The evaluation of dosing mechanisms, with regard to seed distribution, can be carried out visually in the field, by checking the emergence of seedlings of a crop or through laboratory tests, in which the deposition of seeds on mats coated with felt. Although the field visual method is still used, factors intrinsic to the seeds can hide the real performance of the mechanism, for example, non-germination due to a physiological factor. For this reason, tests carried out in laboratories determine the real performance of the doser, since factors extrinsic to these do not allow changes in the performance of the mechanism, guaranteeing greater reliability.
Regarding seed distribution, some researchers recommend that seeders equipped with horizontal honeycomb disc dosers should provide longitudinal distribution of seeds with acceptable spacing levels above 60%.
Regarding errors in seed dosing, the factors that can contribute to reducing the quality of the operation are: seed characteristics; performance and wear of scraper/excluder mechanisms, and angular speed of the dosing disc.
Horizontal honeycombed disc dosers (commonly called mechanical) have a greater sensitivity in adapting the seed to the alveolus, which can influence the filling and release of seeds. In the case of corn, there is still one more factor to be observed, the shape of the seeds. If they are round (R), the recessed ring must be used to avoid damage to the seeds by the exclusion mechanisms; if they are classified as flat seeds (C), the normal ring can be used.
Wear of the scraper/excluder mechanisms can cause failures in the seed individualization process. It is also necessary to check the action of the springs that provide the necessary pressure to activate the scrapers on the dosing discs. Another important factor is the cleanliness of these mechanisms, so that they do not get stuck in a certain position.
The influence of the seeder's travel speed on seed distribution can be assessed by reducing or increasing the peripheral speed of the dosing discs (rotation), to reach the recommended quantity of seeds per linear meter. However, if this speed is high, it may cause failures in filling the alveoli, and may also reduce the efficiency of the scraping mechanisms and their exclusion. Several studies carried out concluded that for seeder travel speeds greater than 7,5km/h, the precision in the longitudinal distribution of seeds in both pneumatic and horizontal honeycomb disc dosers is similar, being an influencing factor regardless of the level of technology. embedded in the machine.
Regarding the productivity of corn crops, the use of high plant populations in areas with high productive potential and also irrigated areas means that there is a need to increase the rotation of the dosing disc in order to reach the pre-established sowing density. Therefore, to minimize errors in dosing and seed distribution, it is necessary to carry out the sowing operation at a lower displacement speed, which will require a lower rotation of the dosing disc.
When seed distribution is not uniform, two problems arise that directly affect the productivity of a crop, double and faulty spacing. In the case of double spacing, intraspecific competition is favored, that is, there is competition between cultivated plants. When faulty spacing occurs, weeds appear in the space where a cultivated plant should exist and compete with the main crop for light, water, nutrients, CO2 and space, in a system called interspecific competition.
Corn is one of the crops most sensitive to variation in the plant population, as it does not have a mechanism to compensate for spaces caused by irregularities in sowing. In situations of high populations, changes in the arrangement of plants in the sowing line may result in a reduction in the size, number of ears and grains per ear, as well as changes in the plant architecture, such as a reduction in the diameter of the stalk, conferring susceptibility to lodging and consequently causing losses at harvest time.
Each production system, depending on its specificities, requires management in order to maximize crop production. This technique can take into account water availability, soil fertility, cultivar, sowing time, spacing between plants and between rows.
Thus, observing factors related to the functioning of metering mechanisms and which can lead to errors in the sowing operation, work was carried out by researchers from the Federal University of Santa Maria, with the aim of evaluating the performance of a horizontal honeycomb disc meter in the distribution longitudinal distribution of corn seeds at four different sowing densities and dosing disc rotations.
The experiment was conducted at the Agricultural Machinery Research and Development Laboratory - Laserg, at the Federal University of Santa Maria. The tests were carried out on a bench made up of a doser support, an electric motor drive system and a mat covered with felt, which simulates the speed of movement of the seeder. A horizontal honeycomb disc doser was used. The disc was selected according to the dimensions of the seeds, allowing a gap between the alveolus and the seed of approximately 10%, greater than their maximum size, so that it does not provide a double dose or obstruct the release of seeds. seeds.
Hybrid corn seeds, Pionner C3, were used, and varying the rotations of the metering disc resulted in four different sowing densities (60; 70; 80; 90 thousand/week/ha) (17,14; 20,00; 22,86. 25,71; 6 rpm), respectively. The simulated working speed on the treadmill was 1,67km/h (XNUMXm/s) for all treatments.
The longitudinal distribution was evaluated by the spacing between seeds, subsequently classified as acceptable, defective and multiple. Acceptable ones are those that appear in a range of 0,5 to 1,5 times the planned theoretical spacing; failures occur when they exceed the upper limit and multiples when they are below the lower limit of acceptable spacings (ABNT, 1994).
The number of spacings observed is in accordance with that proposed by Dias (2012), reducing the number of observations from 250 seeds estimated by ISO 7256/1 (1982) to 105 spacings in corn seeds. A conductor tube with the following conformation was used: length: 46,49cm; seed entry angle 0º; seed exit angle: 33,98º; seed entry measurements (mm): 75x51 and seed exit measurements (mm): 44x19. The experimental design used was completely randomized, with four replications, treatment means were analyzed using linear regression, using Microsoft Excel software.
The results of the experiment showed that increasing the rotation of the dosing disc caused a reduction in the percentage of spacing between seeds classified as acceptable and an increase in those classified as failed and multiple, as shown in Figure 6.
The performance result of the evaluated doser can be considered good, as the treatments presented an acceptable percentage close to 90% at the lowest density. However, the increase in rotation of the dosing disc influenced the reduction in the quality of longitudinal seed distribution. With the increase in sowing density, there was a small tendency towards an increase in the percentage of failed and multiple spacings. This factor can be associated with the occurrence of failures in filling the alveoli of the dosing disc and also with the low efficiency of the double seed scraping mechanism.
Another condition that can be observed is that increasing the rotation of the dosing disc can cause a change in the point at which the seeds fall into the conductive tube, which causes a greater incidence of pealing as the seeds descend to the bottom of the furrow. , changing the fall time and positioning in the sowing line.
The evaluated horizontal honeycomb disc mechanical feeder presented, considering data in the literature, a good performance even at the highest densities evaluated, however, there is a tendency to reduce the quality of longitudinal distribution of seeds with an increase in the angular velocity of the disc (rotation), negatively interfering with its performance.
*Per Airton dos Santos Alonço, Tiago Rodrigo Francetto, Antonio Robson Moreira e Bruno Christiano Correa Ruiz Zart, from Laserg/UFSM
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