​Constant pressure

Brazilian agricultural production breaks records with each harvest, several technologies are part of this process, from seed genetics, sowing, cultural treatments, harvesting, among others. The sowing operation is present in the cycle of agricultural operations for grain production, therefore, the adequate placement of the seed in the soil becomes fundamental, it must be positioned at the correct distance from the fertilizer and at the depth necessary for its germination and emergency.

The Direct Planting System (SPD) is a reality in Brazilian agriculture, which has been growing every year, making it increasingly necessary to modernize and study the topic, given new mechanisms added to agricultural machines. This system stands out for the lower intensity of soil mobilization, that is, preparation located in the sowing line, reduction in the frequency of agricultural machinery traffic on the land and for maintaining a greater quantity of plant mass on the surface, which which characterizes him as a conservationist.

However, soil preparation systems with mobilization across the entire area are still common, as is the case with conventional tillage and also with scarifiers (conservationist tillage). As there are different types of soils in Brazil, from the most clayey to the most sandy and prepared in different ways, the operation with quality seed placement at an adequate depth becomes a difficult task.

Fertilizer seeders feature double discs for creating the sowing furrow and controlling seed depth using two wheels parallel to these discs. The pressure exerted on the double discs is carried out mechanically by spiral springs, which must be adjusted row by row of the machine. The springs have compression and extension movements, their length and the number of spirals provide variation in the pressure exerted on the double discs quite frequently. Another important point to highlight regarding springs is that with constant use they can lose their elasticity.

Therefore, researchers at Unesp in Jaboticabal (SP) carried out a test to evaluate the use of pneumatic springs in the task of exerting pressure on the double seed discs. In the work, a seeder-fertilizer from the Jumil brand, model 3090 PD Exacta Air, was used, which features this technological innovation. The system consists of an electrically driven air compressor and individual pneumatic bags in each seeding row.

The use of new mechanisms developed for seeders-fertilizers can be evaluated using the statistical process control tool, in order to seek improvements in the seeding operation, as well as serving as a quality indicator. Statistical techniques for quality control in mechanized agricultural operations, used in different crops, obtain promising results, as the control of agricultural operations allows a reduction in variability, obtaining results closer to the specified limits (Milan & Fernandes, 2002) . According to Toledo et al Statistical process control (CEP) seeks to improve process quality by reducing variability, however, there is no process without variability, so the solution is to keep it within stability standards.

The JM3090 PD Exacta Air seeder, trailed, was configured for the direct planting system, with seven sowing lines (0,50m), all equipped with pneumatic springs as a pressure mechanism on the seed furrower, and 18” cutting discs. , furrowing rods for fertilizer, 16” double offset disc and floating “V” compacting wheels. During the experiment, the fertilizer and seed deposits were kept at half load. To drive the fertilizer seeder, a Valtra BM 125i tractor was used.

The pneumatic springs were adjusted to work with five pressures, 1bar, 2bar, 3bar, 4bar and 5bar. The pressure of the pneumatic springs is carried out by the compressor, which is activated/controlled by the machine's seeding monitor. For this to happen, simply set the value and enter it with the seeder raised, the pneumatic springs increase or decrease the pressure in all lines at the same time, not requiring adjustment with nuts in line by line.

The sowing depth of the soybean crop was measured after passing the seeder, manually removing the soil in the sowing line until each seed was located at three meters, measuring the distance from the seed to the ground level with a ruler. . It was observed that pressures of 3bar and 4bar showed less variation in relation to the desired depth, which was 5cm (Figure 1). The other pressures (1bar, 2bar and 5bar) showed greater amplitudes.

Figure 1 - Control chart for sowing depth

The average traction force on the bar showed a polynomial regression, and at pressures of 3bar and 4bar it was greater, exactly where the best seeding depth occurred. It can be inferred that, because the seeder works with less oscillation, it demands greater force, however, it works with less vibration and places the seed at an adequate depth.

The peak traction force on the bar showed the same behavior as the average traction force. The analysis of the control charts also makes clear the smaller oscillation of this parameter, at pressures of 3bar and 4bar the amplitude of the data is smaller.

The study concluded that the use of pneumatic springs in relation to spiral springs is a very viable alternative, due to the ease of adjustment, as with just one touch on the panel the pressure in all the machine's springs can be determined and the possibility of maintaining a more uniform the sowing depth.

This article was published in issue 141 of Cultivar Máquinas magazine. Click here to read the edition.