Soybean sowing quality

The sowing process is subject to the interference of several factors, from the correct choice of seed to the mechanisms responsible for its dosage and deposition, which affect the quality of seed distribution in the soil and require attention from producers.

One of the main challenges currently faced in the sowing process is to obtain an adequate plant stand, so that they can express their full genetic potential, with minimal intra and interspecific competition, enabling the achievement of high productivity. However, many factors play a role in obtaining this, such as the soil, the climate, the relief, the cultivar that will be used, the sowing speed and the components of a seeder-fertilizer. Therefore, it is very important that information about factors with the potential to influence the final quality of the sowing process is collected and analyzed, so that sowing errors are minimized and the process optimized, given that this operation is carried out only once during the cycle of a crop and, most of the time, in a short window of time.

The sowing operation, however, must take into account the particularities of each property, as the type and texture of the soil, precipitation and light in the region may influence the determination of the sowing window for the cultivar used, as well as the density. of seeds per hectare. According to recommendations from Embrapa (2013), variations of 200 thousand to 500 thousand soybean plants per hectare could have very similar productivity. However, at lower sowing densities there will be greater susceptibility to the emergence of weeds, as the environment becomes more favorable to their emergence and development, due to less shading in and between rows of the crop, negatively affecting the soybean production cycle. . At higher sowing densities, there is a higher cost to obtain seeds in addition to high intraspecific competition, due to the smaller spacing between plants.

Care when planting

The choice of seeds must also be carried out very carefully, always seeking the greatest possible germination power and vigor, in order to minimize failures arising from the non-germination of seedlings and, as a result, the producer will be increasing the chances of obtaining a stand of plants more uniform. Along with this, it should also be known that each cultivar may have significant differences in terms of size, growth habit, resistance to agrochemicals and expected productivity.

Furthermore, it has become common to sow using seeds with phytosanitary treatments, inoculation and coinoculation, as their use aims to protect the initial seedling stage and the vegetative period, including favoring biological nitrogen fixation, presenting positive effects on the productivity. Due to the use of these products, soybean seeds end up suffering changes in their physical structure and roughness, which can affect their distribution in the sowing process due to friction with the seeding machines' dosing mechanisms. Therefore, one of the alternatives to minimize deposition errors is the use of graphite solid lubricant in the amount of four grams per kilogram (g/kg) of soybean seed (Mantovani, 1999), aiming to improve the flowability of the seeds and minimize the effect of these products on the performance of seed dosing mechanisms.

Another alternative to mitigate the negative effects arising from the use of phytosanitary products in the sowing process is the use of coating polymers, which aim not only to protect the seed and the product that was applied to it, but also to provide greater uniformity in longitudinal distribution. According to Alonço (2018) and Pires (2017), both in horizontal alveolar disc dosers and in collector-dosers with pneumatic assistance, the use of polymers in the sowing process did not present a significant difference when compared to sowing using the addition of the solid graphite lubricant. , which indicates that the use of coating polymers can become a good option for producers. However, it is important to highlight the need to check the options that best suit the property's needs, so that the most profitable and correct procedures are carried out.

Analysis of factors before sowing

There are basically two pieces of equipment to carry out individual soybean sowing, using horizontal alveolar disc dosers or pneumatically assisted catcher-dosers. Firstly, attention must be paid to the size and uniformity of the batch of seeds depending on the size of the alveolus of the dosing disc - they should be approximately 10% smaller than the alveolus of the disc - this way, the deposition of double seeds may occur. be reduced and the filling of the alveoli with seeds will be facilitated. Along with this, you should also try to use a dosing disc with enough cells to meet the planned sowing density. It is possible to find discs on the national market that vary from 45 to 110 alveoli. When using discs with a greater number of alveoli, their peripheral speed will be lower, providing greater exposure time of the seed to the capture hole, thus reducing filling failures and, consequently, faulty spacing. 

In the pneumatically assisted seeder, we must pay attention to the suction pressure that will be used (vacuum). Low pressures may be insufficient for the dosing mechanism to capture, fix and transport the seeds to the release point. According to Becker (2016), at lower densities, the pneumatically assisted doser tends to have better performance than the horizontal disc doser, whereas at higher densities, the same is equivalent. Furthermore, Reis and Alonço (2001) concluded that at speeds up to 7,5km/h, the performance of a pneumatically assisted doser tends to be better and, above 7,5km/h, it tends to be equal. However, in both cases, the use of low densities associated with low displacement speeds provided the highest percentages of acceptable spacing. 

The fact that greater seeding failures occur at high speeds is due to the fact that the speed of the metering discs will also be high, thus leading to failures in filling the alveoli, regardless of the type of meter used. Furthermore, the higher the speed used, the greater the mechanical damage caused to the seeds, due to the need to use high peripheral speeds on the dosing discs, which could compromise the vigor and germination power of the seeds. Therefore, Embrapa (2013) recommendations indicate the use of seeding speeds between 4km/h and 6km/h.

Seeding failures may also be greater when the terrain is sloped. According to Alonço (2014), using pneumatically assisted meter-catchers for sowing soybean seeds, both on positive and negative transversal slopes, there was a significant reduction in the percentage of acceptable spacings in relation to sowing carried out without transversal slope, that is, in the flat. Therefore, it is extremely important to analyze the land on which the sowing will be carried out and, if necessary, carry out operations such as constructing contour lines to reduce the impacts of the slope.

Another very important factor is the correct choice of the conductor tube. As the dosers are located at a certain height above the ground, the conductive tubes are responsible for carrying out and discharging the seeds, from the doser to the sowing furrow. However, it is essential that the seed has its trajectory altered as little as possible, so that the seed does not “repeal” inside the conductive tube, this could be caused by the presence of changes in the internal surface of the tube or the internal diameter. . When it is small in diameter, it may cause greater contact between the seeds and the tube and, depending on the variation in the seed exit end, this may affect the longitudinal distribution in the soil, resulting in multiple and faulty spacings. Studies by Carpes (2015) concluded that conductive tubes with a parabolic shape, facing the back of the seeder, guarantee the best performance when sowing soybeans.

Groove opening

Another important aspect to be observed are the mechanisms for cutting crop residue and opening furrows. According to Becker (2017), each type of cutting disc may present different performances depending on the conditions in which it is subjected, influencing fuel consumption, traction force and soil mobilization. Currently there are smooth, corrugated, corrugated, grooved and scalloped cutting discs.

To open the furrow in which the seed will be deposited, it is necessary to analyze which component is most suitable - furrow rod or double disc. However, as in the choice of other mechanisms in relation to machine-soil, we must observe the characteristics and type of soil, as the performance of the furrowing rods and double discs may be influenced by these factors. According to Silveira (1989), furrowing rods are commonly used in soils where there was previously conventional tillage and without crop residues. Furthermore, they are also often used in places where there is animal trampling. In this way, the furrowing rods also perform the scarification function, decompacting the surface layer of the soil. Double discs, on the other hand, are normally used on heavier soils and with the presence of cultural residues. 

Special attention is also required when adjusting the depth limiting wheels, these play an important role in the sowing process. It is usually recommended by Embrapa (2013) that sowing occurs at depths of 3cm to 5cm, varying depending on the type of soil. In this way, making it possible for the soybean seed to acquire 50% of its weight in water, an amount considered necessary to germinate and still have enough vigor to emerge. Along with this, the compacting wheel must also be adjusted so that it can close and laterally compact the sowing furrow, causing correct contact between the seed and the soil, as if it compacts the soil in excess on the surface, seedlings will emerge. will be difficult, possibly causing unevenness in the plant stand or even making it impossible for seedlings to emerge.

Operator factor

There is an increasing requirement that operators have extensive knowledge about the equipment and factors that may influence the operation they are carrying out, as they will be responsible for checking whether the materials are suitable and, if not, they must know how to identify and correct them. them, in order to extract the full potential of the equipment.

With the increasing modernization of machines, implements and technologies aimed at the agricultural sector, increasingly qualified professionals are being required, who have operational experience, are efficient and who also have sufficient knowledge to use all equipment and computer technologies. on board, applying them to each operation to be carried out, taking into account the needs and particularities of the property; After all, errors in the sowing operation will negatively influence productivity and may make the environment more susceptible to the emergence of weeds and diseases.

Tractor factor

Often purchased solely for power and robustness, the tractor, responsible for pulling the seeder, plays a fundamental role in carrying out the sowing process. The sizing of the number of rows that will be sown must be obtained based on the traction capacity of the tractor that will be used. However, it is not advisable to use tractors with excessive power, as operational efficiency, in this case, will be low, as in addition to the increase in fuel consumption, slipping and wear of parts will be greater, reducing the useful life of the tractor. in addition to harming the longitudinal distribution of seeds in the sowing process.

In addition to this, you should always look for tractors equipped with transmission systems that have adequate scaling between gears, so that gear changes are always smooth, without showing jerks and, thus, contributing to the sowing quality. Currently, agricultural tractors are equipped with sliding mechanical transmissions, partially synchronized, fully synchronized and hydromechanical, so the latter are the ones with the best quality in gear shifting.

Furthermore, the lifting capacity and flow of the hydraulic system pump must also be analyzed, as these will be responsible for lifting the implements at certain speeds. Therefore, the greater the lifting capacity of the hydraulic system and the pump flow, the heavier the implement that the tractor will be pulling, as long as it has the power available to do so and, along with this, the process of lifting and lowering the implement during headland maneuvers will be made easier, as the speed at which this process will take place will be greater, increasing operational efficiency.

Final considerations

The sowing process is subject to the interference of several factors, ranging from the correct choice of seed that will be used to the mechanisms responsible for dosing and deposition, and all of these factors can be influenced depending on the location to which they will be subjected. . Therefore, it is extremely important that the producer knows how to identify the particularities and characteristics of his property and, based on this, choose the most appropriate equipment and technologies to provide him with the best conditions for implementing the crop in the field.

How to assess the quality of plant distribution

The most common and easiest way to analyze the uniformity of seed distribution is by analyzing the spacing between emerging plants. Those considered “acceptable” are those that will be 0,5 to 1,5 times the Xref (“reference X”) of another plant. Spacings considered multiple are those in which the plants are spaced at a distance smaller than 0,5 times the Xref and faulty spacings are when they are greater than 1,5 times the Xref. The Xref being the theoretically ideal distance at which one plant should be from another, that is, if we wish to obtain 13 soybean plants per linear meter, the Xref will be 7,69 centimeters (cm).:

In this example, the spacings considered acceptable will be those in which the plants are 3,8cm to 11,5cm apart, the multiples will be those in which the plants are 3,8cm or less from each other and the faulty ones will be those in that the spacing between plants is greater than 11,5cm, as can be seen in Figure 1.

Pablo do Amaral Alonço, Airton dos Santos Alonço, Dauto Pivetta Carpes, Antonio Robson Moreira, Laserg/UFSM

Article published in issue 186 of Cultivar Máquinas, July 2018.