Soil compaction in coffee

One of the concerns of coffee producers should be the assessment of soil compaction caused by the traffic of different machines in the coffee growing area, a problem that interferes with productivity and the development of the crop.

The different management systems used in coffee farming, especially mechanized ones, are associated with an increase in traffic intensity and the load applied to the axles of tractors, harvesters and agricultural implements, which in some regions of the country can exceed 15 operations in an agricultural year. . All this movement of machines affects the structure and aggregation of the soil, which are attributes that affect the soil's porosity, density and permeability, water retention and movement capacity and compaction, especially in clayey soils.

In these areas, compaction has been identified as one of the main processes causing degradation of the soil structure, compromising its physical quality and making it difficult to maintain or obtain greater productivity. The compaction effect is more effective in the machine traffic line, due to the pressure applied by the wheelsets, as it most of the time exceeds the soil's capacity to resist the pressure exerted by the machinery, called load-bearing capacity, generating plastic deformations. in the soil structure.

Knowing the soil's capacity to resist these compressive forces from machine traffic is of fundamental importance for the sustainability of production systems, since the use of mechanization as a production tool is inevitable and growing, as it allows greater efficiency in operations and provides the viability of coffee crops. Currently, crops depend mainly on reducing costs, and mechanized harvesting can reduce production costs by up to 67% compared to manual harvesting, resulting in higher yields for the producer.

To evaluate the susceptibility to compaction and the appropriate moment to perform mechanized operations in the field, many physical and mechanical attributes of the soil have been used, and some of these properties that are related to the compressive behavior of the soil are obtained from its pressure curve. compression.

In this context, identifying soil compaction has become an important factor for crop production and management, which can be better understood by studying soil compressibility, whose definition is related to the capacity that unsaturated soils have to suffer volume reduction when subjected to external pressure. Therefore, understanding the compressive behavior of the soil becomes important because it is the basis, from a physical point of view, for choosing the most appropriate management.

Additional compaction problems occur when the pressure applied by machine wheels exceeds their load-bearing capacity, generating plastic deformations in their structure. Thus, the assessment of soil compressibility and its load-bearing capacity, under different humidity conditions and different management systems, is of great importance not only to determine the maximum pressures that the soil can withstand under these conditions, but also to minimize the risks of compaction in soils cultivated with coffee. Therefore, the objective of this study was to evaluate the compaction of soil cultivated with coffee under different implementation times.

Assessment work

Fieldwork was carried out in 2017 in an intensely mechanized coffee (Coffea arabica) farm at Fazenda Nossa Senhora, in the municipality of Muzambinho (MG), with the aim of evaluating the compaction and load-bearing capacity of a Red-Yellow Argisol (clay texture).

Three areas were evaluated, and in Area 1, the crop was implemented in 2014 (three years of implementation), with a spacing of 3,6m x 0,6m, in a total area of ​​3,7ha. In Area 2, the crop was planted in 2001 (16 years of implementation), with a spacing of 3,6m x 0,6m, in an area of ​​10,2ha, and in Area 3 the coffee plantation was established in 1985 (32 years of implementation), with a spacing of 4,0m x 1,5m, in an area of ​​1,5ha.

Soil collection to determine soil density, total porosity and load-bearing capacity occurred on the machines' wheelset line in layers of 0-0,10m, 0,10-0,20m and 0,20-0,40. 0,40m. The soil's resistance to penetration was determined along the wheel line to a depth of XNUMX m, using the impact penetrameter.

According to the results of the work, it was observed that in the three areas evaluated, the soil resistance to penetration (RP) was high throughout the soil profile evaluated up to a depth of 0,40m. However, it appears that the 32-year-old area had the lowest soil resistance to penetration to a depth of 0,29m. The lower PR in an area with longer management time is related to a minimization that occurs naturally over the years due to the accumulation of organic material in the surface layer of the soil.

For the critical limit of root growth in coffee, studies record that values ​​between 6 and 7MPa are critical in sandy soils, and 2,5MPa for clayey soils, however, the limiting PR for root growth for most crops is 2MPa . In any case, the soils in the areas under study were classified as clayey, presenting RP values ​​above 2MPa throughout the analyzed profile (Figure 1).

The high soil resistance to penetration, concomitantly with soil density and total porosity (Figure 2), decreases with depth and increasing age of the coffee plantation, which can be justified by the accumulation of organic material in these soils, which in the layer surface occurs due to the deposition of cultural remains.

The soil in the wheel line (LR) showed lower susceptibility to compaction in both layers for the area with 32 years of cultivation, with soil moisture below 33% (Figure 3). With the increase in soil depth, there is also an increase in its capacity to suffer greater pressure from machines, provided that traffic occurs when soil moisture is at field capacity (33%) or lower.

On the other hand, the three-year-old area was the one that presented the greatest consolidation pressure, possibly due to the greater preparation and more recent destructuring, with this, less protection of the organic matter deposited on the soil.

LR promoted a reduction in the absolute values ​​of preconsolidation pressure with an increase in the sampling layer. These results reflect the effect of greater soil compaction at the wheel line of 4,17MPa, in the area with 32 years of management, caused by the traffic of agricultural machinery, mainly during the coffee harvest. However, the ideal is to observe when the soil has a humidity level of less than 33% - you must use machines and implements, as at this humidity the soil can withstand such pressure, without causing damage to its structure and not compromising the development of plants.

Despite this, there is a tendency for soil compaction to occur if the load-bearing capacity is not respected, along with its critical humidity, especially in times of greater soil humidity, that is, periods of greater precipitation. In general, in the three-year area, the ideal is for traffic to be carried out at a humidity level of less than 36%, in the 16-year area, machine traffic should occur when humidity is less than 34%, and in the 32-year area , with humidity less than 32%.

The assessment of soil susceptibility to compaction and changes in its attributes caused by the traffic of agricultural machinery should be a concern for farmers, because limitations can reduce crop productivity and the profitability of agricultural activity.

Machines used in compaction assessment

The following tractors and harvesters were used to manage the crops: Massey Ferguson tractor, model Cafeeiro 275, with 75 hp; Yanmar 1155 4 x 4 Cafeeiro tractor, with 4hp 98TNV55-XAT engine; tractor brand Massey Ferguson 275 Advanced, with A4-4.1/MWM international engine, four cylinders with a displacement of 4.100cm3, 75hp; TDI coffee harvester, Electron model, with MWM D 229-4 67hp engine.

The implements used in the evaluation were: Kmaq fertilizer machine model comander H 10 S, with capacity for 450kg of fertilizers; “sweep everything” coffee blower, Bertanha brand with an average weight of 400kg; Mogiana Spirlandelli 25C coffee collector, Bertanha brand; Jumil brand transshipment trailer, with a capacity of 5mg/ha.

Fábio Henrique Barbosa Sandoval, Zigomar Menezes de Souza, Elizeu de Souza Lima, Ingrid Nehmi Oliveira, Lenon Henrique Lovera, Feagri - Campinas State University; Diego Alexander Aguilera Esteban, Feagri, State University of Campinas and 2Corporación Colombiana de Investigación Agropecuaria; Reginaldo Barbosa da Silva, Unesp - Registration Campus

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