56 MASSACHUSETTS HORTICULTURAL SOCIETY. 



It was once thought that the chemical analysis of a soil would 

 easily reveal its deficiencies in plant food. But later experience 

 has shown this to be, at best, a costly and very defective source of in- 

 formation. Different samples of soil, taken from different places in 

 the same field and at different times, may vary widel}' in composi- 

 tion, and, what is a still greater diflSculty, the chemical tests which 

 prove the presence of a given ingredient in the soil, do not tell 

 whether it is already in such a form that the plant can use it, nor 

 whether or how soon it may become so. And there are many other 

 factors of vital importance to the development of the plant which 

 soil analysis does not reveal. 



To find what materials crops remove from the soil is an easier 

 matter. Thousands of anal^^ses of the more important vegetable 

 products have been made, nearly all in Europe, however, and we 

 have tables prepared from them giving the average composition of 

 our field crops. From these any farmer ma}^ calculate how much 

 plant food a given crop takes, on the average, from his soil. The 

 figures might possibly fit his case no closer than would the calcula- 

 tion of his own weight from that of the average European, but they 

 will suffice well enough for practical purposes. 



Formulas for fertilizers for special crops are frequentlj' based upon 

 calculations of this sort. For instance, a crop of fifty bushels of 

 corn, with the stalks, would take from the soil, on the average, 

 Nitrogen, - - 76 lbs. Magnesia, - - 23 lbs. 



Phosphoric Acid, - 51 " Lime, - - - 27 " 



Potash, - - - 72 " Sulphuric Acid, - 8 " 



Now we may assume that nitrogen, phosphoric acid, and potash, 

 are the only substances the soil will fail to furnish in plenty, or that, if 

 lime and sulphuric acid are needed in addition, there will be enough 

 in the superphosphates and other materials to be used, to supply 

 them. We have then to provide 76 lbs. of nitrogen, 51 lbs. of 

 phosphoric acid, and 72 lbs. of potash, in forms readily available 

 for plant food. 



We could supply the nitrogen in, sa}', 760 lbs. of dried blood, at a 

 cost of about $15.40, the phosphoric acid in 340 lbs. of dissolved 

 bone black, costing $6.00, and the potash in 144 lbs. of muriate of 

 potash, costing, say, $3.20. This would make for our 50 bushel 

 corn crop, 1,244 pounds of fertilizing material, at a cost of $24.60. 

 It would be a costly application, even if it were sure to improve the 

 yield by fifty bushels. 



