WHEN TO PLOW, AND HOW DEEP 203 



factor in dry-land crop production, the shortage of power neces- 

 sary for deep and thorough cultivation at all times is a serious 

 obstacle to profitable farming. 



Deep furrows, as before pointed out, are more apt to be 

 pulverized than shallow; hence to some extent the plow per- 

 forms for the subsoil what pulverizing implements do for the 

 surface layers. Three or four inches of the surface soil must 

 be kept stirred as a dust mulch to check the capillary rise of 

 water and consequent loss by evaporation. Underneath this 

 mulch a dry crust inevitably forms during the growing season; 

 hence the actual feeding area of the roots does not begin until 

 a depth of five or six inches is reached. As between plowing 

 eight inches and ten niches deep there is, therefore, a difference 

 of at least 100 per cent, in the zone available for the maintenance 

 of the plant. 



The moisture reservoir is increased in the same ratio. The 

 deeper the moisture is stored, the greater is the assurance of 

 an abundance for the needs of the crop, as each successive inch 

 dries out more slowly. Professor Buffum says: "A soil weigh- 

 ing one ton per cubic yard weighs approximately 1613 tons 

 per acre, taken one foot deep. If such a soil will absorb and 

 hold 20 per cent, of moisture and is plowed six inches deep, 

 it will take up 161.3 tons of moisture per acre. A rainfall of 

 1.4 inches will supply this amount of moisture and fill up our 

 six-inch reservoir; if the ground is plowed only three inches deep 

 and the subsoil is hard, it would not be able to store a rainfall 

 of more than seven tenths of an inch, and should more water 

 fall at one time, it will be lost and may wash the soil away with 

 it. If plowed nine inches deep and put in good condition, 

 such a soil reservoir would absorb and hold over two inches of 

 rainfall at one time. A soil already containing considerable 

 water would be filled up with less rain, and deep plowing would 

 be still more important. . . . Where the soils are light 

 and winds drift them, shallow plowing may result in all the 

 top soil, down to the sole of the furrow, being blown away. 



