Seed Coating
Seed coating consists of two parts:
film coating and seed pelleting. Coating is the establishment of a thin layer
of different materials on the seed surface that does not significantly change
the shape and size of the seed. Seed pelleting is the addition of different
materials along with fillers in separate layers on the seed surface that change
the volume and shape of the seed. Seed coating is done for various purposes,
including increasing the speed and rate of germination, preventing pest and
disease damage, facilitating seeding operations, uniform seed distribution,
delaying germination, preventing the consumption of seeds by insects and birds.
The basis of the work is spraying different materials in the form of specific formulations
on the rotating seeds in the machine. This technology has developed a lot in
the last two decades in the world and most of the seeds, especially small and
expensive seeds, are marketed as coatings. In Iran, recently, in a limited
level, coating and pelleting has started in several private companies. But
formulations with specific features have not been marketed yet.
Thin
layer coating
Thin
layer coating is done with the aim of applying materials such as dyes or
pesticides and nutrients on the seed surface correctly and uniformly and
presenting valuable and attractive seeds to the market. The materials used in
this method adhere to the seed surface to minimize dusting and loss during
transport and seeding. This thin layer should uniformly cover the seed surface,
not separate from the seed surface and be permeable to water and not have a
negative effect on seed germination. The increase in seed size in this method
is small and between one to ten percent and is mainly used in large seeds that
are produced in large volumes.
The
formulation used in this method is an aqueous suspension consisting of an
adhesive, a pigment, and a filler, which is sprayed onto a rotating seed mass
and, after drying, forms a thin layer on the seed, and various materials adhere
to the seed surface. This formulation is a substrate to which food, pesticides
and other substances can be added according to the purpose of coating. Seeds
that are spherical and uniform in shape, like canola seeds, are easily coated.
But seeds such as beet seeds, lettuce and quinoa are hard to cover. Ready-made
formulations for different seeds and for coating with different purposes are
prepared and marketed .
Seed
coating can serve different purposes depending on the type of material used in
the coating formulation, including:
-
Creating a suitable environment for the
establishment and rapid growth of seeds (growth stimulants, nutrients)
-
Uniform disinfection and effective control of
diseases and pests
-
Effective use of biological materials and low
need for fertilizers with low consumption of trace elements
-
Dealing with stresses (drought, salinity and
flooding ...) by placing moisture-absorbing materials and organic matter on the
seeds
-
Adjusting the emergence time of buds using
temperature-sensitive polymers, simultaneous flowering of mother and father
lines
- Uniformity, monochrome and high marketability
and coding of different varieties
Pelleting
Pellet
means deformation and increase the volume of seeds, which is done by placing
different materials on the seed coat and with the following goals.
- Possibility of mechanized sowing and
precise replacement in the planting bed in depth and with appropriate density,
low seed consumption and facilitate seed sowing and no need for transplanting,
-Possibility of placing different layers of
nutrients, disinfectants, biological materials, etc. on the seeds,
Pesticides are used during the coating or
seed pelleting process and can be used mixed with the coating formulation or
placed separately on the seed surface or at intervals in the coating layers. To
control seed diseases, pesticides are placed on the seed surface and in cases
where they may cause toxicity on the seed surface, it is placed in the cover
layers and away from the seed surface. Macro and micro nutrients can also be
placed in separate layers on the seed.
The coating created should not have adverse
effects on the seeds, should be permeable to water, while having strength on
the seed surface, should be easily dissolved in water and should be economical.
The most commercial use of pelleted seeds is in sugar beet seeds, which are
obtained from almost all European and Japanese crops, and most North American
crops come from pelleted seeds. Other commercial-grade pelleted seeds include
carrots, celery, chicory, leeks, lettuce, onions, peppers, tomatoes, cabbage,
sweet corn, grass, and ornamental flower seeds.
Pelleting is in the early stages of research and
development in Iran and has recently become popular in the commercial level of
tobacco seeds and to a lesser extent in the seeds of medicinal plants and
ornamental flowers.
pelleting can be made less
quickly than film coating. They require more care and cost more, and are
economically justified in the case of small and expensive seeds.