54 
BULLETIN 1377, U. S. DEPARTMENT OF AGRICULTURE 
SUMMARY OF RELATIVE VALUES OF CROP ROTATION AND OF CON- 
JOINT EFFECTS OF ROTATION AND THE USE OF FERTILIZERS 
A summary of the results thus far considered is given in Table 51. 
In studying the content of this table the following points are to be 
kept in mind : (1) All evaluations for rotation and the use of fertilizers 
are based on the increases in yields over cultivation alone or check 
plot in continuous culture; (2) relative values for rotation are based 
on the effectiveness of chemical 
fertilizer or stable manure; (3) the 
relative values for rotation given in 
the upper half of the table are for 
small r — that is, the efficiency of 
rotation as measured in terms of the 
effectiveness of the use of fertilizers 
when practiced independently of 
each other; and (4) the relative val- 
ues for rotation given in the lower 
half of the table are for capital R — 
that is, the effectiveness of rotation 
when conjoined with the use of fer- 
tilizer as measured in terms of the 
effectiveness of the use of fertilizer 
when conjoined with rotation. 
The relative values for rotation 
are arranged in two subcolumns. 
In one are given the values ob- 
tained under acid-soil conditions, 
and in the other the results ob- 
tained under nonacid-soil condi- 
tions or where the soil reaction has 
been altered or changed by liming. 
In the last two subcolumns are 
given the figures showing the addi- 
tive effects of rotation and the use 
of fertilizers when conjoined. 
On the basis of the average results 
of these experiments, the following 
summarizing statements may be 
made: 
(1) Including all crops and all soils 
indicated, crop rotation without the 
use of fertilizers is 77.7 per cent as 
efficient as the use of fertilizers with- 
out rotation in effecting increases in 
crop yields over cultivation alone. 
(2) Crop rotation, when added 
to cultivation and the use of ferti- 
lizers, is about 73 per cent as efficient as the use of fertilizers when 
added to cultivation and rotation, in effecting increases in crop yields. 
(3) In general, crop rotation is practically 75 per cent as efficient 
as the use of fertilizer in effecting increases in crop yields as measured 
from the check-plot yields in continuous culture. 
3/ l z z 
^?//£> /=&/ZT/L/Z£&S 
) &sf/M C/2£0/T££> TO 
c/eo/O /2or>?T/c>/v 
I &>*/// C/Z£0/r£-£> TO 
Fig. 10. 
-Chart showing the effects of soil re- 
action on the efficiency of crop rotation and 
the use of chemical fertilizer, as indicated by 
the yields of cotton at Florence, 6. C. The 
plot numbers are indicated beneath the bars. 
L indicates the plots receiving lime. The 
unhachured space in each of the last two bars 
indicates the interactive effects of rotation 
and the use of fertilizer when one practice is 
conjoined with the other; and it shows also 
how much less the increase effected by the 
combined effects of rotation and fertilizers is 
than the sum of the gains resulting when 
rotation and the use of feritlizers are prac- 
ticed independently of each other. (Com- 
pare with data in Tables 49 and 50.) 
