PREFACE ix 



merits; and if the conclusions I have drawn do not 

 always square with popular opinion, I have none the 

 less set them out in the hope that other experimenters 

 would thereby be led to check or revise them. 

 Agricultural chemistry is still cumbered with a good 

 many a priori deductions resting upon a very slender 

 foundation — first approximations to the truth which fail 

 because they do not take all the factors into account ; 

 it is about many of these opinions that the Rothamsted 

 results suggest scepticism. 



The book is intended for farmers and for the 

 senior students and teachers in our agricultural schools. 

 I have therefore kept the language as non-technical 

 as possible, though some elementary knowledge of 

 chemistry has to be assumed. If sometimes, as in 

 Chapter X., I may seem to have gone rather far in 

 the discussion of theoretical questions, it is in pursuance 

 of my main idea that it is only by thinking about the 

 rationale of manuring we can arrive at right practice. 

 And as the book is intended for those who are using 

 or going to use fertilisers, I have not troubled to say 

 much about their manufacture, nor have I dealt at all 

 with their analysis : these are both technical matters 

 outside the business of the farmer. 



I have meant this to be a companion to my book, 

 The Soil ; they are both written for the same audience, 

 and on similar lines. I hope later to complete the series 

 by a third book, dealing with the chemistry of the grow- 

 ing plant. 



A good deal of the material in the book has already 

 been utilised and in part published in a course of 

 Cantor Lectures delivered before the Society of Arts 

 in 1906, and again in a course of lectures delivered 



