June is, 1925 Effect of Crops onYields of Succeeding Crops in Rotation 1119 
Table VIII.— Summary of results with small grains in Fields II and III for the 
years 1915 to 1923, inclusive, showing the comparative effects of tobacco, pota¬ 
toes, and corn as preceding crops on the yields of wheat, oats, and rye under 
different fertilizer treatments; also, the effects of the fertilizer treatments on the 
yields of wheat, oats, and rye 
Fertilizer treat¬ 
ment 
Yield of wheat 
Yield of oats 
Yield of rye 
After 
to¬ 
bacco 
After 
pota¬ 
toes 
After 
corn 
Aver¬ 
age 
After 
to¬ 
bacco 
After 
pota¬ 
toes 
After 
corn 
Aver¬ 
age 
After 
to¬ 
bacco 
After 
pota¬ 
toes 
After 
corn 
Aver¬ 
age 
X (N+P)-_. 
X (N+K). 
14 (P+K)- 
H (N+P+K)— 
Average... 
Bush. 
14.4 
10.1 
12.0 
12.7 
Bush. 
14.1 
9.2 
13.9 
13.9 
Bush. 
9.5 
6.6 
9.0 
9.1 
Bush. 
12.7 
8.6 
11.6 
11.9 
Bush. 
21 
19.4 
15.7 
16.7 
Bush. 
24.2 
22.7 
18.8 
20.9 
Bush. 
16.1 
12.8 
12.9 
14.4 
Bush. 
18! 3 
15.8 
17.3 
Bush. 
15.8 
14.3 
11.3 
14.1 
Bush. 
19.8 
17.3 
16.7 
20.5 
Bush. 
13.2 
12.1 
12.6 
14.6 
Bush. 
16.3 
14.6 
13.5 
16.4 
12.3 
12.8 
8.6 
n.2 
18.2 
21.6 
14.1 
18.0 
13.9 
18.6 
13.1 
15.2 
Fertilizer treat¬ 
ment 
Yield of wheat straw 
Yield of oats straw 
Yield of rye straw 
(N+P)._. 
H (N+K).. 
X (P+K)- 
X (N+P+K)... 
Average... 
Lbs . 
1,648 
1,208 
1,235 
1,427 
Lbs. 
1,765 
1,207 
1,611 
1,639 
Lbs. 
753 
930 
1,018 
Lbs. 
1,484 
1,056 
1,259 
1,361 
Lbs. 
855 
858 
726 
778 
Lbs. 
1,069 
971 
814 
912 
Lbs. 
751 
580 
551 
631 
Lbs. 
803 
697 
774 
Lbs. 
2,061 
1,731 
1,552 
1,725 
Lbs. 
2,597 
2,191 
2,357 
2,651 
Lbs. 
1,551 
1,398 
1,371 
1,819 
Lbs. 
2,070 
1,773 
1,760 
2,065 
1,379 
1,555 
935 
1,290 
804 
942 
628 
791 
1,768 
2,449 
1,535 
1,917 
while with potatoes and corn as pre¬ 
ceding crops nitrogen and phosphorus 
seem to be of about equal importance. 
In general, the differences in yield under 
the different fertilizer treatments are 
not as great as might be expected. 
Summarizing, it appears that corn, 
in comparison with tobacco and pota¬ 
toes, has a depressing effect on the 
yields of wheat, oats, and rye. Com¬ 
pared with tobacco, corn shows the 
greatest depressing action on wheat 
and the least on rye. Compared with 
potatoes, corn reduces the yields of 
wheat, oats, and rye about the same 
extent. After tobacco the yield of 
wheat is about the same as after 
otatoes, the yield of oats is reduced 
;ss than 20 per cent, while the yield 
of rye is reduced by about a third. 
These crop effects are not greatly 
modified by the different fertilizer 
treatments used. Why the effects of 
tobacco more nearly resemble those 
of potatoes rather than those of corn 
is not clear from the standpoint of 
the plant-food theory. 
The comparative effects of tobacco, 
potatoes, and corn on each of the small 
grains for each year as well as the 
general trend of these crop effects are 
shown graphically in Figures 7, 8, and 
9. The yields shown are the combined 
weights of grain and straw, and are the 
averages of all fertilizer treatments. 
For the most part there is a notable 
similarity in yields of wheat after 
tobacco and after potatoes, but in cer¬ 
tain years production is much greater 
after potatoes than after tobacco. On 
the other hand, with a single exception, 
the relative growth of wheat after corn 
is decidedly reduced each year, and in 
some years the differences are very 
large. In the earlier years of the test, 
oats usually gave considerably better 
results after potatoes than after the 
other two crops, and the yields after 
tobacco and corn were about the same, 
except in 1915. In recent years, how¬ 
ever, yields after tobacco have more 
nearly equaled those after potatoes. 
Throughout the test, the growth of 
rye after tobacco has been closely 
similar though somewhat superior to 
that after corn. Potatoes as a preced¬ 
ing crop greatly stimulated the growth 
of rye at first, but in later years this 
advantage has not been maintained. 
It is of interest to note that there has 
been no progressive decline in yields of 
any of the small grains, even after 
corn. 
The average results with tobacco, 
potatoes, and corn after the three 
small grains on Fields II and III are 
summarized in Table IX. The aver¬ 
age yields of tobacco on corresponding 
control plots of the two fields indicate 
comparative uniformity in productive¬ 
ness of the three cropping units of the 
tobacco sections, while in the potato 
and corn sections the cropping units 
occupied by wheat seem to be some- 
