Seed Processing and Grading
Authors: Ravi Kumawat, Madhu Choudhary, Kana Ram Kumawat

The harvested seed has various factors that affect its sowing, quality, and storability. These factors (inert matter, weed seed, other crop seed, immature seed, damaged seed, diseased seed and undersized seed) are to be reduced up to threshold level to improve sowing seed quality. All the operations from harvesting to storage are performed carefully to improve the sowing seed quality and longevity.

Improvement in the physical quality of seed lot by removal of undesirable material and upgrading of seed quality through removal of damaged and undersized seed by mechanical devices with highest efficiency is defined as seed processing. It involves drying, pre-conditioning, basic cleaning and grading.

Requirements of seed processing

  • Complete separation
  • Minimum seed loss
  • Up grading upto required quality
  • High efficiency
  • Minimum requirement of labour

    1. Preconditioning
    This is the operation that prepares a seed lot for basic cleaning. Equipments required for this operation is generally specific for individual crop. Some important preconditioning equipment is as

    A. Sheller
    It is made up of perforated steel sheet with concave structure to remove kernel (seed) of maize from cob. The perforated steel allows the seed to pass through and retain the cobs and its parts.

    B. Huller
    It removes tightly fixed husk from seeds of grasses to facilitate in the process of sowing and germination. This process is known as hulling.

    C. Debearder
    It removes awn and other appendages from seed of oat and barley that hampers processing of seed lot. This process is known as Debearding.

    D. Scarifier
    It scratches the hard seed coat to facilitate process of germination by increasing exchange of water and oxygen in crops like lucerene, faba bean, and rice bean and this process is known as scarification.

    2. Basic cleaning
    This step of seed processing removes the larger, smaller, lighter and thicker, adulterants as compared to the crop seed, from the seed lot. It is done on the basis of weight, size, and density using cleaner with air screen. This involves following basic steps

    A. Grader
    It separates undersized seeds and coarse impurities viz., trash, soil pads etc. from the normal desirable seed on the basis of seed density and size with the help of screen of different mesh size and their vibration. B

    B. Scalper
    High quantity of inert matter is present with seed after threshing, winnowing or pre conditioning. It is top most screen of a seed cleaner with larger holes than desirable seed size to remove the inert matter of larger size than the seed. This process is known as scalping.

    C. Aspirator
    It removes lighter inert matter and adulterant from the crop seed with the help of air pressure and the process is known as aspiration.

    3. Grading
    Classification of a seed lot on the basis of commercial usages viz., size, shape, density, and colour is known as grading. It is done for further improvement of seed lot as finishing operation. Grading requires different types of separators to removes weed and broken and undesirable seeds. The different type grading equipments are as follows.

    A. Disk separator
    Pieces of broken seeds, weed and other crop seed of round shape can be removed by the disk separators. It has a series of indented disk that are rotated inside a cylinder through which the seeds moves.

    B. Indented cylindrical separators
    It can separate the impurities especially broken seed, other crop seeds and weed seed that are either longer or shorter than the crop seed. It has two types of grading system as Forward grading- removal of impurities of shorter than the required seed size eg. Wheat, rice Reverse grading- removal of impurities of larger than the required seed size

    C. Gravity separators
    Gravity separators exploited the differences of density between the quality seed and undesirable seed. It employs the principal of floatation, in which the seeds are vertically stratified in layer on the deck according to their density by vibration. It improves the germination percentage of seed lot as it removes immature, broken, undesirable seeds.

    D. Spiral separators
    Difference in the roundness or shape of the seed are exploited in the in the spiral or dropper separators for removal of contaminants.

    E. Colour separators
    It can remove seeds of different varieties, crops or weed based on difference in the colour of the seed. Colour separator improves the genetic purity, seed health and separate out weathered and moisture damage seeds.

    F. Surface texture separators
    It removes inert matter based on the surface texture differences to removes rough texture weed and other crop seeds from smooth crop seeds.

    G. Magnetic separators

    It separates the small weed and other crop seed and mechanically damaged seed based on the differences in the seeds affinity for liquids

About Author / Additional Info:
I am pursuing Ph. D from MPUAT, Udaipur