152 LESSONS IX AGRICULTURE 



is being rapidly mined away, large quantities being 

 taken to European countries. In the manufacture of 

 high grade phosphates, the rock is ground fine and is 

 then treated with sulphuric acid, which makes it soluble, 

 and thus available as a plant food. High grade phos- 

 phates contain 15% acid phosphate. Two hundred 

 pounds per acre is an average application. 



Potash. Potash is especially essential in the pro- 

 duction of fruits, potatoes, and root crops. Other con- 

 ditions being favorable, undersized, shriveled, and im- 

 perfect fruits are due to a lack of potash. Here again 

 barnyard manure will supply a good percentage of the 

 element needed. Wood ashes are also valuable as a 

 source of potash. The principal commercial potash fer- 

 tilizers are muriate of potash and sulphate of potash. 

 They contain about 50% of available potash, and are 

 seldom applied in excess of one hundred pounds per 

 acre. 



Lime. Lime is not a fertilizer in the same sense as 

 those discussed above, but it is used in connection with 

 fertilizers because of its chemical effect upon the soil. 

 Lime sweetens the soil, breaks up combinations so that 

 plant food is set free for the use of the plants, and im- 

 proves the physical condition of both clay and sand 

 soils. 



The subject of fertilizers is a large and important one 

 to the farmer. It requires much thought and careful 

 study, and each farmer must work out his own farm 

 needs. 



