AUTHOR'S PREFACE 



-L HE main purpose of this book is to put on record the results of the 

 field experiments with rock phosphates and open hearth basic slags 

 conducted in Essex during the period 1915-20. 



The field trials have been confined to grass land, and the results 

 have been measured by increases in the weight of the hay crop, and 

 by the improvement in the quality of the crop, as determined by 

 botanical analyses. This plan has been adopted for two reasons : first, 

 because it is on grass that the primary and secondary actions of 

 phosphates are most apparent, and most readily measured ; secondly, 

 because on permanent grass, in Essex at any rate, the issue is not 

 complicated by previous applications of artificial manures, and it is 

 therefore easier to follow out the experiment year by year than under 

 arable conditions. 



The objection may be raised that increased weights of hay do not 

 give a true test of the improvement which has taken place, and that 

 such a test can only be obtained through the medium of the animal. 

 While there is much to be said in favour of this contention, it may be 

 safely assumed that, when botanical analysis shows the quality of the 

 herbage is similar, the increased weights of hay bear a definite relation- 

 ship to the live-weight gains, and do afford a satisfactory method of 

 comparing the efficiency of the various phosphates. Moreover, it must 

 be remembered that hay is an important crop, and in Essex, as else- 

 where, it is the prevalent custom to graze and mow the permanent 

 grass in alternate years. 



The Essex results with ground rock phosphates indicate that there 

 are soil conditions under which these types of phosphates may be 

 expected to give as good and as quick results as the more soluble 

 types of phosphatic fertilisers. It is equally clear, however, that under 

 other conditions the advantage is decidedly in favour of the more 

 soluble types. Experiments in progress in the North of Ireland on 

 the turnip crop strikingly bear out this conclusion, and it would seem 

 probable that an explanation of the different results secured elsewhere 

 might be obtained by means of an examination of soil and climatic 

 conditions. 



I have to acknowledge my indebtedness to Dr E. J. Russell, F.R.S., 

 for the great interest he has taken in the work here described. From 



