COTTON FERTILIZERS 319 



However, some clay soils contain a large amount of pot- 

 ash, but in an unavailable form. In this case the potash 

 can often be made available by improved preparation and 

 cultivation and by the addition of vegetable matter. The 

 sandier the soil and subsoil the greater is the need for 

 potash. Even on sandy lands, this fertilizer may not be 

 needed in any considerable amount unless cotton rust 

 commonly occurs on such soil. 



286. Nitrogen. The proper proportion of nitrogenous 

 fertilizer to acid phosphate in a fertilizer formula for 

 cotton depends more on the recent cropping and manur- 

 ing of the field than on the character of the rocks from 

 which the soil has been derived. One can usually 

 decide if nitrogen is needed by considering the following 

 facts : 



(1) Small stalks (if not due to climatic influences, poor 

 cultivation, etc.) are usually an indication that nitrogen 

 is needed. 



(2) Excessive stalk or " weed " growth of cotton is an 

 indication that nitrogen can be dispensed with, wholly or 

 partially. 



(3) The fresher the land the less the need for nitrogen. 



(4) Phosphate hastens maturity and may make more 

 severe the injury from cotton rust. 



(5) A luxuriant growth of cowpeas or of any other legume 

 just preceding cotton largely dispenses with the necessity 

 for nitrogen in the fertilizer ; so does a recent heavy dress- 

 ing of stable manure or cotton seed. 



However, the only positive means of determining the 

 exact fertilizer requirement of any soil is by making on it 

 an experiment with fertilizers. 



