74 THE SOIL, 



soil to be fertile for cultivated plants, must, as a pri- 

 mary condition, contain in sufficient quantity the nutri- 

 tive substances required by those plants. .But chem- 

 ical analysis, which determines this relation, gives but 

 rarely a correct standard by which to measure the 

 fertility of different soils, because the nutritive sub- 

 stances therein contained, to be really available and 

 effective, must have a certain form and condition, which 

 analysis reveals but imperfectly. 



Rough uncultivated ground, and soil formed from 

 the dust and dried mud of the highroads, are speedily 

 overgrown with weeds, and though often still unfit for 

 the cultivation of cereal and kitchen plants, may yet 

 prove not unfruitful for other plants, requiring, like 

 clover, sanfoin, and lucerne, a large amount of food, 

 and which are often seen thriving luxuriantly on the 

 slopes of railway embankments formed of earth that 

 has never been under cultivation. A similar relation is 

 shown by the subsoil of many fields. In many of them 

 the earth from the deeper layers improves the surface 

 soil, and increases its fertility ; in others, the subsoil 

 mixed with the surface soil destroys the fertility of the 

 latter. 



It is a remarkable fact that rough uncultivated soil, 

 unsuited for cereal and kitchen plants, may by diligent 

 cultivation during several years, and by the influence 

 of the weather, become fertile enough to produce those 

 plants which it formerly refused to bear. The dif- 

 ference between fertile arable land and barren untilled 

 soil is not the result of any dissimilarity in the nutritive 

 substances which they contain ; because in cultivation 

 upon a large scale, to convert the untilled rough soil 

 into fertile arable land, the ground, so far from being 

 enriched, is rather impoverished by the cultivation of 

 other plants on it. 



The difference between the subsoil and the arable 

 surface soil, or the crude and the cultivated soil, sup- 

 posing that both contain the same amount of nutritive 

 substances, can only be founded upon this, that the cul- 

 tivated ground contains the nutritive substances of 



