CROP ROTATION IN RELATION TO SOIL PRODUCTIVITY 
19 
The soil on which the Missouri experiments are conducted is des- 
ignated as Putnam silt loam. It is described as a dark brownish 
gray soil "9 to 12 inches deep, grading into a grayish subsurface 
layer 4 to 6 inches thick." Below this there is another gradation 
into a brown, heavy clay loam, rather impervious in character. At 
depths from 13 to 18 inches the soil is a yellowish-gray, silty clay 
loam, more friable than the layer above it. "The surface drainage 
is generally good. * * * The soil of the field is * * * fairly 
uniform in fertility." As a rule, Putnam silt loam is in need of lime 
(10, p. 5). The Missouri experimental results herein presented have 
been obtained on an unlimed soil. 
EXPERIMENTAL DATA 
Since, in these particular experiments, the different fertilizer treat- 
ments in continuous culture are the same as those in rotation, it 
seemed best, at the outset, to present in detail all the data on which 
this study of the Missouri experiments is based. The data are given 
in several tables, each table containing comparable yields of a partic- 
ular crop grown both in rotation and in continuous culture. In 
Table 8, for example, are given the yields of corn obtained on the 
unfertilized and manured plots for each year that it has been grown 
in the 6-year rotation, up to, and including, 1916. In the other 
portion of the same table are given the yields on similarly treated 
plots in continuous culture for each year that corn has been grown 
in the rotation. 
SIX-YEAR ROTATION AND CONTINUOUS CULTURE 
Table 8. — Comparable yields of corn in the 6-year rotation and in continuous 
culture, Missouri 
[Yields in bushels per acre) 
6-year rotation (corn, oats, wheat, clover, timothy, 
timothy) 
Continuous culture 
Year 
No fer- 
tilizer, 
plot 13 
Farm manure ' 
No fer- 
tilizer, 
plot 17 
Farm 
manure, 1 
plot 18 
Plot 11 
Plot 14 
Plot 20 
Average 
or 
summary 
1892 
25.7 
25.1 
85.4 
54.2 
39.4 
19.0 
37.9 
27.0 
37.9 
27.0 
78.7 
43.8 
52.3 
28.0 
42.1 
23.9 
29.5 
17.1 
1.9 
7.4 
51.4 
1898 
25.6 
1903 
78.7 
55.5 
1904 
43.8 
51.6 
13.4 
1910 
52,9 
6.5 
1916 
28.0 
14.6 
6-year average. 
41.5 
44.6 
20.3 
27.8 
1 The mean application of manure in all cases is 6.8 tons per acre annually, in both rotation and continu- 
ous culture. 
