PREFACE TO THE SECOND EDITION 



IN this edition I have carried on the tables for a further 

 decade, and made the necessary alterations in the text. Some 

 of the deductions drawn in the first edition have required 

 modification, but no great change has been made : the picture 

 is essentially as Mr Hall painted it. Two new chapters have 

 been added : one by Mr Hall, on the secondary effects of 

 manures on the soil, gives a connected account of the important 

 investigations he carried out here on this very difficult and 

 important subject. The other chapter, by myself, contains a 

 summary of the investigations made during the past ten years, 

 and still continuing, on the biochemical processes in the 

 soil. 



I hope when conditions become more normal that it will 

 be possible to arrange for a proper statistical survey of the 

 mass of valuable data accumulated at Kothamsted. The 

 greatest pains are taken to ensure the reliability of the data, 

 and I cannot help thinking that the application to them of 

 modern statistical methods would yield information of high 

 value both to the man of science and to the practical agri- 

 culturist. We have not yet learnt anything like all the 

 lessons the Kothamsted fields can teach us. 



E. J. R. 



HARPENDEN, 1917. 



