Il8 AGRICULTURE 



Phosphoric Acid. Many soils contain phosphorus in forms 

 unavailable to plants; these soils need thorough tillage, and stable 

 manure and lime to combine with the phosphates and form phos- 

 phoric acid. The chief commercial sources of phosphoric acid 

 are guano, ground and crushed bones, and phosphate rocks. 



There are large deposits of phosphate rocks in South Carolina, 

 Florida, Virginia, North Carolina, Tennessee, and other states. 

 These are supposed to be the accumulated remains of ancient 

 animals. The phosphoric acid in them is insoluble and cannot 

 be used by plants; it is made soluble, and so available, by being 

 treated with sul phu'ric acid. Some preparations contain free sul- 

 phuric acid, and if these be used year after year on land, it will 

 become 'baked' and lose, instead of gain, fertility. 



The insoluble forms of phosphates, such as bones and untreated 

 phosphate rock, decay slowly and should be applied some time 

 before needed. They do not injure the soil, are slow and lasting 

 in effect, and are especially Useful for slow-growing crops. 



Potash. It is difficult to estimate the amount of available potash 

 in a soil, as plants vary greatly in their ability to get it; it is un- 

 available for some, where others collect all they need. Tobacco, 

 grass, potatoes, legumes, and fruit trees use much potash. 



The chief commercial sources of potash are wood ashes and the 

 .products of the Stass'furt mines in Germany. These mines are in 

 a vast salt bed formed probably by the evaporation of water from an 

 inland sea, leaving the substances leached from the land. Potash 

 is shipped from these mines in various forms, such as kain'it, 

 mu'ri ate of potash, and sul'phate of potash. Common salt 

 is the chief impurity in kainit and in muriate of potash. Sulphate 

 or nitrate of potash is used on such crops as tobacco, potatoes, 

 and fruit, of which the quality would be injured by the salt in 

 muriate of potash and kainit. 



