856 
Journal of Agricultural Research 
Vol. V, No. 18 
expedient to assemble the data obtained up to the present time and to 
offer them as a preliminary contribution along this line. The fact that 
many of the data are rather positive in nature has been an added reason 
for presenting them at this time. Portions of the results have been 
published in other connections, while others have not previously been 
reported, but in either case average results only are included here. 
FIELD SOILS STUDIED 
Three series of field plots have been used in this work, one consisting 
of 14 plots one«tenth of an acre in size, located on a uniform soil in the 
Wisconsin drift-soil area, and classed by the United States Bureau of 
Soils as Carrington loam. 
Prior to 1907 it had been under a regular 4-year rotation and had 
been subjected to no special treatment of any kind. In that year the 
plots were differentiated according to the following plan: 
Plot No. Treatment. 
601.Continuous com. 
602^ 
^ |.2-year rotation: Com and oats. 
604) 
605!.3-year rotation: Com, oats, and clover, 
606 J 
607^ r2-year rotation: Com and oats, clover plowed under after the 
608/. \ oats. 
609'! j'2-year rotation: Com and oats, cowpeas plowed underafter 
610J.\ the oats. 
901 1 f2-year rotation: Com and oats, rye plowed under after the 
902/.I oats. 
903 .Continuous clover. 
904 .4-year rotation: Com, oats, and clover. 
The first tests of these soils were carried out in 1911, the fourth year 
of the special treatment. Results were secured also in 1912 and 1913, 
only a few data being obtained in the latter year owing to the pressure 
of other work, but the ammonification studies were complete. During 
each season only those plots under corn were examined, as the effects of 
previous treatment could, of course, hardly be studied on plots under 
different crops, and furthermore it would be evidently impossible to 
compare the crop yields on the various plots if the same crop were not 
grown. Different plots in this series were thus examined in the different 
years, but in each case the same treatments were included in the study. 
The second series of plots consisted of 5 one-tenth-acre plots on the 
same soil area and on the same soil types as the previous series. In the 
fall of 1910 these plots were subjected to the special treatments indicated 
below: 
Plot No. Treatment. 
1004 ...Check. 
1005 . 8 tons of manure per acre. 
1006 .^2 tons of manure per acre. 
1007 ...16 tons of manure per acre. 
1008 ...20 tons of manure per acre. 
