COMMERCIAL FERTILIZERS 105 



121. Phosphate rock. Rock containing a large amount of 

 phosphorus is found in the Carolinas, Florida, Tennessee, and 

 in other Southern as well as some Western states. The most 

 important phosphate deposits in the world are found in these 

 states. Standard grades of rock phosphate contain from 12 to 

 1 3 per cent of phosphorus. The raw phosphate rock, very finely 

 ground, is used to a considerable extent as a fertilizer. Large quan- 

 tities also are treated with sulphuric acid for making acid phos- 

 phate. The raw rock acts slowly and should be used only on soils 

 that contain considerable organic matter, or should only be applied 

 with a green-manure crop (Fig. 44), barnyard manure, or decaying 

 sod, in order that the phosphorus be made available to plants. 



122. Acid phosphate. Acid phosphate contains from 5 to 

 7 per cent phosphorus, most of which is soluble. Acid phos- 

 phate is used to a large extent in the Eastern and Southern 

 states. It is also one of the most important materials used in 

 compounding mixed fertilizers. 



123. Basic slag. Basic slag, sometimes known as Thomas 

 meal, is a by-product of the steel mills. It is ground to a fine 

 powder and used in much the same way as raw phosphate rock. 

 A good grade of slag contains about 8 per cent of phosphorus 

 in a form somewhat more available than that in raw rock. 



124. Where phosphates are used. Phosphatic fertilizers are 

 the most widely used fertilizing materials. The acid phosphate, 

 the quick-acting form of phosphorus, is most extensively used 

 in the Southern and Eastern states. The bone meals and the 

 basic slag are moderately quick acting, the former being used 

 largely in central United States near the large slaughterhouses, 

 the latter in European countries. The raw phosphate rock is 

 used mainly in the corn belt. 



125. Potassium fertilizers. The main source of potassium 

 fertilizers for the world is the Stassfurt mines of Germany. It 

 is calculated that there is sufficient potash in these mines to 

 last the world five hundred thousand years at the present rate of 

 consumption. The most common crude salt is known as kainite, 

 which contains approximately 10 per cent of potassium. The 



