UNITED STATES DEPARTMENT OF AGRICULTURE 



BULLETIN No. 699 



Contribution .rom the Bureau of Soils 

 MILTON WHITNEY, Chiei" 



Washington, D. C. 



October 16, 1918 



ANALYSIS OF EXPERIMENTAL WORK WITH GROUND 

 RAW ROCK PHOSPHATE AS A FERTILIZER. 



By W. H. Waggaman and C. R. Wagnee, Scientists in Investigation of Fertiliser 

 Resources, assisted by R. F. Gakdineb, Scientist in Soil Laboratory Investir 

 gations. 



CONTENTS. 



Introduction 1 



History 2 



Theoretical considerations 3 



Methods of studying the subject 5 



Laboratory work 5 



Pot and greenhouse work 17 



Field experiments 18 



Results of experiments 28 



Experience of farmers with raw rock phos- 

 phate as a fertilizer 112 



Summary 115 



Conclusions 120 



INTRODUCTION. 



Much doubt and difference of .opinion exists concerning the ferti- 

 lizer value of ground raw rock phosphate. Some agronomists and 

 agricultural chemists have reported satisfactory results from its use 

 both in pot and field experiments, others have decided that while 

 the material is beneficial to a number of crops when applied under 

 certain conditions, it is so inferior to acid phosphate that it is unwise, 

 under normal conditions, to depend upon it as a source of phosphoric 

 acid when one can obtain the more soluble superphosphate. Several 

 experiment stations have concluded that ground raw rock phosphate 

 is entirely unprofitable on most of the soils in their particular States 

 under their present crop systems. 



The use of ground raw rock phosphate directly as a fertilizer, how- 

 ever, has slowly increased during the last decade until now the annual 

 consumption is in excess of 91,000 tons, involving an expenditure by 

 the farmer of over $750,000 annually. 



Most of the demand has been in the corn belt of the middle West- 

 ern States, particularly in Illinois, where the State Agricultural 

 Experiment Station has strongly recommended this material and out- 



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