REVIEW AND ( ONOIX'SIOX. 367 



be detefted by the tests employed. This soil was mostly 

 naked and destitute of vegetation, and ils composition 

 shows tlie absence of any crop-producing 2>o\ver. 



Relative Importance of the In^^redients of the Soil. 



— From the general point of view of vegetable nutrition, 

 all those ingredients of tlie soil which act as food to the 

 plant, are equally important as they are equally indispens- 

 able. Absence of any one of the substances which water- 

 culture demonstrates must be presented to the roots of a 

 plant so that it shall grow, is fatal to the productiveness 

 of a soil. 



Thus regardeil, oxide of iron is as important as phos- 

 phoric acid, and chlorine (for the crops which require it) 

 is no less valuable than potash. Practically, however, 

 the relative importance of the nutritive elements is meas- 

 ured by their comparative ahundance. Those which, like 

 oxide of irou, are rarely deficient, are for that reason less 

 ])rominent among the factors of a crop. If any single 

 substance, be it phosphoric acid, or sulphuric acid, or pot- 

 ash, or magnesia, is lacking in a given soil at a certain 

 time, that substance is then and for that soil the most im- 

 portant ingredient. From the point of view of natural 

 abundance, we miy safely state that, on the whole, availa- 

 ble nitrogen and phosphoric acid are the most imj^ortant 

 ingredients of the soil, and potash, perhaps, takes the next 

 rank. These are, most coaimoidy, the substances whose 

 absence or deficiency impairs fertility, and are those 

 which, when added as fertilizers, j^roduce the most frequent 

 and remarkable increase of productiveness. In a multi- 

 tuile of special cases, however, sulphuric acid or lime, or 

 magnesia, assumes the chief prominence, Avhile in many in- 

 stances it is scarcely possible to make out a greater crop- 

 producing value for one of these substances over several 

 others. Again, those ingredients of the soil which could 

 be spared for all that they immediately contribute to the 



