No. 4.] SOIL FERTILITY. 123 



to be something like the following : plants contain certain 

 elements, some of which are indispensable to their growth ; 

 certain of these indispensable elements are contained in soils 

 only in very small proportions, and when compounds contain- 

 ing these elements are added to the soil, a marked increase 

 of crop often occurs ; consequently, a low productive power 

 of the soil is due to the absence below sufficient quantities of 

 certain elements of plant growth. This is the syllogism 

 Avhich was placed before my mind as a student of agricul- 

 tural chemistry nearly thirty years ago, and it forms the basis 

 of what farmers have ever since been taught to be a chief 

 consideration in the maintenance of the fertilit}^ of their 

 farms. 



Let us glance at what are some of the results that have 

 proceeded from this point of view. The chief result is what 

 I have designated above as the discussion of fertility on a 

 mathematical basis. This discussion is very largely centred 

 around tables showing the average amounts of nitrogen, 

 phosphoric acid and potash contained in our farm crops. We 

 have pointed to these tables, and told the farmer that, for 

 instance, a crop of two hundred bushels of potatoes removes 

 from his soil so many pounds of nitrogen, phosphoric acid 

 and potash; and that, when the crop is sold, his form is 

 thereby so much the i)oorer in the essential elements of fer- 

 tility. The farmer has been assured that he need not trouble 

 about other elements, because his soil contains them in abun- 

 dance, and will always continue to do so. A natural and 

 inevitabk? conclusion from such premises has been, that the 

 way to maintain the fertility of the soil is either to adopt 

 such a system of farming and such care of manurial residues 

 as would prevent loss from the farm of the peculiarly valu- 

 able elements of fertility, or to purchase and return to the 

 soil an equivalent of the nitrogen, phosphoric acid and potash 

 which is sold in crops or other products. I do not assert 

 that other factors in fertility have not been more or less dis- 

 cussed, ])ut I am sure I am correct in saying that the con- 

 siderations as I have outlined them are those to which the 

 farmers' attention has chiefly been drawn. 



Again, it is not too nmch to say, and I think you will 



