Polymer coating of vegetable seeds

Abstract

The seed coating process involves all aspects of sticking materials onto the surface of seeds. The term 'coated seed' has been applied to a seeds, which was either pelleted covered with an adhesive film. Such procedures are adequate for about 90 per cent of small seed species. The costs and benefits of the coating procedure should be evaluated prier to selecting the seeds for the operation. Some seeds of high aggregated value like hybrid flower seeds, usually obtained in small amounts should never be coated because the risks involved with the process may far exceed the benefits (Taylor and Harman, 1990). On the other hand for many species of seeds, the coating process is worthy to be applied with consequent improvement on the seeds quality and maintenance of properties after storage. Seed coating is a process designed to create a nutritious environment in the immediate vicinity of the germinating seed. This provides a " boost " for the seedling in its critical early stages of development. Coated seed was first manufactured in Canada in 1977. It was readily accepted by most users and now has a definite role to play in Canadian agriculture. Coated seed benefits the plant in its critical seedling stage thus ensuring early vigor and maximum establishment. There is some carryover effect from this increased seedling vigor but once the fertilizer coat has been assimilated by the plant, it cannot be of any further direct benefit in its future development. The present economic, nutrient and chemical benefits, which are available to coated seed users today, make it a very worthwhile product. The conventional treatment of seeds uses chemical products to protect the seeds and seedlings against diseases, insects and other plagues. The treatment is well accepted today as an agronomic practice for the seeds of most species and it is routine at the seed processing unit. However, the conventional seed treatment is limited as for the diversity of products to be applied and it also presents risks for the operator's health due to dust and handling poisonous products. Therefore, a new process, the seed wetting was developed. Since 90's, this technology is in the top of the sowing industry, due to the relative concerns with safety for workers and environment protection, as well as the sowing the precision, since the process serves to improve the plantability of the seeds. In recent years, film–coating methods have been developed to overcome these problems. In film coating, the chemicals are applied in a polymer that is sprayed on the seeds as they fall though a specialized machine. The polymer is rapidly dried, so that the seeds emerge with a complete, dry polymeric coating. Some novel applications have also been developed using the film coating method. For example, artificial polymers have been developed that exhibit temperature-sensitive permeability to water. These polymers are permeable to water at warm temperatures, but not at cool temperatures. Seeds coated with these polymers will not imbibe water – that is, absorb water and swell–if the temperature is below the set point of the polymer, potentially protecting the seed from chilling injury or germinating in an unfavorable environment.