COTTON FERTILIZERS 331 



amounts of rotting vegetable matter. Hence, raw phos- 

 phate mixed with stable manure is sometimes as effective 

 as an equal weight of acid phosphate. The use of raw 

 phosphate for cotton should probably be restricted to 

 cases where it can be thus used with manure or leaf-mold, 

 or to soils on which a large amount of vegetable matter 

 is being plowed under. Even in the latter case acid phos- 

 phate is usually the more profitable the first year. 



It is generally believed that the residual effects, that is, 

 the effects subsequent to the year when it is applied, are 

 greater with raw phosphate than with acid phosphate; 

 but the difference in residual effect is not sufficient to 

 overcome the usual greater efficiency of acid phosphate 

 in the year in which it is applied. 



304. Other sources of phosphoric acid. Another 

 source of phosphoric acid is slag phosphate ; this is more 

 available than raw phosphate. Still another source of 

 phosphoric acid is ground bone, which is not extensively 

 used by cotton growers. 



The principal phosphate mines are in South Carolina, 

 Tennessee, and Florida. Some authorities estimate that 

 unless new phosphate mines are discovered, or the export 

 of phosphate to foreign countries decreased, the supply of 

 high-grade phosphate rock will be exhausted long before 

 the close of the present century. This is one of the con- 

 siderations that should lead farmers to utilize on the farm 

 the substances rich in phosphoric acid. Richest of these 

 are the bones of animals. Cotton seed, and all other seeds, 

 contain considerable phosphoric acid, which is retained 

 on the farm when these seed are there fed to live- 

 stock. 



