CHAPTER VIII 



PHOSPHORUS AND LIMESTONE 



The three most important elements in the soil are nitrogen, 

 phosphorus and potassium. Of these three soil elements, 

 nitrogen is required in the largest amount. While nitrogen 

 is no more essential to the growth of corn than the other 

 two, it is the element most easily lost from the soil. As we 

 have stated under "Leguminous Crops," nitrogen can be 

 gathered from the air and stored in the soil by the growing 

 of such crops as clover, cowpeas and soy beans. 



For this reason the growing of clover for the first time 

 on over-cropped corn land often makes the soil very produc- 

 tive for years to come because the supply of phosphorus and 

 potassium has not yet become lowered. But the supply of 

 phosphorus, like that of nitrogen, can become so low that 

 farm crops (especially clover) will not do well until enough 

 phosphorus has been replaced to bring the supply back to 

 normal. 



On many soils in the Corn Belt the crop yield is limited 

 by the lack of phosphorus rather than by the lack of nitro- 

 gen. Now, the only way by which phosphorus can be added 

 to the soil is to buy it in some form or other and apply it to 

 the land. If the phosphorus content of the soil is actually 

 lower than the nitrogen content, there is no doubt but that 

 the application of phosphorus would be a profitable invest- 

 ment; but to apply phosphorus to soil that is already very 

 low in humus and nitrogen is nothing less than throwing 

 money away. If clover crops grow large and luxuriant on 



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