June is, 1925 Effect of Crops onYields of Succeeding Crops in Rotation 1113 
Table V. — Summary of results with tobacco, potatoes, and corn on Field I for the 
years 1916-1922, inclusive, showing the comparative effects of each crop on yields of 
succeeding crops of tobacco, potatoes, and corn under different fertilizer treatments 
Fertilizer treatment 
Yield of tobacco leaf 
Yield of potatoes 
Yield of corn 
After 
b tc 
After 
tatoes 
After 
Aver¬ 
age 
After 
to¬ 
bacco 
After 
po¬ 
tatoes 
After 
com 
Aver¬ 
age 
After 
to¬ 
bacco 
After 
po¬ 
tatoes 
After 
corn 
Aver¬ 
age 
Lbs. 
Lbs. 
Lbs. 
Lbs. 
Bush. 
Bush. 
Bush. 
Bush. 
Bush. 
Bush. 
Bush. 
Bush. 
M(N+P).. 
825 
1,006 
868 
900 
64.1 
54.8 
37.8 
,52.2 
49.1 
50.2 
33.8 
44.3 
J4(N+K). 
804 
923 
60.3 
48.9 
37.8 
49 
53.7 
49.5 
41.5 
48.2 
M(P+K). 
904 
937 
960 
933 
48.3 
34 
47.1 
49.6 
46.5 
42.3 
46.1 
HCN+P+K). 
1,099 
1,118 
1,196 
1,138 
76.1 
57.4 
43.1 
58.9 
53.1 
51.8 
48.1 
51 
Average. 
908 
996 
969 
958 
64.9 
52.4 
38.2 
51.8 
51.4 
49.5 
41.4 
47.4 
Fertilizer treatment 
Yield of tobacco stalks 
Yield of corn stover 
After 
tobacco 
After 
potatoes 
After 
com 
Average 
After 
tobacco 
After 
potatoes 
After 
corn 
Average 
M(N+P).. 
M(N+K). 
H(P+K>- 
H(N+P+K).. 
Average. 
Pounds 
428 
376 
492 
658 
Pounds • 
574 | 
486 
556 ! 
742 
Pounds 
528 
448 
568 
768 
Pounds 
510 
437 
539 
723 
Pounds 
3.282 
3.283 
3,437 
3,560 
Pounds 
3,290 
3,317 
3,160 
3,613 
Pounds 
2,757 
2,903 
2,913 
3,302 
Pounds 
3,110 
3,168 
3,170 
3,492 
489 
590 
578 
552 
3,391 
3,345 
2,969 
3,235 
883, and 905 pounds, indicating close 
agreement in productivity of the plots 
involved. It appears, therefore, that 
taking the average of all fertilizer 
treatments, continuous tobacco culture 
gives somewhat reduced yields as 
compared with tobacco after potatoes 
and after corn. As a matter of fact, 
there has been a progressive decrease 
in yield of tobacco under the continu¬ 
ous culture system, while good yields 
were obtained in the early years, so 
that the average result does not fully 
portray the situation. It is surprising 
that there is no substantial difference in 
yields of tobacco after potatoes and 
after corn. From the standpoint of 
parasitic disease as a factor, it will 
be recalled that tobacco and potatoes 
belong to the same family. From 
the standpoint of nutrition require¬ 
ments, the corn crop removes much 
larger quantities of plant nutrients 
from the soil than does the potato 
crop. The omission of either nitrogen, 
phosphorus, or potassium from the 
fertilizer has materially reduced the 
yield, the omission of phosphorus 
having the greatest effect, and of 
nitrogen the least (pi. 5). The fertil¬ 
izer effect has been greater than the 
crop effect, but the former does not 
overcome the latter. In view of the 
definite response to even the com¬ 
paratively small additions of fertilizers 
made here, it is not clear why the 
potato crop does not produce a decided 
increase in yield of tobacco as com¬ 
pared with the effect of the corn crop. 
It may be added that for 1924, with a 
very wet spring, the growth of tobacco 
after com has been very poor as com¬ 
pared with the growth after potatoes 
and after tobacco itself, especially 
where a complete fertilizer is not used. 
It may be, therefore, that earlier 
results will soon be reversed. 
The yields of potatoes have been 
quite small, but some interesting dif¬ 
ferences have been obtained. Recall¬ 
ing the relationships between tobacco, 
potatoes, and corn as bearing on plant- 
disease factors and on comparative 
withdrawal of plant nutrients from the 
soil, it will be seen that the yield of 
potatoes is considerably better after 
tobacco than when potatoes are the 
preceding crop. On the other hand, 
continuous culture gives decidedly 
better yields than are obtained after 
corn. Moreover, the yield after to¬ 
bacco is almost double that after 
corn. In this instance fertilizers ap¬ 
parently have not greatly influenced 
the result, the crop effects being much 
greater than the fertilizer effects. In 
continuous culture the tubers are 
severely affected with scab while there 
is little evidence of the disease after 
tobacco and corn. The average yields 
of tobacco on the control plots for pota¬ 
toes in continuous culture and in rota¬ 
tion with tobacco and with corn are, 
respectively, 921, 883, and 868 pounds 
