CROP ROTATION IN RELATION TO SOIL PRODUCTIVITY 
15 
Table 6. — Effects of crop rotation and the use of fertilizers on the yields of wheat 
and barley at Rothamsted 
[Rotation and fertilization practiced separately] 
Crop and cultural conditions 
Relative 
value of 
Increase 
crop rota- 
Average 
over check 
tion as com- 
yield per 
plot in con- 
pared with 
acre 
tinuous 
fertilizer in 
culture (c) 
effecting 
larger 
1 yields J 
Bushels 
Bushels 
Per cent 
24.05 
11.72 
104.2 
23.58 
11.25 
7.75 
21.81 
27.8 
41.89 
27.83 
Wheat: 
Rotation without fertilization (r) * 
Use of fertilizer without rotation (/) 3 . 
Barley: 
Rotation without fertilization (r) 
Use of fertilizer without rotation (/) — . 
1 Relative value of rotation obtained by dividing the increase from rotation (r) by the increase from the 
use of fertilizer (/). 
* Small r indicates the effect of rotation when practiced independently of fertilization. 
» Small / indicates the effect of fertilization when practiced in the absence of rotation. 
It is to be observed that, in case of wheat, crop rotation without 
fertilization is 104.2 per cent as efficient as the use of chemical fer- 
tilizer without rotation in effecting increases over the check plot in 
-continuous culture; whereas in case of barley, rotation is only 27.8 
per cent as effective as the chemical fertilizer. 
In Table 7 are shown the conjoint effects of crop rotation and the 
use of fertilizer. Under the caption heading of the fourth column 
are given the values of rotation (R) and the use of fertilizer (F). 
Capital R represents the average increase in crop yield that was 
effected by adding rotation to cultivation and the use of fertilizer, 
as derived from the formula cfr — cf; and capital F represents the 
average increase that resulted when to cultivation and rotation was 
conjoined the use of fertilizer, as derived from the formula cfr — cr. 
In the fifth column are given the relative values for R, as obtained 
in each case by dividing the absolute value for R by the absolute 
value for F. 
In the last two subcolumns are compared the sum of the increases 
effected by rotation and fertilization when practiced independently 
of each other and the actual increase effected when the two practices 
are combined. 
Table 7. — Relative values of rotation and additive effects of rotation and the use of 
fertilizers when the two practices are combined 
[Rothamsted, results of 72 years] 
Cultural conditions 
Average 
yield 
per acre 
Values of R 
and.Fi 
Additive effects of 
rotation and fer- 
tilization 
Crop 
R 
F 
Relative 
value 
of R ^ 
Sum of 
increases 
effected 
by rota- 
tion and 
fertiliza- 
tion w hen 
practiced 
separate- 
ly (r+f) 
Actual 
increase 
effected 
by con- 
joining 
rotation 
and fer- 
tiliza- 
tion 
Wheat 
Barley 
Rotation and use of fertilizer. 
do 
Bushels 
32.49 
35.27 
Bushels 
8.91 
-6.62 
Bushels 
8.44 
13.46 
Per cent 
105.6 
-49.2 
Bushels 
22.97 
35 58 
Bushels 
20.16 
21.21 
1 Capital R indicates increase effected by adding rotation to fertilization. Capital F indicates increase 
effected by adding fertilization to rotation. 
» Relative value of R as R:F, or R+F. 
