This time of the year many livestock producers have begun to plant their cool season forages. Due to new technologies more and more forage seeds are being sold as coated. This has led to me receiving numerous calls regarding seed quality, planting rates, economics, etc. The below information is a Timely Information sheet written by Dr. Don Ball, a retired Extension Agronomist, and addresses many of those questions.
An ever-increasing percentage of commercially available forage crop seed is being coated prior to being marketed. The coating process involves treatment with an adhesive followed by application of some type of material that clings tightly to the seed. This coating may consist of any of several materials, often with lime as the base material, but sometimes clay or degradable plastic. Often the coating material contains a dye that gives the seed some bright color.
Coating of seed is especially common with forage legumes. In fact, almost all commercially available seed of alfalfa, white clover, and red clover is coated, and the amounts of other legume seed that is coated increases each year. Coating of legume seed is popular mainly because it allows the seed to be pre-inoculated with Rhizobium bacteria, thus saving the forage producer from having to perform this task. The commercial coating process also tends to increase the number of these nitrogen-fixing bacteria that are stuck to the seed, and subsequently protects them from the elements. This tends to increase bacterial survival, resulting in better infection of legume roots and ultimately more nitrogen fixation.
Current seed coating technology allows incorporation of a fungicide, and insecticide, and/or fertilizer nutrients onto the seed coat. For example, almost all alfalfa seed has a fungicide incorporated into the seed coat to help prevent “damping off” diseases during seedling establishment. While only small amounts of any material can be provided in the seed coating, this approach does offer the advantage of making certain that the desired material is in close proximity to the germinating seed.
For example, coated seed of small-seeded species such as bermudagrass are much easier to plant with a drill because coating increases the seed size and improves the rate of flow, plus the seed tend to be distributed more evenly if broadcast-planted.
The material used to coat seed obviously takes up space and has weight, which raises questions about seed value and seeding rates. Is a producer getting his money’s worth if a third or more of the contents of a bag of “seed” is coating material? Should he plant the same number of pounds of seed that he would have used if it had not been coated?
A good deal of research has been aimed at answering these questions. Typical results have shown that even though there are significantly fewer seed in a given volume or weight of coated seed as compared to uncoated seed, stands obtained are similar or better with coated seed. Planters usually need adjustment though, because of the larger diameter of coated seed and also the fact that coated seed tend to flow faster than uncoated seed.
Seed coating is not limited to forage crops, of course. In particular, the seed of many high-value vegetable and turf crops are coated as well. Coating seed does not overcome all the challenges associated with crop establishment, but it helps increase the chances of obtaining a stand. In view of the advancements that are being made in seed coating technology, it seems likely that an increasingly higher percentage of seed will be coated in the future.