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 Main subject - may/june 2008
continuation: Film coating in relation to seed covering
Analyzing the results obtained, we verified that the seeds that were weighed without any treatment varied in weight, from 100mg to 185mg, with an average of 142.5mg (fig. 1). The seeds that were treated only with fungicide had values from 106mg to 230mg, with an average of 168mg (fig. 2). However, the seeds that were treated with fungicide + polymer, the values varied from 116mg to 196mg, with an average of 156mg (fig. 3). The figures show a big difference in the distribution of weight in the seeds because of the treatments, in which some are concentrated around the average, as is the case of the seeds without treatment and those with polymers, while the seeds treated only with fungicide present a larger dispersion of the data.
From this point of view, we can infer that when treatment of seeds is done only with fungicide, there are seeds that remain with little coating of the product and others in which the product adheres in larger quantities to their surface, because the amplitude of the weight of the seeds was much larger than that verified with film coating. The larger the concentration of the values around the average, the more uniform is the treatment.
This shows that when polymers are used, there is a better distribution of the products in the treatment in the whole lot of seeds treated (the treatment becomes more uniform in all the seeds), becoming very similar to the figure of the data of untreated seeds.
The discovery that film coating increases the efficiency in covering of seeds with different products means that the risks of having a super dosage and, with this, phytotoxicity, are minimized, as having seeds in which there is practically no covering with products to increase their performance (fungicide, insecticide, hormones, etc.).
Some considerations of treatment efficiency in seeds
In discussing the coating of seeds, some important issues that should be considered can be put forward, as:
Small Seeds x Large Seeds
A perception exists that there is a great difference in terms of the area to be treated according to the size of seeds. Thus, analyzing the situation and using soybean seeds as an example, we have the following situation from the seeds coming from the 5 and 6,5mm sieves:
- 5mm Sieve. Presents 10 seeds/gram and each one with an area of 78,54 mm2. Thus, 1kg has around 10,000 seeds, which represent 785,400 mm2 of area to be treated (surface of seeds).
- 6,5mm Sieve. Presents 5.9 seeds/gram and each one with an area of 132.73 mm2. So, 1kg has around 5,900 seeds, which represent 783,07 mm2 of area to be treated (surface of seeds).
Soybean seed characteristics screen 5 and 6,5 mm
This shows that the area to be treated, in terms of seed weight, be it small or large, is practically the same. The small seeds have a smaller area, but have a larger number per weight, compensating the difference.
Dosage x Number of Seeds
What interests us in the treatment of seeds is the dosage in each seed, because each one will probably produce a plant, regardless of its treatment or weight. Therefore, let us analyze the dosage per seed in 1 kg of soybean seeds with a 5mm sieve, and 1 kg of soybean seeds with a 6.5mm sieve according to the table in the text. Soybean seeds with a 5mm sieve have around 10,000 seeds/kg, while the soybean seeds with a 6.5mm sieve have 5.900 seeds/kg. Hence, the recommendation of 3ml of polymer per kg/seed means 0.0003ml for the small seeds and 0.0005ml for the large ones. Therefore, the large seeds will receive a dosage that is 50% superior to that of the small ones, requiring that the small seeds receive an adequate adjustment of polymer (as well as of other products) to fulfill their function. In this manner, the treatment of the small ones requires a bigger investment to increase their performance.
Film coating is an operation to increase the efficiency of seed covering, emphasyzing the improvement of seed coating, avoiding a super and a sub-dosage of the product. It also underlines the cost/benefit relation of the application of film coating, constituting itself in the lower cost element. Another aspect approached in this article is that considering film coating in 1kg of seeds, the smaller seeds receive a lower dosage per unit, which should be taken into consideration in the coating process.
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