162 ' PRACTICAL FARM CHEMISTRY. 



it would be a matter of grave doubt, whether we 

 could afford to buy it for making wheat of it 



Thus in many cases it is with potatoes. We might 

 see our way clear to purchase manure for potato 

 growing, and make it pay, while we could not use it 

 for wheat production without loss. Plant foods 

 seldom have a greater commercial value than in the 

 form of market garden crops. In this form they 

 can be expected to give us the highest returns. 

 Only the florist, the nurseryman, and the seed 

 grower know how to transform plant foods into 

 articles of still greater commercial value. No prin- 

 ciple is of greater importance than this that our 

 raw materials of plant food should always be used 

 for the manufacture of those among the crops we 

 grow which will bring us the most money. 



Another fundamental principle has already been 

 explained. It is this, that the use of complete fer- 

 tilizers involves a waste in all cases where the soil 

 already contains an abundance of one or two of the 

 chief elements of plant food, and requires only the 

 supplementary addition of the missing one or two 

 elements to give us all the results we could expect 

 from the complete fertilizer. 



Another fundamental principle requires the use 

 of plant foods in most readily available condition 

 for crops that develop and mature in a short period. 

 This applies especially to nitrogen and phosphoric 

 acid. Spinach, radishes, lettuce, and similar crops 

 that come to perfection in a few weeks, need soluble 

 food. Trees and shrubs can in time utilize plant 

 foods that are not immediately available. Winter 

 wheat sometimes produces as good a yield on floats 

 as on superphosphate, etc. 



Of not less importance is the observation that a 



