THE SOIL AND SOIL FORMATION 



roots and the plant feeds in the upper soil zone which con- 

 tains the most plant food. Where the recently plowed fur- 

 row-slice is very porous and loose, it also acts as a mulch 

 to retard the upward flow of moisture by capillarity. 



Dust blanket and dirt mulch. The use of a dirt mulch 

 or dust blanket is illustrated in Figure 34. Here the 

 furrow-slice, D, rests upon the subsoil, E, with which it 

 is in intimate contact, so that the capillary water may 



rise into it. To pre- 

 vent the water from 

 rising entirely to the 

 surface, there by the 

 aid of the sun's heat to 

 be evaporated into the 

 atmosphere, the upper 

 zone of soil, C, is kept 

 broken up and made 

 too mellow and open 

 for the water to rise 

 through it by the force 

 of capillarity. The 

 moisture line here is at 

 the bottom of C, thus bringing the moisture zone up so 

 as to include the lower two-thirds, F, of the furrow-slice 

 D, and allow the roots of crops to feed in this portion 

 of soil, which is not only the richest in plant food, but is 

 the most congenial for the roots of plants and for their 

 little helpers, the soil bacteria. 



The general movements of water in the earth. The 

 surface of the water in our wells shows that the ground 

 water does not actually rise near the surface. The 

 upper part of the earth acts as a storage sponge, and 

 gets its supply of water annually from the rainfall, ex- 

 cepting cases where irrigation is practiced, or in rare 

 cases where water seeps out of hillsides and forms moist, 

 springlike areas, or flows along porous layers under- 



Figure 35. Shows a pervious mass over a 

 layer of impervious clay or stone, B. Water falling 

 on the upland at D, sinks down to the im- 

 pervious layer of clay and seeps forward until 

 the hillside is reached, and there flows out, re- 

 sulting in a seepy hillside, as at K, or possibly 

 forming a definite spring. 



