Soil compaction care

Conventional soil preparation can bring about several changes in its structure, highlighting compaction, which under intense conditions weakens plant root growth.

Do plants like compaction? Yes, the plant likes compaction, but in mild conditions and not excessively, as this way the roots will have greater contact with the soil, providing greater efficiency in absorbing adequate amounts of water and nutrients. However, if there is excess compaction, it will lead to problems with root development and, consequently, in the absorption of water and nutrients. Therefore, it is necessary to know the phenomenon of soil compaction and understand its causes and consequences.

The soil compaction effect is the result of clay agglomeration in a certain portion of the soil, resulting in a less permeable layer. Therefore, this effect can be an aggravating process for lower crop production and problems associated with the physical qualities of the soil, such as, for example, infiltration and water retention, aeration and macroporosity, soil density, resistance to root penetration , in addition to causing less nutrient availability to plants, which leads to restriction of root growth. Soil penetration resistance increases with compaction, but is also highly dependent on soil moisture.

The increase in soil density can be caused by natural factors in the soil, and when this occurs, it is called densification, which is the migration of an accumulation of clay from the surface layers to the subsoil, causing a reduction in the permeability of the site. , this occurs in argisols, for example. But the compaction itself is caused by external factors, with the formation of compaction islands, resulting in less permeable layers, due to the traffic of machines and implements and the passage of animals, etc. Thus, soil preparation directly influences the formation of compacted areas in the soil.

According to Santiago & Rossetto (2007), conventional soil preparation consists of turning surface layers to reduce compaction in the mobilized layer, incorporating correctives and fertilizers, increasing pore spaces and, consequently, increasing permeability and air and water storage. on the ground.

Compaction can be determined by different assessment methods, such as: a) Visual: observe whether the area is waterlogged, underdeveloped plants, malformed roots, etc.; b) Soil density: undisturbed soil samples are collected, and the percentage of macropores is also analyzed; c) Soil Mechanical Resistance to Penetration (RMSP): carried out using penetrometers, evaluating the resistance that the soil offers to its penetration into the ground; d) Others, such as opening trenches to analyze the soil profile, etc. The RMSP assessment is a widely used method, and presents good correlation in the assessment of soil compaction. It is a process that presents greater agility in sampling, in which results are obtained in less time, in addition to the work being less tiring and more comfortable for the operator.

In this way, with the assessment of the Soil's Mechanical Resistance to Penetration, together with the humidity corresponding to the soil layer studied, it is possible to analyze the impacts of compaction and whether it interferes with the development and productive potential of the crop. Therefore, this work aimed to evaluate the effects of three conventional soil preparation equipment on the mechanical resistance of the soil to penetration and on the production of green and dry matter of corn for silage. 

Periodic soil preparation was carried out using: 1) disc plow, followed by two harrows for loosening and leveling; 2) intermediate harrow, also followed by two harrows for declogging and leveling; and 3) rotary hoe. The effects on soil mechanical resistance to penetration (RMSP) and its relationship with soil compaction were evaluated under field conditions.

The study was conducted in an experimental area, in the municipality of Rio Paranaíba (MG), which has an average altitude of 1.100 meters. The soil in the region is classified as a dystrophic red – yellow latosol, with a clayey texture, with 42% clay, in flat relief, and has been managed with the same soil preparation systems since 2014 for grain production.

IN THE FIELD

After preparing the soil, the corn crop for silage was installed, with the hybrid MG 744 Morgan. The statistical model used was a completely randomized design (DIC) with three treatments and four replications, with the primary soil preparation treatments being: disc plow, off set intermediate declogging harrow and rotary hoe; thus resulting in a total of 12 experimental units, each measuring 10m x 10m (100m²). Among them are carriers, of the same size as the plots, designated for machinery traffic, maneuvers and equipment adjustments. 

To prepare the soil, a Baldan disc plow, model AF-3, with three discs and a working depth of 20cm was used; intermediate declawing harrow, off set, Köhler model GAC300 equipped with 14 discs and action depth of 15cm; rotary hoe, brand MEC-RUL, model ERP 200 B, equipped with eight flanges and 48 blades and an action depth of 10cm. In all soil preparation operations, the equipment was coupled to the New Holand TL85E tractor, at 2.000rpm, third gear and an average speed of 5km/h.

To determine the soil's mechanical resistance to penetration (RMSP), an impact penetrometer, model IAA/Planalsucar-Stolf, was used, and to collect soil to assess moisture, a Dutch auger was used. To evaluate the RMSP, three random points were chosen in each experimental unit and this selection was made along the soil profile at these points from the 0cm – 10cm layer to the 50cm – 60cm layer, with the impacts being recorded every 10cm.

To assess soil moisture, deformed samples were collected, in the same layers, next to the points randomly chosen for the RMSP assessment. The two assessments were carried out 90 days after sowing the corn, taking care to collect moisture following the collection of penetrometer data in each plot, so that there was no change in humidity at the site. 

The data collected with the impact penetrometer provided in “impacts/dm” were transformed into MPa (Stolf, 1990). The data obtained were tabulated and subjected to analysis of variance and when significant, the Tukey test was applied, at 5% probability, to compare the means of resistance to soil penetration.

The parameter used in this study to evaluate soil compaction was the soil's mechanical resistance to penetration (RMSP). In layers 0cm - 10cm and 10cm - 20cm, a higher value of resistance to penetration was found for the intermediate crushing harrow compared to the disc plow (Table 1), in which the corresponding values ​​for humidity were statistically equal for these two pieces of equipment, Therefore, it can be said that the intermediate crushing harrow provided a greater compaction effect, a factor explained by the defined depth adjustments of its active organs.

This difference found may be the result of equipment adjustment, with the disc plow working at a greater depth, turning the soil more and causing a lower RMSP value in these layers. The rotary hoe and the intermediate declawing harrow, as the active parts are fixed to the same axis, have greater difficulty in penetrating the soil, which does not happen with the plow due to this equipment having each of the active elements connected separately to the chassis. by a column. Thus, soils prepared by this equipment can generate higher RMSP values ​​in the surface and subsurface layers. 

However, the values ​​found in the surface layer 0cm – 10cm are below the value of 2,5MPa. This lower value of resistance in the surface layer of the soil is related to the fact that this layer undergoes upheaval, loosening and leveling, caused by the equipment used in periodic soil preparation, thus resulting in increased soil aeration (macroporosity).

It is noted that, with the increase in depth, there was a significant reduction in the RMSP, which can be justified by the small effect of the active organs of the equipment used for the deeper layers of the soil, that is, it is the result of a diluted effect of the load of agricultural equipment when observed at greater depths, as also observed in the works of Gamero and Benez, 1990, and Silva, 2015.

It can be observed for the harrow and the rotary hoe, that there was an increase in RMSP from 10cm, while for the disc plow the increase occurred from 20cm, characterized by the formation of a “sill”, depending on the adjustment depths. defined. 

For humidity, only the 0cm – 10cm layer showed a statistically significant difference for the equipment used. In this layer, the intermediate harrow provided a lower value for moisture compared to the rotary hoe.

Based on the data presented in Table 2, where productivity can be observed in relation to green matter and dry matter, the producer can choose any of the equipment, based on statistical results and not on absolute values, since the CV was close of 20%, but considered normal for this type of evaluation carried out in the field.

The harrow and rotary hoe, when compared to soil preparation with a plow, provided greater resistance to penetration in the most superficial layers, without being influenced by soil moisture (Table 1). However, this increase in resistance did not affect corn silage productivity (Table 2). Thus, the crushing harrow could be recommended as a form of periodic preparation, as long as there are no erosion problems in the cultivated area, for flat relief, as it provides better operational capacity and consequently lower costs in adapting the soil for sowing (Silva, 2015 ). Possibly, the harrow would be preferable because it has greater usable width and is more common compared to the rotary hoe. 

In view of the data presented in this study, it can be concluded that there is an inverse relationship between RMSP and soil moisture. Below the mobilized layer, there was an increase in the RMSP due to the different depths of equipment adjustments, this being more superficial for the harrow and the rotating hoe. Regardless of the equipment used, there was a reduction in RMSP at greater depths, due to the dilution of its effects in these layers. The equipment used in soil preparation influenced the mechanical resistance of the soil to penetration, but did not influence the productivity of corn for silage.

Letícia Almeida, Luiz Fernando Costa Ribeiro Silva, Alberto Carvalho Filho, Renato Adriane Alves Ruas, Pedro Ivo Vieira Good God, Liliane Evangelista Visôtto, Federal University of Viçosa

Article published in issue 185 of Cultivar Máquinas, June 2018.