June is, 1925 Effect of Crops on Yields of Succeeding Crops in Rotation 1101 
RAINFALL 
It is of considerable interest to in¬ 
quire as to what extent weather con¬ 
ditions, especially rainfall, may modify 
the effects of a crop on succeeding 
crops. The available records of rain¬ 
fall on the experimental fields during 
the spring and summer months for the 
period of the experiments are given in 
Table II. 
SPECIAL CROPPING TESTS WITH 
TOBACCO 
The plots used in these tests are 
one-fourth acre in size. The numbers 
of plots and treatments for each crop¬ 
ping test are as follows: 
IV a, b, c: Tobacco, wheat, and red clover in a 
three-year rotation; tobacco fertilized. 
V a, b: Tobacco, wheat, and crimson clover in 
a two-year rotation; tobacco fertilized. 
VI a: Tobacco each year, crimson clover as a 
cover crop; no fertilizer used. 
VI b: Tobacco each year, crimson clover as a 
cover crop; tobacco fertilized. 
VI c: Tobacco each year, hairy vetch as a cover 
crop; tobacco fertilized. 
VI d: Tobacco each year, rye as a cover crop; to¬ 
bacco fertilized ‘ 
VI e: Tobacco each year, no cover crop; tobacco 
fertilized. 
VII a, b: Tobacco, wheat, and cowpeas in a two- 
year rotation; tobacco fertilized. 
VII c, d: Tobacco, wheat, and cowpeas, in a two- 
year rotation: no fertilizer used. 
The location and arrangement of 
these plots and the general character 
of the soil are shown in the soil map, 
the plots being numbered there as 
above. (Some of the plots included in 
the survey relate to experiments not 
involved in the present discussion.) 
All of the tests were begun in 1912, ex¬ 
cept those on Plots VI d and VI e, 
which were begun in 1916, a period of 
four years having been allowed to fully 
establish the legume features of the 
tests. In Series IV, V, and VII, tobac¬ 
co was grown on Plot a in 1912, Plot 
b in 1913, and so on, in regular sequence. 
In 1922 plots were added immediately 
south of Series V a, 6 for the purpose of 
growing tobacco every second and third 
year, respectively, in rotation with 
weeds. Fertilizer has been applied 
each year to the tobacco crop, but none 
has been used on the wheat or soil-im¬ 
proving crops. For the years 1912 to 
1916, inclusive, the fertilizer consisted 
of 100 pounds nitrate of soda, 500 
pounds 14 per cent acid phosphate and 
100 pounds 50 per cent sulphate of 
potash per acre. Beginning with 1916 
the application of nitrate of soda was 
reduced to 60 pounds per acre but no 
change was made in the quantities of 
acid phosphate and sulphate of potash 
used. In the years 1912, 1913, and 
1914 air-slaked burned lime was applied 
at the rate of 10 bushels per acre to 
the plots in each series at the time of 
turning under the legumes in prepara¬ 
tion for tobacco. No lime was used in 
1915. Beginning with 1916 ground 
limestone has been applied in all cases 
after tobacco, prior to seeding wheat. 
Each plot in Series IV and VI has re¬ 
ceived 1,000 pounds per acre once in 
each three-year period, and the plots in 
Series V and VII have received 650 
pounds once in each two-year period. 
All legumes have been plowed under, 
except that one crop of hay has been 
cut each year from the first-year red 
clover. 
In general, excellent stands and good 
growth of red clover have been obtained 
with but little winter killing (pi. 1, 
A) . Crimson clover grown in the two- 
ear rotation with tobacco and wheat 
as usually made excellent growth when 
it has escaped winter killing. Rather 
frequently, however, it has suffered 
severely frem cold, and, altogether, has 
not been a dependable soil-improving 
crop. In recent years the crimson 
clover has been damaged considerably 
by stem-rot disease. With continuous 
tobacco culture, with fertilizer, crim¬ 
son clover has been somewhat less suc¬ 
cessful than in the two-year rotation 
for the reason that the tobacco crop 
comes off too late to allow seeding of 
the clover at the proper time. Where 
no fertilizer is applied to the tobacco, 
crimson clover has been almost a com¬ 
plete failure. Hairy vetch has proved 
to be a thoroughly dependable winter 
cover crop, and there has been no win¬ 
ter killing of consequence in spite of 
the fact that it has been necessary to 
seed it very late in the fall (pi. 1, 
B) . The vetch has furnished large 
quantities of organic matter for the soil. 
The cowpeas have always made good 
growth where fertilizer was applied to 
the tobacco (pi. 2, A), but the growth 
has been much less where no fertilizer 
was used. Data have been obtained 
on the yields of wheat in these tests 
but will not be considered in this 
discussion. 
The yields and gross value of tobacco 
produced under the several systems of 
cropping are summarized in Table III. 
The values of the crops from the dif¬ 
ferent plots are based on the judg¬ 
ment of local tobacco buyers. 
