UTILIZING OUR SOIL RESOURCES — SALTER 329 



There are real opportunities in making more efficient use of the rain 

 water that falls on the land. In the humid area — east of the Missis- 

 sippi — we are losing about one-third of the annual rainfall through 

 runoff, which underscores the importance of soil and crop practices 

 that conserve moisture and make more efficient use of it. Numerous 

 improved tillage and terracing practices that conserve moisture are 

 already in use. Other practices that will serve this end are now being 

 developed. Extensive use of such measures can do much to increase 

 production and reduce losses from erosion. 



Farming on the contour, for example, can reduce water runoff and 

 erosion losses and increase crop yields on millions of acres of sloping 

 land where contouring is not now being practiced. The Soil Con- 

 servation Service in cooperation with State experiment stations has 

 gathered much evidence on this point. Reports from Iowa show that 

 contour farming cuts soil losses in half and raises corn yields as much 

 as 7.4 bushels per acre. Reports from Illinois show that corn yields 

 7 bushels per acre more on contoured jBelds than on fields cultivated 

 up and down the slope. Work in Illinois, Iowa, and Missouri, showed 

 between 11 and 12 percent increase in soybean yields from contouring. 

 Evidence from 10 States shows that average wheat yields were in- 

 creased 20 percent by contouring. 



Of course, the greatest value from conservation practices results 

 when they are used in combination, as demonstrated by studies in 

 Indiana. Here, adequate fertilization, liming, return of crop resi- 

 dues, and contouring in a four-year rotation of corn, soybeans, wheat, 

 and grass-legume meadow resulted in 34 bushels more corn, 7 bushels 

 more soybeans, 7 bushels more wheat, and an extra ton of hay, per 

 acre. Without conservation farming, the soil lost 12.6 percent of the 

 rainfall during the growing season. Runoff under the conservation 

 treatment amounts to only 5.1 percent. Thus, the improved measures 

 saved 7.5 percent more rainfall during the growing season. 



There is good opportunity, too, for materially increasing the po- 

 tentialities of some soils to hold water and grow crops by deepening 

 the zone of soil in which roots can grow. Most productive soils are 

 characterized by deep friable surface layers. In this country we have 

 lost much topsoil through erosion. Furthermore, the soils over a 

 large area have naturally shallow surface layers. 



We are exploring the possibilities of improving the structure and 

 nutritional qualities of the subsoil as a means of expanding the rooting 

 zone for plants. Remarkable increases in crop production have been 

 produced in this way on some soil types. It is not unreasonable to 

 expect that we could substantially deepen the root zone in many soils 

 and make available to crops increased quantities of both plant nu- 

 trients and water through the use of deep-rooted legumes in cropping 



