On account of the low germination of much of the sweet-clover seed
offered for sale it is very important that seed be tested for
germination before planting. Low germination usually is due to the
fact that many of the seeds remain hard after they have been in
the germinator or soil for a month or more. The seed coats of hard
sweet-clover seeds become permeable to water very slowly, if at all, in
storage. The germination of such seeds is greatly increased, however,
when they are subjected for a time to alternating temperatures, such as
freezing and thawing. It is on this account that unhulled seed, which
germinates poorly in the laboratory, often will produce good stands
when sown during the winter. When sweet clover is to be sown in the
spring it is very important that only hulled seed which germinates
75 per cent or more be sown. As explained later under the heading
"Seeding," unhulled seed which has a low germination should be used for
seeding only during the winter months, so that there will be sufficient
time for the alternating temperatures of winter and early spring to
cause it to germinate during favorable weather.
Hulled seed usually germinates much better than unhulled seed, as is
shown in Table I.
Table I.--_Germination and hard seed content of samples of
sweet-clover seed, hulled, and unhulled, from different sources._
Average percentage of--
Number of
Description. samples. Germination. Hard Seed.
--------------- ---------- ------------ ----------
Kind of seed:
Hulled 237 53.25 18.7
Unhulled 45 11.8 70.9
Source of seed:
Southern 22 14 60
Northern 22 37 43
Imported 28 56 12
Table I shows that northern-grown seed germinates better than
northern-grown seed and imported seed better than either. The low
germination of the southern-grown seed is probably due to the fact that
a very large percentage of it is flailed out and sown in the hull.
Northern-grown seed generally is thrashed with either a grain separator
or a clover huller. Imported seed always is hulled. In hulling seed the
rasps or concaves of the machines scratch the seed coats sufficiently
to permit water to penetrate them, so that the germination is greatly
increased. Apparently there is no reason why southern-grown seed when
it is properly hulled should not germinate as well as northern-grown
seed.
Since the Ames scarifying machine (fig. 8)[7] has been placed on the
market, it is possible to buy scarified seed. This machine is so
constructed that the seed is forced through a conveyor, part of which
is covered with sandpaper. When the seed comes in contact with the
sandpaper it is scratched, so that water will penetrate the seed coats.
When this machine is run properly the germination of seed is greatly
increased, but when carelessly operated germination may be lessened, as
many of the seeds may be broken.
[7] This machine was invented by Prof. H. D. Hughes, of the Iowa State
College at Ames. A United States patent covering this device has been
issued and dedicated to the free use of the public.
[Illustration: Fig. 8.--Ames hulling and scarifying machine.]
The retarded germination of sweet-clover seed may be overcome by
soaking it in commercial concentrated sulphuric acid for 20 minutes.
It should then be washed quickly, using running water if possible, as
sulphuric acid becomes very hot when mixed with small proportions of
water. A great deal of water therefore is necessary in order to lessen
the danger of burning. The seed should be dried quickly by spreading
it out on a floor or canvas, and it should be stirred at intervals.
Unhulled seed should never be treated with sulphuric acid. When only a
small quantity of sulphuric acid comes in contact with the hulls a very
high temperature will result and the seed will be killed. The treatment
of seed with sulphuric acid for seeding on a field scale is not to be
recommended, in view of the fact that as good or better results may be
obtained by using scarified seed.
It is very important that seed of the desired species be obtained.
Many lots of sweet-clover seed offered for sale on the market consist
of mixtures of the yellow and white species, and many samples also are
adulterated with alfalfa. Seed which is simply labeled sweet clover
should never be purchased, as seed so labeled may be any one of the
several varieties offered for sale. It is always best to state the
specific kind of seed ordered and then submit a sample to either your
State Agricultural experiment Station or one of the seed laboratories
of the United States Department of Agriculture[8] for identification
before purchasing.
[8] Samples of seed may be submitted for analysis or identification to
the Seed Laboratory of the United States Department of Agriculture at
Washington, D. C., or to any of the following laboratories maintained
through the cooperation of the Department: Branch Seed-Testing
Laboratory, Agricultural Experiment Station, Columbia, Mo.; Branch
Seed-Testing Laboratory, Agricultural Experiment Station, Baton Rouge,
la.; Branch Seed-Testing Laboratory, Oregon Agricultural College,
Corvallis, Oreg.; Branch Seed-Testing Laboratory, Purdue University, La
Fayette, Ind.; Branch Seed-Testing Laboratory, California Agricultural
Station, Berkeley, Cal.
The Seed Laboratory of the United States Department of Agriculture
during the winter of 1915-16 obtained 172 trade samples of sweet-clover
seed and, as may be seen from Table II, many of the samples were not
true to name.
Table II.--_Trade samples received in response to requests for
white sweet clover seed._
Key to Columns
[A] White sweet clover.
[B] Biennial yellow sweet clover.
[C] White and biennial yellow sweet clover.
[D] Annual yellow sweet clover.
Number of Seed when tested
Seed labeled-- samples. found to be-- Alfalfa and--
[A] [B] [C] [D] [A] [B] [C]
White flowering sweet
clover, white sweet
clover, or Holhara
clover, or _Melilotus
alba_. 147 91 10 28 -- 13 1 4
Sweet clover 22 6 4 2 5 5 -- --
Not labeled 3 1 -- -- 2 -- -- --
---- ---- ---- ---- ---- ---- ---- ----
Total 172 98 14 30 7 18 1 4