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| MAY183
Gog October 3, 1908,
United States Department of Agric

BUREAU OF PLANT INDUSTRY—Circular No. 15.

B. T. GALLOWAY, Chief of Bureau.

THE FERTILIZING VALUE OF HAIRY VETCH FOR
CONNECTICUT TOBACCO FIELDS.

By T. R. Ropinson,
Assistant Physiologist, Soil Bacteriology Investigations.

INTRODUCTION.

In connection with the introduction of a leguminous cover crop on
tobacco lands in Connecticut it became at once desirable to know to
what extent such a crop would lessen the need for fertilizers, especially
those supplying nitrogen. Many experiments, mainly based on analyses
of legumes, might be cited to show the amount of nitrogen which
legumes furnish to a succeeding crop. Their very disparity serves to
indicate, however, that the results may be largely influenced by soil
and climatic conditions, so that for any one locality the results obtained
elsewhere might prove misleading.

ADAPTABILITY OF HAIRY VETCH TO TOBACCO FIELDS.

Mr. A. D. Shamel, of the Bureau of Plant Industry, published in
1905, in cooperation with the Connecticut Agricultural Experiment
Station, the preliminary facts in regard to ‘‘a new and valuable cover
crop for tobacco fields,”’ namely, Russian or hairy vetch ( Vicia villosa) 4
This legume was found to be resistant to cold, heat, and drought;
occupied the ground during the fall, winter, and spring; decayed rapidly
when turned under; and enriched the soil by its ability to ‘‘fix’’ or
utilize atmospheric nitrogen when properly inoculated—that is, when
the bacteria were present to cause the formation of root nodules. Unless
the bacteria were artificially supplied it was found that the desired
inoculation was lacking or very tardy on the tobacco lands of the Con-
necticut Valley.?

18ee Conn. Agr. Expt. Sta. Bul. 149.

2“The roots of plants from inoculated seed bore many tubercles, some aggre-
gations of them being as large as corn kernels. When the seed was not inocu-
lated the roots bore few, if any, nodules and the growth of the plants was much
less vigorous.’’ (Conn. Agr. Expt. Sta. Bul. 149, p. 6.)

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2 FERTILIZING VALUE OF HAIRY VETCH.

IMPORTANCE OF INOCULATING HAIRY VETCH.

If hairy vetch was to prove at all valuable as a fertilizer, it was nec-
essary to get the crop well inoculated. Plat experiments in collabora-
tion with Mr. Shamel were therefore undertaken in the autumn of
1906 at Hockanum, Conn., by the Office of Soil Bacteriology Inves-
tigations to determine, if possible, the value of hairy vetch as a fertili-
zer on the soil of that region. Tobacco following uninoculated vetch
has shown but little advantage over that following a rye cover crop, but
where hairy vetch has been inoculated and an abundance of root
nodules have resulted the tobacco following has been greatly benefited
both as to yleld and as to quality. When one compares the growth of
inoculated and uninoculated vetch this will be easily understood.

The yield of hairy vetch in 1907 at Hockanum, Conn., as found
from sample cuttings on 1 square rod of our test plats, amounted to 7
tons 400 pounds an acre (green weight) for the inoculated vetch and 2
tons 240 pounds an acre for the uninoculated vetch. Rye on this land
made a vigorous growth, yielding at the rate of 7 tons 720 pounds an
acre.

To determine further whether the difference in yield in this test could
be due to any difference in soil nitrogen, determinations of total nitro-
gen in samples of the soil were made by the Bureau of Chemistry. It
was found that the soil where vetch was growing without inoculation
contained 0.19 per cent of total nitrogen, or more than that found on
either the plats of rye (0.17 per cent) or inoculated vetch (0.14 per
cent). Yet with this greater source of nitrogen in the soil the vetch
lacking nodules made less than one-third the growth attained where
the plants were properly inoculated. It may be said that in one case
nodules were absolutely lacking, while in the other the nodules were
so abundant that when the vetch was plowed under the upturned soil
was dotted white with the glistening nodules.

POT EXPERIMENTS WITH HAIRY VETCH.

To check under controlled conditions the results obtained in the tests
at Hockanum, Conn., a quantity of soil from the uninoculated plat was
shipped to Washington and some experiments were undertaken in the
greenhouse. This soil was placed in large pots (holding about 30
pounds of soil each) and planted with seed of hairy vetch, ten plants
to a pot. One-half of the pots were sown with seed treated with a pure
culture of the vetch-nodule organism, the remainder being untreated.
The pots were watered throughout with water sterilized by boiling.
Despite this precaution and a preliminary sterilizing of the pots and
seeds, a partial inoculation of the control plants took place—probably
due to insects traveling from the inoculated pots. This chance inocu-
lation occurred, however, too late to benefit the control plants as much

FERTILIZING VALUE OF HAIRY VETCH. 3
as those inoculated at the start, and the difference was still noticeable
after three months’ growth (December 11, 1907, to March 19, 1908).

Rye was grown under the same conditions but did not make a very
good growth. Plants were taken off for weighing when fiowers began
-to appear, and sampies from each lot were analyzed. The results are
shown in the following table:

TABLE I.—Results of greenhouse tests of rye and inoculated and uninoculated
hairy vetch.

noe Total nitrogen
Two pots, conta‘ning twenty | Green weight.| Dry weight. Nitrogen. furnished by
plants. plants.
| Grams. Grams. Per cent. | Grams.
Hairy vetch, control plants___.__-- 5 25 3.41 0.82
Hairy vetch, inoculated nents posh 215.5 44 3.49 1.33
1 OATES ae i te SS aa PE 72 16 1.69 0.27

It will be seen that even when partial inoculation of the vetch took
place the highest results both as to yield and percentage of nitrogen
were obtained when artificial inoculation was practiced and that both
lots of the legume were superior to rye in furnishing nitrogen.

Asacheck against chance inoculation, a few smal] pots of the same soil
as that used in the greenhouse test were sterilized by autoclaving for 1
hour at 140° C., part of them being planted with inoculated vetch seed.
The pots were kept in a glass cage, carefully protected against insects
or dust infection, and were watered with sterile distilled water. The
checks remained free of nodules throughout the experiment, while those
inoculated were plentifully supplied with nodules. The soils were so
injured by the heating that neither set of plants made a normal growth,
their chief difference being in color. The check plants were pale green,
while the inoculated plants were healthy in color.

NITROGEN FURNISHED BY HAIRY VETCH TURNED UNDER.

If the percentages shown in Table I are taken as representing the
nitrogen content of the field-grown vetch previously mentioned, it will
be seen what an enormous gain was effected by abundant inoculation.
Assuming one-fifth of the green weight to represent the dry weight of
the vetch, the following amounts of nitrogen were furnished on the
cover-crop plats at Hockanum, Conn.::

TABLE, Il.—Comparison of nitrogen in cover crops of rye and inoculated and unin-
oculated hairy vetch grown at Hockanum, Conn.

: Green weight, - Dry weight, Shs
Plat. 4 per acre. aa per acre. Nitrogen.
Pounds. | Pounds. Per cent ae Pounds a acre:
Hairy vetch, inoculated____._______ 14,400 2,880 3.49 100.51
eee vetch, uninoculated. ___.___- 4,240 |: 848° | 3.41 28.91
EV Cane mene uasneme niga rill Eaeea TT a ee 14,720 | 2,944 1,69 49.75

4 FERTILIZING VALUE OF HAIRY VETCH.

The difference in the quantities of nitrogen furnished by the two
lots of field-grown vetch is probably even greater than that shown here,
owing to the partial inoculation of the pot-grown vetch plants from
which the percentage of nitrogen was obtained. It is not to be con-
cluded, however, that 100.51 pounds of nitrogen in one case represents
the net gain from growing inoculated vetch, or even that the difference
between 100.51 pounds and 28.91 pounds (71.6 pounds) represents
exactly the amount of nitrogen abstracted from the air by the root-
nodule bacteria. A very considerable part of the nitrogen even in the
case of an inoculated plant is derived from the soil. The more vigor-
ous the plant and more wide spreading its root system, the greater will
be its ability to secure nitrogen from the soil.

If, however, this 71.6 pounds of nitrogen is counted as clear gain
(that is, taken from the store of atmospheric nitrogen) it can not be
assumed that this becomes at once available for the succeeding crop.
There is reason to believe that the greater portion of it becomes avail-
able under favorable conditions within a comparatively short time, but
it can not be stated as proved, for instance, that this amount of nitrogen
turned under (71.6 pounds) is equivalent to the application of 475
pounds of nitrate of soda (15 per cent nitrogen).

POT EXPERIMENTS WITH TOBACCO.

To carry the pot experiments still farther the soil in each pot was
thoroughly stirred and prepared for setting out tobacco plants. In part
of the series the vetch or rye was turned under and in part removed
entirely from the pot. The pots were kept moist for four weeks, tap
water being used, to allow for the decomposition of the plants turned
under.

Sodium nitrate was chosen as a carrier of nitrogen to compare with
that furnished by the plants turned under and was supplied at the rate
of 200 pounds to the acre three days before setting out the tobacco plants.
To get the maximum effect of this fertilizer some duplicate pots on
which no cover crop had been grown were fertilized at the rate of 200
and 500 pounds of sodium nitrate to the acre.

Selected tobacco plants from Connecticut seed, apparently of equal
size and vigor, were set out in the pots, a single plant to a pot. The
pots were watered with tap water from this time to the completion of
the experiments (April 16 to July 22, 1908). The tobacco did not do
especially well under greenhouse conditions, but all plants were affected
alike. As all the vetch plants turned under were considerably inocu-.
lated when taken up, no separate account. was kept of the inoculated
and control series. The fertilizer used was 200 pounds of sodium
nitrate to the acre. The results, given in terms of the green weights of
the plants cut off at the surface of the soil, follow: _ pigs

Cr

PERTILIZING VALUE OF HAIRY VETCH.—

Ounces of

Cover crop and method of use. Treatment. tobacco.®
Hairy vetch turned under_______- No fertilizer su 2 sees 5. 75
Hairy vetch removed ___________- ertrliize chy a Oi eis a 5,28
Hairy vetch turned under_______- Bertilized(ia 23 ea 75 005)
hyeiurned under 2220008 2 eee INO fertilizers. 2s 4, 25
RVeRbemoved 2 24 hoki ee ss ertilizediy cae: s ies ou 0a" 5. 25
Rye turned under ____________=_- ‘Hentilizedinn limi Wi anakes 6. 25

a Average of four pots.

It would thus appear that the turning under of the inoculated hairy
vetch was slightly superior to the application of 200 pounds of sodium
nitrate to the acre, while the turning under of rye was inferior to the
application of the fertilizer. When the cover crops were turned under
and fertilizer added the vetch again showed greater fertilizing power
than rye. In pots which had borne no cover crop the application of
nitrate of soda at the rate of 500 pounds to the acre was no more efiec-
tive than the use of 200 pounds to the acre.

CONCLUSIONS.

In presenting this report, no mention has been made of the influence
on the soil of the hairy vetch crop aside from its property when inocu-
lated of furnishing nitrogen, thus allowing a considerable reduction in
quantity of the expensive nitrogenous fertilizers. As a preventive of
wind and water erosion the matlike growth of hairy vetch gives it great
value; as a source of humus its extensive root system and the readily
decomposable nature of the whole plant are peculiar advantages, and it
seems to possess in addition, on land successively cropped to tobacco,
a green-manuring value considerably above its purely chemical content
and the physical improvement of the soil resulting from its use. The
full nature and amount of these benefits will require more extensive
tests, but the results here reported are presented as a partial guide to
those interested in the utilization of hairy vetch as a cover and fertiliz-
ing crop.

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