Soil Fertility 89 



as to the availability of the materials used and the percentages 

 of plant-foods contained. The laws of the several states differ 

 in some respects, but in general the manufacturers are required 

 to pay a state tax for each brand and to print on the bags con- 

 taining the mixture (1) the quantity of fertilizer in the bags, 

 (2) the name, brand, or trade mark, (3) the name and address 

 of the manufacturer, (4) the guaranteed chemical composition 

 of the fertilizer. 



The quantities of plant-food ingredients in a fertilizer are 

 expressed in percentages and are figured on a ton basis of 

 2000 pounds. Thus if a fertilizer is said to contain 3 per 

 cent of nitrogen, 6 per cent of phosphoric acid, and 10 per cent 

 of potash, the quantities in pounds of the ingredients are : 



Nitrogen 2000 (ton basis) X .03 = 60 



Phosphoric acid 2000 (ton basis) X .06 = 120 



Potash 2000 (ton basis) X .10 =200 



The composition of fertilizers is often designated by giving 

 the percentages only, the names of the ingredients being omitted. 

 Thus the fertilizer just considered is usually spoken of as a 

 3-6-10 fertilizer. As a rule the percentage of nitrogen is given 

 first, that of the phosphoric acid second, and that of potash 

 last, but in some parts of the country the order of the first 

 two is reversed, making the above a 6-3-10 fertilizer. 



Laws in the different states vary as to what shall be guar- 

 anteed by an analysis. Some states require a statement as 

 to the percentage of both nitrogen and ammonia, others require 

 that the percentage of nitrogen only shall be given. Some 

 require the percentage of the soluble, reverted, and total phos- 

 phoric acid; others only that of the soluble and the reverted. 

 In the case of potash some states require only the percentage 

 of soluble ; others, that the total be given. The best kind of 

 a guarantee is one that gives not only the percentage of the 

 ingredients, but also their availability. Some states have 

 this requirement. Formerly it was the custom among ferti- 



