CROP ROTATION IN RELATION TO SOIL PRODUCTIVITY 
41 
Table 41.- 
-Relative value of rotation (R) and additive effects of conjoining rotation 
and the use of fertilizers, Urbana, III. 
Cultural conditions 
Average 
yield per 
acre 
Values of 
if and F 
Additive effects of ro- 
tation and use of 
fertilizers 
Relative 
value of 
R 
Sum of 
increases 
effected by 
rotation 
and use of 
fertilizer 
when 
practiced 
separatelv 
(r+/) 
Actual 
increase 
effected by 
conjoining 
rotation 
and use of 
fertilizers 
Bushels 
Rotation and use of fertilizers 67. 6 
Rotation without use of fertilizers 51.2 
Use of fertilizers without rotation. 32.6 
Bushel* Bushels 
35. 16. 4 
Per cent 
213.4 
Bushels Bushels 
37. <*4. 2 
Z2r 
£6 
These results indicate that, under 
the conditions of the Urbana experi- 
ments, crop rotation is three times as 
effective as the use of fertilizers in in- \\, 
creasing the yield of corn, over culti- J\> 60 
vation alone, when rotation and the £ 
use of fertilizers are practiced inde- ^ *^ 
pendently of each other: and when one f , 
practice is conjoined with the other. \*& 
rotation (R) is over twice as effective u 
as the use of fertilizers (F). And \j 
further, when rotation and the use of >!j 
fertilizers are conjoined, their com- 
bined effects are more than fully ad- 
ditive, as determined by the increase 
in yield over the check plot in contin- 
uous culture. 
The results obtained on the Urbana 
field are visualized in Figure 5. It is 
to be observed that the hachure show- 
ing the values for R and F overlap to 
the extent of 7.2 bushels, as indicated 
by the crosshatching. This measures 
the interactive effects of rotation and 
the use of fertilizer when these practices 
are combined, and it shows how much 
greater the increase effected by con- 
joining rotation and fertilization is 
than the sum of the gains resulting 
when rotation and the use of ferti- 
lizers are practiced separately. 
FLORENCE EXPERIMENTS WITH COTTON 
The South Carolina results herein 
considered are those obtained with 
wilt-resistant cotton (Dixie variety) on the rotation and contin- 
uous-culture plots of the Pee Dee^ Experiment Station located at 
/d? 
/<? 
I &*/// C&E0/7JE0 TO 
ceo/? e&z4T/c?// 
\0->?//V C&££>/TjE£> 
TO ^£jeT/£/Z££S 
Fig. 5. — Chart summarizing the results on 
corn at Urbana, 111., showing the average 
yield from cultivation alone, the increase 
effected when crop rotation or the use of 
fertilizers is combined with cultivation, 
and the increase effecred by the conjoint 
effects of rotation and the use of fertilizers 
