UNITED STATES DEPARTMENT OF AGRICULTURE 
LLETIN No. 699 , 
Contribution .rom the Bureau of Soils a 
MILTON WHITNEY, Chiei 
Washington, D.C. Vv October 16, 1918 
ANALYSIS OF EXPERIMENTAL WORK WITH GROUND 
RAW ROCK PHOSPHATE AS A FERTILIZER. 
By W. H. WaccaMAN and C. R. WAGNER, Scientists in Investigation of Fertilizer 
Resources, assisted by R. F. GARDINER, Scientist in Soil Laboratory Investi- 
gations. 
CONTENTS. 
Page. | Page. 
TATOO HEHOMamacsccesccsssacesesaceaca= cc c= I) Resultsiofiexperimentss.c.scccsccesecceson ee 28 
ISNA Kd soe ddedonstsecekaeacoesneuoceueeoos 2 | Experience of farmers with raw rock phos- 
Theoretical considerations..............-.--- 3 phate!asia fertilizers 522-0 hs onsen 112 
Methods of studying the subject............. Och) Summarys sos: Gs osc eeweaceaniags sneer 115 
WaApOraLOby WOEKs. 2c 2--e0cce-ss0ce~ = DE | A CONCIUSIONS  oaccssaccsccssaacccccoce adeeeaes 120 
Pot and greenhouse work...........--.-- 17 
bie lGlexperimMentS soc cesecensc-ssccccscce 18 
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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