326 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1951 



a well-managed plan. Many Corn Belt farmers already follow this 

 practice, but not all of them. Even many who do, fail to realize the 

 full potentials from the system. Kecent experimental evidence 

 strongly indicates that on many soil types, use of adequate amounts of 

 mineral nutrients will give a substantial boost to the system. 



In the Corn Belt there are at least 7 or 8 million acres of small gi'ain 

 planted each year without an accompanying legume — where a legume 

 could be used. Probably on another 7 or 8 million acres, legume 

 stands are poor or fail because of inadequate fertilization or for other 

 reasons that could be corrected. In total there are between 10 and 15 

 million acres of small grain where potentialities from a legume catch 

 crop are not being realized. Increases in corn yields resulting from 

 this practice would vary, but a conservative estimate would be from 12 

 to 15 bushels per acre. 



If all such small-grain acreage in the Corn Belt is properly fertilized 

 and seeded with a legume crop for 1952 and is plowed under as green 

 manure in the spring of 1953, it can easily increase corn production by 

 200 million bushels in 1953. Such a system certainly is not sacrificing 

 immediate production. And the legume crop in such a rotation, 

 accompanied with the use of adequate fertilization, would about offset 

 the losses in soil productivity from both the corn and small-grain crops. 



Similar gains could be realized from other uses of legumes and 

 grasses. Recent experiments have shown, for example, that on much 

 land, improved meadows and pastures can be made to produce as much 

 total digestible nutrients per acre as high-yielding corn crops, and at 

 less cost and with less labor. 



Animal Tnanures arid crop residues. — The return of crop residues, 

 including animal manures, is a highly important factor in building 

 soil productivity. Much crop residue is now being returned to the 

 soil, but we are not realizing the full potential from animal manures — 

 nowhere near it. 



One billion tons of manure, the annual product of livestock on 

 American farms, if completely recovered, carefully preserved, and 

 efl&ciently used, should produce six billion dollars' worth of increase in 

 crop production. The potential value of this agricultural resource is 

 three times that of the nation's wheat crop. The organic-matter con- 

 tent is twice the soil organic matter destroyed in the growing of the 

 nation's grain and cotton crops. 



Not more than one-fourth to one-third of the potential crop-produc- 

 ing and soil-conserving value of animal-manure resources of the coun- 

 try is now realized on harvested crops. That it is economically feas- 

 ible to prevent much of this loss has been conclusively demonstrated 

 both experimentally and by farmers in Europe and in this country. 



Animal manure is valuable in several ways. It increases the size of 

 crops, tends to lessen the effect of destructive crops, and increases the 



