Seed Processing
- Seed processing includes different operations starting with seed cleaning, drying, sizing, pelleting and storage.
- The freshly harvested seeds are dried under shade to facilitate easy seed shattering and collection under controlled environments.
Stages of seed processing
Seed Cleaning:
- Field grown seeds contains substantial amount of debris from less than 20% to over 80% by volume, depending upon the crop and method of harvest.
- The seeds of low growing plants are cut at the soil line e.g. Alyssum, contains more field dirt.
- The seeds are cleaned manually or mechanically.
- In mechanical method, the seed is first put through a screen cleaner, which is the most widely used equipment for removing both plant parts and soil particles.
- After the initial removal of plant and field debris, additional rounds of seed cleaning are required if the seed contain outer coat structures that impede simulation in packaging and sowing, or water uptake during germination.
- It is customary to remove hairy layers on the seed coats of gazania.
- The development of seed cleaning and grading methods begin with mechanical separation of seed particles based on difference in their physical properties.
- Mechanical seed separation techniques are effective in cleaning out field debris from the crop seeds besides removal of broken and immature seeds.
Seed Sizing:
- Seed sizing is a process in which a heterogeneous population is physically separated by size to create a more homogeneous group of seeds.
- The traditional method for sizing the seed is to pass it through a set of stacked screens declining sequentially in aperture size.
- The screen types are generally made up of a wire or nylon woven mesh or a perforated metal sheet.
- Seed sizing is a challenging factor in extremely small sized seeds. For example there are approximately 10,000 petunia seeds in one gram.
- For very small seeded crops, a sonic sieve can be used for size separation.
Pelleting
- A seed pellet is a substance applied to the seed which obscures its shape, thereby making flat or irregularly shaped seeds more round, and making small and light seeds larger and heavier, thus enhancing precision planting and accurate placement by seeders.
- Most seeds are pelleted in a rotating drum to which the pelleting material and water are periodically added.
- Pellets are typically composed of fillers such as clays, diatomaceous earth, graphite, powdered perlite, or a combination of these and other materials
- A binding or cementing agent is also applied at specific concentrations which facilitates adhesion of the filler to the seed, thereby adding durability.
- The filler materials, as well as the binder, can be modified to regulate the water-holding capacity of the pellet.
- Since the pelleting process employs water as the solvent/binder for the pelleting material and cementing agents, it can also be absorbed by the seed during the pelleting process. As a result, seed storage life can be reduced for pelleted seed if the pelleting process is not carefully controlled during its application.
- Seed pellet is one of the most important recent seed enhancement innovations in flower plug production because they improve seed plantability and performance.
Seed Packaging
- Seeds are packed in different containers to protect them from extraneous environmental factors, to facilitate easier handling during storage and to enhance their marketability.
- Normally seeds are packed in cotton, jute, paper bags, polythene bags, laminated aluminum foil pouches, or aluminum cans.
- For long time storage hermetic containers such as laminated aluminum foil pouches or cans are used.
- Pouches are effective in maintaining desired levels of seed moisture for fairly long periods.
- Laminated pouches are handy and attractive, can withstand temperatures from 20 to 40° C, and occupy less space during storage.
- In open storage, humidity is controlled using a dehumidifier, while at low temperatures moisture proof containers are used to protect seeds from high humidity.
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