June is, 1925 Effect of Crops on Yields of Succeeding Crops in Rotation 1111 
stone was applied to all plots in 1918 
or 1919, and in 1922 a mixture of 2 
tons calcite limestone and 1,000 pounds 
dolomitic limestone containing up¬ 
wards of 20 per cent magnesium car¬ 
bonate was applied. Beginning with 
1922 sufficient land plaster to furnish 
the equivalent of the S0 3 content of 
the sulphate of potash has been ap¬ 
plied to the plots which receive no 
potash. By increasing the size of the 
cropping units the number of fertilizer 
treatments may be increased. In 
later experiments, undertaken in other 
tobacco-growing sections, plots have 
been added to include a lime test and 
the effects of doubling the normal 
rate of the complete application and 
of omitting all fertilizer. The size of 
the present fertilizer plots is approxi¬ 
mately one-fortieth acre. 
the indicator crops on the control plots 
may be somewhat affected by the crops 
of neighboring plots. For these rea¬ 
sons the control plots have not given 
uniformly satisfactory evidence of rel¬ 
ative productiveness in all cases, but 
for the most part the data are reason¬ 
ably consistent. In the years 1916 and 
1917 the complete fertilizer was applied 
at the normal rate to the cropping con¬ 
trol plots on those fields which were 
occupied by the hoed crops, but no 
fertilizer has since been applied to the 
control plots. 
TOBACCO, POTATOES, AND CORN IN CON¬ 
TINUOUS CULTURE AND IN ROTATION 
This test, which was begun in 1916, 
requires only a single field. This is 
designated as Field I. The location 
CONTROL PLOTS 
In order that information may be 
had as to the comparative productive¬ 
ness of different parts of the experi¬ 
mental fields, each cropping unit con¬ 
tains a “cropping control plot,” which 
constitutes the middle plot of the unit. 
These control plots, of course, are 
cropped uniformly, tobacco and wheat 
having been used thus far as indicator 
crops, though it is now proposed to 
substitute corn for tobacco. If suffi¬ 
cient land were available, two control 
plots in each cropping unit would be 
desirable. It has been observed that 
different indicator crops may give dif¬ 
ferent results as to relative productive¬ 
ness of different plots. Also, it appears 
that under the conditions of the tests 
and general plan of the field and the 
characteristics of the soil are shown on 
the soil map and accompanying report. 
The dimensions of the plots and inter¬ 
vening spaces, the fertilizer treatments 
and the cropping plan are shown in 
Figure 4. 
In 1916 tobacco was grown on Sec¬ 
tion A, early potatoes on Section B, 
and corn on Section C. In 1917 
tobacco was grown on Division I 
extending across the upper third of the 
three sections, potatoes were similarly 
grown on Division 2, and corn on 
Division 3. In 1918 the three crops 
were again grown on their respective 
sections, while in 1919 the boundaries 
of the crops again followed the boun¬ 
daries of the divisions, and so on. It 
will be observed that tobacco is grown 
