SOIL FERTILITY AND PLANT GROWTH 245 



Commercial phosphorus fertilizers. Phosphorus fer- 

 tilizers are supplied commercially in the form (1) of the 

 bones of animals killed at the slaughter-houses; (2) of min- 

 eral deposits in phosphate rock, immense beds of which are 

 found in Tennessee, South Carolina, Florida, Wyoming, 

 Utah, Idaho and Montana; and (3) of slag from the fur- 

 naces where certain ores containing phosphorus are smelted. 



Bone phosphate is sold either as ground bone, which is 

 raw bone ground up ; or bone meal, which is made by grind- 

 ing after the bones have been steamed under high pressure 

 to remove the fats and oils. 



Mineral phosphate is sold in two forms, (1) that first 

 treated with sulphuric acid, and (2) the natural rock finely 

 ground. The first form has the advantage of being more 

 immediately available for plant use. The second form is 

 considerably less expensive and, when mixed with organic 

 matter like some form of manure, proves equally as valu- 

 able as the more expensive compound. 



Commercial potassium fertilizers. Potassium fertil- 

 izers are available in several commercial forms, none of 

 which is produced in large quantity in this country. The 

 potash mines of Germany are the chief source of supply. 



The crude potash may be used on the soil directly as 

 mined, or it may be made into more concentrated form. 

 It is sold commercially as a fertilizer (1) as muriate of pot- 

 ash, (2) as saltpeter of potash, and (3) as kainit. Since this 

 product has to be imported it is naturally more expensive 

 than if produced at home. From one hundred to two hun- 

 dred pounds to the acre, applied at intervals of from one to 

 three years, will, however, usually prove sufficient to keep 

 up the supply. 



The application of commercial fertilizers. Because 

 commercial fertilizers are so expensive, and also for the 

 reason that the application of a fertilizer when it is not 



