32 



BULLETIN 699, U. S. DEPARTMENT OF AGEICULTURE. 



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 

 withoiit the use of phosphate. 



Treatment. 



Rotation. 



Yield per acre. 



Corn. 



Oats. 



Clover. 





2-year, corn and oats 



Bushels. 

 34 

 54 

 70 



Bushels. 



■ 32 



47 



70 



Tons. 



Do . ...'. 



4-year, corn, corn, oats, and clover. . . 

 do 



1.5 



Phosphate rock, 1,000 pounds every 

 4 years. 



2 5 







The results given in Table IX indicate strongly that medium appli- 

 cations of raw rock phosphate were very effective on this particular 

 soil and farm. No field or plots were emploj^ed 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, Hosier, Pettit, and Eeadhumer ^ in 1911. 



A field of 10 acres located on a typical Middle Illinoisan 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 roclv 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. 



»ni. Agr. Expt. Sta.. Circular No. 149 (1011). 



«II1. Agr. Expt. Sta., Soil Kept. No. 4, pp. 7-9 (1912). 



