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 Main subject - jan/feb 2004
Seed Coating
Leopoldo Baudet
lmbaudet@ufpel.edu.br
Wolmer Peres
wolperes@uol.com.br
Imagine a farmer, having at his disposal a package that contains exactly what he wants in order to have security of a good protection, germination, emergence and uniform stand of his crop. Imagine that this package is adhered to the own seed, that is to say, the package is in each seed that he bought. The seed is covered with fungicides, insecticide, herbicide, hydrophobic materials, etc; it still has his favorite team's color. This package is the result of a high quality seed treatment, accomplished with safety to protect the seeds from several pathogens and to improve its flow and sowing capacity. That is possible in the agriculture today and it will be discussed in this work.
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 coating was developed. Since the 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 with precision, since the process serves to improve the plantability of the seeds.
Coating was first used by chineses, where they covered rice seeds with mud to avoid it from floating. The first steps of this technology, decades ago, were given in vegetable seeds. The cost of vegetable crops, specifically in the case of carrot, used to reach very high levels, mainly of work force, because of the need to uniformize the stand. The coating of vegetable seeds came to solve this problem with uniform size and format of the seeds, assuring sowing precision and application of chemical products.
Seed coating consists of the deposition of a fine and uniform layer of a polymeric and other products on the surface of the seed. In general, the process represents a one third of the covering and the seed two thirds (the coated seed can reach up to 50 material parts and one seed part). It can be used jointly with the chemical and biological treatment, a protecting material and with minimum impact on the environment. This makes this technology highly efficient in the protection of the seeds, when combining fungicides with insecticide (active ingredients) and with a layer or pellicle made of polymeric liquid (sticker).
As for the application methodology, the seeds are mixed with a sticker, so that each seed is hidden. The stickers should be soluble in water and the polymeric usually used are organic, starches, natural resins, sugars, glues that are dispersed in water. The solids are added right after. When the seed gets in touch with the soil, the recovering should not offer resistance to the radicle and to the structure that it will form the aerial part of the plant, allowing the passage of water and oxygen so that the embryo begins to develop naturally.
Specific details of the methodology used are usually commercial secrets; therefore, there are only available general descriptions. The key of the success includes the selection of the appropriate sticker, of the appropriate formulation, intensity of the appropriate mixture and of the appropriate balance among the parts of the system: seed, sticker, work method, time of drying and duration of the treatment.
This advanced technology allows combining hormones, micro elements, fungicides, insecticide and composed buffer, modifying the permeability to gases and moisture of the seeds. It must allow an easy degradation of the pellet and be of biodegradable nature. It must allow the seeds to germinate and emerge under conditions below ideal.
In the case of hybrid corn seeds, coating was developed to delay the germination of the seeds and consequently its flowering. This helps the adjustment of the flowering period of the paternal line that usually must be sowed later, since it ripens earlier. Other advantages are: a pollen distribution in a longer period, which could increase the income up to 50%; the availability of the pollen in a longer period, which tends to produce more flat seeds of medium sizes. The use of the polymeric in the control of the germination period in hybrid corn seeds was reported by Landec Ag. The polymeric is permeable or impermeable to the water, in agreement with the temperature.
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