Compaction in sugarcane harvesting

The mechanized harvesting of sugar cane is a reality in practically all cultivated areas in the country. However, it is necessary to be aware of the impacts that soil compaction has on the productivity and longevity of sugarcane fields and make the necessary adjustments to achieve the best economic gains.

Mechanized sugarcane harvesting has grown exponentially in the last decade, going from 25% to practically 95% of adoption of this system compared to manual harvesting. The gains related to cost reduction in reais per ton with the use of mechanized harvesting are indisputable, however a detailed analysis regarding the impacts that machines (harvesters + tractors and transshipments) cause in the sugarcane field must be taken into account and analyzed in detail to that agricultural management actions are taken seeking, in addition to cost reduction, productivity and profitability gains.

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When we compare the evolution of productivity in crops such as corn, soybeans and cotton, we note that in the same period there was an increase of around 30 to 40% in productivity, while in Brazilian sugarcane fields the average productivity remains stagnant between 75 and 80 t/ha . Obviously, this stagnation is related to other technological obstacles and not exclusively to the use of machines in crops, but it is worth remembering that the plants and producers that have been adopting the best agricultural mechanization practices are those that have been able to achieve average productivity above 95 t /ha, that is, an increase of between 20 and 30% (BELARDO, 2016a)

An extremely relevant factor is related to the harvest period and harvest time, which increased by 50% during the rainy season as the harvest, which was previously carried out from May to November, is now carried out from March to December, often starting in January or February. during the period of greater rainfall (MAZZA, 2016) and the traffic of machines in areas of greater humidity result in greater soil compaction.

COMPACTION IMPACTS

To understand the impact of machines on sugarcane harvesting, we first need to make some field observations, where it is often possible to observe situations resulting from the action of compaction and widespread trampling of sugarcane lines.

Situations like this inevitably lead to a drop in productivity in subsequent years and a drop in the longevity of sugarcane fields. Compaction is greater the greater the curvature of the furrow, and the sum of the compaction of the line and between the lines, when intense rainfall occurs, this results in runoff of water, soil, as well as herbicides and fertilizers, which inevitably ends up overloading the terraces (MAZZA, 2016).

Furthermore, the impact of soil compaction is directly related to the lower amount of sugarcane rooting and root confinement in smaller areas in the soil, resulting in less water and nutrient absorption by the plant, greater susceptibility to dry spells and dry periods and productivity losses. .

To try to measure productivity losses related to compaction and trampling of the sugarcane line, we can use some research data from the CTC that estimates losses between 10 and 15 t/ha per harvest year. Considering these assumptions, we have between 10% and 20% of productivity drop from one year to the next in t/ha, which at the end of a 5-year sugarcane plantation period would imply the loss of one crop year or approximately 75 t/ha ( BELARDO, 2016a).

TRAMPING AND TRAFFIC CONCEPTS

It is evident that the impact of compaction in the row and between the row of sugarcane and the trampling of ratoons are extremely relevant and that the machine x sugarcane interaction must be better managed.

To better understand the concept of trampling and traffic in sugarcane cultivation, it is essential that there is a safety distance between the machine and the crop which, according to Mialhe (2004) corresponds to the lateral distance, on both sides of the axis of the sugarcane crop. row of plants, from which the passage of the wheel is harmless to both the aerial part and the root system.

Ripoli and Ripoli (2009) comment that in sugarcane we must have a minimum distance of 25 cm between the edge of the tread of the tire or mat closest to the cane row and the center of the ratoon line. We know that sugarcane has a lateral tillering behavior towards the row and in general, we can consider that a sugarcane ratoon is approximately 40 cm wide (20 cm on each side of the center of the row).

Therefore, converging Mialhe's concept of safety clearance with the definition of Ripoli and Ripoli, we can state that in a sugarcane field with a ratoon approximately 40 cm wide, we would have 15 cm of safety clearance for sugarcane harvesting. (BELARDO, 2016b).

SUGAR CANE MACHINES AND SPACING

Based on these premises, we will carry out a technical analysis of the main harvesting sets (Harvesters + Tractors and Transshipments) and the main spacings adopted in Brazil (single of 1,50 m and alternating double of 0,90m X 1,50m).

When we evaluate the main spacing adopted in Brazil, the simple one of 1,50 m and the interaction of the machines with it, we observe that with the use of single-line sugarcane harvesters with gauges of 1,90 m and tractor + transshipment sets with gauge of 3,0 .12 m the problem related to safety clearance is in the harvester which has a distance of 15 cm, below the minimum of 23 cm, while the tractor + overflow set has 1 cm (figure 16a). There is the option of using narrower conveyors in sugarcane harvesters with a 40-inch wide “shoe” (18 cm) and with the use of this option, the safety clearance of the harvester would increase to 1 cm, that is, within the minimum required. to do so (figure XNUMXb).

This option confirms what has been practiced by most plants in Brazil that control traffic effectively using this harvesting system with a simple spacing of 1,50 m.

Evaluating the machine x sugarcane interaction in the alternating double spacing of 0,90m The problem becomes the overflow, which is 1,50 cm apart and below the recommended limit, while the harvester is 2,40 cm apart (Figure 3,0a). When we analyze the composition for two-row harvesters and the tractor + overflow set, both with a gauge of 12 m, the harvester remains at 32 cm and the overflow remains at 2 cm of safety distance, that is, within the acceptable limit (Figure 2,40b).

What happened in some areas where the use of alternating double planting was adopted and which we have observed to this day in the field is that despite the suitability of the harvesters for the spacing, the old tractor + transshipment set with a gauge of 3,0 m is often maintained and which it does not meet the minimum safety distance, in other words, there is no point in changing the spacing if you do not adjust the equipment to meet this gauge, as the stump trampling ends up being inevitable, mainly due to overflow (BELARDO, 2016c).

It is worth remembering that the possibility of deviation of the tractor + transshipment set is greater than that of the harvester. In this case, any carelessness on the part of the tractor operator can result in the sugarcane stubble being trampled on, especially when this set is made up of a tractor and two or more overflows, which are much more difficult to control and normally deviate from the original route in areas of greater slope (BELARDO et al 2015).

Evaluating the most recent option of harvesting two 1,50 m lines by harvesters, we observed that both sets would have gauges of 3,0 m and that the safety distance for the harvester would be 45 cm while for the tractor + transshipment set would be 23 cm, in this case, it would be the best option among all those analyzed related to the minimum safety distance (Figure 3).

The best solution to avoid this problem due to any deviation in the operation that impairs safety clearance has been the use of automatic pilot with signal correction via RTK, an efficient tool to control traffic and minimize the trampling of stumps and soil compaction, making it possible to travel with errors of the order of 2 to 5 cm. Baio and Moratelli (2011) proved that without the use of GPS with RTK correction the average error is 17 cm and they managed to achieve average results of 3,3 cm using the system, confirming that the use of this equipment is controllable and positive for traffic control.

As previously mentioned, we know that the deviation of transfers is greater than that of the tractor and more recently Passalaqua and Molin (2016) evaluated the occurrence of errors between passes of tractors and transfer trailers on flat terrain, sloping terrain without curvature and terrain downhill with curvature.

The result shows that despite the use of an autopilot system with correction via RTK signal, the deviations found for the tractor, even though they were smaller than the overflows, were above the acceptable value in all scenarios evaluated, but with values ​​closer to the terrain. flat with a straight route and higher elevations on slopes and curved routes. When observing the last axis of the second overflow, the deviation reflects, in its worst case scenario, its passage over the ratoon of the adjacent row, with the error exceeding the separation distance between two rows of sugarcane.

It is worth remembering that the sugarcane harvester has always been seen as the “villain” in relation to ratoon trampling and soil compaction, however, as we observed in previous analyses, we see that the major problem of ratoon trampling is related to the tractor + transshipment set due to to the slightest safety distance and possibility of deviation from the route.

Regarding soil compaction and the pressure exerted by the equipment, the harvester, which weighs approximately 20 t, distributes its weight more evenly due to the greater contact area between the conveyor belt and the soil. The tractor set with a weight of 13 t and two transshipments with an unladen weight of 6 t each plus a sugarcane load of 10 t each, would have a total of 32 t distributed in a more concentrated way, generating a higher density in kg/cm² and consequently greater compaction.

A good option to minimize the trampling of stumps due to traffic diversion and less compaction of transshipment is the gradual replacement of sets of one tractor + two transshipments with transshipments with greater load capacity and a greater number of axles, such as 21 t and four axles that carry the same amount of cane, but bring benefits such as more uniform weight distribution over the tires and operational gains such as less maneuvering and overflow time, in addition to obviously having less deviation in the route.

CONCLUSIONS

In general, we need to improve our analyzes of mechanized harvesting sets, because as we have seen, for each spacing model it is necessary to adapt the equipment to better control traffic and minimize the trampling of stumps and compaction of the row and between rows.

In this article we mainly address the machine x sugarcane interaction during harvesting, but we know that to maximize and improve agricultural operations we have to organize the work with good planning, mainly aiming at better harvesting efficiencies.

This planning begins with the definition of spacing, management zones and systematization of areas, going through soil conservation practices, such as the use of vegetation cover, crop rotation and reduced soil preparation, which combined with the adequacy of equipment and use of a control system of traffic, can generate further cost savings and productivity gains with averages above 100 t/ha, also increasing the longevity of sugarcane fields to more than 6 years. All this obviously with the ultimate objective of better economic results.

Guilherme Belardo, Unesp

Article published in issue 175 of Cultivar Máquina