xii AUTHOR'S PREFACE 



the discussions which took place during his annual visits to the various 

 experimental centres many helpful suggestions came. 



For the method of estimating nitrates I am indebted to Mr D. J. 

 Matthews, till recently of the Rothamsted Experimental Station, and, 

 for the nitrate determinations, to my former colleague, Mr R. G. 

 Baskett. For the bacterial counts in Tables XLV and XL VI I am 

 indebted to Mr James Bryce, B.Sc. ; for the mechanical analyses in 

 Table XXXIX to my former colleague Capt. H. H. Nicholson, M.A. 

 (Cantab.) ; for the rainfall data to Mr Carle Salter, the Superintendent 

 of the British Rainfall organization, and for the illustrations of Nauru 

 and Ocean Islands to Mr A. F. Ellis, the Commissioner for New Zealand 

 on the Board of the British Phosphate Commissioners. 



I should also like to record my thanks to Messrs B. Smith, N. F. 

 Miles, T. Wood, C. L. Petheybridge and A. Freshwater, on whose 

 farms the more important of the field trials were laid down, for the 

 care they have taken of the plots and for the ready help they have 

 given through the whole period of the trials. 



Finally, I have to express my keen appreciation of the kindness of 

 the Agricultural Education Committee of the Essex County Council, 

 who provided unique facilities for the work and gave me a free hand 

 in the carrying of it out. To the generosity of the members of this 

 Committee is due, in no small measure, the opportunity of submitting 

 this book to all who are interested in the progress of Agriculture. 



G. S. R. 



THE QUEEN'S UNIVERSITY OF BELFAST, 

 January, 1922. 



