much of the 

 water that falls does not enter the soil at all, but runs 

 away over its surface. When the dense soil is broken 

 up and especially by deep plowing supplemented by sub- 

 soiling, the water that falls, or much of it, goes down. If 

 the land is summer-fallowed the first season, it goes down 

 usually to the depth of 2 to 3 feet. The more frequently 

 that the land is summer-fallowed and also cultivated, as 

 through the growing of a cultivated crop, the more 

 deeply will the water that falls from the skies go down 

 into trie subsoil. It penetrates but slowly into the dry 

 ground below, but within a very limited term of years it 

 will work down in the subsoil to the depth of, say, 6 to 

 10 feet. As moisture works down into the subsoil, the 

 more quickly will that which falls work downward, 

 hence the more will be the proportion of that which 

 falls that will work down into the subsoil, on the suppo- 

 sition that the surface soil is properly tilled. 



The advantages of storing moisture in the subsoil, 

 as far as this may be practicable, include: (1) the fact 

 that moisture is much less readily lost from the subsoil 

 than from the ordinary tillable areas of the same, and (2) 

 that because of this the subsoil may furnish a reserve of 

 moisture at a critical time when it may be impossible to 

 obtain a supply from any other source. Experiments in 

 Utah have shown that in 7 days the first foot of soil that 

 contained 23.22 per cent, lost 13.30 pounds of the same, 

 while another soil, that contained but 16.64 per cent, lost 

 only 8.48 pounds. The total water in these two soils to 



