18 BULLETIN 1377, U. S. DEPARTMENT OF AGRICULTURE 
conjoined with fertilization under more comparable conditions 
remains a question. Nevertheless, the division of the third bar 
in the barley series illustrates the actual results obtained under 
the conditions of the experiment: Cultivation alone gave an 
average yield of 14.06 bushels; combining rotation with cultivation 
effected an increase of 7.75 bushels; and combining fertilization with 
cultivation and rotation resulted in an additional increase of 13.46 
bushels. This seems to be the more reasonable and practical inter- 
pretation of these results, especially since the conjoint action of rota- 
tion and fertilization effecting the total increase of 21.21 bushels 
over cultivation alone involves the fertilizer treatment made in rota- 
tion on the Agdell field and not the annual application made in 
continuous culture on the Hoos field. 
COLUMBIA EXPERIMENTS WITH WHEAT, CORN, AND OATS 
The long-continued experiments at Columbia, Mo., were begun 
in 1888 (11). Comparable yields suitable for this study begin with 
the year 1889 for wheat, 1890 for corn, 1891 for oats and 1896 for 
timothy. These experiments now include 39 one-fourteenth-acre 
plots, of which the following are herein considered : 
Six-year rotation, corn, oats, wheat, clover, timothy, and timothy: 
Plot 13, unfertilized. 
Plot 3, fertilized with chemical fertilizers. 
Plots 11, 12, 14, 19 and 20, fertilized with farm manure. 
Four-year rotation, corn, oats, wheat and clover: 
Plot 39, unfertilized. 
Plots 34, 35, 37 and 38, fertilized with farm manure. 
Three-year rotation, corn, wheat and clover: 
Plot 27, unfertilized. 
Plot 28, fertilized with farm manure. 
Two-year rotation, wheat and clover. 
Plot 33, unfertilized. 
Plots 31 and 32, fertilized with farm manure. 
Corn in continuous culture. 
Plot 17, unfertilized. 
Plot 18, fertilized with farm manure. 
Oats in continuous culture: 
Plot 16, unfertilized. 
Plot 15, fertilized with farm manure. 
Wheat in continuous culture: 
Plot 9, unfertilized. 
Plot 2, fertilized with chemical fertilizer. 
Plots 5, 10, 21, 24, 30 and 36, fertilized with farm manure. 
Timothy in continuous culture: 
Plot 23, unfertilized. 
Plot 22, fertilized with farm manure. 
As in case of the Rothamsted experiments, no provision has been 
made for a replication of the plots representing the different rotations. 
For this reason, unfortunately, the effectiveness of the four rotations 
can not be compared, since, for example, the average yield of corn 
in one rotation represents a different combination of seasonal effects 
than the average yield in another rotation. However, in all the 
systems of cropping the effect of rotation on crop yields may be com- 
pared with the effectiveness of the use of farm manure, and, in case 
of wheat in the 6-year rotation, with the use of a complete chemical 
fertilizer. 
