CROP ROTATION IX RELATION TO SOIL PRODUCTIVITY 
39 
Table 37. — The effects of crop rotation and the use of fertilizers on the yields of 
tobacco, Germantown, Ohio 
[Rotation and use of fertilizers practiced separately] 
Relative 
value of 
crop rota- 
Increase 
tions, as 
Average 
over check 
compared 
Plot NO. 
Cultural conditions 
yield per 
plot in 
with ferti- 
acre 
continuous 
culture 
lizers, in 
effecting 
increases 
over culti- 
vation alone 
Pounds 
Pounds 
Per cent 
12 
Crop rotation without the use of chemical fertilizer (r) — 
524 
213 
28.3 
9 Use of chemical fertilizer without rotation (J) 
1,064 
753 
9 Without rotation and without the use of chemical fertilizer 
311 
512 
32 Crop rotation without the use of manure (r) 
177 
32.8 
875 
540 
1, 4, 7, 10 
Without rotation and without the use of manure 
335 
Note.— Because of the arrangement of the manured plots in continuous culture it seemed advisable to 
average the yields on plots 1, 4, 7, and 10 to obtain a check-plot yield in the manure series. 
Table 38. — Relative values of rotation (R) and additive effects of conjoining rotation 
and the use of fertilizers 
[Tobacco, Germantown, Ohio] 
Average 
yield per 
acre 
Values of R and F 
Relative 
value of 
R 
Additive effects of rota- 
tion and use of fertilizer 
Cultural conditions 
R 
F 
Sum of in- 
creases ef- 
fected by 
rotation 
and use of 
fertilizer 
when 
practiced 
separately 
(r+y) 
Actual 
increase 
effected by 
conjoining 
rotation 
and use of 
fertilizers 
Rotation and use of chemical fertilizer. 
Rotation and use of manure 
Pounds 
1,141 
993 
Pounds 
77 
118 
Pounds 
617 
481 
Per cent 
12.5 
24.5 
Pounds 
966 
717 
Pounds 
830 
658 
These results show that under the conditions of the Germantown 
test, the 3-year rotation of tobacco, wheat, and clover is only 28.3 
per cent as effective as the use of 840 pounds of a complete fertilizer 
per acre and only 32.8 per cent as effective as the use of 10 tons of 
manure when rotation and use of fertilizers are practiced independ- 
ently of each other, and only 12.5 per cent and 24.5 per cent as 
effective as the use of chemical fertilizer and manure, respectively, 
when the one practice is combined with the other. 
The combined effects of rotation and the use of chemical fertilizer 
or manure are somewhat less than fully additive; that is, in effecting 
increases in the yields of tobacco over the check plots in continuous 
culture. 
URBANA EXPERIMENTS WITH CORN 
The Morrow plots at Urbana, 111., furnish results on corn which 
may be given consideration in this study of the value of crop rotation. 
The Morrow field "consists of three plots divided into halves. On 
one corn is grown continuously, on the second corn and oats are 
