Techniques: Pelleting

Seed pelleting is the process of adding inert materials to seeds to change their size and shape for improved plantability.

 

Seed pelleting is the process of adding inert materials to seeds to change their size and shape for improved plantability. Small and irregularly shaped seeds, such as lettuce seeds, can  be treated as larger, round-shaped seed thanks to pelleting. Pelleting simplifies singulating seeds in the field and planting them in precise locations. For crops like onion, precise seed placement is of great advantage as uniform bulb development is assured with equal distance planting.

A range of benefits

Over the years, the benefits of pelleting have grown to include:

  • Increased oxygen penetration/availability
  • Wider pellet density range allowing more accurate spacing of seed in a wide range of planting conditions
  • Pellet loading
  • Better field visibility
What kind of seeds are pelleted?

Seeds of various sizes are commercially pelleted, from relatively large seeds like onion and tomato to very small seeds like lettuce species. For onion, the seed can increase in weight 6-fold due to pelleting; there are approximately 230 raw seeds per gram, and after pelleting the diameter may be 13.5/64th of an inch (0.54cm). The volume for 1000 propagules is 3.7 cm³ for raw seed compared to 18.0 cm³ after pelleting. The smallest seed that Seed Dynamics pellets is Begonia. Median seed weight for raw begonia is 88,000 seeds per gram. After pelleting, the seed count can average 857 seeds per gram, an increased mass of over 100-fold.

Ideal for mechanical seed metering

Pelleting is ideal for mechanical seed metering/planting in direct fields and culture applications. In the coastal and desert valleys of California and southwest Arizona (as in other areas of the world), it is common to use precision vaccuum planters, as well as a host of others.

Split-pellet technology for increased oxygen penetration

Historically, the primary obstacle for pellet use has been slow and erratic emergence  associated with insufficient oxygen supply to the seed. The development of a splitting pellet like our High-Density, Medium-Density or Light-Density lettuce pellets are especially beneficial to growers that plant lettuce under saturated soil-water conditions caused by irrigation after sowing. A pellet that can split open upon hydration allows oxygenated water to move directly to the seed.

 

Varying pellet weights to fine tune planting

We've developed different pellet weights and density to meet growers needs to "fine-tune" planting and make seed handling easier.

 

Lighter seeds for greenhouse planting

For example, the greenhouse industry sows pepper seeds for transplanting in plug-trays commonly using vacuum-drum seeders. Greenhouse managers prefer a light, smooth pellet that permits rapid adherence with a tight seal, "seed to vaccuum hole," on the planting drum.  Our Gro-Coat® LD  and Prep-Coat® LD pellets have a 50% lower weight per pellet than conventional pellets such as those used in direct field seeding applications.

Lighter pellets weigh less per box or pail (boxes and pails are packed by seed number), so shipping costs are lower and handling is easier.

 

Denser seeds for precise "drops"

"Drop" refers to the distance between the soil and the sowing metering device. When the drop is great, pellet weight is  important. Pellet weight also depends on the speed of the tractor sowing the seeds. For example, lettuce seed sowing tractor speeds in the Yuma and Imperial Valleys can be twice as fast as speeds used in the coastal valleys of California due to larger fields and tighter planting schedules. Growers using the higher tractor speeds prefer a heavier-weighted pellet. The higher the pellet weight, the better the pellet "drop". Straighter drops during planting produce less bouncing in the seed furrows, thus field singulation and uniform plant spacing are maintained. Grower preferences in different regions of the US have initiated the development of different pellet weights.

Pelleted seed ingredients: bulking and binder

There are two components to a seed pellet: bulking (or coating) material and binder.

The bulking material can be either a mixture of several different mineral and/or organic substances or a single component. The coating material changes the size, shape, and weight of the seed. Good coating materials allow for uniformity of particle size distribution while lacking any phytotoxicity.

The second component, the binder, holds the coating material together. Binder concentration is critical because too much binder will delay germination. Too little binder will cause chipping and cracking of pellets in the planter box, which can cause skips and/or wide gaps in the plant rows. Many different compounds have been used as binders, including various starches, sugars, gum arabic, clay, cellulose, vinyl polymers, and water. All pellets have the same volume; only the weight, and thus the density, of the pellet is different.

Product name

Pellet to seed
weight ratio*

Weight (g)
per 100 pellets

Pellets (x10³)
per kg

Light Density LD

Prep-Coat® LD

Gro-Coat® LD

Prep-Coat® Special LD

1 to 17

2.0

49

Medium Density MD

Prep-Coat® MD

Gro-Coat® MD

Prep-Coat® Special MD

PULSE® Prep-Coat®

PULSE® Gro-Coat®

1 to 25

2.7

37

High Density HD

Prep-Coat® HD

Gro-Coat® HD

Prep-Coat® Special HD

1 to 35

3.8

26

* The average pellet weight divided by the average seed weight