RELATION OF SOILS TO GROWTH 71 



acre, with normal rainfall of region such as the black 

 loam bottom land soils of the Mississippi drainage basin, 

 and certain areas of black upland or drained swamps. 

 This soil is well drained, well supplied with organic mat- 

 ter, minerals, and rainfall, and usually commercial fertil- 

 izers will show little or no effect. The total area is small, 

 probably not greater than 1 per cent of the Corn Belt. 

 This may be termed the ideal corn soil. 



2. Soils producing 35 to 50 bushels per acre, with favor- 

 able climatic conditions. 



(a) This includes the greater part of the cultivated 

 lands in the surplus corn States of Ohio, Indiana, Illi- 

 nois, Iowa, Nebraska, Kansas, and Missouri. These 

 soils have been cropped for fifty to seventy-five years, 

 during which time the ability to yield has decreased 

 25 to 50 per cent. All these soils respond quickly to an 

 application of manure, or are increased 25 to 50 per cent 

 in productivity by growing a crop of clover or alfalfa. 

 They seem to need organic matter and available nitrogen 

 more than anything else. The supply of minerals is gen- 

 erally sufficient, but in many cases the application of both 

 potassium and phosphates gives increased yields, though, 

 as a general rule, the increase is not sufficient to be profit- 

 able. Rotation, the use of legumes, and manure are to 

 be relied on at present as the principal means of main- 

 taining or increasing the yield. 



(6) All the "good corn land " through the Eastern and 

 Southern States is also included in this class. 



3. Land producing 25 to 35 bushels under favorable 

 climatic conditions. 



(a) Through the Eastern and Southern States are 

 large areas which are fairly productive when first brought 

 under cultivation, but which have been cropped for 



