EXPERIMENTAL WORK WITH RAW ROCK PHOSPHATE. 33 
_ While it is stated that raw rock phosphate was applied at the rate 
of 1 ton per acre at the beginning of the experiment, it is not clear 
if there were any subsequent applications during the remaining six 
vears of the experiment. No other commercial fertilizers were em- 
ployed in this test; therefore the data allows no comparison of the 
¥relative values of the different phosphates. 
All of the plots of this experiment field, with the exception of two, 
received applications of organic matter either in the form of crop 
residues or as farm manure. 
In Table X the results obtained on eight plots of each series are 
given. 
TABLE X.—Average yields per acre from two scries of plots, Auburn field 
(1905-1911). 
Corn, 7 Oats, 3 Clover, 2 
Treatment. crops. crops. crops. 
Bushels. Bushels. Tons. 
UAT EROCKUDHOSPMACCLA. ecicin ck cle w= «citi a Sala sie decisis Ubecke wbiccece ee al.9 45.3 2. 16 
HOR a4 2bo5 6 BS SS GHB GES SABA RABE SEH BE ASR SA pIN OE RAE IeESCrCre oe 46. 2 38. 2 1. 66 
EN CACC CAlIMOL RAWALOCKi os coc ces els oe cece ccssiaceeeesescece sac 5.7 deal | 0. 50 
In commenting on this experiment Hopkins and his coworkers 
state that “on the whole, the data from favorable seasons strongly 
indicate a cumulative or increasing effect from the phosphate treat- 
ment, as we have reason to expect and as is shown in the latest crops 
of corn, oats, and clover, the increase amounting to about 25 per 
cent for oats, 34 per cent for corn, and 48 per cent for clover.” 
Hopkins? also published a paper in 1912 entitled “Shall We Use 
Complete Commercial Fertilizers in the Corn Belt?” in which he 
quotes the work of the Indiana and Ohio Experiment Stations with 
a view to showing that complete mixed fertilizers are inferior and 
much more expensive than the simple phosphate carriers, and that 
raw ground rock is the most economic form of phosphoric acid. No 
data from the Illinois Experiment Station farms are contained in 
this circular. 
In 1913 Hopkins? published a paper entitled “ Bread from Stones,” 
which consists of a description of an impoverished farm in southern 
Tllinois which the author has made productive by the so-called h- 
nois system of permanent fertility. The particular tract considered 
in this paper is a 40-acre field which had been agriculturally aban- 
- doned for five years prior to the experiment. During the 10 years 
1J7ll. Agr. Expt. Sta., Circular No. 165 (1912). 
211). Agr. Expt. Sta., Circular No. 168 (1913). 
56841°—Bull. 6993—18—-3 
