294 LEGUMES AND FERTILIZERS 



based upon brand but upon the composition of the mixture and 

 the sources of the elements. 



The purchase of nitrogen-bearing fertilizers is least profitable 

 because nitrogen can be so easily secured by the growing of legumes. 



Sources of Phosphoric Acid. — Ground rock phosphate is the 

 chief source of phosphate used in commercial fertilizers. It is a 

 combination of phosphoric acid with lime and is mined abundantly 

 in South Carolina, Tennessee, Florida and elsewhere. It may be 

 applied to soils in the "raw" condition or may be treated with 

 sulfuric acid. In the latter form it is called acid phosphate or 

 superphosphate, and is much more available as plant food. It 

 contains sixteen to twenty per cent phosphoric acid. 



Ground bone is also rich in phosphate and may be used in the 

 steamed form or may also be treated with sulfuric acid. When 

 merely ground and steamed it is slowly available for plants and 

 will last several seasons. It may contain twenty per cent of 

 phosphoric acid and four per cent nitrogen. When treated with 

 acid it becomes soluble and is more quickly used by plants. 



Bone tankage is another source of phosphoric acid. It is obtained 

 from packing houses, and is quite variable in composition. 



Sources of Potash. — Wood ashes furnish potash for the home 

 garden. Unleached hard-wood ashes contain from three to eight 

 per cent of potash, with an average of about six per cent. They 

 also contain some phosphoric acid and fully thirty per cent of 

 lime. For use as fertilizer ashes may be either spread on the soil as 

 made, or may be stored under cover till needed. 



Saltpeter waste contains five to twelve per cent of potash. It 

 must be bought only on analysis. 



Sea-weeds and similar plants are rich enough in potash to 

 warrant burning them to secure this product. The ashes contain as 

 much as five per cent of soluble potash. 



Potash is obtained from burning or rotting tobacco stems, corn 

 cobs, cottonseed hulls, straw, weeds, and other things. 



Potassium nitrate contains about twelve to fourteen per cent of 

 potash. 



Potassium carbonate from the Caucasus region is often ninety 

 per cent pure. It may be used as fertilizer when necessary. 



The Strassfurt potash salts, known as car-nall-ite, kainit, and 

 syl-vin-it, are ground and used as fertilizer, containing twelve 

 per cent or less of potash. They are usually refined, yielding two 

 concentrated products: (1) sulfate of potash with forty-eight per 



