PART II 



SYSTEMS OF PERMANENT 

 AGRICULTURE 



FOR practically all of the normal soils of the United States, and 

 especially for those of the Central states, there are only three con- 

 stituents that must be supplied in order to adopt systems of farm- 

 ing that, if continued, will increase, or at least permanently 

 maintain, the productive power of the soil. These are limestone, 

 phosphorus, and organic matter. The limestone must be used to 

 correct acidity and sometimes to supply the element calcium. The 

 phosphorus is needed solely for its plant-food value. The supply 

 of organic matter must be renewed to provide nitrogen from its 

 decomposition and to make available the potassium and other 

 essential elements contained in the soil in abundance, as well as 

 to liberate phosphorus from the raw mineral phosphate naturally 

 contained in or applied to the soil. 



Other fertilizer materials have some value, and sometimes great 

 'value, on uncommon or abnormal soils, and certain other substances 

 are powerful soil stimulants, especially on soils deficient in organic 

 matter; and, if applied with intelligence, they may sometimes be 

 used temporarily with advantage and justification, but they are 

 unnecessary and, as a very general rule, they are unprofitable, in 

 good systems of soil improvement. 



There are, of course, numerous and more or less extensive 

 areas of abnormal soils, such as the residual sands and the peaty 

 swamp lands (both of which are very deficient in potassium), and 

 also soils exceedingly rich in phosphorus, as in the geologic neigh- 

 borhood of the natural phosphate deposits in the Central Basin of 

 Tennessee and the Blue Grass Region of Kentucky. 



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