MANURES 41 



elements that he desires in it, and it is not necessary to 

 pay freight on sand or other filler. One is apt also to make 

 more of a study of the effectiveness of the mixture if he is 

 thoroughly familiar with its makeup. Usually the cost 

 is less when the materials are purchased separately. The 

 Massachusetts experiment station gives very clear direc- 

 tions for computing mixtures, which we quote as follows: 



'The calculation of amounts of different materials 

 needed to make a fertilizer of given composition is simple. 

 It is necessary first to know the composition of the materials. 

 This is usually correctly stated by the guarantee. The 

 selection of materials to furnish any given element is 

 determined by relative prices and fitness. For the element 

 nitrogen it is best in most cases to use nitrate of soda, blood, 

 or sulphate of ammonia and something like tankage or 

 fish, thus securing different rates of availability to insure 

 a supply throughout the growing season. 



A part of the needed phosphoric acid (rather slow 

 acting) will be furnished by tankage or fish. The balance 

 may be derived either from acid phosphate or slag rrieal 

 as crop or soil may make best. The needed potash should, 

 as a rule, be derived from high-grade sulphate. 



Example Showing Method of Calculation. 



Potato fertilizer to contain: 



Nitrogen, 3.5% 



Phosphoric acid, 8% 



Potash, 10% 



Nitrogen at 3.5% = 3.5 Ibs. in 100, or 70 Ibs. in a ton 



Phosphoric acid at 8. % = 8. Ibs. in 100, or 160 Ibs. in a ton 

 Potash at 10. % = 10. Ibs. in 100, or 200 Ibs. in a ton 



