COMPACTION AND WATER INFILTRATION CAPACITY OF A CAMBISOL BY THE TRAFFIC OF MACHINES AND CATTLE TRAMPLING

porosity. These changes in the proportion of the solid and gaseous soil phases are often associated to restrictions to


INTRODUCTION
For the good development of cultivated plants, the water availability for the root absorption of plants is fundamental.Water should be slowly made available by soil to plants, according to their growth stage and the demand of each plant species.According to Azevedo and Dalmolin (2004), in clayey soils, 40-60% of the soil volume is occupied by porous space.Micropores, soil pores with diameter smaller than 0.06 mm, are responsible for the storage and subsequent supply of water to plants, while macropores, with diameter greater than 0.06 mm, do not store water and are responsible 2002).In well structured soils, there is a balance in the proportion of macro and micropores and adequate capacity of storage and supply of water to plants.
According to Denardin et al. (2009), from the decade of 1980s, the no-tillage cropping system was conceptualized as a complex of technological processes for agricultural exploration, considering: soil mobilization, only in the row or sowing pit; permanent maintenance of the soil cover; and species al. (2009) in crops under no-tillage cropping system, the environmental impacts of agricultural crops are reduced, with reduction in soil erosion and leaching, as well as carbon sequestration in the soil.On the other hand, the evolution of agriculture promoted the machines, which causes negative effects on the soil structure, even in the no-tillage system (Collares et al., 2008).According to Castro Neto (2001), soil compaction occurs more strongly in soils subject to high rainfall and irrigation rates, i.e., soil compaction occurs when pressure is exerted by heavy machinery on soils (Lopes et al., 2011).
Soil compaction is a limiting factor to increased productivity and continuous use of notillage cropping system, mainly in clayey soils (Collares et al., 2008).Therefore, optimizing soil use and management is the basis for the sustainability of agricultural production systems.According to Jimenes et al. (2008), in compacted soils, there is an increase in the proportion of micropores in relation to macropores and soil density.As a consequence, there is greater resistance to soil penetration by roots and, due to their limited development, there is a reduction in the volume of soil explored.In addition, the reduction of soil porosity decreases water and oxygen retention and root development of plants.It also favors the increase of nitrogen loss due to the The aim of the present work was to estimate clayey Cambisol under compaction condition induced different soil moisture conditions.

MATERIAL AND METHODS
The experiment was carried out in rural property located in the community of São Vitor, municipality of cropping system for more than 15 years, with soybean / ryegrass succession.Treatments were carried out during the post-harvest period of the soybean crop (Glycine max L.), with dry mass cover of approximately 3 t ha - 1 , composed exclusively of soybean stubble.According Eutrophic Haplic Cambisol and presents 61.2% of clay, 25% of silt and 13.8% of sand by the densimeter method as very clayey texture, according to Lemos and Santos (1984).
The experiment was installed in a completely randomized design with four treatments and four replicates.The four treatments were composed of different soil compaction conditions: treatment composed and volume of 80 mm; cattle trampling after rainfall with before rainfall; control treatment without compaction.
Soil moisture was determined at the time of each treatment, soil volumetric moisture (%) was determined, as described by Embrapa (1997).After collection, samples were oven dried at 105oC for 24 hours.Volumetric soil moisture was determined by subtracting the wet sample weight (before drying) by the dry sample weight and dividing the product of this subtraction by the sample volume, according to the formula below: Volumetric soil moisture = (%) = 100 * (wet sample weight (g) -dry sample weight (g)) / sample volume (cm 3) At the time prior to the 80 mm rainfall, when the the soil moisture content was 267 mL of water per liter of soil, equivalent to 26.7%.After the 80 mm rainfall at the moment of cattle trampling after rainfall and tractor was 387 mL of water per liter of soil, equivalent to 38.7%.
done with the passage of a tractor, and soil sample collections were made in a position of recurrence of the front and rear tires, at the point of greatest pressure of tires on the soil, at its most rigid extremity, the diagonal band.The tractor used was a Massey Fergusson MF 291 4 x 4, year 2009, which according to the manufacturer's description, has total weight of 6,245 kg.The static weight division is 2,513 kg on the front axle, 1,265.5 kg on each wheel, and 3,732 kg on the rear axle, 1,866 kg on each wheel.Regarding soil compaction induction by cattle trampling, soil samples were collected after the Bos taurus), at the point where there was recurrence of trampling of the front legs with the hind legs.The caw used was a Holstein cow weighing 500 kg.
Four soil samples collected from 0 to 5 cm in depth were sampled in each treatment, three days after the 80-mm rainfall.For this, rings of 5 cm in depth and 97 cm³ in volume were used.For each of these samples, the following parameters were determined: soil density (g.cm -3 ), density of solids (g.cm -3 ) and total soil porosity (%).
Soil compaction levels were determined by soil density.This method is applicable, since soil compaction approaches solid particles that compose it, reducing porous spaces, increasing its density.For this, the volumetric cylinder method known as "Kopeck Ring" was used (Kiehl, 1979;Klein, 2012).After drying in laboratory at temperature of 105 ºC for a period of 24 hours, samples were weighed to determine the dry mass of solids.Dividing the dry mass of solids by the volume of cylinders, the soil density in all treatments was obtained (Troeh andThompson, 2007, Klein 2012), according to the following formula: Soil density (g.cm-3) = dry weight of solids (g) / volume of cylinders (cm3) To determine the density of solids, the of dry soil were added and the volume of 50 ml of each (2012).The density of solids was calculated according to the formula below: volume -volume of alcohol added) The total soil porosity was determined by the difference between soil density and the density of solids, according to the formula below, described by Klein (2012).evaluated in the Control Treatment without compaction on humid soil treatment was also evaluated, with four replications per treatment.In the cattle trampling after compaction (increase in soil density) was observed this way, it was considered, for the study objectives, only the VIB measurement in the control treatment and Bernardo et al. (2006), consisted of the introduction of a PVC cylinder of 150 mm in diameter and 450 mm in height.The cylinder was introduced 15 cm deep into the soil, with constant pressure to reach the desired depth.The constant pressure for the introduction of the cylinder reduces its misalignment, as well as the lateral pressure to the ground, which could cause a crack between the ground and the cylinder wall.For this purpose, a hydraulic jack was used, supported on the cylinder, using the ballast of an agricultural tractor on it in order to exert resistance to the hydraulic force of the jack, pushing the cylinder down.
Data were submitted to analysis of variance and test of means (Duncan, 5%), using the SISVAR statistical software (Ferreira, 2000).

RESULTS AND DISCUSSION
There was an increase in soil density and (T3) and cattle trapping after rainfall treatments (T4), which indicates changes in the physical soil structure to a condition of greater compaction (Table 1).Cattle trampling after rainfall treatment (T4) induced higher The control treatment (T1) was the one with the lowest soil density, but there was no difference between this With the results presented in Table 1, it was cattle trampling after rainfall treatments (humidity compared to control treatment (T1).According to Klein and Libardi (2002), changes in soil density due to management promote lower soil moisture at the point of saturation and higher soil moisture at the permanent wilting point, which means lower proportion of water available under conditions of water stress.trampling after rainfall (T4) was approximately 95% of observed in the tractor before rainfall treatment (T2), before rainfall, there was no difference in density in T2 compared to control treatment, and this is due to the lower soil moisture content at the compaction time.
For a given compaction energy, there is a great (Ohu et al., 1989;Braida et al., 2006).According to Braida et al. (2006), for the same compaction energy, soil density depends on soil moisture, since density increases with increasing humidity until a certain value and then decreases.This behavior is explained by the behavior of water in the soil, which at low humidity, the friction between them, facilitating the rearrangement of particles and consequent compaction.Thus, the higher the soil density, the lower the total soil porosity, which can be calculated from the compose the soil are of mineral or organic origin, having different densities.According to Troeh and Thompson (2007), for the conditions of tropical and subtropical soils, in the calculation of total porosity, one can assume 2.65 g.cm³.The total soil porosity was determined in the different treatments studied, as well as the relationship of porosity of treatments compared to the control treatment (Table 2).It was observed that the relationship between the increase in soil compaction and the decrease in total soil porosity is directly proportional.In cattle trampling after rainfall treatment (T4), the highest soil density and 2).A very similar condition was observed in the tractor after rainfall treatment, 0.88 of the total porosity was observed in relation to the control treatment, or 53.33% of total soil porosity, while in the control treatment, 60.67% of total soil porosity was observed (Table 2).In porosity was observed in relation to control treatment, or 54.30% of total soil porosity, against 60.67% of control treatment.trampling after rainfall treatments, an increase in the same time that soil density increases in these These indicatives determine the reduction in the capacity of compacted soil to contain water and air in its composition, being potentially restrictive for good root growth, water supply, aeration and nutrient supply for cultivated plants.
As a result of the increase in soil compaction, there is a higher energy demand for soil mobilization (Mentges et al., 2010) and mainly increased resistance to soil colonization by roots (Stone et al., 2002;Denardin, (Stone et al., 2002).In this sense, some authors, such as Rosa Filho et al. (2009) consider the increase in soil density as a limitation to crop yield.Thus, it is necessary to plan activities in rural properties, so as not to submit soil to heavy loads, especially when they are in a high humidity condition.rainfall (T3) and control treatments (T1) were compared.different treatments, and throughout the evaluation period, rainfall treatment was much lower compared to the control velocity in the different treatments was remarkable in the which is equal to 120 mm / h.In the interval between 5 was maintained (Figure 1).

Figure 1.
On the other hand, in the control treatment (T1), 10 minutes.In the control treatment, the reduction of in the control treatment (T1) was 3.5 times higher than the treatment with compacted soil (T3) (Figure 1).strip, inducing less water passage through its pores, of soil erosion, especially if it is associated with the absence of straw on the surface and on sloping ground (Bertoni and Lombardi Neto, 1985; da Costa, root growth and nutrient input in deeper layers, the conservation of good soil porosity also contributes to better soil conservation, since the larger the volume this sense, soil porosity is an important feature for the mitigation of erosive processes, both in conventional and no-tillage cropping systems.The measurement of the accumulated water importance of the soil structure and its fundamental participation as part of erosion control and conservation of soil fertility conditions, as well as the in soil with induced compaction was 61 mm less than in the control treatment during the 45 minutes of observation.In this sense, the restriction to soil water water runoff and soil erosion, with nutrient losses, and can even cause root diseases or death of plants by asphyxiation (Filizola, 2012).
In this way, it could be concluded that there is no difference between soil densities when compacted by or cattle trampling after rainfall.Greater soil compaction after rainfall, compared to soil without compaction.
Lower soil water infiltration velocity (VIB) and lower accumulated infiltration with tractor traffic after rainfall are observed, compared to soil without compaction.

Table 1 .
Soil density after soybean harvest with induced compaction.

Table 2 .
Total soil porosity in post-harvest soybean, with induced compaction.