Correct choice of subsoilers

When selecting and purchasing subsoilers, a careful evaluation is necessary, taking into account the conditions in which they will be used, the depth at which they wish to work and the power of the tractor that will be pulling. Then just choose from the more than 130 models sold in Brazil and choose the one most suitable for your property.

Due to the expansion of cultivation areas, the need to obtain high productivity, the evolution of technology used in agricultural machinery and implements, in addition to the availability of credit lines, there has been an increase in demand for various agricultural implements that promote soil preparation, resulting in a market increase in the industry that develops them.

Agricultural soil preparation operations can be defined based on the power source, such as manual or mechanized methods. These aim to promote favorable conditions for sowing, seed germination, seedling emergence, destruction and incorporation of cultural residues, elimination of weeds, in addition to decompacting soil with the aim of improving water infiltration, as well as assisting in root growth of the crop.

Currently, due to the competitiveness of the agricultural market, the aim is to obtain high productivity with the aim of optimizing the extraction of resources from agricultural soils and meeting the costs of implementing and investing in farming. As a consequence, there is a large-scale increase in the intensity of use of these soils, implying an increase in the trafficability of agricultural machines and implements for managing the exploited areas.

These factors, linked to inadequate management conditions, favor major structural changes in agricultural soils, with compaction being identified as the main cause of these changes. Compaction is the change in the shape and structural stability of soil properties, thus modifying the arrangement of constituent particles. In this way, there is a reduction in its volume (lower total porosity), affecting the most diverse physical, chemical and biological processes. These impediments, in addition to reducing the productive potential of the areas, can favor erosion and/or limit the root growth of plants, which harms the exploration of soil areas in search of water and nutrients.

Compaction is a problem that plagues the productive scenario of farmers, being one of the factors promoting the emergence of the direct planting system and controlled traffic agriculture, which aims to concentrate the passage of machines in the same location in the field. In this context, subsoilers can be mentioned, as the growth in their use for mechanical decompaction of soil on agricultural properties has made them one of the most offered and purchased implements on the national market.

However, for the correct selection and adjustment of this equipment, it is essential to observe the information contained in the technical catalogs and manuals made available by companies, which are a form of communication with commercial and informational objectives.

These materials do not necessarily need to convey all the information about a given product, as an excess of data can cause difficulty in assimilation by the receiver, consequently dissatisfaction (Schmid, 2006). However, the correct choice of information that will be made available, together with its quality, are essential requirements for creating a complete technical catalog.

From this, the objective was to analyze, relate and evaluate the technical dimensional and weight characteristics (relative to the mass) of national agricultural subsoilers, in order to support the selection of the model most appropriate to the specific needs of the farmer.

Firstly, national manufacturers of agricultural subsoilers were identified. Soon after, the models sold were cataloged and the dimensional and weight characteristics of this equipment were surveyed, which were obtained through technical catalogues, manuals and leaflets, totaling 139 models made available by 25 companies.

From this, a bank of information organized in an electronic spreadsheet was built, analyzing and quantifying the variables separately, namely: working width (m), mass (kg), required power (hp), number of rods and depth of work (cm). After completing data collection, a classification was created according to the number of stems described in Table 1.

The power/working width (RPL) relationship can be observed in Figure 1. This relationship (RPL) behaved in a constant manner, showing proportionality between the averages, that is, the increase in width leads to an increase in power demand in all classes studied. This is due to the fact that the working width is generally increased in greater proportion with the increase in the number of rods, generating an increase in power demand. Observing the variation in the number of rods in the implements and, therefore, in the working width depending on the classes, there is no tendency for a proportional increase or reduction in power with either the increase in width or the reduction.

Remembering that the working width is associated with the spacing between the rods, which in turn is influenced by the working depth, which is determined by the width of the tip (see Box 1). Therefore, it is the width of the tip that influences these important adjustments, and in certain implements, structural problems can interfere with the appropriate adjustments for the chosen tip. For example, the depth limiting wheel may not allow the desired depth to be reached and the structural shape of the chassis, which may prevent the rods from being properly arranged.

Figure 2 shows the power/working depth relationship for each class of agricultural subsoilers. For this relationship, which is also called specific force, we observe that with the increase in the number of rods there is an increase in power per unit of depth, this increase being more pronounced in class IV, as this classification includes subsoilers with up to 17 rods. , thus presenting a range of results of up to 11 hp/cm. Another fact is that subsoilers that have a greater number of rods require a larger and more resistant structure (chassis), which have a greater mass, which consequently requires greater power, this case can also be seen in Figure 4. The reasons Average, Maximum and Minimum, between the mass and the rod number, are shown in Figure 3.

Regarding the ratio between the mass and the number of rods, there is an increase in the mass of the subsoilers with the increase in the number of rods due to the larger size of the tool-holding structure (chassis). Despite this increase in averages occurring with the increase in classes, we can observe that in classes II and III the maximum values ​​were much higher. This is because these classes included subsoilers destined for the sugarcane sector. These are designed to break compactions up to 62cm deep, so the coupling structure of the organs (chassis) requires a greater amount of material to withstand a greater degree of effort (iron, metal).

The variation in the mass to power demand ratio, for the different classes of subsoilers, is illustrated in Figure 4. There was an increase in the mass of the tool holder chassis and rods in relation to the power demand, that is, the greater the implement (number of rods), the greater the power demand required or used just pulling the structure. This means that rolling resistance is greater as the number of rods increases. This fact is also reflected in the power-to-depth relationship, as rolling resistance (traction demand to pull the implement without preparing the soil) is greater with increasing class.

It is concluded that, when selecting and purchasing equipment, there is a need for a careful evaluation, as the particularities of each one must meet the needs that it will perform. The power to working width ratio behaves constantly, regardless of the number of rods, and can be used to help select the tractor/implement set. With an increase in the number of rods (working width), the mass of the subsoilers increases, consequently the power requirement.

BOX - Working depth

5 to 7 times the width of the tip.
Spacing between rods:
For first tips 1 to 1,5 times the depth;
For winged tips 1,5 to 2 times the depth.

Rafael Sobroza Becker, Airton dos Santos Alonço, Tiago Rodrigo Francetto, Dauto Pivetta Carpes, Bruno Zart, Laserg/UFSM 

Article published in issue 168 of Cultivar Máquinas