Pneumatic planters are the ideal machines for producers looking for homogeneous seed distribution and more practicality when adjusting the equipment.
The objective of precision seeders is to distribute a certain quantity of seeds on the soil with a predetermined density, regulated according to the number of seeds per linear meter and spacing between rows, whether in plowed and harrowed soil, or by direct planting.
To carry out all operations in a single pass, seeders have specific sectors that perform the functions of opening a furrow in the soil, dosing a quantity of seeds and positioning them on the ground, covering the furrow and firming the soil around the seeds. Normally, seeders also have the function of distributing fertilizer and other products, distributing them in the same pass – these machines are also called seeders-fertilizers.
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The seeders must also allow for regular depth and seed distribution in the row, perfect alignment and spacing, significant seed savings and greater speed of work. And to achieve the aforementioned objectives, they must be designed with systems that allow versatility in relation to the type of seeds, regular distribution and easy adjustment, constant depth and the possibility of working at high speeds.
The seeders must serve the different production systems of the main summer and winter crops in Brazil – cotton, peanuts, rice, beans, castor beans, corn, soybeans, oats, canola, rye, barley, wheat, among others and, therefore, They have systems for opening and closing furrows, and dosing and distributing seeds and fertilizers with various adjustments to meet the differences between seed sizes and densities.
Currently, the seeder-fertilizer is one of the agricultural machines used in the agricultural production process that most incorporates technology. Precision during the seeding operation is guaranteed by well-designed, efficient and precise mechanisms. However, there are several factors that influence its accuracy, mainly its seed distribution mechanism.
Precision seeders are the most used in the country and allow the distribution of seeds individually at a distance from each other in a line, aiming to facilitate cultural treatments and efficient harvesting. Seed spacing and planting lines depend on the desired population per hectare and, to achieve these goals, seeders need to have a specific device for dosing seeds in their reservoir and adjusting lines on the chassis.
In precision seeders sold in Brazil, the main seed dosing systems are mechanical, with a perforated horizontal disc, and a pneumatic system. Both systems have advantages and disadvantages, but when it comes to efficiency in relation to filling discs, the pneumatic system has the greatest advantage, where there are practically no flaws in seed selection, resulting in greater use of the planted area, with better uniformity. in the distribution of seeds in the soil. Another advantage presented is the lower rate of mechanical damage to the seeds, as they do not suffer the mechanical action that occurs on dosing discs in perforated disc machines.
The main disadvantages are that it is a system that requires more dedicated and specialized maintenance, due to numerous connections and joints of the pneumatic and hydraulic systems, in addition to having a higher acquisition cost compared to mechanical seeders. In some comparative studies of mechanical and pneumatic systems, the acquisition of a pneumatic seeder is not justified by the cost-benefit aspect, since it presents a small difference in relation to the quality of longitudinal seed distribution, but has a large difference in relation to the price. , compared to a mechanical machine with the same number of lines.
Pneumatic systems can be of the positive pressure or vacuum type, the latter being the most widespread among the main manufacturers. In this system, a vertical dosing disc, mounted in each planting row, selects the seeds from a small reservoir located at the base of the disc. Seeds are supplied to the reservoir from a main store.
A negative pressure (vacuum) is responsible for keeping the seeds adhered to the holes located on the periphery of the discs while they rotate. Normally, the pressure comes from a central fan powered by the PTO or hydraulic motor driven by the tractor's hydraulic system, or from fans mounted in each line driven by electric motors.
A cleaning device, or singulator, is responsible for eliminating excess extra seeds that may be stuck in the same hole in the dosing disc, avoiding failed seeds and double seeds. A vacuum cutting mechanism is responsible for interrupting the action of negative pressure and causing the seed to fall as it passes over a tube, where the seed is sent and deposited in the soil.
The tube, in a curved shape, allows the seed to fall freely, giving it an impulse contrary to the movement of the seeder, avoiding rebounds and ricochets during the fall, improving the uniformity of longitudinal distribution of the seeds.
When there is a need to change seeds, according to the crop to be planted, it is necessary to choose a disc with holes compatible with the new seed, in addition to adjusting the pressure of the pneumatic system according to the density and weight of the seed. . These are procedures that are carried out quickly by the machine operator.
After use in planting, several parts must be inspected for periodic maintenance of the system, paying particular attention to wear on plastic parts that come into contact with the seeds, the presence of pressure leaks, obstructions, wear or warping in the seed ducts. and play in the axle bearings.
Ricardo Ferreira Garcia, Uenf
Article published in issue 147 of Cultivar Máquinas.
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