When to Fertilize 379 



The chemical contents vary in the different seasons and in 

 the different parts of the plant, and also with the soil in 

 which the plant grows; the plant may take up more than 

 it needs when some element is abundant. Even the wid- 

 est variation in any one ingredient will be amply cov- 

 ered by the large quantity of fertilizer ordinarily applied. 

 Consider, for example, that the fruit of a tomato com- 

 prises .05 per cent of phosphoric acid and .37 per cent of 

 potash. If the crop is ten tons of fruit to the acre, more 

 than the average quantity of required phosphoric acid is 

 ten pounds and of potash fifty-four pounds. It is safe 

 to assume that the land itself would supply at least three- 

 fourths of these amounts. We will assume that one-fourth 

 is to be supplied by the addition of fertilizer. We should 

 then apply to the acre two and one-half pounds of phos- 

 phoric acid and about fourteen pounds of potash. As a 

 matter of fact, however, the smallest quantities ever 

 applied are many times in excess of these figures. Fer- 

 tilizers must necessarily be applied in excess of theoretical 

 needs. It is impossible to distribute a very small quan- 

 tity; roots do not occupy every part of the ground. Much 

 is risked in the chance that some of the material may be 

 used. 



Another difficulty in the giving of advice is the vari- 

 able nature of the soil. This is particularly the case in the 

 Northern States, in which the soil is largely drift and is 

 therefore very uneven in kind and depth. In the long 

 stretches of sand on the Atlantic coastal plain or in the 

 red clays of the South, and in nearly all alluvial soils, 

 the problem of choosing a fertilizer is less complex. The 

 sandier and more uniform the land, the more marked, as 



