**2. Material and methods**

#### **2.1 Study area**

#### *2.1.1 The watershed of the Arroio Pelotas*

The study area in the municipality of Pelotas is inserted in the Arroio Pelotas watershed (**Figure 2**). The hydrographic basin of this watercourse is located under two phytogeographic regions: pioneer formation areas and the semidecidual seasonal forest, according to the classification of the Brazilian Institute of Geography and Statistics [22]. The two phytogeographic regions are distinct and conditioned by the geomorphological characteristics of the relief. The areas of pioneer formations, as [23] *Physical Quality of Soils in a Toposequence of a Forest Fragment under Livestock Activity… DOI: http://dx.doi.org/10.5772/intechopen.106560*

#### **Figure 2.**

*Hydrographic basin of the Arroio Pelotas map, Pelotas, RS, Brazil.*

called restinga are located predominantly in the internal and external coastal plain with vegetation of dry and humid fields, bathed, riparian forests, and capons of restinga forests. The other region, called semidecidual seasonal forest, was the site of this study and forest vegetation is typical (**Figure 3**) [22].

#### **Figure 3.**

*Illustrative scheme of the topographic profile of the forest areas sampled along the relief in Pelotas, RS, Brazil. •= quematic distribution of soil sample collections. Source: Adapted Image of Phytogeographic Manual of Brazilian Vegetation IBGE [22].*

#### *2.1.2 Soils in the Arroio Pelotas river basin*

The area is inserted in the geomorphological province of "escudo Sul-Rio-Grandense" besides being ancient, is geologically very complex, because it comprises several plutonic igneous rocks, mainly of granite composition associated with belts of metamorphic rocks, which were covered by sequences of sedimentary rocks and volcanic rocks [24]. On the edges of this heterogeneous geological province, is inserted approximately half of the area of the municipality of Pelotas. In this region, three main soil units are found: association LUVISSOLO HÁPLICO Órtico with NEOSSOLO REGOLÍTICO Distro-úmbrico, ARGISSOLO VERMELHO-AMARELO Distrófico and PLANOSSOLO HÁPLICO Eutrófico associado with GLEISSOLO MELÂNICO Tb Eutrófico, covering respectively the high, middle and low relief of the slope of the Escudo Sul-Rio-Grandense [24].

#### **2.2 Soil sampling**

#### *2.2.1 Description and collection of soil profiles*

For soil classification, the environmental characteristics of the site (external characteristics, such as relief, drainage, erosion, vegetation, and source material) were described, which constitutes the general description, and the morphological characteristics of the soil, such as thickness, arrangement, transition and characteristics between horizons and horizon characteristics (color, texture, structure, and consistency, etc.) as Santos et al. [25]. Soil profiles were described and collected at the top, on the upper slope, on the middle slope, and on the lowered slope. Soil horizon samples were physically and chemically characterized in the laboratories of the Soil Department of FAEM/UFPel<sup>1</sup> following the methodology set out in Teixeira et al. [26], and were subsequently classified according to the Sistema Brasileiro de Classificação de Solos, developed by the National Soil Research Center [27], and world reference base for soil resources [28].

### *2.2.2 Survey of soil physical attributes along the toposequence*

Deformed samples (unpreserved structure) and undisturbed samples (preserved structure) of soil were collected in six different treatments distributed along two environmental gradients of the toposequence in the Pelotas Stream. For each gradient with three sample blocks distributed on the upper slope, on the middle slope, and on the lowered slope on the margin of the watercourse (**Figure 3**). The low slope and top relief sections were not sampled by the absence of adequate forest fragments in the study region. The gradients were divided into an area with access to cattle grazing and areas without grazing, witness for comparison. The control of areas of isolated forest fragments without access to animals and in conditions of relief similar to treatments with livestock access. The maximum distance between the areas is approximately 1400 m. The altitude of the plots ranged from 39 to 116 meters at sea level. Forest fragments were distributed in three small rural properties.

The undisturbed samples (preserved soil structure) were collected using the volumetric ring method [26]. The rings were 3 cm tall and 4.8 cm in diameter, with an

<sup>1</sup> FAEM: Faculty of Agronomy Eliseu Maciel of Federal University of Pelotas (UFPel).

#### *Physical Quality of Soils in a Toposequence of a Forest Fragment under Livestock Activity… DOI: http://dx.doi.org/10.5772/intechopen.106560*

average volume of 54.9 cm<sup>3</sup> per sample. For the collection in the field, the insertion site of the ring was cleaned in the soil, removing the litter until the soil was fully discovered for the insertion of the rings. After the rings were inserted, using shovels, the ring was carefully removed from the ground, so as not to disaggregate the sample. Subsequently, each ring was wrapped in aluminum foil, sealed and labeled. The undeformed samples on the foil were carefully transported to avoid damage to the soil structure contained inside the ring.

Fourteen samples were collected per sample block, totaling 42 total samples per gradient, seven rings in the 0–5 cm layer and seven other rings in the 5–10 cm layer. The sampling points were approximately 10 meters from each other, inside the sample block of the collection of native forest vegetation (**Figure 3**). With the excess of soil in the layers of 0–5 and 5–10 cm, the deformed samples were collected, where they were placed in plastic bags, sealed, and labeled.

The deformed and undeformed samples were taken to the pedology laboratory, sample preparation room, and to the soil chemistry and physics laboratories of Faculty of Agronomy Eliseu Maciel of Federal University of Pelotas. The deformed samples were placed to dry at room temperature in the sample preparation room. After 5–7 days they were destroyed with a wooden roll and passed in 2 mm sieves, and then placed in plastic bags labeled and stored in the Pedology Laboratory/UFPel, constituting the air-dried soil samples. The undeformed samples were stored in the pedology laboratory and taken to the soil physics laboratory FAEM/UFPel, for the preparation and evaluation of attributes of soil density, microporosity (pores smaller than 0.05 mm), macroporosity (pores greater than 0.05 mm), and total porosity.

The determinations of the chemical attributes of the soil were made according to Tedesco et al. [29] and Teixeira et al. [26]. The determinations of pH (H2O), pH (KCl), Ca, Mg, K, Na, and Al e P available were carried out in accordance with Tedesco et al. [29]. Organic carbon and H + Al were used in the study by Teixeira et al. [26]. The texture of the soil profile layers was analyzed by the granulometry method following the methodology proposed by Teixeira et al. [26].

The pH in water (active acidity) was determined at the ratio of 1:1 (soil:water) by immersion of a glass electrode connected to a pot. The pH in KCl (potential acidity – H + Al) was extracted with calcium acetate and determined by titration with NaOH. Calcium extraction (Ca+2), magnesium (Mg+2) e aluminum (Al+3) exchangeable were made with KCl 1 mol L�<sup>1</sup> and determined in the atomic absorption spectrophotometer (Ca+2 e Mg+2) and by titration with NaOH (Al+3). Potassium content (K+ ) available and sodium (Na<sup>+</sup> ) were estimated by the double extractor method of Mehlich�<sup>1</sup> and analyzed by flame photometry. Based on the results of the analyses, the base saturation was calculated (BS%), the cation exchange capacity (CEC), and aluminum saturation (m%). Base saturation is calculated by the sum of the bases Ca+2, Mg+2, and K+ e Na<sup>+</sup> . A CTC = (Sum of bases + H+ + Al+3). Aluminum saturation (m%) is calculated by Eq. (1) below:

$$\mathbf{m} \text{ (\%)}=\left[\mathbf{Al}^{+3}/\left(\mathbf{SB}+\mathbf{Al}^{+3}\right)\right]\times\mathbf{100}\tag{1}$$

SB = sum of bases

Soil physical attributes were determined by the volumetric ring method, using the dry soil mass in a greenhouse to 105°C for 24 hours in the volumetric ring of known volume [26]. To calculate soil density by mass, the equation was used (2):

$$\mathbf{Bd} = \mathbf{Dsm/Va} \tag{2}$$

Bd = soil bulk density (g.cm�<sup>3</sup> )

Dsm = dry soil mass contained inside the volumetric ring (g)

Va = volumetric ring volume (cm<sup>3</sup> )

The determination of the porosity of the total soil was performed by the tension table method, using volumetric rings [26]. Through total porosity, the microporosity and macroporosity of the soil were determined, using the height of the suction water column of 60 cm to obtain a 0.006 MPa. The total porosity was calculated by Eq. (3) shown below:

$$\mathbf{Pt} = \left[ (\mathbf{P1} - \mathbf{P3}) - \mathbf{P4}/\mathbf{Va} \right] \times \mathbf{100} \tag{3}$$

Pt = total porosity (%)

P1 = saturated sample weight with fabric and rubber alloy (g)

P3 = weight of rubber alloy and saturated fabric (g)

P4 = weight of the kiln-dried sample (g)

Va = volumetric ring volume (cm<sup>3</sup> )

Microporosity (mp) was calculated from Eq. (4) below:

$$\mathbf{mp} = [(\mathbf{P2} - \mathbf{P4})/\mathbf{Va}] \times \mathbf{100} \tag{4}$$

mp = micropores (%)

P2 = balance sample weight (g)

P4 = weight of the kiln-dried sample (g)

Va = volumetric ring volume (cm<sup>3</sup> )

Macroporosity (Mp) was calculated by the difference of total porosity by microporosity (mp), through the Eq. (5):

$$\mathbf{M}\mathbf{p} = \mathbf{P}\mathbf{t} \text{-mp} \tag{5}$$

Mp = macroporosity (%)

Pt = total porosity (%)

In the soil physics laboratory, for each volumetric ring, the aluminum foil packaging was first removed. After removal of the package, the sample toilet was performed with the use of a stiletto, scissors, knife, and water spray. The toilet consisted of the process of removing excess soil at the lower and upper ends of the ring to equalize the ring volume with the volume of the soil sample. Following the toilet procedure, at the bottom of the ring was placed a piece of appropriate fabric fastened with rubber alloy [26]. The fabric has the function of handling possible sections of soil that detach from the ring. In the sequence, each ring was numbered and placed for saturation in trays by capillary rise, with water placed up to ¾ from the height of the ring, outdoors in the laboratory environment for at least 48 hours [26]. Subsequently, the rings were removed from the water and weighed on a precision scale, and then the saturated rings were placed for drainage on a tension table and a tension corresponding to 60 cm of water column height corresponding to macropore drainage was applied.

The samples of the volumetric rings were placed in Richard's pressure chamber and remained until the drainage of the excess moisture for each voltage ceased. After the volumetric rings came out pressure chamber, these were weighed to obtain the weight of the ring in balance and discounted the weights of the fabric and rubber alloy saturated. Subsequently, the rings in equilibrium were placed to dry in a greenhouse

*Physical Quality of Soils in a Toposequence of a Forest Fragment under Livestock Activity… DOI: http://dx.doi.org/10.5772/intechopen.106560*

for 48 hours at a temperature of 105°C [26]. The rings were removed from the greenhouse and weighed on a precision scale to obtain the weight of the dry soil.

After obtaining the weight of the saturated soil, the balance soil weight and the dry soil weight of each volumetric ring, the soil of the ring was removed, which was washed, dried, and weighed to obtain the weight of the ring without soil to use in the subtraction in the weight of the samples. For each volumetric ring, it was measured, the diameter and height for calculating the volumetric ring volume, using the Eq. (6) below:

$$\mathbf{Va} = \mathfrak{x} \times \mathfrak{r} 2 \times \mathfrak{h} \tag{6}$$

Va = volumetric ring volume (m<sup>3</sup> )

д = pi = 3.1428

r = geometric radius of the ring (m)

h = height (m)

The results were submitted to statistical analysis, which was performed by the PAST software with the Kruskal–Wallis nonparametric test with a significance level of 5%. The means of the physical parameters of soil in the same toposequence and layers with and without the presence of livestock were compared.

## **3. Results and discussion**

The pedological survey was carried out with a methodology that aims to identify, characterize, and classify soil profiles [25]. Soil classification resulted in three soil classes at the order level: Leptosol, regosol, and acrisol, according to the classification proposed by IUSS working group WRB [28], and in two soil classes at the order level: Neossolo and Argissolo, according to the classification proposed by Santos et al. [27] (**Table 2**; **Figure 4**). It has been classified as Argissolo in the downloaded and Neossolos on the middle slope, top slope, and top (**Figure 5**). Soil classification was performed by means of analytical data interpretation (**Tables 3** and **4**), physic and chemical attributes, and morphological description of profiles.

The class of Argissolos in general, are soils of varying depth, from strong to imperfectly drained, with reddish or yellowish colors and rarely brunadas or grayish. It has a sandy texture to clayey on horizon A and medium to very clayey on horizon B, always having a textural gradient of clay from horizon A to B, which characterizes the textural horizon B (Bt). The transition usually between horizons A and Bt is clear, abrupt, or gradual. They are strong to moderately acidic soils, predominantly kaolinitic with high or low base saturation [27].

