THE ORANGE IN CALIFORNIA FERTILIZATION. 141 



crops; and the same principle is recognized in the practical 

 fertilization of the root crops with fertilizers that include 

 chiefly potash, while for grain a combination of nitrogen and 

 phosphoric acid is usually given and found most profitable. 



Supplying Deficiencies. The reason why in many cases the 

 return of one or two of these fertilizing ingredients can be 

 omitted from the replacement is that the soil itself frequently 

 contains a larger proportion of one or several of these same 

 ingredients in a form available to plants; that, moreover, these 

 ingredients, usually occurring in the soil chiefly in a difficult 

 soluble condition, are gradually set free by the " fallowing" 

 action of the atmosphere from their insoluble combinations, 

 so as to become available to plants; and that if the soil is 

 naturally rich in one or more of these ingredients, the return 

 of such ingredient may be omitted, either after a fallow or after 

 a crop that has drawn but lightly upon it. Thus, after a root 

 crop phosphoric acid may usually be omitted from fertilization, if 

 the soil is known to be (naturally or artificially) rich in phos- 

 phoric acid; and the same, of course, is true of potash and 

 nitrogen in other cases. In so doing, the husbandman draws 

 upon the natural resources of the land, availing himself of the 

 advantages of a rich soil; but those who cultivate soils nat- 

 urally poor may be compelled to return in every case each one 

 of the three or four ingredients needed for and commonly used 

 in fertilization. 



Wasteful Practice. Were the immediate return of everything 

 that the crop takes away necessary on every soil, the possessor 

 of rich land would have no advantage over the owner of poor 

 land, for as soon as the first flush of fertility is exhausted in 

 the virgin soil, both would be equally obliged to supply the full 

 amount of ingredients withdrawn from the soil by each crop. 

 But the experience of centuries has shown that such integral 

 replacement is altogether unnecessary on very many lands, and, 

 as a result, the use of a " complete " fertilizer is in Europe a 

 rare exception, save as regards stable manure. Farmers buy 

 the individual ingredients as furnished in commerce, according 

 to the supposed requirements of the land, as deduced either 

 from its previous history or from the known richness of the 

 soil in either one or the other ingredient in question. 



