Ever since itís inception in New Zealand during the 1950ís,
coated seed has been seen to best advantage in the type of stress
conditions found in many land reclamation areas in Canada. These
areas are often dry and unfertile, making legume and grass
establishment difficult. Legumes can be more difficult to
establish than grasses, as many land reclamation areas are devoid
of the native rhizobium populations necessary to cause effective
nodulation. In addition, the NEED for inoculation is
often overlooked. Coated seed is designed to remove the necessity
for inoculation of legumes prior to seeding and to assist in
overcoming other typical land reclamation stress conditions.
Although coated seed has been available in Canada for several
years, many people are not aware of the benefits it offers
especially in relation to land reclamation work.
The history of coated seed goes back a long way. Coatings of an
organic nature were used by farmers of earlier times with notable
success and recorded references to coated seed can even be found
in the Bible. Modern day coated seed was pioneered in New Zealand
in the 1950ís where the rugged hill country proved to be an
ideal testing ground. The successful establishment of clovers and
grasses on many thousands of acres of the South Island high
country was mainly due to aerial applications of coated seed.
The coating technology was soon extended to cover other legumes
as well as a wide range of forage and turf grasses. Gradually, the
original technology spread from New Zealand to North America and
Europe, where virtually any type of seed that the market requires
is now available in coated form.
THE REASONS WHY WE COAT SEED
The six most important reasons why we coat seed are:
l. Pre-inoculation of legumes
2. Nutrient benefits
3. Protection from stress conditions
4. To improve ballistic properties and simplify
5. Safe application of agricultural chemicals
6. Protection from rodents, birds and the harmful effects of
Seed coating is a process designed to create a nutritious
environment in the immediate vicinity of the germinating seed and
to provide a "boost" for the seedling in its
critical early phase of development. This is particularly
important under the type of stress conditions found in many land
Phosphorus is the main nutrient supplied by the coating to the
seed. The type of phosphorus used in the coating varies with the
different manufacturers. As it is placed in the immediate vicinity of the seed, it is
utilized by the growing plant before being fixed and becoming
In the past, many people have expected coated seed to allow
them to ignore good seeding techniques at planting time and to
provide large yield increases as well. Coated seed does provide
major advantages but good cultivation and planting techniques
should still be followed wherever possible.
Today coated seeds benefit the plant in its critical seedling
stage ensuring early vigor and in the case of legumes, fast,
effective nodulation. There is obviously some "carry
over" effect from this increased seedling vigor, but once the
plant has nodulated and the fertilizer in the coat has been
assimilated by the plant, the coating cannot directly benefit the
plant in its future development. The increased use of agricultural
chemicals and slow release fertilizers may offer additional
benefits in the future. However, present economical, nutritional
and bacterial benefits make coated seed worthwhile in most land
reclamation projects today.
The need for nodulation is obvious. Effectively nodulated
legumes can fix large amounts of nitrogen from the atmosphere.
This nitrogen is utilized not only by the legume but also by other
plants growing in association with it. Pure alfalfa stands in
Ontario are capable of fixing approximately 150 kilograms of
nitrogen per hectare per year.
In the past, seed has been inoculated using a variety of
methods, many of which are unsatisfactory. One of the more
effective methods of inoculation is by spreading a sticker over
the seed and sprinkling dry peat based inoculant onto this. This
method will result in effectively nodulated plants providing it is
done immediately prior to seeding. However, this is not always
possible, especially when aerial seeding or hydroseeding remote
land reclamation sites. Pre-inoculation is the obvious answer. It
ensures that the rhizobia are "in the right place at the
Seed coating was initially the subject of some controversy when
it was first introduced to North America, however, one statement was
always made without fear of contradiction. That was and still is
that "seed coating is the most effective method of
pre-inoculation available in North America today".
This is the single most important reason why legume seeds are
coated and it is particularly important in areas where the legume
being seeded has not been grown previously.
Pre-inoculation is the addition of nodule bacteria (rhizobia)
to the seed, weeks or even months in advance of sowing. It ensures
that the bacteria are in close proximity to the roots of the
germinating seedling and thus in a position to cause fast,
effective nodulation. Increasing numbers of people are now
recognizing the need for legume inoculation, particularly when
seeding in the harsh conditions prevailing in most land
reclamation areas. The need for inoculation is very important in
the case of trefoil, as there are few, if any, native populations
of the rhizobium necessary to induce nodulation in trefoil present
in Canadian soils.
It is true that many soils in Ontario do have large populations
of rhizobium meliloti and that in many cases, un-inoculated
alfalfa seed would nodulate when sown in these soils. It is also
true that the yields of many of the plants infected by these
native bacteria have been significantly greater had they been
infected by the far more effective strains of rhizobium used in
modern seed coating processes.
Large amounts of money are spent by Agriculture Canada research
scientists each year in an attempt to develop new stains of
rhizobium which can utilize the rhizobium/legume association far
more effectively than many of our native rhizobium strains.
2. NUTRIENT BENEFITS
Seed coating creates a nutritious environment around the
germinating seed. This increases seedling vigor during its
critical early development. Up to 20% of all grass seed coatings
and 9% of the legume coating is phosphatic fertilizer. Phosphorus
is essential for plant growth and is especially critical for young
seedlings, as it ensures normal root development and vegetative
growth during the critical early stages of establishment. Even on
soils with phosphorus levels sufficiently high to sustain normal
growth, localized placement is very beneficial. It is particularly
desirable from the standpoint of accessibility to the establishing
seedling and in order to reduce fixation. Phosphorus does not
travel in the soil, therefore, the nearer it can be placed to the seed,
the easier it can be utilized by the seedling.
Lime, an important component of the coat, can have a beneficial
effect in low pH soils and in addition, it combines with the
phosphorus to form an excellent carrier for rhizobia. Although
coated seed does have significant nutrient benefits it should be
emphasized here that the coating does not negate the need for
normal cultivation and fertilization techniques at seeding time
3. PROTECTION FROM STRESS CONDITIONS
The fact that seed coating offers the seed significant
protection from the typical stress conditions found in many land
reclamation areas is a very important factor in its use in such
areas. The principal means by which the various stress conditions
are overcome are:
a. Moisture Stress. Bare seeds which find
a successful germination site can draw small but sufficient
quantities of moisture, particularly overnight from soil or
foliage, thereby initiating germination. Such seedlings may die in
large numbers where moisture availability remains insufficient to
sustain growth such as during a week or two of dry weather
following over-sowing. When coated seed is used and moisture
conditions are good enough for coat penetration to the seed
within, it is less likely that subsequent germination will fail
from absolute moisture deficiency of soil or foliage.
b. Wind and High Temperatures. Wind and
high temperatures are particularly harmful to over-sown legume
seeds. This is because the death rate of rhizobia is increased
dramatically by the drying effects of such conditions. It has been
shown that even under controlled climatic conditions, rhizobia on
bare seed suffer a severe decrease in viability in as little as
2-4 hours after inoculation. The coating around the seed offers
protection for the rhizobia and ensures their survival, which in
turn ensures an effectively nodulated legume plant.
c. Nutrient Deficiencies. The benefits
available to the seed from localized placement of fertilizer are
well known. Seed coating is a means of placing fertilizer in the
immediate vicinity of the plant where it is most effective. Most
coatings contain phosphorus, however, other nutrient deficiencies
in the soil can be overcome by the use of slow release fertilizers
which have been shown to have a significant effect several months
To be able to utilize these fertilizer benefits it is essential
that soil pH be as near optimum for nutrient uptake as possible.
Although seed coating will not replace the need for liming, it has
been shown that the lime in the coat has a pH buffer effect which
helps to protect the seed from acidic soil conditions.
4. BALLISTIC PROPERTIES
Most coated grass seeds are at least twice as heavy as bare
seed. This factor is particularly important when land reclamation
sites are being aerial seeded. Bare seed is much lighter with poor
ballistic properties thus it frequently fails to penetrate foliage
to a satisfactory soil germination site. On the other hand, the
increased weight of coated seed substantially increases its aerial
velocity. This allows penetration of the foliage and often results
in improved germination.
5. PROTECTION FROM RODENTS, BIRDS AND THE HARMFUL EFFECTS OF
Rodents and birds often fail to recognize coated seed as food.
This may be due in part (particularly in the case of birds) to the
increased size of the seed but more often can be attributed to the
taste of the phosphorus and lime in the coating.
Mixing bare seed with some fertilizers can have serious effects
on both the germination of the seed and in the case of legumes,
will destroy the rhizobium on the seed. These two factors are both
overcome by the protective effect of the coating, which allows all
seeds to be successfully mixed with fertilizers prior to seeding.
6. AGRICULTURAL CHEMICALS
The use of agricultural chemicals is particularly important in
Canadian agriculture. Coated seed has been utilized as a carrier
for fungicidal treatments such as Captan and Thiram for some time.
Seed coating is a safe, reliable and economical method of applying
agricultural chemicals to the seed, especially when these
chemicals are available in flowable formulations.
Coated seed has a very important part to play in land
reclamation projects in Canada. Many of the reasons for this have
been discussed earlier in this paper.
The concept of coated seed and especially
"hydrocoated" seed is still relatively new in Canada and
requires further research.
Coated seed has been used in the following types of reclamation
Northern Alberta - Tar sands
2. Northern Manitoba - Conversion of native bush to
3. Cape Breton Island - Mine land
To ensure that coated seed can be used in such reclamation
projects, several different types of coat have had to be
developed, including a "hydroseeding coat". Coated seed
normally breaks down very quickly in water. In the past, it could
not be hydroseeded as the coat dissolved and all its benefits,
including the pre-inoculation system, were lost. Technology has
been developed that produces a coated seed which will withstand at
least 40 minutes vigorous agitation in the hydroseeder tank and
still retain its coat. Laboratory and plot trials with this
coating material show no reduction in germination compared to
conventionally coated seed. Further modifications to the process
have allowed it to be used on legume seeds without any harmful
effects to the rhizobia
Many land reclamation projects involve the use of aerial
seeding. Coated seed is particularly valuable for this purpose.
One rather interesting aspect of aerial seeding is the reclamation
of large areas of native bush in Northern Manitoba. This operation
involves spraying the trees with herbicides and following this up
by over-sowing with coated seed. Several areas in Manitoba were
seeded this way and after the bush died had a very good covering
of grasses and legumes and eventually became excellent
Coated seed is not the answer to every seeding problem either on
land reclamation sites or in good pasture lands, however, it does
have its role to play in Canadian agriculture.
This role is best suited to the unique land reclamation
problems that exist in Canada. The single most important problem
in many of these areas is the lack of effective native strains of
nodule bacteria. Coated seed undoubtedly offers the best
pre-inoculation system for legumes under the stress conditions
found in these areas. This reason alone is sufficient to warrant
its use in most land reclamation projects.
The nutrient properties of the coating are significant,
although coating technology canít replace the need
for additional fertilizer at seeding time. The other significant
benefits, which include protection from stress conditions and
improve ballistic properties, make coated seed an excellent choice
for most land reclamation work.