FlGrRE 3. 



also front cover.) 



milds up tl 



For real soil building it is necessary to turn to permanent sod. A 

 permanent sod will increase the organic matter in the soil, chiefly by 

 its root growth. A healthy grass sod produces new 

 Grass, the roots every year, and the decay of the old roots adds 

 Real Soil to the organic matter, most of which is retained be- 

 Builder cause the soil is undisturbed. Gustafson, of Cornell 



University, cites a case where a virgin Illinois prairie 

 sod was found to contain 27,000 pounds per acre of live roots. These 

 roots die and are renewed constantly and in a comparatively short 

 time really build up the organic-matter content of the soil. This 

 indeed is doubtless the origin of the organic matter in most of the 

 fertile lands of the central Corn Belt. In the forested area, however, 

 where the organic matter has been derived from fallen leaves and the 

 decaying roots of trees and other vegetation it has taken a long time 

 to build up the organic-matter content of the soils, time that must be 

 expressed in geologic terms rather than in terms of human genera- 

 tions. Trees build soil too slowly for man's immediate use. A grass 

 sod, if not utilized, is therefore probably the only practical 100-percent 

 soil-building cover. If it is grazed or if hay is taken off, it may be 

 necessary to add plant food, but even then the protection from ero- 

 sion that such a oover offers, together with the increase in organic 

 matter by root growth, makes such a crop (fig. 3) the ideal of the soil 

 conservationist. Of course all land cannot be treated in this way, 

 and, in the main, crops should be called soil-conserving rather than 

 soil-building. 



It is quite possible by using proper crops, proper rotations, appli- 

 cations of lime and minerals where necessary, and approved anti- 

 erosion practices to conserve our soils so as to prevent the steady 

 decline in yields that has characterized soil-mining practices. 



8 



U. S. GOVERNMENT PRINTING OFFICE: 1936 



Fcr sale by the Superintendent of Documents, Washington. D. C. 



Price 5 cents 



