June 15 ,1925 Effect of Crops on Yields of Succeeding Crops in Rotation 1097 
under irrigation in Utah catch crops of 
vegetables and small fruits exercised 
characteristic effects on color of foliage 
and growth of peach trees. In pot 
tests with a well-fertilized soil, cover 
crops of tomatoes, potatoes, oats, rye, 
rape, mustard, crimson clover, peas, 
and beans affected young peach trees 
somewhat differently. Oats and rye 
were most injurious, while beans and 
clover were beneficial. In a field test 
at Gizeh, Egypt, under arid conditions, 
Fletcher (7) grew corn and sesamum 
in alternating rows, different sections 
of the rows receiving different quanti¬ 
ties of water and fertilizer. The corn 
greatly retarded the growth of the 
sesamum, and this effect was not over¬ 
come by the watering and fertilizing. 
Skinner {19) made the observation 
that cabbages did not grow well on a 
peat soil at Middle River, Calif., 
which had previously grown sesame. 
The Howards {12) found that early 
turning under of a green-manure 
crop is essential for best results with 
tobacco, for sufficient time must be al¬ 
lowed for decay of the green manure 
before the tobacco is transplanted. It 
is stated that, for tobacco, green- 
manuring with Crotolaria juncea is 
successful only on light, high-lying, 
well-drained soils. On heavy or water¬ 
logged soils, green manure reduces the 
yield of tobacco. Stress is laid on the 
necessity of adequate soil aeration in 
tobacco culture. Hartwell and asso¬ 
ciates {9, 10) conducted a field experi¬ 
ment in which 16 crops were grown on 
separate plots for two seasons, while a 
single crop'was grown on all the plots 
in the third season. All plots were 
fertilized alike. After the various 
crops the yields of onions ranged from 
13 to 412 bushels per acre;' the yields of 
buckwheat ranged from 4 to 34 bushels; 
the yields of clover hay ranged from 
2.5 to 4.3 tons. When the soil was 
limed to neutrality, the differences in 
the effects of the various crops on those 
which followed were much reduced. 
The effects of the preceding crops were 
not proportional to the quantities of 
plant nutrients removed from the soil. 
The soil acidity was affected differently 
by the several crops. According to 
Sewell {18) it is the general observa¬ 
tion in the Great Plains area that wheat 
does not yield as well after Kafir as 
after Zea mays and in a field plot test 
extending over six years a gain of 3 
bushels per acre was obtained with 
wheat after corn over the yield ob¬ 
tained after Kafir. The unfavorable 
effect of the Kafir is attributed to its 
toxic action on wheat. 
Tobacco has been an important crop 
in certain sections for more than three 
centuries, and by farmers the crop has 
long been regarded as one which ex¬ 
hausts soils and some have considered 
it as especially injurious to the crop- 
producing power of the soil. Cocke 
{5, p. 19) in 1860 wrote: “Tobacco has 
been literally the besom of destruction, 
which has swept over this once fertile 
region [the tidewater region of Vir¬ 
ginia], and reduced it to a state too 
poor to remunerate labor employed in 
its production.” One reason for the 
development of this view is that a 
large portion of the tobacco crop has 
always been grown on light, sandy soils 
which naturally have a comparatively 
low crop-producing power. On the 
other hand, certain of these soils yield 
the best quality of tobacco, so that 
the tendency has been to grow tobacco 
;ar after year on the same soil. 
nder these circumstances, the system 
of farming rather than any peculiarity 
of the tobacco crop might account for 
the decline in general productiveness of 
these tobacco soils. 
The early settlers learned that, in 
general, tobacco grew especially well 
on virgin soil, and it at once became 
the practice to constantly clear new 
land for tobacco. It was soon ob¬ 
served, however, that decline in tobacco 
yields under continuous culture of the 
crop is not always due to general ex¬ 
haustion of the soil. Jones {18, pp. 
86-42), writing in 1724, states: “ When 
land is tired of tobacco it will bear 
Indian corn or English wheat, or any 
other European grain or seed, with 
wonderful increase.” Some types of 
tobacco are grown on exceedingly rich 
soils, but, nevertheless, it is not possible 
to grow on such soils more than one 
or two satisfactory crops of tobacco in 
a period of some eight to ten years. 
In other cases exceedingly heavy appli¬ 
cations of manures and fertilizers nave 
failed to restore, for tobacco growing, 
the productiveness of soils on which 
the tobacco yield has declined under 
continuous culture. Finally, the yield 
of tobacco under continuous culture of 
the crop does not necessarily decline 
on all soils. In some sections tobacco 
has been grown each year on the, same 
soil for more than a half century with¬ 
out decrease in yield. 
PURPOSE AND GENERAL PLAN OF 
THE EXPERIMENTS 
As the area of cleared land in the 
older tobacco-growing sections con¬ 
stantly increased, the practice of resting 
