Benefits of agricultural traffic control for soil

With the modernization of agriculture and intense adoption of agricultural mechanization, especially mechanized harvesting, concerns arise in the sugarcane management system regarding soil compaction and its harmful effects on the physical attributes of the soil and root development. Currently, there is great concern about the increase in agricultural areas with compaction problems, which, in part, is due to the excess weight of machines and their traffic without considering humidity and the load-bearing capacity (CSC) of the ground.

Soil compaction is characterized by compression of the soil, with changes in the organization of particles, with an increase in density and a reduction in soil porosity. The extent of the problem on the ground varies according to vehicle mass, soil type, soil water content, machine speed, contact pressure, number of passes and the interactions of these factors with agricultural practices.

Compaction is caused by the static load applied to the soil and dynamic forces, caused by vibration of the tractor and implement, wheel slippage, sudden changes in direction and changes in acceleration/braking. It is known that, when the pressure applied to the soil exceeds its internal resistance, additional compaction occurs with changes in its attributes, creating restrictions to root development. It is essential that the soil presents favorable conditions for root growth, which allows the exploration of a greater volume of soil in depth, increasing access to water and nutrients and reducing the risks of water deficit, allowing the crop to express its greater productive potential.

A management alternative that can be successful for sugarcane cultivation in Brazilian sugarcane fields is the use of management with traffic control. This management system separates traffic zones from areas where plants grow, concentrating the passage of tires on permanent lines, thus, a smaller area will be reached. To achieve this, there must be a change in the crop spacing and/or in the gauge of the machines. Sugarcane plantations that already adopt traffic control use sugarcane spacing of 1,5m and tractor and transshipment gauge of 3m, diverging from traditional management that uses spacing between 1,4m and 1,5m and machine gauge of less than 2m.

In addition to adjusting the crop spacing and machine gauge, the assisted steering system, better known as autopilot, has been used. This equipment is used to guide agricultural machines in field operations, in such a way that movement always occurs in parallel lines, which results in greater uniformity in spacing, with better use of the land and less traffic on the cultivation lines. In sugarcane fields, adjusting the machine gauge to the crop spacing combined with the use of autopilot contributes to reducing the area covered by agricultural tires by 26%, due to the overlapping of tire passes in the center of the rows.

In management with traffic control, the concept of “sugarcane bed” arises, that is, an area of ​​40cm on each side of the cultivation line does not receive wheel traffic from the tractor-transshipment set, while in traditional management, tire traffic occurs. next to or even on the ratoon, which harms the growth and longevity of sugarcane fields. Therefore, traffic control can be a management practice that aims to preserve ideal soil conditions for crop growth in untrafficked areas , contributing to increasing the longevity of the crop.

Another effective measure to prevent soil compaction is the use of lighter machines or carrying out traffic on drier soils, applying pressures lower than the load bearing capacity (CSC) of the soil. The load-bearing capacity of the soil represents a relationship between the pre-consolidation pressure of the soil and its moisture, such that an increase in moisture reduces the pre-consolidation pressure in the soil and, consequently, the CSC. The pre-consolidation pressure of the soil is the greatest pressure suffered by the soil in the past, therefore, the application of pressures on the soil greater than the pre-consolidation pressure causes non-recoverable deformation, that is, additional compaction and degradation of the soil structure. .

Fieldwork was carried out in the 2010/2011 harvest in an intensely mechanized commercial sugarcane farm in the municipality of Pradópolis-SP (Usina São Martinho) with the objective of evaluating the load-bearing capacity of a dystrophic Red Oxisol ( clayey texture and flat topography) and root development in traditional management systems and with traffic control. A Case MX tractor was used to manage the crops, with an engine power of 270 hp and a mass of 12 tons. In harvesting the sugarcane, the Case A-7700 tracked harvester was used, with a track type wheel, engine power of 335 hp and mass of 19 t and the same Case MX tractor, dragging a transshipment of three compartments with a total mass (loaded) of 40 t.

According to the results of the work, management with traffic control provided lower soil density and greater porosity in the planting line (LP, ratoon), compared to traditional management. This occurred due to the absence of tractor tire traffic and overflow on, or close to, the ratoon, in handling with traffic control. In the center of the line (EL), the soil presented greater density and lower porosity in handling with traffic control, as tire traffic overlaps along the machines' passes. Thus, the adjustment of the tractor and transshipment gauge and the use of the autopilot combine a better traffic condition between the rows, with the absence of traffic in the planting line and sugarcane bed, which preserves the physical quality of the soil. in the region of root development.

In the center of the line, the soil with traffic control showed higher CSC compared to traditional management, for any moisture content. It is recommended to carry out machine traffic with soil moisture below the plasticity limit (34% dry weight), that is, in a friable or tenacious soil condition. It is worth mentioning that the friability region represents a range of soil moisture, where the water content is adequate for mechanized operations, mainly soil preparation. For the research conditions, taking this value as an example, there is a greater load-bearing capacity in handling with traffic control (335kPa), compared to traditional handling (299kPa). The results reflect the effect of greater soil compaction in the center of the planting row in management with traffic control, caused by the overlapping of the passes of the tractor tires and the transshipment, which increases the traction of the machines, promoting fuel savings and gains in service income. However, it should be noted that soil compaction can develop laterally towards the sugarcane bed and, thus, harm the roots and mask the benefits of this management system.

For any soil moisture value, traditional management showed greater load-bearing capacity in the planting line. Considering again the humidity of 34%, the CSC in traditional management was 315kPa, while in management with traffic control it was 292kPa. This greater soil resistance in traditional management in the planting line is characterized by the effect of agricultural tire traffic close to the sugarcane stump, throughout the cultivation cycles, making the soil more compacted and more resistant to new deformations. Soils with high values ​​of pre-consolidation pressure have greater mechanical resistance to root penetration, which can restrict root growth and sugarcane productivity.

A possible problem in managing traffic control in Brazilian sugarcane fields, and present in this work, is the use of harvesters with a gauge different from the gauge of the machines, which promotes conveyor belt traffic close to the planting line (site region). In this case, the harvester has a gauge of 1,88m and applies a contact pressure of 132kPa to the soil surface. This pressure is lower than the soil CSC, for any soil moisture, in the planting line in both management systems, avoiding additional soil compaction. This result indicates high internal resistance between particles and aggregates, which provided greater structural stability to the soil. One of the main factors responsible for compaction in sugarcane fields has been tractor traffic and transshipment during harvesting, and self-propelled machines when applying inputs, as these have a small contact area between the tire and the soil, exerting pressure on the soil surface that can exceed 450kPa.

From a practical point of view, the increase in the contact area of ​​the wheelset with the ground is efficient in reducing the risk of compaction caused by machine traffic. Another preventive measure has been monitoring soil moisture and attempting to carry out mechanized activities in conditions of humidity lower than the limiting humidity, indicated in the CSC model. For example, a tractor used in agricultural operations exerts a static pressure on the ground surface of 363kPa, so this machine must travel on the ground in conditions of humidity below 29%, for handling with traffic control (Figure 2). For traditional management, the same pressure must be exerted, in conditions of humidity below 18% (Figure 2). Thus, management with gauge adjustment and use of automatic pilot favors work schedules in agricultural companies, due to less dependence on soil moisture (which is influenced by weather conditions), as it allows agricultural machines to work on the soil more humid.

The work also made it possible to observe the greater rooting of sugarcane in the use of traffic control in relation to traditional management. These results express the benefits of traffic control management for sugarcane cultivation. A decrease in root dry matter was observed, from the planting row to the center of the row, in the two management systems evaluated. The smaller number of roots between the rows is mainly related to physical limitations of the soil caused by machine traffic. Greater soil compaction restricts root growth and reduces the volume of soil used, which can cause loss of productivity, especially in rainfed crops.

The sugarcane management system with traffic control promoted greater CSC of the soil between rows and enabled the traffic of agricultural machines in soils with higher moisture content, due to the higher values ​​of pre-consolidation pressure (the adjustment of the tractor gauge and transshipment to 3m and the use of autopilot contribute to the preservation of the physical quality of the soil, in the ratoon region, and to the greater development of the sugarcane root system).

Assessing soil susceptibility to compaction and changes in its attributes caused by agricultural machinery traffic should be a concern for farmers, because limitations can reduce crop productivity and the profitability of agricultural activity. The use of traffic control in intensely mechanized areas represents a rational form of management, which minimizes the effect of compaction on the sugarcane and its root system, contributing to making the activity more sustainable and competitive. We would like to thank Usina São Martinho for providing the study area and for assistance with fieldwork.

This article was published in issue 137 of Cultivar Máquinas magazine. Click here to read the edition.