DAVIS] STUDIES OF COMMERCIAL FERTILIZERS 129 



acid phosphate may be purchased (including freight) for $8.00 

 per ton. How much can be saved in cost per pound of phos- 

 phoric acid by applying phosphate in this way compared with 

 using acid phosphate (14 per cent phosphoric acid) at $16.00 per 

 ton? 



Application: 



The foregoing problems illustrate the application of simple 

 arithmetic in calculating amounts of fertilizer ingredients, and in 

 estimating comparative values of fertilizers. Home mixing may 

 be easily done with a scoop shovel on a tight bam f^oor. The 

 calculated amount by weight of each ingredient is piled on the 

 floor and uniformly mixed with the others. 



The waste of nitrogen in straw and manure is shown in problems 

 5, 6 and 7. These materials also have much value in improving 

 soil texture by adding humus to the soil, and by furnishing organic 

 material for action of soil bacteria. Problem 8 suggests a further 

 saving by making use of rock phosphate, a much cheaper means 

 of supplying phosphoric acid than by the use of acid phosphate. 

 In most soils except in very sandy soils there is a sufficient store 

 of potash for cereal crops. 



A reasonable farm practice in keeping up soil fertility would 

 be to provide nitrogen, the most expensive plant food (costing 

 about 19 cents a pound when bought), by use of manures and 

 straw and by rotation of crops with legumes (clover and the like), 

 to liberate phosphoric acid by mixing ground phosphate rock or 

 bone meal with manures, and to add potash only for special 

 crops. Sometimes a complete fertilizer may be needed. In such 

 cases home mixing is often more economical than the purchase of 

 materials already mixed. 



Miami University, Oxford, Ohio. 



