40 BULLETIN 699, U. S. DEPARTMENT OF AGRICULTURE. 
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 fields 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 fields 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 1902 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 appled 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 Ae phosphate-rock treatments (seven years) are 
given: 
2Tll. Agr. Expt. Sta., Soil Rept. No. 14, pp. 7-16, October (1916). 
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