SOIL PROPERTIES, CONDITION AND SOIL LOSSES FOR SOUTH AND EAST BRAZILIAN FOREST AREAS
soils, which normally have low natural fertility. According to Tardy &
Nahon (1985), the occurrence of quartz, kaolinite and goethite is the typical
paragenesis for permanently humid tropical red or yellow soils.
FIGURE 3 X-ray diffraction patterns of soils from Espírito Santo. FX =
dystrophic Haplic Plinthosol (Phinthaquox); PA1 =
dystrocohesive Yellow Argisol (Hapludult); PA2 = moderately
rocky Yellow Argisol (Hapludult); HIV = hydroxy-interlayered
vermiculite; K = kaolinite; G = goethite; A = anatase; and R =
rutile.
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FIGURE 4 X-ray diffraction patterns of soils from Rio Grande do Sul. PVe
= eutrophic Red Argisol (Rhodudalf); CXbd = dystrophic Haplic
Cambisol (Dystrudept); PVA = dystrophic Red-Yellow Argisol
(Hapludult); HIV = hydroxy-interlayered vermiculite; Q = quartz;
K = kaolinite; G = goethite; and H = hematite.
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FIGURE 5 X-ray diffraction patterns of soils from Minas Gerais. LV =
dystrophic Red Latosol (Haplustox); PVA = dystrophic Red-
Yellow Latosol (Haplustox); Gb = gibbsite; K = kaolinite; G =
goethite; and H = hematite.
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Through the SiO2/Al2O3 molecular ratio, it can be inferred that the
soils are within advancing process of silica removal, since every soil
presented molecular ratio less than 2.2 (Table 1). The gibbsite occurrence in
Minas Gerais’ Oxisols (Figure 5) was possibly the reason for the lowest
SiO2/Al2O3 molecular ratio values. These soils also showed the smallest
value of SiO2/(Al2O3 + Fe2O3) molecular ratio. In such soils would be
expected the lowest values for CEC, because they are very weathered.
However, soils from Minas Gerais showed the highest CEC values (Table
1). This fact can be explained since the relatively high organic matter
content (Table 1), which is the most important factor for negative charge
development in soils with predominance of clay minerals 1:1 (Meurer,
2004). In addition, the highest clay content also was found on the soils from
this region (Table 2).
The iron extraction by sulfuric attack (Fes) ranged from 16 g kg
-1 to
77 g kg-1 (Table 1). These relatively low values of Fe2O3 are probably due to
the parent material dominance of granitic gneisses rocks (Cenibra, 2001).
The small Feo/Fed ratio (Table 1) is expected in tropical soils due to the
removal of silica and oxidation of organic matter, favoring the more stable
iron oxides (Fed) (Kämpf & Curi, 2000).
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TABLE 1 Chemical and mineralogical soil properties of the A horizon from representative soils
cultivated with eucalyptus.
State
ES
MG
Soil CEC OM Feo Fed Fes SiO2 Al2O3 TiO2 P2O5
cmolc dm-3 ----------------------- g kg-1 ----------------------- Feo/Fed Fed/Fes Ki Kr
PA1 3.9 14 1.52 13.23 34 98 87 22.4 0.11 0.115 0.389 1.77 1.41
PA2 8.3 33 1.63 16.44 40 158 153 22.4 0.28 0.099 0.411 1.76 1.51
FX 9.1 31 2.81 12.15 28 72 70 20.6 0.19 0.231 0.434 1.79 1.42
LV 11.4 42 3.18 63.44 69 177 235 13.6 0.19 0.050 0.919 1.28 1.08
LVA 11.6 34 1.82 44.68 77 116 173 16.6 0.50 0.041 0.580 1.14 0.89
PVA 6.5 19 1.59 11.62 16 33 26 5.16 0.05 0.137 0.726 2.19 1.56
RS PVe 8.4 41 2.73 49.68 53 159 140 9.9 0.34 0.055 0.937 1.92 1.59
CXbd 10.4 36 2.91 27.52 53 103 82 17.5 0.88 0.106 0.519 2.15 1.52
PA1 = dystrocohesive Yellow Argisol (Hapludult); FX = dystrophic Haplic Plinthosol (Phinthaquox); PA2 =
moderately rochy Yellow Argisol (Hapludult); LVA = dystrophic Red-Yellow Latosol (Haplustox); LV =
dystrophic Red Latosol (Haplustox); PVA = dystrophic Red-Yellow Argisol (Hapludult); PVe = eutrophic
Red Argisol (Rhodudalf); CXbd = dystrophic Haplic Cambisol (Dystrudept); CEC = cation-exchange
capacity; OM = organic matter; Feo = iron extracted by ammonium oxalate; Fed = iron extracted by
dithionite-citrate-bicarbonate; Fes = iron extracted by sulfuric attack; Ki = SiO2/Al2O3 molecular ratio; Kr =
SiO2/(Al2O3 + Fe2O3) molecular ratio.
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The results of physical characterization of the soils showed different
textural classes (Table 2). The soils corresponded to the following textural
classes: clay (LV and PVe), sandy clay (PA2 and LVA), sandy clay loam
(PA1 and CXbd), and sandy loam (FX and PVA). Silt content ranged from
28 g kg-1 to 206 g kg-1, which can produce surface sealing in bare soils when
the content is high which greatly reduces the infiltration capacity. The high
content of fine sand and very fine sand can also reduce the infiltration
capacity and increase runoff, consequently, increasing water and soil losses.
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TABLE 2 Soil physical properties of the A horizon from representative soils cultivated with
eucalyptus.
ρbulk ρparticle Perm Clay Silt Sand VCS CS MS FS VFS
State Soil Texture
---- Mg m-3 --- mm h-1 ----- g kg-1 ----- ----------- g kg-1 ------------
PA1 1.52 2.54 11 269 28 703 SCL 70 175 217 187 54
ES PA2 1.47 2.49 17 394 72 534 SC 175 128 102 96 34
FX 1.47 2.55 22 188 87 725 SL 69 146 211 225 75
LV 1.18 2.56 54 598 71 331 C 20 74 132 86 20
MG LVA 1.13 2.50 55 425 109 466 SC 83 94 144 122 22
PVA 1.58 2.59 39 125 159 716 SL 71 232 232 140 42
RS PVe 1.46 2.43 39 419 206 375 C 50 66 98 122 39
CXbd 1.20 2.49 52 288 188 525 SCL 63 109 142 146 65
PA1 = dystrocohesive Yellow Argisol (Hapludult); FX = dystrophic Haplic Plinthosol (Phinthaquox); PA2 =
moderately rochy Yellow Argisol (Hapludult); LVA = dystrophic Red-Yellow Latosol (Haplustox); LV =
dystrophic Red Latosol (Haplustox); PVA = dystrophic Red-Yellow Argisol (Hapludult); PVe = eutrophic
Red Argisol (Rhodudalf); CXbd = dystrophic Haplic Cambisol (Dystrudept); ρbulk = bulk density; ρparticle =
particle density; PERM = soil permeability; SCL = sand clay loam; SC = sand clay; SL = sand loam; C =
clay; VCS = very coarse sand; CS = coarse sand; MS = medium sand; FS = fine sand; VFS = very fine sand.
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Results of the different parameters obtained from the analysis of the
moisture characteristic curve for fast and slow wetting are presented in Table
3. The soils demonstrated a stability ratio from 0.59 for the FX to 0.85 for
the PA2. All the soils had a stability ratio higher than 50%, suggesting a high
level of aggregate stability (Levy & Miller, 1997). Through statistic analysis
(Table 3) soils did not show a great difference in SR, since Oxisols was
statistically equal to the Inceptisols, which represent the extreme in terms of
pedogenetic development. The non-plowing of the soil within eucalypt areas
during seven-year production cycle, besides soil preparation only at the
eucalypt planting time should provide the elevated SR values. In addition,
the VDP ratio was also more than 50% for all soils (Table 3). This
observation indicated that aggregate stability breakdown due to fast wetting
did not result in a loss of more than 50% of the drainage pores (Levy &
Miller, 1997).
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TABLE 3 Results of the analysis of the moisture characteristic (MC) curves using the modified
seven-parameter van Genuchten model (Pierson and Mulla, 1989), from soil samples
under eucalypt cultivated forest in Brazil.
Site Soil Modal suction VDP Structural index VDP ratio Stability ratio
--- cm --- --- g g-1 --- --- g g-1 cm-1 ---
Fast Slow Fast Slow Fast Slow Mean StDev Mean StDev
PA1 13.3 12.3 0.133 0.193 0.010 0.016 0.69 bc 0.04 0.63 b 0.04
ES PA2 13.0 12.2 0.219 0.242 0.017 0.020 0.91 a 0.19 0.85 a 0.15
FX 13.0 12.2 0.106 0.171 0.008 0.014 0.62 c 0.13 0.59 b 0.16
LV 13.6 11.6 0.286 0.320 0.021 0.028 0.89 ab 0.12 0.75 ab 0.13
MG LVA 13.4 12.8 0.198 0.293 0.015 0.023 0.68 bc 0.08 0.66 ab 0.10
PVA 13.3 12.5 0.125 0.187 0.009 0.015 0.67 bc 0.15 0.63 b 0.13
RS PVe 13.0 12.3 0.228 0.276 0.018 0.022 0.84 abc 0.16 0.79 ab 0.09
CXbd 13.4 12.6 0.219 0.285 0.016 0.023 0.77 abc 0.08 0.72 ab 0.07
VDP = volume of drainable pores; Means followed by the same letter are not significantly different (LSD
test at = 0.05).
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Conversely, in other studies (e.g. Levy & Miller, 1997; Levy &
Mamedov, 2002; Levy et al., 2003; Norton et al., 2006; Ruiz-Vera & Wu,
2006), the soils studied did not show strong relationship between stability
ratio and clay content (Table 4). Furthermore, Norton et al. (2006), Lado et
al. (2004), and Mamedov et al. (2007) reported that aggregate stability
increased with an increase in clay content due to high aggregation ability of
clayey soils, whereas, for kaolinitic soils, which is the majority mineral in
the studied soil (Figures 3, 4 and 5), the trend was less pronounced probably
due to the presence of a large amount of oxides (Six et al., 2000b). For
kaolinitic soils associated with iron oxides, the mineralogical effect may
overshadow the long-term land use effects (Norton et al., 2006).
Espírito Santo soils showed the extreme values of aggregate stability
ratio (Table 3). The lowest SR was found for the FX, which had the greatest
amount of iron in non-crystalline forms (highest Feo/Fed ratio) (Table 1), and
small clay content (Table 2). Moreover, the FX soil was classified according
to textural class as sand loam, with high content of fine sand and very fine
sand (Table 2). These combinations contributed to generate the smallest SR.
In fact, the removal of the Fe-oxides played a very high disaggregation in
Oxisols and Inceptisols (Pinheiro-Dick & Schwertmann, 1996). This way,
iron oxides indicate their participation on soil aggregation (Lima &
Anderson, 1997; Muggler et al., 1999). Aggregation in the Oxisols on
Tertiary sediments in Minas Gerais state seems to be strongly influenced by
iron oxides (Muggler et al., 1999). Nevertheless, the present study showed a
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