June 15, 
Effect of Crops on Yields of Succeeding Crops in Rotation 1131 
tobacco plants, the size of the leaves, and 
quantity of water transpired, but these 
data need not be given here. As 
shown in Plate 7, A, the roots of 
potatoes retarded the growth of to¬ 
bacco, while the tops somewhat in¬ 
creased the rate of growth. The 
same results were obtained with the 
roots and tops of hairy vetch. Corn 
roots retarded growth somewhat, while 
no harmful effect was observed with 
tobacco roots. The tops and roots 
of vetch used in the tests were from 
fresh plants while the other plant 
material was from the growth of the 
preceding summer. 
A field test was made on the experi¬ 
mental" farm with fresh tops and roots 
of hairy vetch and crimson clover. 
The land used had been cropped to 
tobacco for several years. The plant 
material was applied in the row at 
the rate of two tons green weight per 
acre. The material was applied May 7, 
and the tobacco was set June 26. No 
fertilizer was used. Alternate rows 
were used as controls. With both the 
vetch and clover the tops gave in¬ 
creased growth, while the vetch roots 
retarded growth and the clover roots 
seemed to have no decided effect 
(pi. 7, B). These preliminary tests 
seem to indicate that the injurious 
effects of certain crops on tobacco are 
due to the roots. If this be true, it 
would seem to present new problems 
in the matter of supplying desirable 
forms of organic matter to the soil and 
at the same time of insuring adequate 
aeration. 
CONCLUSIONS 
Fairly extensive field experiments 
have been in progress in southern 
Maryland for several years to deter¬ 
mine whether legumes and other soil¬ 
improving crops, combined with com¬ 
mercial fertilizers, can be used success¬ 
fully in applying intensive methods to 
tobacco culture; and to.study the com¬ 
parative effects of various crops on 
those which follow in rotation, with 
special reference to tobacco. The soil 
used is the fine sandy loam type of the 
Collington series. The results to date 
do not support the view which has 
been often advanced that tobacco is 
especially injurious to the general 
productiveness of the soil. On the 
other hand, it appears that the tobacco 
plant is particularly sensitive to the 
effects of preceding crops, and attempts 
to apply intensive methods, as turning 
under soil-improving crops freely or 
applying large quantities of manures 
and fertilizers, are likely to fail. The 
growth of the tobacco plant may be 
seriously retarded as a result of the 
effects of preceding crops of tobacco 
itself or of various other plants. Under 
the intensive methods in question, re¬ 
duced yields of tobacco do not involve 
a reduction in the general productive¬ 
ness of the soil. 
In special cropping tests with to¬ 
bacco, moderately fertilized, use of 
hairy vetch, crimson clover, and rye 
as soiling crops in continuous tobacco 
culture has given rather large increases 
in yield of tobacco during the first few 
years of the tests. In later years, 
however, the yields of tobacco have 
been very variable, depending largely 
on weather conditions. In dry years 
the yield has been rather good, while in 
wet years it has been less than that of 
the control plot, and the quality of the 
leaf has been poor. There is a ten¬ 
dency toward very uneven growth, but 
both large and small plants contain a 
high percentage of nitrogen. Much 
the same results have been obtained 
with crimson clover and cowpeas used 
as soiling crops for tobacco in a two- 
year rotation with wheat. For the 
period of the tests the general trend in 
yield of tobacco since the initial in¬ 
crease from the soiling crops has been 
downward. In a three-year rotation 
of tobacco, wheat, and red clover, both 
the yield and the quality of the tobacco 
have been more stable and have aver¬ 
aged considerably higher than those of 
the control plot. It is possible, how¬ 
ever, that these results are due largely 
to the fact that the land is substantially 
in a resting condition for the greater 
portion of the rotation period rather 
than to any specifically favorable 
influence of the red clover. In any 
event, it is a striking fact that none of 
the cropping systems tested have given 
results with tobacco equal to those 
obtained on rested land, that is, land 
occupied for a period of years by ad¬ 
ventitious vegetation. Leaving out of 
account instances of infestation with 
Thielavia root-rot, at the present time 
the only system of soil management 
known to be effective in restoring to 
normal the yield of tobacco which has 
declined under intensive methods is the 
simple expedient of allowing the soil to 
remain idle for a period of years. 'It 
appears that while limited use of soil¬ 
improving crops under favorable cir¬ 
cumstances may give profitable re¬ 
turns with tobacco, conditions may 
easily arise where their use would be 
positively detrimental. In the present 
series of tests, use of soil-improving 
crops combined with liming but with¬ 
out use of commercial fertilizer has 
soon resulted in practical failure of the 
tobacco crop. 
