Seed coating is the practice of covering seed with external material to improve handling, protection, and to a lesser extent, germination enhancement and plant establishment.
Seed coating is the process of applying exogenous materials to the surface of the natural seed. Physical properties of seed are enhanced by this technique and active ingredients are added to seed. The aim of physical modification of seed is to handle the seed through standardization of seed size and weight.
In some cases, aim is to reduce friction and improve flow ability, a thicker coverage is applied to expensive morphological uneven seed. Seed coating technology have been developed mostly on crop and vegetable species and to lesser extent on turf grasses, pastures, and flowers
Types of Seed Coating
There are three different techniques used for seed coating:
- Wet coating
- Split coating
- Film coating
The melt coats dissolve when wet and gradually wash away from around the seed. The melt coats often require more water to wash the coating material away from the seed, and more time for oxygen to reach the seed through the saturated coating material.
Melt coats may offer advantages when soils are saturated, but oxygen availability always influences the speed, uniformity, and total percentage of germination.
Split coats initially retain their shape when wet and, by capillary action, pass moisture through the pill to be imbibed by the seed. The seed swells and cracks the pill by internal turgor pressure. The split coats often permit germination with less water and, as they split, allow uniform, rapid oxygen access to the surface of the seed.
A thin polymer film smooths the seed surface for better flow-ability. The polymer also influences water uptake and the adherence of chemical fungicide treatments. Film-coating only increases the raw weight of seed by 1% to 5%, far less than powder coatings.
Seed coating machine having a spinner and rotater is preferably used for seed treating. The seed is suspended in an upward-moving controlled temperature air stream.
The particles are directed (not scattered) in a cyclic path through the coating zone as many times as required to receive the desired increments of coating.
Thus, each seed is exposed to the coating zone. The warm air stream also serves to dry the product while it is being coated. The coating material is atomized on seed and dried by hot dry air.
The rapid drying action prevents overheating of the seed. In this manner, the desired quantity of coating is laid down on the seed.
Seed Coating Objectives
- Enhance germination process and percentage
- Enhance viability and vigor
- Prevent seed and soil borne diseases
- Early and uniform establishment and growth of seedling
- Enhance nodulation
- Uniform crop stands even in adverse soil conditions
Seed coating enhances germination potential (Stand Establishment), vigor of the seedlings, physiology and ultimately yield of crops.