70 COBN CROPS 



CAUSES OF LOW PRODUCTION 



53. Assuming rainfall to be sufficient, a good corn soil 

 should produce 75 bushels per acre. Only a small per- 

 centage of the corn land in the United States will yield 

 this at present, due to certain causes which may be 

 summarized as follows : — 



1. Poor drainage. Corn suffers more than do other 

 cereals from poor drainage, as it requires a " warm " 

 soil, and also available nitrogen in rather large quantities. 

 Nitrifying processes are hindered in waterlogged soils. 



2. Surface soil depleted through erosion, very com- 

 mon on rolling lands in regions of large rainfall. 



3. Soil once fertile but depleted through constant crop- 

 ping without return of organic matter or minerals. 



4. Soils which in a virgin state were deficient in organic 

 matter or lacking in some mineral element. 



Each of the above soils will be found deficient in one 

 or more of the following : — 



(a) Drainage. 



(b) Organic matter. 



(c) Nitrogen. 



(d) One or more mineral elements. 



(a) is corrected by drainage, (6) and (c) by manure or 

 the growing of legumes, (d) by manure or commercial 

 fertilizers. 



CLASSIFICATION OF CORN SOILS IN THE UNITED STATES 

 ACCORDING TO PRODUCTIVENESS 



54. For the regions east of the Rocky Mountains the 

 corn soils may be classed according to productivity into 

 four general groups. 



1. Soils capable of producing 75 bushels or more per 



