168 MASSACHUSETTS HORTICULTURAL SOCIETY. 



There is another reason why I would not buy the ordinary- 

 brands of superphosphates, as a supply of plant food for the 

 forcing house and market garden, viz. : The three ingredients, 

 nitrogen, phosphoric acid, and potash are not combined in the 

 right proportion for use under these conditions. Not long ago I 

 took occasion to ascertain the proportion of nitrogen to available 

 phosphoric acid and potash soluble in water in fifty-eight brands 

 of fertilizers sold in Maine. I found that for each 100 pounds of 

 nitrogen these goods contained on the average 460 pounds of 

 available phosphoric acid and 120 pounds of potash. These 

 proportions are very different from those existing in the quick 

 growing food plants most common to horticulture. I find that the 

 average proportions in twelve of the most important vegetables 

 is, nitrogen 100, phosphoric acid 50, and potash 160. This shows 

 that in the average fertilizer the ratio of phosphoric acid to 

 nitrogen is nine times greater than it is in the average of twelve 

 vegetables. The ratio existing between the nitrogen and potasli 

 is not greatly different in the two cases. This means then, that if 

 the fertilizer is t© correspond to what the plant uses it must be 

 compounded quite differently from the average formula found in 

 the market : in no case, out of the fifty-eight fertilizers examined,, 

 did I find a ratio of nitrogen to phosphoric acid greater than one 

 to two, which would give a proportion four times less than in the 

 crops distinctively horticultural. 



But should a fertilizer contain the elements of plant food in the 

 same relative proportions that they are found in the plant? 

 Perhaps never just the same — perhaps sometimes very widely 

 different — but the degree of approximation to this must depend 

 upon circumstances. It is true in the abstract that a crop grower 

 purchases plant food most wisely when he buys just enough of 

 certain ingredients to make good the deficiencies of his home 

 resources. What those deficiencies are is determined by several 

 factors, the important ones being the soil, the crops grown in the 

 rotation, and the kind and quantity of products sold. I would 

 never advise the general farmer to adopt as a principle of action 

 special fertilizers whose formulas are based wholly upon the 

 composition of the crops he is to produce, for to do this is to 

 ignore the greatly varying capacities of soils, the unlike feeding 

 power of different plants, the use of legumes as a source of 

 nitrogen supply, — is to ignore, indeed, all but one of those factors 



