The fertilizing value of hairy vetch for Connecticut tobacco fields


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The fertilizing value of hairy vetch for Connecticut tobacco fields
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Robinson, T. Ralph
United States -- Bureau of Plant Industry
U.S. Dept. of Agriculture ( Washington, D.C )
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aleph - 29621585
oclc - 43563430
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B. P.I.-404. li I d October 3, I14 .
United States Departmeiit of A,&yrit T
B. T. GALLOWAY, Chief of Bureau "

z Libr-ar
By T. R. ROBINSON, -... -
Assistant P1I ',',1..(., Soil Bact -. .i j ,t,'*...

In connection with the introduction of a 1' ,liiii,', cover crop onl
tobacco lands in Connecticut it became at once desiralble to know to
what extent such a crop would lessen the need for fertilizers, especially
those upplyin., nitrogen. M.m11 experiments, mainly based on analyses
of legumes., miilijt be cited to show the amount of nitr._'.2ni which
it-lgumes furnish to a :-,i i.,.in" crop. Their very disparity serves to
indica e, however, that the results imay he largely intlluenced by soil
and climatic mun litii,- so that for any one locality the results obtained
elsewhere might prove misleading.

Mr. A. D. Shamel, of the Bureau of Plant Industry, published in
t0I',. in cooperation with the Connecticut Agricultural Experiment
Station, the preliminary facts in r,2., d to "a new and valuable cover
crop for tobacco lihld-.'' namely, Russian or hairy vetch ( V'icia illos(i).*
This leguin, was found to be resistant to cold, heat, and drought;
oc1uie,1 the ground luringw, the fall, winter, and spring; decayed rapidly
when turned under; and enriched the soil by its ability to fix" or
utilize atmospheric nitr,'i.n when properly inoculated-that is, when
the bacteria were pri-.iit to cause the formation of root nodules. I lesss
the bacteria were artificially supplied it was found that the desired
inoculation was kilnl or very tardy on thle tobacco lands of thle Con-
necticut Valley.2
'.,_ Conn. Agr. Expt. S Ma. Bul. 119.
2 "The roots of pants from inoc ulited sfeel bore mnmv tult rcles, soenic 'r,
'.tliii- of them h, in,, a. larre as corn kernes. When thlie seed wais not inoctu-
lated the roots bore few, if ainy, nodules and tile i-..-.thi of thei pIints was Imunch
less vig..rii-." (Conn. Agr. Expt. :i i. Bill. 1 ', p. 6.)


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
16'1; 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 yield 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 Hlockanum, Conn., as found
from sample cutfiiz.. on 1 square rod of our test phit:t, 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
To determine further whether the difference in yield in this test coy '
be due to any difference in soil nitrogen, determinations of total ni
gen in samples of the soil were made by the Bureau of Chemistry.
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.

To check under controlled conditions the results obtained in the tests
at Hockanum, Conn., a qu.mtity 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 ir_:1imn. the remainder being untreated.
The pots were watered throughout with water sterilized by boiling.
Despite this precaution and a preliminary st,-rili.ii. of the pots and
seeds, a partial inoculation of the control plants took place-probably
due to insects tr.iv'liin from the inoculated pots. This chance inocu-
lation occurred, however, too late to benefit the control plants as much


ais those inoculated at the start, and the difference was still lnoticelableh
:ilttr three months' _,i-mth (D)ecember 11, 1907, to March 19, lVM)S).
Rye was ','I'. ii under the same conditions but did not nmke a very
good growth. Plants were taken .fli for v., i.:liiii' when tlHl wrs began
to appear, and iiples from each lot were analyzed. The results are
shown in the following table:

hairy retch. wilb en that evf wl'if het n parftfiaifl' u inouaionl 0f timn'1 vetci'i. t l~~i
'Twopts t he 1 i i Wtley (ipct'il oriihto Dry y i eifriht. Nitr( g n f' -.

wGrams. a hmcina hew c*It o rdeam sl
Hairy vetch, Iontriil plCnt ...... 11114 5 25 0-S2 0
lt e ia V t cl2l, i ntll a le rs I nll itut 2I5.5 r 4.1 a l i 1 ,:I
I. ,... . ... . .. .. .. ... . . .. .... .... 7 16 1 '.' 0 ..7

It will be seen that even when partial inoculation of the vet(ch took
place te t h i;.se -t results both as to yield and p, tI, td ,i of niti .
were obtained when artificial inoculation was practiced and that both
cets of the 1 '2fi1,., wVere superior to rye in furt isl,;t nitri gen.
wh ns a check against chance inoculation, a few small pots of t same soil o
the thadt used in tle greeniihouse test were sterilized by autoclavi fror 1
of ur at 140e C., part of them I ih, planted with inoculated vetch seed.
The pots were kept in a n l.i-. i ._ carefully y brOteuted against insects
or dust infection, and( were watered with sterile distilled water. Tlie
checks remained free of nodules iig.'i, u the experimenll t, while those
inoculated were plentifully supp)lied Withl nodules. Te soils were so
inju red t lie h1, It I.I t Iat neither set of plaIi nts I a1 de r formal growth ti,
their chief difference being in color. The check plants were pale green,
while the inoculated Ilants were healthy in color.


If thLe percent.,_ shown in Table I are taken as represrn4'ir4, the
nitrogen content of the field-grown vetch previously m, ntioned, it will
be seen what 'n enormous ..iin was effected by abli ldant inorulation.
.-um iiiii;. one-fifth of tile green weight to represent the dry v, 1-lit of
the vetch, the follohwii, amounts of niti,'-,n were furnished on the
cover-crop plats at r'ockanum, Conn :
TABLE II.-Coarion of itrogn in covr crops o(f ryt' m oculatd hairy -etch gfroucn rPlat d |2 Green w("i1ht. I i t, itro (
1),r acre p r a<'(,

| fla ,,* h,, : .. lilated ...... ...... 1 ,l fioO -'.., ;S qf ]Wi.:,i
Fl n r' i, i l r i culated .. ... ... r' 4 210 L i. 1 t, i i} .'
Ie ..... ... ...... 1t.7 *".*I1 l .i >l' .


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 lit-grown vetch plants from
which the percentage of ijitrig-n 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 thle air by the root-
nodule bacteria. A very considerable part of the nitnr,.,ii 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 gaihi
(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).


To carry the pot experiments still farther the soil in each pot was
tljirmIglily 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 plant-, turned
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:


ounces o f
Cover crop and method of use. Treatment tobacco
Hairy vetch turned under ...... No fertiize .......... 5..
TT.ii vetch removed --l -- F(,rtilized 5..'
flairy vetch turned under, .... Frrlilizfcd 7.7)
Rye turned n der. .- -...- ....- No f. i i i ......... .'
Rye removed Fertilizt d 5 .25T
R(ve turned lender F I .I . .. 2.
N j,", of four pots.
It would thlius appear that the ttirili-, iundelr of tlhe inoculated hairy
vetch was slightly supelrior to the application of 2(.)() pounds of sodium
nitrate to the acre, while the ttiiz.-1 utd(er of rye was inferior to the
application of the fertitlizer. Whein tlie cover crops wver(e turniied under
and fertilizer a(ided the vetch .I, tll shiolowed grater fertilizinig power
than rye. In pots which hlad1 borne no cover crop tlie application of
nitrate of soda at tlie rate of 50)0 pounds to the acre was no more elt'ee-
tire than the use of 200 pounds to the acre.


Ini present li-,' this report, no mention has been made of the influence
on the soil of thle hairy vetch crop aside fro)im its property when inocu-
lated of furnis,'iii, niti,,'-, i. thus allot, i,.- a considerablee reduction in
quantity of thlie expensive nii",-', iitI- fertilizers. As a preventive of
wind and water erosion the niatlike -i,'iah of hairy vetch gives it ',.i
value; as a source of hum tus its extensive root systeimi amd the readily
decomposabhle nature of the whole plant are peculiar alv.,ii?.,r.. and it
seems to possess in addition, on laud successively cropp)edt to tobacco,
a .'1i,.,.i l, ,jii, value considerably above its purely chemiical content
and the physical improvemielnt of the soil result, 'front its use. 'T114'
full nature and amount of these benefits will require more extensive
tl-, but tlhe results here reported are prcmse'nted as a partial 'iiid. to
those interested in thi utilization of hairy vetch ats i cover and fertiliz-
I: crop.

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