Soil variability in different landscape positions in the Porto Alegre Botanical Garden, Southern Brazil

Abstract

Knowledge of soil characteristics in areas where activities related to the environment are developed, such as Porto Alegre Botanical Garden (JB-PoA), is a fundamental condition for the sustainable use of this natural resource. The objective of this study was to characterize, classify and evaluate some issues about soil formation in Porto Alegre Botanical Garden, as well as relate their distribution on the landscape according to environmental characteristics. For the morphological description and collecting samples four profiles were selected (P1 to P4), located in the summit-shoulder transition, backslope, footslope and toeslope, respectively. Granulometric distribution of the P1 and P3 profiles indicated sharp textural gradient, with presence of textural and “plânico” B horizons, respectively, according to Brazilian System of Soil Classification. There is predominance of low values of pH, and low base saturation, with exception of P4, indicating probable deposition of solution material at this area. The Fed/Fes relationship was greater in the profile located in the summit-shoulder transition (P1), indicating higher weathering. The Feo/Fed relationship increased in P3 and P4 profiles, indicating greater participation of iron oxides of low crystallinity in reducing environment. The occurrence of some pedogenic processes may be inferred, like lessivage in P1 (Ultic Hapludalf), due to clay skins and higher values of fine clay:total clay relationship in subsurface; ferrolysis and gleization, by low pH value and high Feo/Fed relationship in E and EB horizons of P3 (Oxyaquic Hapludalf), being the last also present in P4 (Humaqueptic Endoaquent), indicating gleization occurrence.

Full text

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SOIL VARIABILITY IN DIFFERENT LANDSCAPE POSITIONS IN THE
PORTO ALEGRE BOTANICAL GARDEN, SOUTHERN BRAZIL
Variabilidade de solos em posições distintas da paisagem no
Jardim Botânico de Porto Alegre, sul do Brasil
Luís Fernando da Silva1, Paulo César do Nascimento2, Alberto Vasconcellos Inda2, Edsleine Ribeiro Silva2
ABSTRACT
Knowledge of soil characteristics in areas where activities related to the environment are developed, such as Porto Alegre
Botanical Garden (JB-PoA), is a fundamental condition for the sustainable use of this natural resource. The objective of this study
was to characterize, classify and evaluate some issues about soil formation in Porto Alegre Botanical Garden, as well as relate their
distribution on the landscape according to environmental characteristics. For the morphological description and collecting samples
four proles were selected (P1 to P4), located in the summit-shoulder transition, backslope, footslope and toeslope, respectively.
Granulometric distribution of the P1 and P3 proles indicated sharp textural gradient, with presence of textural and “plânico” B
horizons, respectively, according to Brazilian System of Soil Classication. There is predominance of low values of pH, and low
base saturation, with exception of P4, indicating probable deposition of solution material at this area. The Fed/Fes relationship was
greater in the prole located in the summit-shoulder transition (P1), indicating higher weathering. The Feo/Fed relationship increased
in P3 and P4 proles, indicating greater participation of iron oxides of low crystallinity in reducing environment. The occurrence
of some pedogenic processes may be inferred, like lessivage in P1 (Ultic Hapludalf), due to clay skins and higher values of ne
clay:total clay relationship in subsurface; ferrolysis and gleization, by low pH value and high Feo/Fed relationship in E and EB
horizons of P3 (Oxyaquic Hapludalf), being the last also present in P4 (Humaqueptic Endoaquent), indicating gleization occurrence.
Index terms: Soil-landscape relationship; pedogenic processes; lessivage; ferrolysis; gleization.
RESUMO
O conhecimento das características dos solos em áreas onde são desenvolvidas atividades relacionadas ao meio ambiente,
como no Jardim Botânico de Porto Alegre (JB-PoA), é condição fundamental para o uso sustentável desse recurso natural. Objetivo-
se, com este estudo, foi caracterizar, classicar e avaliar aspectos da formação dos solos do Jardim Botânico de Porto Alegre, bem
como relacionar a sua distribuição na paisagem às características do ambiente. Para a descrição morfológica e coleta de amostras
foram selecionados quatro pers (P1 a P4) localizados, respectivamente, no terço superior, terço médio, sopé e planície de inundação.
A granulometria dos pers P1 e P3 indicou gradiente textural acentuado, com horizonte B textural e B plânico, respectivamente,
segundo o Sistema Brasileiro de Classicação de Solos. A relação Fed/Fes foi maior no perl do terço superior (P1), indicando maior
intemperismo. Houve predomínio de baixos valores de pH e de distrosmo, com exceção do P4, indicando provável deposição de
materiais em solução nessa área. A relação Feo/Fed aumentou nos pers P3 e P4, com maior participação dos óxidos de ferro de
baixa cristalinidade em ambiente redutor. Alguns processos de formação predominantes podem ser inferidos, como a lessivagem,
pela cerosidade e maior relação argila na:argila total em P1 (Argissolo); a ferrólise e gleização, pelo baixo valor de pH e alta relação
Feo/Fed nos horizontes E e EB de P3 (Planossolo), sendo esta última também presente em P4 (Gleissolo), indicando ocorrência
de gleização.
Termos para indexação: Relação solo-paisagem; processos pedogenéticos; lessivagem; ferrólise; gleização.
1Universidade Federal do Rio Grande do Sul/UFRGS – Departamento de Solos – 91540-000 – Porto Alegre – RS – Brasil – luisf_agro@yahoo.com.br
2Universidade Federal do Rio Grande do Sul/UFRGS – Departamento de Solos – Porto Alegre – RS – Brasil
Received in april 14, 2015 and approved in june 2, 2015
INTRODUCTION
Knowledge of the characteristics of natural
resources in areas where are developed activities related
to the environment is a fundamental condition for the
sustainable use of these resources. In these, the soil
occupies a prominent position, because it is expression
of environmental factors related their formation (Buol et
al., 2003). In areas for Environmental Conservation Unit,
soil characterization constitutes a subsidy for planning
in order to optimize the use of this resource within the
inherent activities to these places. In the Porto Alegre
Botanical Garden (JB-PoA), site where are carried out
research activities of ora of the Rio Grande do Sul State
(RS), environmental education, leisure and recreation,
there are no detailed studies that investigate the soil
characteristics of park associated with their formation
environment.
In the city of Porto Alegre, preliminary soil
survey (Schneider et al., 2008) identied, according to

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Brazilian System of Soil Classication (EMBRAPA,
2013), the occurrence of Argissolo on top and slope
of hills with gently sloping relief; Cambissolo and
Neossolo in granitic hills with moderately steep and
steep relief; and Hydromorphic/Aluvial soils in low
and oodplain areas. The steep relief of hill areas
contributes to the formation of thinner soil and chemical
characteristics which reect a low weathering degree
(Medeiros et al., 2013).
The insertion area of JB-PoA shows smooth
relief and less steep than hill areas of Porto Alegre. The
geomorphic characteristics indicate an area with knoll
forms, with at or convex summit positions, and more
gentle slopes in relation to hill areas (Moura; Dias, 2012).
These features are reected in major water inltration,
resulting in deeply weathered soil proles. Based on this
knowledge, the hypothesis is that specic characteristics
of relief and parent material of the study area imply in
similarities with hill areas, but with formation processes
in greater denition and intensity, resulting in soils with
high degree of pedogenetic development. The objectives
were: characterize and classify the representative soil
proles of the occurrence of taxonomic units in the JB-
PoA, according to Brazilian System of Soil Classication
(EMBRAPA, 2013) and the Soil Taxonomy (Soil
Survey Staff, 2010); and indicate the inuence of soil-
environment relationship, through soil forming process
of JB-PoA.
MATERIAL AND METHODS
The Porto Alegre Botanical Garden (JB-PoA) covers an
area of 39 hectares, limited to the coordinates 30°02’51” and
30°03’20” (S) – 51°10’19” and 51°10’51” (W) in the urban area
of Porto Alegre (FZB, 2009). The weather is humid subtropical
with a long-term average annual temperature of 19.5 °C and
long-term average annual rainfall of 1,300 mm, with rainfall
well distributed throughout the year. The long-term annual
effective rainfall (precipitation minus evapotranspiration) is
430 mm (SEMA, 2010). The parent material is composed of
“Gnaisse Porto Alegre” and “Alterito Serra de Tapes”. The
gneiss has dark color to black, with quartz, feldspars and biotite
composition. The alterite was formed from coluvial deposits,
consisting of kaolinite and iron oxides (Schneider et al., 2008).
The local relief consists in smooth hills, with inuence of
aluvial terraces of the “Arroio Dilúvio”.
To study the soil genesis were selected four proles
(Figure 1), located in the summit-shoulder transition (P1),
sloping from 13 to 15%; backslope (P2), sloping from 18
to 20%; footslope (P3), sloping from 0 to 2%; toeslope
(P4), sloping from 2 to 3%.
The trenches were opened to the description of the main
pedogenetic horizons of the soil, according to methodology
described by Santos et al. (2005). Horizons Bt3 (P1), Cr2 and
Cr3 (P2), Btg2 (P3) and Cg2 (P4), were collected by auger. The
soil samples were dried, ground and sieved in mesh 2 mm for
separation of ne earth fraction dried in air (TFSA).
Figure 1: Schematic representation of topographic location of the study proles.

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The granulometric distribution and clay dispersed
in water were determined according to EMBRAPA (1997),
while the ne clay fraction (< 0.2 µm) according to method
of Jackson (1956). With these data were calculated the ne
clay/total clay relationship (Claf/Cla) and soil occulation
(SoF). To identify possible lithologic discontinuities
in the soil proles were calculated ne sand/total sand
relationship (FS/TS) and the uniformity value (VU)
(Schaetzl, 1998).
In relation to chemical characteristics, the pH in
water and KCl, the exchangeable cations (Ca2+, Mg2+, Na+,
K+ and Al3+), the potential acidity (H++Al3+) and the organic
carbon content were determined according to EMBRAPA
(1997). Were calculated cation exchange capacity (CEC),
clay fraction activity (CFA) and base saturation (V). The
sulfuric attack was carried out to quantify the Fe2O3, Al2O3
and SiO2 constituents of clay minerals (EMBRAPA, 1997).
Selective dissolutions were performed to iron oxides with
dithionite-citrate-bicarbonate (DCB) at 80 °C by Mehra and
Jackson (1960), and ammonium oxalate (OXA) according to
Schwertmann (1964) to determine the Fe and Al content in
pedogenic oxides (Fed; Ald) and low crystallinity (Feo, Alo).
The content of the elements Fe, Si and Al was determined
by atomic absorption spectroscopy. With these data were
calculated Ki index, Fed/Fes and Feo/Fed relationships, used
to evaluate the soil weathering stage and the crystallinity
degree of oxides (Kämpf; Curi; Marques, 2009).
Mineralogical composition was determined by
X-ray diffractometry analysis, conducted in sand, silt and
clay granulometric fractions, with a Bruker-D2 Phaser
equipment in non-oriented blades (powder samples). The
samples were irradiated in the range from 4 to 40° 2θ, with
a scan rate of 2° 2θ min-1. Halite was added as an internal
standard for the measurements of the spacings in clay
fraction. The results are interpreted according Brindley
and Brown (1980).
RESULTS AND DISCUSSION
The soils developed significant variation of
thickness (Table 1), being observed thicker solum in P1
(Ultic Hapludalf) and P3 (Oxyaquic Hapludalf). The
greatest slope (20%) in P2 (Oxic Dystrudept) inuenced
its low pedogenetic development compared to P1, through
the low water inltration, which resulted lower weathering
in depth (Kämpf; Curi; Marques, 2009). This characteristic
of P2 is evidenced by contact with Cr horizon less than
90 cm depth (Figure 2). The P4 prole (Humaqueptic
Endoaquent) also showed lower development, having
contact with the Cg horizon from 40 cm depth, which can
be attributed to the stagnant water and lower weathering
intensity in this landscape position.
In the proles of upper portion of the landscape
(P1 and P2) there are red and yellow colors (hues between
2.5YR and 7.5YR), which indicates the predominance of
crystalline iron oxides as hematite (Fe2O3) and goethite
(FeOOH) in good to moderate drainage conditions
(Kämpf; Schwertamnn, 1983).
In the Bi horizon of P2, the more reddish (2.5YR
4/8) and variegate colors (7.5YR 4/6) in condition of good
drainage, indicated a weathered clay matrix, with presence
of minerals that have a low stage of weathering (Schneider;
Klamt; Giasson, 2007). Gray colors in the P3 and P4
proles suggest the occurrence of anaerobic bacterial
activity, which reduces soil oxidized compounds, resulting
in low chroma related to iron mobility and occurrence of
soil gleization (Ponnamperuma, 1972).
In the Bt2 horizon of P1, the presence of clay skins
coating surface of aggregates and the blocky structure may
be related to illuvial clays (Costa; Libardi, 1999). The
surface horizons of the proles studied showed weak or
moderate structure, small to medium, granular or crumb,
condition associated with increase of organic matter
on the soil surface. The massive structure in the deeper
horizons of P2 (Cr), P3 (Btg1) and P4 (Cg1) shows the
little pedogenetic evolution.
The P1 and P3 proles showed sharp textural
gradient (Table 2). In the P1 prole, the B/A textural
relationship was 1.88, classied as B textural horizon.
In the P3 prole, the abrupt textural change between EB
and Btg1 horizons, associated with hue 10YR and chroma
lower or equal to 3 in the B horizon, classied it as B
“plânico” horizon (EMBRAPA, 2013).
Unlike P1 and P3, the P2 and P4 proles showed
little textural variation between horizons. However, in P2
stood out the clayey texture compared to other landscape
proles, being possible the change in parent material.
According to Teramoto, Lepsch and Vidal-Torrado (2001),
marked differences in soil texture on a topographic transect
may indicate the variation of parent material.
In all proles the variation of ne sand/total sand
relationship between horizons was lower than 0.14, which
combined with uniformity value (VU) lower than 0.60, rule
out possibility of lithologic discontinuity between horizons
of each prole (Schaetzl, 1998). The P1 prole showed
low soil occulation in A and AB horizons, favoring the
vertical transport of ne clay by water from eluvial A
horizon and the deposition in illuvial B horizon, when the
pores of smaller size are lled by clay (Almeida; Klamt;
Kämpf, 1997; Santos et al., 2010).

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Table 1: Morphological attributes of Porto Alegre Botanical Garden soils.
Hor(1) Depth, moist Munsell color, texture, structure, moist consistence, waxiness, transition
-------------------(P1) Ultic Hapludalf-------------------
A0-15 cm; 7.5YR 4/3 (moist); sandy loam; weak/moderate, small/medium, granular; very friable; slightly plastic
and slightly sticky; gradual and plan boundary.
AB 15-46 cm; 7.5YR 3/3 (moist); sandy clay loam; moderate, small/medium, subangular blocky; very friable;
slightly plastic and sticky; gradual and plan boundary.
Bt1 46-68 cm; 7.5YR 4/6 (moist); clay loam; moderate, medium/big, subangular blocky; friable; plastic and sticky;
clear and plan boundary.
Bt2 68-102 cm; 5YR 4/6 (moist); clay loam; moderate, medium/big, subangular blocky; friable; plastic and sticky;
common and moderate waxiness.
Bt3 102-135+ cm (collected by auger); 5YR 4/6 with small and little mottle 10YR 5/6 (moist); clay loam/clay.
----------------------(P2) Oxic Dystrudept----------------------
A0-25/30 cm; 10YR 3/4 (moist); sandy clay loam; moderate, small, granular, moderate, small/medium, subangular
blocky; very friable; slightly plastic and slightly sticky; clear and irregular boundary.
A/B 25/30-55/60 cm; 2.5YR 4/8 with small and little mottle 10YR 3/6 (moist); clay loam; moderate, small/medium,
subangular blocky; rm; slightly plastic and sticky; clear and wavy boundary.
Bi 55/60-80/85 cm; 2.5YR 4/8 with variegate 7.5YR 4/6 (moist); clay loam; moderate, medium/big, subangular
blocky; rm; slightly plastic and sticky; gradual and wavy boundary.
Cr1 80/85-120 cm; 5YR 5/8 (moist); sandy clay/sandy clay loam; massive, which breaks in subangular blocky;
very friable; slightly plastic and slightly sticky.
Cr2 120-140 cm (collected by auger); 5YR 4/6 with small and little mottle 2.5Y 8/1 (moist); sandy clay/sandy
clay loam.
Cr3 140-160+ cm (collected by auger); 7.5YR 8/4 (moist); sandy clay/sandy clay loam.
-------------------(P3) Oxyaquic Hapludalf------------------
A0-20/27 cm; 10YR 3/3 (moist); loamy sand; moderate, small, granular, moderate, small/medium, subangular
blocky; very friable; not plastic and not sticky; clear and wavy boundary.
E20/27-60/62 cm; 10YR 4/4 (moist); sand; moderate, small, granular, moderate, small, subangular blocky; loose;
not plastic and not sticky; gradual and plan/wavy boundary.
EB 60/62-105 cm; 7.5YR 4/3 (moist); sandy loam; moderate, medium/big, subangular blocky; friable; slightly
plastic and slightly sticky; clear and plan boundary.
Btg1 105-120 cm; 10YR 4/3 (moist); sandy clay loam; massive; plastic and sticky.
Btg2 120-150+ cm (collected by auger); 10YR 6/1 with medium and abundant mottle 10YR 5/8 (moist); clay; rm;
very plastic and sticky.
-----------------(P4) Humaqueptic Endoaquent-----------------
A0-15 cm; 7.5YR 3/2 (moist); sandy clay loam; crumb; very friable; not plastic and slightly sticky; clear and
plan boundary.
AC 15-40 cm; 10YR 3/2 with small and little mottle 5YR 4/6 (moist); sandy clay loam; weak, medium, subangular
blocky; friable; slightly plastic and slightly sticky; clear and plan boundary.
Cg1 40-60 cm; 10YR 3/1 (moist); sandy clay loam; massive; slightly plastic and slightly sticky.
Cg2 60-90+ cm (collected by auger); 10YR 4/2 with small and little mottle 10YR 5/6 (moist); clay loam; very
plastic and sticky.
(1) Hor: horizon.

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Figure 2: Looking from left to right, prole image of the Ultic Hapludalf (P1), Oxic Dystrudept (P2), Oxyaquic
Hapludalf (P3) and Humaqueptic Endoaquent (P4), showing the variation of solum depth (depth of A and B horizons)
related to soil development.
The occurrence of clay skins in the Bt horizon and
increase of ne clay/total clay relationship from A horizon
to Bt horizon indicated lessivage of clays in P1. Besides
the low soil occulation be a prerequisite to lessivage,
according to Quénard et al. (2011) the translocation of clays
is favored in humid weather (when the precipitation is higher
than evapotranspiration at least 150 mm) and in planar or
sub-planar surfaces. Therefore, the humid weather of Porto
Alegre and the location of P1 prole (summit-shoulder
transition) in the landscape allow lessivage process.
The soil proles showed low pH with values lower
than 5.5 (Table 3). The pH KCl are smaller than 5.0 in all
proles, and in conjunction with negative ΔpH (pH KCl –
pH H2O), indicate the absence of “ácrico” character and,
therefore, the predominance of negative charges in all proles
(EMBRAPA, 2013). The higher base saturation found in the
A and Cg2 horizons of P4 seems indicate the importance of
the concave relief in the formation of eutrophic character,
with the lateral movement of soluble cations by water ow,
towards the upper third for the ood area. The CEC of clay
fraction (CFA) of B or C horizons in all proles was lower
than 27 cmolc kg-1, featuring soils with low clay activity.
In the P3 prole, besides the sharp acidity (pH of
4.5 in water) in E and EB horizons, soil CEC is less than
4.0 cmolc kg-1. According to Brinkman (1970) the soil
condition under successive cycles of wetting and drying
favors the destruction of clay minerals by pedogenetic
process of ferrolysis, resulting in horizons with low pH,
low clay content and low soil CEC, these characteristics
found in P3. These results are similar to those obtained by
Mafra et al. (2001), noting that ferrolysis is manifested in
sharp acidity (pH 3.0 to 4.0) and produces sandy horizons.
Also in the Cg1 horizon of P4, low pH (4.4) associated
with the lower clay content and exchangeable cations, even
as high exchangeable aluminum content, may indicate an
initial process of ferrolysis of clays in this prole section.
Barbiero et al. (2010) monitored changes in pH and
electrical conductivity of soil at different times of the year
to explain the occurrence of ferrolysis. During the rainy
season, they observed an increase in the pH of soil solution
due to reduction reactions that consume H+ ions. At the end
of the rainy season happened high weathering, resulting
in low pH, where oxidation reactions in soil produce H+
protons which penetrate the octahedral structure of clay
minerals, destabilizing them.
The Fed/Fes relationship in all proles showed
values between 0.53 and 0.98 (Table 4), which indicates
a moderate to advanced weathering for all soils. In the
P2 prole, the high Fed/Fes relationship in A, A/B and
Bi horizons identies front of weathering, with clear
reduction in this value in Cr1 horizon less weathered.
However, the Cr3 horizon showed an increase of Fed/Fes
relationship (0.89), highlighting the sudden decrease in Fes
content of Cr3. This data allows note small amount of iron
in this horizon, which was observed in eld descriptions
through the light color and low chroma. Smaller values of
Fed/Fes relationship in the surface horizons of P3 and P4
are related to lower oxidation environment and subject to
lower rates of weathering (Pereira; Anjos, 1999; Santos
et al., 2010).

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The Ki index in all proles was higher than 3.0,
not agreeing with values of low clay activity and Fed/Fes
relationship moderate to high, that conrm a moderate to
advanced weathering for all soils. An explanation for the
high Ki index observed in all proles is the solubilization
of silicon from silt and sand fractions, indicating inadequate
extraction method for soils with high quartz content in these
fractions (Oliveira, 2011). The high Ki index in P3 reinforces
this hypothesis, given the fact that the silt and sand fractions
have signicant participation in soil texture. Remarks of this
condition were cited in Rolim Neto et al. (2009), Medeiros
et al. (2013), and Nascimento, Lani and Zoffoli (2013).
In P1 and P2, the Feo/Fed relationship was equal
or less than 0.1, indicating the predominance of crystalline
forms such as hematite and goethite (Pereira; Anjos, 1999;
Meireles et al., 2012). This condition is coherent with the
soil location in landscape, because they are located in upper
positions and good drainage, therefore favorable condition
for formation of crystalline oxides.
The higher values of Feo/Fed relationship were
observed in P3 and P4, indicating greater participation of low
crystallinity iron oxides, which represents an environment
with poor drainage and favorable to pedogenetic process
of gleization (Costa; Bigham, 2009). In the Btg2 and Cg2
Table 2: Physical attributes of Porto Alegre Botanical Garden soils.
Hor Gra
%
CS FS Silt Clay FS/TS VU Sil/Cla Claf/
Cla
SoF
%
------------g kg-1-------------
(P1) Ultic Hapludalf
A5 396 284 150 170 0.42 -0.41 0.88 0.60 29
AB 4 251 249 220 280 0.50 0.04 0.79 0.69 11
Bt1 4 214 196 190 400 0.48 -0.06 0.48 0.78 16
Bt2 3 181 159 190 470 0.47 0.22 0.40 0.77 21
Bt3 3 232 188 180 400 0.45 -0.45 0.69 100
(P2) Oxic Dystrudept
A11 213 177 200 410 0.45 -0.03 0.49 0.71 13
A/B 12 166 114 190 530 0.41 0.33 0.36 0.73 82
Bi 17 181 69 180 570 0.28 0.51 0.32 0.67 97
Cr1 8 288 92 170 450 0.24 -0.08 0.38 0.44 100
Cr2 8 246 74 170 510 0.23 0.14 0.33 0.56 94
Cr3 6 315 115 160 410 0.27 -0.39 0.16 100
(P3) Oxyaquic Hapludalf
A1 478 262 160 100 0.35 -0.32 1.60 0.61 30
E2397 333 180 90 0.46 0.24 2.00 0.64 28
EB 1 431 229 230 110 0.35 -0.56 2.09 0.58 14
Btg1 1 232 178 360 230 0.43 0.23 1.57 0.58 9
Btg2 1 270 200 320 210 0.43 -1.52 0.58 5
(P4) Humaqueptic Endoaquent
A 2 288 232 270 210 0.45 0.09 1.29 0.67 26
AC 5 307 223 270 200 0.42 0.26 1.35 0.70 33
Cg1 4 356 264 190 190 0.43 -0.35 1.00 0.70 26
Cg2 4 240 190 280 290 0.44 -0.97 0.58 3
* Hor: horizon. Gra: gravel. CS: coarse sand. FS: ne sand. VU: uniformity value = {[(Silt+FS)/(TS-FS)]SURFACE HORIZON / [(Silt+FS)/
(TS-FS)]SUBSURFACE HORIZON} – 1,0. FS/TS: ne sand/total sand relationship. Sil/Cla: silt/clay relationship. Claf/Cla: ne clay/total
clay relationship. SoF: soil occulation.

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horizons of P3 and P4, respectively, it perceives a decrease
of Feo/Fed relationship, indicating greater participation of
crystalline forms of iron oxides, which can be attributed to
the presence of mottles in these horizons.
Duarte et al. (2000) observed these decreasing
values in proles with poor drainage, because the iron
minerals precipitated in mottles had higher degree of
crystallinity than those located in the soil matrix. In the EB
horizon of P3, the high values of Feo/Fed (0.60) and Alo/
Ald (0.50) may be related to the existence of temporary
water table in this prole section, with the interference
of ferrolysis in the low crystallinity of iron oxides and
aluminosilicates, above of the clayey Btg1 horizon
(Coelho; Vidal-Torrado, 2003).
The X-ray diffraction (Figure 3) in the sand and silt
of P1, P2, P3, and similarly P4 (data not shown) showed the
occurrence of feldspar and quartz, with higher occurrence
of feldspar in P2. The predominance of kaolinite in the
clay fraction of all soils is related to an environment with
moderate to advanced weathering, which was conrmed
by low clay CEC. The presence of mica reections in the
clay of P2 indicated that the steep position occupied in
the landscape (transition to steep slope relief) caused the
lower weathering compared to other soils.
Table 3: Chemical attributes of Porto Alegre Botanical Garden soils.
Hor
pH --------------------------Sorption complex-------------------------- VmSOC
H2OKCl Ca2+ Mg2+ K+Na+SB H+Al Al3+ CEC CFA
-------------------------------cmolc kg-1----------------------------- ---%--- g kg-1
(P1) Ultic Hapludalf
A5.2 4.2 1.3 0.6 0.26 0.02 2.18 2.6 0.2 4.78 28 46 89.7
AB 5.2 4.1 2.0 0.5 0.20 0.02 2.72 3.0 0.6 5.72 20 47 18 5.0
Bt1 5.0 3.8 1.4 0.7 0.21 0.01 2.32 4.5 1.8 6.82 17 34 44 4.9
Bt2 4.9 4.0 1.1 1.2 0.10 0.02 2.42 3.0 1.1 5.42 12 44 31 2.2
Bt3 5.0 3.9 1.1 1.3 0.09 0.02 2.51 3.1 1.2 5.61 14 45 32 1.8
(P2) Oxic Dystrudept
A5.2 4.3 2.5 1.8 0.73 0.03 5.06 3.9 0.5 8.96 22 57 9 12.0
A/B 4.9 3.9 1.8 1.5 0.62 0.03 3.95 4.7 2.1 8.65 16 46 34 8.5
Bi 4.9 3.9 1.2 1.6 0.30 0.03 3.13 4.5 2.6 7.63 13 41 46 2.5
Cr1 5.0 3.9 0.7 1.2 0.11 0.03 2.04 3.8 2.2 5.84 13 34 52 1.3
Cr2 4.9 3.8 0.5 1.1 0.09 0.03 1.72 4.3 3.0 6.02 12 28 64 2.7
Cr3 5.0 3.9 0.5 1.0 0.08 0.02 1.60 2.8 2.7 4.40 11 36 63 1.0
(P3) Oxyaquic Hapludalf
A4.9 3.8 0.6 0.3 0.10 0.01 1.01 3.2 0.8 4.21 42 24 44 6.8
E 4.5 3.7 0.4 0.1 0.04 0.01 0.55 2.6 1.1 3.15 35 19 65 1.7
EB 4.5 3.8 0.4 0.1 0.05 0.02 0.57 2.8 1.0 3.37 28 18 63 2.3
Btg1 4.8 3.7 0.7 0.4 0.05 0.04 1.19 3.2 1.1 4.39 20 27 48 3.2
Btg2 5.1 3.7 1.2 1.3 0.08 0.10 2.68 1.7 0.6 4.38 21 61 18 0.8
(P4) Humaqueptic Endoaquent
A5.4 4.8 6.6 1.5 0.13 0.22 8.45 3.3 0.1 11.75 56 72 1 27.0
AC 4.8 4.0 2.3 0.7 0.10 0.15 3.25 5.0 0.4 8.25 41 40 11 18.0
Cg1 4.4 3.6 0.9 0.5 0.13 0.07 1.60 3.6 0.9 5.20 27 31 36 6.3
Cg2 5.7 4.6 1.9 1.8 0.23 0.11 4.04 1.2 0.1 5.24 18 77 2 2.6
* Hor: horizon; SB: sum of exchangeable bases; CEC: cation exchange capacity in pH 7.0; CFA: clay fraction activity; V: base
saturation; m: aluminum saturation; SOC: soil organic carbon.

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Ciênc. Agrotec., Lavras, v. 39, n. 5, p. 477-487, set./out., 2015
The P1 profile, with B textural horizon was
classied as Argissolo Vermelho-Amarelo Distróco típico
(EMBRAPA, 2013), being classied as Ultic Hapludalf
in the Soil Taxonomy (Soil Survey Staff, 2010). The
attributes of P2 prole did not suggest a more developed
formation process, and the occurrence of B incipiente
horizon was decisive to classify it as Cambissolo Háplico
Tb Distróco típico, being classied as Oxic Dystrudept.
In the P3 prole, the presence of B “plânico” diagnostic
horizon, according EMBRAPA (2013), defined the
occurrence of Planossolo Háplico Distróco gleissólico,
being classied as Oxyaquic Hapludalf. In the P4 prole,
the presence of glei horizon and organic carbon content
suitable for A “húmico” horizon (EMBRAPA, 2013),
dened as Gleissolo Melânico Tb Eutróco típico, being
classied as Humaqueptic Endoaquent.
Table 4: Content of sulfuric attack oxides (Fe2O3, SiO2, Al2O3), oxides extracted by dithionite-citrate-bicarbonate
(Fe2O3, Al2O3), oxides extracted by ammonium oxalate (Fe2O3, Al2O3), and relationship between them.
Hor
----Oxides by sulfuric----
attack
Ki
DCB OXA Relationship
Fe2O3SiO2Al2O3Fe2O3d Al2O3d Fe2O3o Al2O3oFeo/
Fed
Alo/
Ald
Fed/
Fes
-----------g kg-1----------- ------------------g kg-1------------------
(P1) Ultic Hapludalf
A10.3 44.4 21.6 3.50 8.7 4.8 1.3 1.2 0.15 0.25 0.84
AB 18.1 97.6 46.1 3.60 17.7 9.6 1.7 2.9 0.10 0.30 0.98
Bt1 30.6 166.0 82.3 3.43 21.9 13.2 2.2 4.3 0.10 0.33 0.72
Bt2 35.8 194.1 105.0 3.14 27.6 14.2 2.3 4.3 0.08 0.30 0.77
Bt3 26.0 171.3 78.4 3.71 20.4 10.7 2.1 3.9 0.10 0.36 0.78
(P2) Oxic Dystrudept
A27.5 163.5 72.0 3.86 22.0 11.1 2.0 3.8 0.09 0.34 0.80
A/B 42.2 221.4 111.1 3.39 39.1 15.7 2.4 4.8 0.06 0.31 0.93
Bi 40.5 223.4 122.5 3.10 32.0 13.3 2.5 4.9 0.08 0.37 0.79
Cr1 29.8 195.5 101.1 3.29 17.3 7.2 1.4 3.2 0.08 0.44 0.58
Cr2 25.0 192.7 98.1 3.34 18.4 8.7 1.7 3.3 0.09 0.38 0.74
Cr3 7.3 100.3 49.1 3.47 6.5 4.6 0.6 1.4 0.09 0.30 0.89
(P3) Oxyaquic Hapludalf
A8.1 37.6 13.7 4.66 7.0 3.3 1.6 0.8 0.23 0.24 0.86
E 7.4 38.5 16.6 3.95 6.1 3.2 1.5 0.9 0.25 0.28 0.82
EB 7.9 48.9 16.1 5.15 7.5 3.6 4.5 1.8 0.60 0.50 0.95
Btg1 19.8 77.1 37.5 3.50 12.4 5.3 3.7 1.6 0.30 0.30 0.63
Btg2 25.5 83.6 32.3 4.40 16.6 3.7 2.7 0.5 0.16 0.14 0.65
(P4) Humaqueptic Endoaquent
A 20.8 87.0 35.6 4.16 16.9 5.1 8.9 2.1 0.53 0.41 0.81
AC 16.6 70.9 39.0 3.09 12.6 4.6 4.7 1.8 0.37 0.39 0.76
Cg1 13.3 79.4 42.3 3.19 7.5 4.0 2.9 1.7 0.39 0.43 0.56
Cg2 17.9 119.9 67.1 3.04 9.5 5.5 2.0 2.1 0.21 0.38 0.53
* Ki: relationship (1.7*SiO2)/Al2O3. Feo: Fe2O3 extracted by ammonium oxalate. Alo: Al2O3 extracted by ammonium oxalate. Fed:
Fe2O3 extracted by dithionite-citrate-bicarbonate. Ald: Al2O3 extracted by dithionite-citrate-bicarbonate. Fes: Fe2O3 extracted by
sulfuric attack.

Soil variability in different landscape... 485
Ciênc. Agrotec., Lavras, v. 39, n. 5, p. 477-487, set./out., 2015
CONCLUSIONS
The soil distribution in the landscape of the
Porto Alegre Botanical Garden followed the form
observed in hill and knoll areas of Porto Alegre,
with major pedogenic development in P1 (depth, soil
forming process development), whereas incipient soil
development occurred in P2, in condition of steep
slope, which was corroborated by high presence of
feldspar and mica. It is believed that steep slope implies
lower inltration of water in this landscape position,
affecting the clay translocation in depth (non-occurrence
of lessivage) or the progress of other soil forming
processes.
The good drainage in summit-shoulder transition
and backslope, and the sharp hydromorphism in footslope
and toeslope positions, showed the inuence of the relief
forms in the soil genesis, which was corroborated by
attributes like soil color and degree of crystallinity of iron
oxides. The highest degree of soil weathering was observed
in P1 located in upper third of landscape, not in steep slope,
which was conrmed by the high Fed/Fes relationship.
The lessivage process could be inferred in P1 by
clay skins and increase of ne clay/total clay relationship
until the beginning of illuvial horizon; while the ferrolysis
and gleization processes were indicated by low pH and high
Feo/Fed relationship in E and EB horizons of P3, being the
last also present in P4, indicating occurrence of gleization.
Figure 3: X-ray diffraction of sand, silt and clay of the pedogenetic horizons of P1, P2 and P3. Qz – quartz; Ft –
feldspar; Mc – mica; 2:1 – clay minerals 2:1; Ct – kaolinite; Gt – goethite; Hm – hematite; Ha – halite.

SILVA, L. F. da. et al.
486
Ciênc. Agrotec., Lavras, v. 39, n. 5, p. 477-487, set./out., 2015
ACKNOWLEDGMENTS
To “Fundação Zoobotânica” of Rio Grande do Sul
State (FZB-RS), for supporting the study. To biologist
Robberson Setubal and agronomist Walmir Gamboa, for
their efforts to carry out the work. To “Conselho Nacional
de Desenvolvimento Cientíco e Tecnológico” (CNPq –
471446/2012-2) and “Coordenação de Aperfeiçoamento
de Pessoal de Nível Superior” (CAPES), for the nancial
support and scholarship to the rst author.
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