Speed ​​assessment with mechanical and pneumatic seeders

One of the biggest bottlenecks in soybean sowing quality is related to careful adjustment and maintenance of the seeder. The uniform distribution of seeds along the furrow directly affects the good productivity of all crops.

A group of researchers, formed from a partnership between Aprosoja Mato Grosso, Embrapa Milho e Sorgo and the Direct Planting Group (GPD) of FCA/Unesp Botucatu (SP), evaluated the quality of soybean sowing in different regions of the state of Mato Grosso, the main soy producing state in Brazil. The data was collected by the Aprosoja and Embrapa teams during the Technological Circuit – Soy Stage in 2018.

In a survey carried out in the state of Mato Grosso after the start of the 2018/2019 harvest, it was noted that 27% of producers had sowing quality with acceptable seed spacing below 50%, which is worrying in terms of good productivity.

During the process of implementing a crop, the most relevant aspects for success are related to the performance of the seeder-fertilizer, such as efficient cutting of straw, opening of the furrow, dosage of fertilizer, deposition of seeds in the correct quantity and depth and mainly the planting speed.

Research and field observations show that seeders, when at high speeds (above recommended), remove the precision character, thus reducing the sowing quality and increasing the rate of multiple and failed spacings. Thus, according to literature data, the ideal speed for pneumatic metering seeders would be 6km/h, depending on field conditions, it is tolerable to work up to 7,5km/h without affecting distribution accuracy. For the mechanical dosing system (horizontal disc), it is recommended to work at a speed of 5km/h, with a speed of up to 5,5km/h being tolerable, within field conditions.

Seeders equipped with pneumatic dosers (vacuum) generally have superior quality in the longitudinal distribution of seeds when compared to mechanical dosers (horizontal disc), at the same speed. It is important to highlight that, by increasing the speed of the tractor-seeder set, the precision in seed deposition is exponentially impaired in both dosers.

A survey carried out on soybean farms in the state of Mato Grosso, with approximately 180 machines, revealed that 35,75% sow their areas with a mechanical seeder and 64,25% use a pneumatic seeder (Graph 1) and, furthermore, 20,32 %% of producers sow at the speed recommended for each dosing system.

In the mechanical metering system (Table 1), the data shows that more than 80% of producers sow their crops at speeds above the speed range considered tolerable for this metering system. In pneumatic seeders (Table 2), it is noted that 31% of producers work at speeds above what is tolerable.

In addition to the speed for both dosers, the sowing quality was surveyed (acceptable, multiple and faulty spacings), evaluating the effectiveness of the distribution of these dosers. High speeds cause the seeds to collide against the walls of the conductor tube, altering their falling time, directly interfering with the spacing between them in the sowing furrow. In addition to the interference with deposition, another point where speed interferes is the soil disturbance at the opening of the furrow, compromising the distribution and seeding depth.

In the mechanical dosing system, the plantability index (Table 3) reveals that 62,50% of producers have a seed distribution quality between 50% and 70% of acceptable spacings and that 37,50% have below 50%. This reinforces that there is a large margin of multiple or faulty spacing, directly compromising productivity.

In pneumatic seeders (Table 4), the plantability index is more satisfactory, showing that 13% of seeders have a seed distribution accuracy greater than 70%. And less than 19% with results below 50%.

The incorrect distribution of seeds along the furrow compromises the initial development of the plants, resulting in less use of resources such as water, nutrients, light, etc. Multiple plants generate competition between plants, causing etiolation and a decrease in pod set. There are other problems, such as competition for light, fewer branches, with reduced individual production, smaller stem diameter, leaving plants more prone to lodging. The flaws are the absence of plants in the field, allowing the development of invasive plants, many of which are difficult to control, such as horseweed (conyza bonariensis) and bittergrass (Digitaria insularis).

Linked to maintenance and adjustment problems, the travel speed of the tractor-seeder set is one of the main points of interference in the longitudinal distribution of seeds along the furrow. Therefore, problems with adjusting the seeder on the cutting disc, pressure on the cart and seed depth are exacerbated by excessive speed.

Emerson Borghi, Embrapa Corn and Sorgo; Paulo Roberto Arbex Silva, Júlio César Santos Pereira, Luiz Henrique Menck Rusconi, Unesp; Murilo Alves Moreira, LDC