40 BULLETIN 699, TJ. S. DEPAETMENT OF AGEICULTURE. 



series of plots and the results of two years on another series have 

 been thus far reported, so they are not repeated in detail. 



Two experiment jfields have been established at Urbana ^ to test out 

 the fertilizer value of raw rock phosphate in both grain and live- 

 stock farming systems. One field is on what is known as the " North 

 Farm " and one on the " South Farm." The soil of both fiields is 

 the typical brown silt loam prairie land of that region. 



The field on the North Farm was in three tracts, which after 20 years 

 or more of pasturing had grown corn in 1895, 1896, and 1897 (when 

 careful records were kept of the yields produced) and had then been 

 cropped with clover and grass on one tract, oats on another, and oats, 

 cowpeas, and corn on the third until 1901. The yields obtained in 

 this preliminary period are not reported in Soil Report No. 12. It 

 is probable, however, that the tracts were not at that time divided 

 into plots, so the relative natural fertility of the 10 plots into which 

 each series was divided for the subsequent experiment is not known. 



From 1902 up to the close of 1910 a three-year rotation of corn, 

 oats, and hay was followed, and in 1911 two more series of plots 

 were introduced and a four-year rotation of wheat, corn, oats, and 

 clover (or soy beans) was followed on four series of plots for five 

 years, while on the fifth series alfalfa was grown for five years. 



From 19D2 to 1908, inclusive, phosphate was applied annually as 

 steamed bone meal at the rate of 200 pounds per acre, but since 1908 

 one-half of each phosphate plot has been treated with ground raw 

 rock at the rate of 600 pounds per acre per annum — the practice 

 being to add and plow under at one time enough for one complete 

 rotation. Potash was applied at the annual rate of 100 pounds of 

 potassium sulphate per acre. 



In the following table only the average results obtained since the 

 introduction of the phosphate-rock treatments (seven years) are 

 given : 



1 lU. Agr. Expt. Sta., Soil Kept. No. 14, pp. 7-16, October (1916). 



