INTRODUCTORY 3 



upon and not replaced. But in a Kentish hop-garden 

 or other land where an intensive system of cultivation 

 is practised, the crop does not remove as much as it 

 receives ; often the land is intrinsically poor, and owes 

 its value to the manner in which it will elaborate 

 the raw material supplied as manure. And not only 

 are these very special soils gaining, rather than losing 

 fertility with each crop, but, from a general point 

 of view, all countries that are being highly farmed, 

 like parts of Great Britain, are steadily increasing in 

 fertility at the expense of other countries which are 

 growing crops on virgin soil ; in the linseed, the maize, 

 the cotton seed, that are fed to our stock, there travels 

 to our soil some of the wealth of the lands upon which 

 these crops were grown. Hence the study of the 

 inherent resources of the soil is perhaps less important 

 than an examination of the manner in which the soil 

 deals with such materials supplied under cultivation. 



The complete knowledge of the soil and the part it 

 plays in the nutrition of the plant requires investigation 

 along three lines, which may be roughly classed as 

 — chemical, physical or mechanical, and biological ; 

 naturally these points of view are not independent of 

 one another, but are only so separated for convenience 

 of study. 



In the first place, we know that the plant derives 

 certain substances necessary to its development from 

 the soil: nitrogen and all the ash constituents reach 

 the plant in this manner. We have, therefore, to 

 investigate the proportions in which these constituents 

 are present in the soil, the state of combination in 

 which they may respectively exist, and the variations 

 in these factors normally exhibited by typical soils, 

 all of which questions may be described under the 

 head of chemical analysis. Further investigations of a 



