42 PRINCIPLES OF FARM PRACTICE 



If another similar brand should have a calculated value 

 of $22.00, and another of $25.00, these three brands should 

 sell at nearly the same price. A difference of five dollars 

 in the price would be unreasonable, for all three are relatively 

 the same in value. 



Prices of fertilizers vary from year to year. Those quoted 

 in the above example have not reached the pre-war level but 

 they serve to illustrate the method of an approximate deter- 

 mination of the value of a fertilizer. 



Home mixing of fertilizers. Where large amounts of 

 fertilizers are used, it is often more economical to buy the 

 ingredients separately and mix them at home. A clean floor, 

 a shovel, and a pair of scales with which to weigh the correct 

 amount of each ingredient, are necessary. 



After the ingredients have been weighed, the lumps should 

 be pulverized and the material thoroughly mixed. The 

 method of calculating the amounts is as follows : 



All calculations are based upon the percentages of nitrogen, phos- 

 phoric acid, and potash in the materials purchased. The following are 

 the percentages of the most common forms of fertilizing materials: 



Nitrate of soda, 16 per cent nitrogen. 



Sulfate of ammonia, 20 per cent nitrogen. 



Dried blood, 10 per cent nitrogen. 



Acid phosphate, 14 to 16 per cent phosphoric acid (the guaranteed 

 analysis will give the exact percentage). 



Muriate of potash, 50 per cent potash (the guaranteed analysis will 

 give the percentage of potash in other forms of potash). 



The amount of nitrogen in a ton (2000 pounds) of nitrate of soda is 

 found by taking 16 per cent of 2000. (2000 X .16 = 320.) A ton of 

 nitrate of soda will therefore contain 320 pounds of nitrogen. 



If a ton of a mixture containing 2 per cent of nitrogen is wanted, the 

 quantity of nitrate of soda needed to furnish this amount of nitrogen 

 (2 per cent) may be found as follows: A ton (2000 pounds) containing 

 2 per cent of nitrogen will have 2 per cent of 2000 (2000 X .02 = 40), or 



