2 IO THE FIRST BOOK OF FARMING 



call the " unit basis," a " unit " meaning one per 

 cent, of a ton or twenty pounds of plant food. A 

 ton of nitrate of soda, for instance, contains 310 

 pounds or 15^ units of nitrogen, which at $3.20 

 cents per unit would cost $49. Buy your mixture 

 of a reliable firm, find out the actual amounts of the 

 plant foods in the mixture and pay a fair market 

 price for them. 



