44 
BULLETIN 1377, U. S. DEPARTMENT OF AGRICULTURE 
Table 45. — Relative value of rotation (R) and additive effects of conjoining rotation 
and the use of fertilizers 
Average 
yield of 
seed cot- 
ton per 
acre 
Values of 
R and F 
Relative 
value of 
R 
Additive effects of ro- 
tation and use of 
fertilizers 
Cultural conditions 
P 
F 
Sum of 
increases 
effected by 
rotation 
and use of 
fertilizer 
when 
practiced 
separately 
(r+/) 
Actual 
increase 
effected by 
conjoining 
rotation 
and use of 
fertilizers 
Rotation and use of fertilizers. . 
Pounds 
1.880 
1,621 
1,816 
Pounds 
64 
Pounds 
259 
Per cent 
24.7 
Pounds 
795 
Pounds 
559 
Rotation without fertilizer. 
Use of fertilizer without rotation . 
These results with cotton obtained under the conditions of the , 
South Carolina experiments show that when crop rotation and the j 
use of fertilizers are practiced independently of each other, rotation | 
is 60.6 per cent as efficient as the use of fertilizers in effecting in- 
creases in the yield, as measured from the check plot in continuous 
culture. On the other hand, when rotation is conjoined with the 
use of fertilizers it is only about 25 per cent as efficient in effecting 
increases in the yield as the use of fertilizer when conjoined with 
rotation of crops. In other words, the value for R is only about 
one-fourth as great as the value for F. These results also show 
that the conjoint effects of rotation and the use of fertilizers on the 
yield of cotton are additive, though less than fully .additive. 
The chart in Figure 6 is a graphic summary of these South Caro- 
lina results on cotton, showing the average yield obtained from cul- 
tivation alone, the £ain resulting when to cultivation is added rota- 
tion or the use of chemical fertilizer, and the average gain obtained 
when to cultivation are added rotation and the use of fertilizer. 
In the third bar, the diagonal hachures represent the values for R 
and F. The unhachured space, representing an unallocated gain 
of 236 pounds, measures the interactive effects of rotation and the 
use of fertilizer when one practice is conjoined with the other; and 
it also shows how much less the increase effected by the conjoint 
action of rotation and fertilizers is than the sum of the gains effected 
by rotation and the use of fertilizers when practiced independently 
of each other. 
ROTATION AND FERTILIZER EFFICIENCIES AS AFFECTED BY SOIL 
REACTION 
With the exception of the Illinois results on corn, where the soil 
treatment consists of applications of ground limestone, manure, and 
phosphates, and the Rothamsted experiments, the experimental 
data presented in the foregoing tables have been obtained on soils 
that are somewhat acid in character. It is a fact universally recog- 
nized that, when the acidity of soils having from medium to strong 
degrees of acidity is reduced or corrected, the average yields of the 
crops in a rotation are usually increased, regardless of the fact that 
