1126 
Journal of Agricultural Research 
Vol. XXX, No. 12 
In the case of potatoes, the results 
generally are similar to those with to¬ 
bacco except that, as compared with 
wheat, oats as well as rye have a de¬ 
pressing effect on yields. Vetch, crim¬ 
son clover, and cowpeas are of little 
value in increasing the yields of 
potatoes when either oats or rye is the 
preceding crop. Soy beans have failed 
to increase yields even with wheat as 
the preceding crop. Grass has greatly 
depressed the potato yields in all cases. 
The effects of soy beans and grass on 
the yields of potatoes are shown graphi¬ 
cally in Figure 13. There are no sig¬ 
nificant general differences in yields of 
corn with wheat, oats, and rye as pre¬ 
ceding crops, and legumes generally 
are effective in increasing the yield. 
The similarity in effects of the three 
small grains are shown in graphic form 
in Figure 14. Soy beans give almost 
as good results as the other legumes. 
Grass depresses yield, but to a lesser 
extent than is the case with tobacco 
and potatoes. 
Some of these results are difficult to 
interpret. As in the preceding tests, 
in which no soil-improving crops were 
used, tobacco behaves more like pota¬ 
toes than corn in its response to the 
influence of preceding crops. Why 
intervening leguminous crops intensify 
rather than dissipate the differences in 
effects of wheat, oats, and rye as pre¬ 
ceding crops is not clear. Judged by 
the older tests previously discussed, 
the initial increases in yields of tobacco 
resulting from the addition of legumes 
to the rotation may be expected to be 
followed by declining yields. The de¬ 
pressing effect of vetch on the growth 
of tobacco, in fact, is plainly indicated 
in the crop of 1924. One of the sur¬ 
prising results is the inability of tobacco 
and potatoes to effectively utilize the 
nitrogen supplied by soy beans. Corn 
apparently appropriates the nitrogen 
from the soy beans almost, if not quite, 
as readily as that from other legumes. 
It seems possible that the unfavor¬ 
able effect of grass on the hoed crops 
is due in part to some factor other than 
those concerned in the preceding crop 
effects, for this effect extends to all of 
the three hoed crops. Each of these 
crops following grass has shown a yel¬ 
lowish-green color suggestive of nitro¬ 
gen hunger, and it is possible that this 
is one of the important factors involved. 
Bizzell (2) has investigated this phase 
of the effect of crops on those following 
in the rotation. It has been observed, 
also, that liming partially overcomes 
the unfavorable effect of grass. Inter¬ 
ference with the nitrogen supply, how¬ 
ever, is not the only way in which 
grass may depress the growth of to¬ 
bacco. It has been the experience of 
growers in the Connecticut Valley that 
tobacco frequently makes very poor 
growth for the first year or two follow¬ 
ing timothy sod, even though heavy 
applications of nitrogenous fertilizers 
are made. The part played by the 
grass here may be similar to that of 
the legumes. 
It remains to consider the effects of 
introducing the soiling crops into the 
rotation on the small grains following 
after the hoed crops. The data are 
summarized in Table XIII. 
Table XIII. —Summary of results with small grains on Fields IV and V for the 
years 1917-1923, inclusive, showing the comparative effects of tobacco, potatoes, 
and corn as preceding crops on the yields of wheat, oats, and rye, when soiling 
crops are included in the rotation ; also the residual effects of the soiling crops on 
the yields of wheat, oats, and rye 
Soiling crop 
grown 
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 
i After 
to¬ 
bacco 
After 
pota¬ 
toes 
After 
! corn 
Aver¬ 
age 
Vetch_ 
Crimson clover.. 
Fallow_ 
Cowpeas. 
Soy beans_ 
Grass__ 
Bush. 
17.2 
16.9 
13.1 
15.5 
17.0 
13.3 
Bush. 
18.1 
18.6 
17.5 
21.0 
22.1 
18.3 
Bush. 
13.2 
13.2 
10.3 
13.0 
10.5 
9.1 
Bush. 
16.2 
16.2 
13.6 
16.5 
16.5 
13.6 
Bush. 
44.2 
42.6 
27.2 
42.6 
37.8 
27.6 
Bush. 
54.5 
53.4 
37.9 
48.2 
42.9 
32.2 
Bush. 
25.5 
23.3 
15.1 
18.6 
19.4 
14.8 
Bush. 
41.4 
39.8 
26.7 
36.5 
33.4 
25.2 
Bush. 
23.9 
18.5 
15.8 
18.2 
18.3 
i 17.3 
1 Bush. 
\ 28.3 
i 25.4 
21.7 
26.1 
22.4 
21.9 
! Bush. 
1 14.7 
12.1 
12.3 
15.6 
14.1 
13.3 
Bush. 
22.3 
18.7 
16.6 
20.0 
18.3 
17.5 
Average. _. 
15.5 
19.3 
11.6 
15.4 
37.0 
45.0 
19.5 
33.8 
| 18.7 
24.3 
13.7 
18.9 
Soiling crop 
grown 
Yield of wheat straw 
Yield of oats straw 
Yield of rye straw 
Vetch_ 
Crimson clover.. 
Fallow_ 
Cowpeas.... 
Soy beans_ 
Grass_ 
Lbs. 
1,972 
2,019 
1,306 
1, 809 
1,873 
1,399 
Lbs. 
2,358 1 
2,485 ! 
1,938 
2,714 ! 
2, 777 j 
2,285 ! 
Lbs. 
1,572 
1, 404 
966 
1, 329 
1,133 
837 
Lbs. 
1,967 
1,9710 
1,403 
1, 951 
1,927 
1,508 
Lbs. 
2,332 
1,886 
1,126 
1, 800 
1,766 
1,103 
Lbs. 
3, 237 
2,694 
1,631 
2,083 
1,806 i 
1,489 
Lbs. 
1,196 
829 
632 
780 ; 
690 
647 
Lbs. 
2,255 
1,803 
1,130 
1,554 
1,421 
1,080 
Lbs. 
2,980 
2,187 
1,806 
2,437 
2, 277 
2,047 
"2, 289 
Lbs. 
3,770 
3,382 
2,934 
3, 627 
3,138 
2,938 
Lbs. 
1,866 
1,311 
1,335 
1,876 
1, 653 
1, 543 
Lbs. 
2,872 
2,293 
2,025 
2, 647 
2,356 
2,176 
Average... 
1, 730 
2,426 i 1,207 
1,788 
1, 660“ 
2,157 796 | 
1,541 
3, 298 
1, 597 
2,395 
