Seed Conditioning and Handling

Seed as it comes from the field is never pure. It usually arrives at the cleaning plant containing large quantities of trash, green leaves, weeds, other crop seeds, and insects. If it contains such materials as green leaves and other high-moisture materials, it cannot be safely stored, efficiently handled, nor accurately seed conditioning until most of the foreign material has been removed.

Seed Conditioning and Handling

The process of removing these unwanted materials from a seed lot is known as seed conditioning.


The seed conditioner has five objectives when cleaning seed:

  1. Complete separation-removal of all contamination,
  2. Minimization of seed loss-some good seeds are removed along with contaminants in almost every conditioning operation and this loss must be kept at a minimum,
  3. Upgrading-improvement of seed quality through removal of decayed, cracked, broken, insect-damaged, or otherwise injured or low quality seed,
  4. Efficiency-the highest capacity consistent with effectiveness of separation, and
  5. Minimization of labor-labor is a direct operating cost and cannot be recovered.

Seeds can be separated by mechanical means only if they differ in some physical characteristic that can be detected by some mechanical or electrical process. Thus, the seed conditioner uses differences in physical characteristics of the seed crop being cleaned and those of seeds of other crops and weeds as well as inert matter.

Inert matter such as chaff, stems, and stones is usually the easiest to remove other crop seeds and weed seeds may be much more difficult, especially those similar in appearance and physical characteristics. Physical characteristics that are used to separate seeds are: size, length, width, thickness, shape, weight (specific gravity), surface texture, color, affinity for liquids, and electrical properties.


The seed conditioner should carefully analyze each seed lot as it comes from the field to determine what the conditioning problem will be and which machine or machines will do the best job. Since usually more than one machine must be used to completely condition a given seed lot to maximum purity and germination, their sequence of use is also important.

Pre-cleaning Equipment


  • Most commonly used pre-cleaning machine.
  • Rough clean various kinds of Trash from the seed lot.
  • Light particles removed -chaff, stem
  • Small and big particles removed
  • Normally much higher output than fine cleaning

De Bearding/De Awner

  • Before air screen cleaner
  • Optional- it can be bypassed
  • To break up the seed clusters of chaffy grasses
  • Seed flows much better in rest of cleaning process

Basic Cleaning

Manual Basic Cleaning

  • Remove unwanted seeds
  • Depending on species
  • Hand Picking
  • Hand sieves with fan or wind
  • Investment is minimum
  • Time consuming

Air Screen Cleaner

  • Basic seed-cleaning machine in most conditioning plants
  • Separate seed on the basis of size, specific gravity, and resistance to airflow
  • Many sizes of air screen cleaners exist-
    • Two-screen farm models
    • Large industrial cleaners with seven or eight screens and three or four air separations.

Gravity Separator

  • Best machine for upgrading seed quality
  • Remove undesirable seed and inert contamination that are so similar to the crop.
  • Remove deteriorated, moldy or decayed seed which are usually similar in size but have a lower specific gravity.
  • Heavy non-seed particles such as mud balls, soil particles, and: stones can also be removed.
  • Seeds are introduced from the feed hopper onto the porous metal or fabric deck
  • Where the combination of shaking and air mixing up through the deck causes them to stratify according to specific gravity.

Seed Conditioning

Dimensional sizing equipment

Several types of seed conditioning machines separate or upgrade seeds on the basis of thickness, length, or width.

  • Length Separator
  • Width and thickness separator
  • Texture separator
  • Spiral separator
  • Color separator

Indented Cylinder

  • Separates by length
  • Particularly useful for removing broken seeds
  • You can remove short from long and vice versa

Roll Machine/Velvet roll

  • Separates by roughness of surface
  • Also called dodder mill- effective in removing dodder from alfalfa
  • Remove rough textured seeds from smooth-textured seeds
  • Rough seeds are separated by their tendency to cling to the velvet-covered rolls.

Spiral Separator

  • Separates by speed of rolling
  • Only works with spherical seed
  • The round seeds move at much faster speeds and are thrown by centrifugal force

Color Sorting Machine

  • Originally design for removing broken seeds in soy bean
  • Most expensive and sophisticated equipment
  • Separate by color or light reflection
  • Light bulb reads the color of seed, air flow separates them
  • High precision
  • New versions have digital analysis or x ray to see embryo.

By Muhammad Asad Naseer

Research Associate/Graduate Student, Seed Physiology Lab, Department of Agronomy, University of Agriculture, Faisalabad.