202 



NITROGEN, PHOSPHORUS AND POTASSIUM 



Basic slag, bone meal and rock phosphate are good fertilizers 

 to use for crops like corn, grain, and potatoes, when grown on acid 

 soils. Basic slag acts well on clayey soils. 



For plants and soils which need liming, phosphates give more 

 economical returns when lime is added to the land. This is particu- 

 larly true in case of acid phosphates. 



Rock Phosphate vs. Acid Phosphate. The comparative fertil- 

 izing values of rock phosphate and acid phosphate have been much 

 discussed. Most available data seem to indicate that, in general, 

 acid phosphate is the more profitable. 6 On some of the black 

 prairie soils of the Middle West, certain results have shown that 

 rock phosphate is to be compared favorably with acid phosphate. 



Potash Fertilizers. The common potash fertilizers are: 



The fertilizing constituent of potash fertilizer may be expressed 

 either as the element potassium (K), or as the oxide of the element 

 " potash" (K 2 O). To reduce " potash" to the element equivalent, 

 multiply the number of per cent or pounds of " potash" by 0.83. 



Sources of Potash. The main source of potash fertilizers is 

 crude salts mined near Strassfurt, and in Alsace. No other deposits 

 of potassium salts are so extensive as these. It has been estimated 

 that the Strassfurt mines alone are capable of supplying the world 

 with potash for thousands of years. 



There are several sources of potassium in the United States, 

 among which are : Dried-up salt lakes, sea weed, wood ashes, potas- 

 sium-containing rock minerals, and as a by-product in cement 

 manufacture. The potassium salts obtained from these sources 

 have thus far been used in making mixed fertilizers. Tobacco 

 stems used as potash fertilizer are shown in Figure 134. 



Muriate of Potash. Muriate of potash is a prepared product 

 derived from crude potash salts. This is the most common of the 

 potash fertilizers. It is all soluble in water. 



6 This conclusion is based on prices paid for fertilizers before the World War. 



