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 Main subject - may/june 2008
Film coating in relation to seed covering
Alexandre Levien
amlevien@gmail.com
Silmar T. Peske e Leopoldo Baudet
The chemical polymeric industry is the one that has presented the largest development in the last decade. Commercial products from several companies are commercialized in the agricultural market for seed coating. Polymers are characterized for being the combination of various atoms, very often from several classes and/or multiple connections (the biggest examples of a polymer in application are plastic and paint). Polymers for the coating of seeds have the characteristic of already possessing adhesive and dye, which in specific formulations for the treatment of seeds has the aim of improving the process and the final quality of the treated seeds. An ideal polymer should not be permeable to water steam, but should compulsorily allow the absorption of water by the seeds.
The coating of seeds consists of the depositing of a fine and uniform layer of a polymer on the surface of the seed. It is used together with chemical and biological treatment, being protecting material applied in a very precise quantity and with a minimum of impact on the environment. This makes the technology highly efficient in the protection of seeds, as it combines fungicide with insecticide and other compositions with a fine layer or film made of liquid polymer (film-coating).
Due to the protection imposed by polymer on the seeds, in relation to variations of temperature and humidity in the soil as well as in the storage, the poymerized seeds tend to present better germination and emergence, mainly under adverse conditions. This reverberates significantly in the success of the establishment of the plantule and in turn of the cultivation. It also improves the solidification of the defensives used in the treatment of seeds and makes the addition of other products possible, like micro and macro nutrients, hormones, and in some cases, powder products. However, the benefit is not verified only in the seeds; that is, apart from improving the appearance and plantability of the seeds, it improves the handling and the application of chemical products, giving a better protection to the workers and to the environment.
Polymer is a slightly more viscose material than the majority of chemicals used as defensives in the treatment of seeds. Consequently, its use demands equipment for the treatment of seeds able to apply the product with uniformity and dosage preciseness. In Brazil, this usage requirement can be obtained with conventional tractors from machine manufacturers, who are worried in innovating and providing total conditions in their products, that is, with specific adaptations for the application of products.
There are no restrictions in the use of polymer, being able to be used in small seed species (tobacco and carrot), as well as in big ones (soybean, corn, and cotton), as long as the dosage applied to the seeds is uniform, principally in the case of irregular formed seeds, those of which require more precision in the treatment.
The polymer acts like an extra layer, forming an "envelopment" of the seed, together with any other product applied to it, be it with the objective of protecting from the adversities coming from pathogens and the environment in general, or of providing better conditions for germination and emergence of the seeds, significantly improving the efficiency of any intended treatment. This issue is directly related to the establishment of the plants in the production field, providing more probability of reaching the population of plants per intended area by the producer, which is essential in the success of the final production of the culture. Its effect is even more evident in vegetables and hybrids in general, where the uniformity of emergence and the adequate population of plants are crucial, mainly due to the value of the seed, and often to the lower density of the sowing, a situation in which the seeds are better represented in the population.
From a commercial point of view, another advantage is related to the appearance or the image of the polymerized seed, allowing its identification by different colors, species, cultivars, treatments, or any other differentiations.
Cost/Benefit Relation
Treatment of seeds (using polymer + fungicide + insecticide) represents one of the lowest financial investments that a producer can have, however, with a great return potential in the investment. Efficient application is essential to guarantee that all the seeds are coated with an adequate quantity of the chemical product, so that the advantages of the seed treatment are maximized.
The cost of usage of the polymer should remain between 2 to 3% at the most of the cost of the seeds. Be they from big cultures, like soybean, corn, or cotton, or in vegetables and forage.
The cost/benefit relation is always favorable, independent of the situation. However, its visibility is clearer in hybrid seeds and vegetables.
To exemplify, we have the following situations for corn seeds:
- Total cost of the bag of hybrid corn seeds: US$84,00 / bag of 20kg
- Cost of the seeds themselves: US$ 66.00 (78,57%)
- Cost of the insecticide: US$ 11.00 (13,09%)
- Cost of the fungicide: US$ 5.40 (6,43%)
- Cost of the polymer: US$ 1.60 (1.91%)
If we consider the possibility in the need to have a re-sowing of the area, the cost/benefit relation is very favorable. This is a very probable situation for several cultures, even for soybean.
Seeds are essential components of any cultivation system. Yet, it has been generally considered a factor of less importance for the tillage planning. In the past, the farmers were more worried with the price of seeds than with their intrinsic potential to improve the performance of the cultures. The success in the cultivation of the land is in the use of high quality seeds. Temperature, humidity, and the action of fungus and insects present in the seed and in the soil are conditions that can harm germination, initial growth, and the establishment of plants, and consequently a good stand of the tillage.
Nowadays, with the development of new hybrids and varieties, through conventional breeding and biotechnology, the obtainers are incorporating a more genetic value to the seeds and increasing, like this, the productive potential of the crops. With this, it is extremely important that seed treatment be done, to protect seedlings in the initial stages of their development, originating, with this, vigorous and productive plants.
Improvement of the treatment with the use of polymers
As exposed before, the placement of the polymer on the seed can be considered as an essential process, due to various reasons already mentioned, underlining among them that of providing an adequate distribution of the products in the seed, in which practically all of them will have the same dosage of products. To emphasize this characteristic of the use of polymers, a study was conducted to demonstrate their efficiency. The tool usually used to verify the efficiency of the application of the polymer is color. Nevertheless, this is a quality that can easily be misleading. So, a more precise tool was investigated, involving the weight of the seeds, in which the register is done with a number, minimizing contingent mistakes.
The study was carried out with soybean seeds, where the seeds were standardized for size, with sieves of 6.5 and 6.0 in diameter. Immediately the treatment was performed on 50kg of seeds with fungicide in the recommended dosage by the manufacturer and another 50kg of seeds treated with fungicide and a polymer, also in the recommended dosage by the manufacturers. After having performed the treatments (seeds without treatment, seeds treated with fungicide, and seeds treated with fungicide and polymers), 800 seeds from each treatment were weighed one by one on an analytical precision weighing machine with four decimal figures.
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