198 NITROGEN, PHOSPHORUS AND POTASSIUM 



Expressing Eqmvalents.— The fertilizing constituent of phos- 

 phate fertilizers may be expressed in three ways: as "phosphorus 

 (P)/' as "phosphoric acid (P2O5)," and as "bone phosphate of lime 

 (BPL)." The per cent of "phosphoric acid'' is always higher 

 than the per cent indicating the phosphorus content of a fertilizer; 

 and the per cent expressing the equivalent of bone phosphate of 

 lime is higher still; to illustrate, thirteen per cent phosphorus (P) 

 equals thirty per cent phosphoric acid (P2O5) equals sixty-five 

 per cent bone phosphate of lime (BPL) . 



Phosphoric acid (P2O5) and bone phosphate of lime (BPL) 

 may be reduced to the common elemental name as follows: 



Per cent or pounds phosphoric acid X 436 ==per cent or pounds of phos- 

 phorus, respectively. Per cent or pounds of bone phosphate of lime X 2 = 

 per cent or pounds of phosphorus, respectively. 



Rock Phosphate. — ^Rock phosphate is finely pulverized phos- 

 phate rock. The main sources of this fertilizing material in the 

 United States are deposits in Tennessee, South Carolina, Florida, 

 Arkansas, Kentucky, Utah, Wyoming, Montana and Idaho. 

 Because of its insolubility, this fertilizer gives best resuJts on 

 most soils when it is mixed with manure or plowed under with 

 a green manuring crop. On some muck and peat lands it has given 

 very good results when applied directly to the soil and thoroughly 

 mixed with it, at the rate of about 800 pounds per acre. In soil 

 improvement plans, especially when the phosphorus supply is to 

 be increased and maintained, it has been foimd good practice to 

 mix rock phosphate with stall manure by sprinkling it in the 

 gutters in the barn duoring winter feeding, at the rate of from fitfty 

 to one hundred pounds to the ton of manure produced. This is 

 equivalent to approximately two to four quarts to the cow daily. 

 Rock phosphate may also be dusted over the manure when loaded 

 on spreaders. * 



Basic slag, or Thomas slag meal, is pulverized slag of Bessemer 

 steel converters. The phosphorus is withdrawn from the molten 

 phosphorus-containing iron. This fertilizer is much used in Euro- 

 pean countries and to a certain extent in eastern United States — 

 it being imported from Europe. The phosphorus-containing iron- 

 ore in Alabama, which is being converted into steel, may prove 

 a valuable source of this fertilizer. 



Groimd Steamed Bone Meal. — ^This fertilizer is pulverized 

 steamed bone. The bones from meat-packing plants are steamed, 

 or otherwise treated, to remove the fat and sometimes the gelatine 



