June 15,1925 Effect of Crops on Yields of Succeeding Crops in Rotation 1125 
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Fig. 12 .— Effects of cowpeas, soy beans, and grass as soiling crops on the 
average yield of tobacco in the rotations with wheat, oats, and rye. For the 
comparatively short period covered, cowpeas show a favorable, though 
variable, effect on the growth of tobacco. Soy beans, on the other hand, 
have failed from the outset to produce decided increase in growth and in 
some years they have actually depressed the yield. Grass as a cover crop 
has caused a marked downward trend in the tobacco yield 
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Fig. 13.—Effects of soy beans and grass as soiling crops on the average yield of 
potatoes in the rotations with wheat, oats, and rye. The results are similar 
to those with tobacco, as shown in Figure 12. Soy beans in the beginning 
showed a beneficial effect on potatoes, but in later years the effect has 
been either nil or injurious. Grass as a cover crop has resulted in a decided 
downward trend in yield of potatoes 
Fig. 14.—Comparative effects of wheat, oats, and rye on the corn crop when 
intervening soiling crops are included in the rotations. There is a notable 
similarity in the effects of the three small grains, although, on the whole, 
wheat appears to exert a somewhat more favorable action than oats or rye. 
The upward trend in yield since 1918 is considered due to the action of the 
soiling crops. This result differs from the results with tobacco and potatoes 
shown in part in Figures 12 and 13. The yields of corn are the combined 
weights of grain and straw 
