o2 BULLETIN 699, U. S. DEPARTMENT OF AGRICULTURE. 
In the early part of 1911 the Illinois station issued a circular by 
Hopkins and Mann.‘ In the first part Mann gives some results 
obtained with raw ground rock phosphates on his farm, the sub- 
divisions of which were fairly well-drained fields of 85 acres each. 
Prior to the experiment a 4-year rotation of corn, corn, oats, and 
clover had been conducted on most of the fields for 30 years. It is? 
not stated if the fields had received applications of lime or other 
fertilizers. Raw rock phosphate was applied at the rate of 1,000 
pounds per acre every four years to the clover just before it was 
plowed under for the succeeding corn crop. The soil of this farm 
is largely the brown silt loam of the Early Wisconsin glaciation, 
commonly called the black prairie land of the corn belt. 
The average results of five years’ work are given below in Table IX. 
TABLE IX.—Five-year average yields per acre of corn, oats, and clover with and 
without the use of phosphate. 
Yield per acre. 
Treatment. Rotation. 
Corn. Oats. Clover. 
Bushels. | Bushels. Tons. 
INO Rann: oso esbonBoonosccouns 2-year, corn and oats...............- 34 BI lis ns cheen ere 
1S oye Rae oe Es 2 iad Seas DLA Ie Ss SS 4-year, corn, corn, oats, and clover... 54 47 1.5 
Phosphate rock, 1,000 pounds every |..-..- dO. ceeeee oak. cosa one mers eee 70 | 7 2.5 
4 years. 
The results given in Table LX indicate strongly that medium appli- 
cations of raw rock phosphate were very effective on this particular 
soil and farm. No field or plots were employed in this experiment, 
however, on which acid phosphate was applied, so a comparison of 
the relative merits of the two forms of phosphoric acid is not possible. 
In this same circular Hopkins reviews the field work of the Illinois 
Experiment Station, but gives no detailed results obtained from the 
use of raw rock phosphate. 
The results of seven years’ work with raw rock phosphate on the 
Auburn experiment field, Sangamon County, were published by Hop- 
kins, Mosier, Pettit, and Readhumer? in 1911. 
A field of 10 acres located on a typical Middle Ulnoisan brown 
silt loam was selected for this experiment. The previous history of 
the land, however, is not given, nor are any data presented showing 
the uniformity of the field. Two series of plots were employed, each 
series containing eight plots, four of which received raw rock phos- 
phate and four no phosphate. A four-year rotation of corn, corn, 
oats, and clover was followed, corn being represented every year and 
oats and clover in alternate years. 
1Tll. Agr. Expt. Sta., Circular No. 149 (1911). 
2]ll. Agr. Expt. Sta., Soil Rept. No. 4, pp. T-9 (1912), 
