146 COBN CROPS 



Special cases : There are exceptions to the above rules, 

 a striking example of which are certain rich muck lands in 

 Illinois, well supplied with all elements except potassium, 

 where an application of potassium salts pays large returns.^ 



It is not to be inferred that fertilizers do not afford a 

 stimulus and give increased production, for they do ; but 

 the gross income from an acre of corn is not sufficiently 

 increased to paj' the cost of fertilizer, except in certain 

 cases when used in connection with manure and legumes. 

 This makes it apparent that profitable corn growing 

 must be carried on as a part of a general farming scheme 

 in which the soil fertility is principally maintained by the 

 use of green manures or barnyard manure, which may be 

 supplemented in a limited way with commercial fertilizer. 



NITROGEN 



104. A large or excessive supply of available nitrogen is 

 not considered favorable for most of the cereals, as wheat, 

 oats, or barley ; the effect being to produce an excessive 

 growth of straw, and often a decreased yield of grain. 

 Corn, however, is not so affected, and is most productive 

 on heavily manured land or on newly drained alluvial or 

 swamp lands where the available nitrogen is so abundant 

 that wheat or oats would " run to straw " and produce 

 little or no grain. In fact, a well-manured clover sod 

 where available nitrogen is in greater excess than any 

 other necessary element is ideal corn land. 



A large supply of nitrogen has sometimes been found a 

 disadvantage early in the season, as it may stimulate a 

 growth of plant too large to be adequately maintained 

 during the remainder of the season. For example, the 



1 Hopkins, C. G. Soil Fertility and Permanent Agriculture, p. 471. 



