98 THE BOOK OF CORN 



to become more rapidly available ; and in the third 

 place, the cultivation assists materially in unlocking 

 and providing food otherwise unavailable. 



It must be remembered, too, that owing" to the 

 widely varying conditions of soil and climate in those 

 states in which corn can be grown, the requirements 

 in reference to manures may also vary widely even on 

 the same character of soil. In the more northern sec- 

 tions, where the season is short, a relatively greater 

 abundance of available food in the soil is required than 

 would be the case in the more southern sections, where 

 the season of growth is much longer, or in the middle 

 western sections, where the period of hot, bright, grow- 

 ing weather is longer. 



MANURES AND FERTILIZERS I THEIR CHARACTER AND 



FUNCTIONS 



With these general considerations concerning the 

 crop, and its characteristics, arises the special question 

 of its feeding, and, in order that a proper understand- 

 ing of the subject may be obtained, it is necessary to 

 discuss the question of manures and their functions 

 in some detail. 



What Is a Manure? — In the first place, a manure 

 in the broad sense may be regarded as a substance that 

 will cause an increase in crop. Still, this is indefinite. 

 The idea that should be conveyed by the term "manure' , 

 is that it shall contain those constituents that are liable 

 to exist in soils in minimum amounts, and which are 

 carried away in maximum amounts by the crops re- 

 moved. These essential constituents are usually lim- 

 ited to three, namely, nitrogen, phosphoric acid and 

 potash. The term "essential" does not mean that they 

 are more essential to the growth of the plant than 

 others required by it, like lime, iron, sulphur, etc, but 



