Deforestation of Caatinga and inadequate land use of these dry environments have impacted soil quality in Northeastern Brazil. The objectives of this study were: (a) to evaluate the effect of deforestation and different agricultural uses on the physical and chemical properties of soil, and humic fractions of soil organic matter in dry environments; and (b) to detect the soil properties that were most affected by anthropic actions. We evaluated four dry areas in Chapada do Araripe, NE Brazil: preserved native vegetation; degraded native vegetation; cassava conventional cultivation; and eucalyptus agro-energy cultivation. Soil fertility, total organic carbon and humic fractions of soil organic matter were lower in the degraded native vegetation area. The best indicators for soil quality evaluation were: macroporosity; bulk density; soil resistance penetration; sum of bases (mainly Ca2+); available P; and saturation by Al3+. Total organic carbon and humic acid fractions of soil organic matter were important in improving soil quality. These properties were influenced by deforestation and agricultural uses, suggesting that the deforestation of native vegetation in dry environments has high capacity to degrade the soil, preventing its regeneration.
Deforestation and inadequate use of soil in semi-arid regions, along with the unfavorable climatic conditions of these regions, poorly developed soils and low biomass production, influence the regenerative capacity of the vegetation and soil degradation. Therefore, the use of more efficient and sustainable management systems is necessary for mitigate these negative effects on vegetation and soil in these regions (
The gypsum mining in the Araripe region of the Brazilian semi-arid region presents a high biomass demand for the calciners, which is responsible for the high rates of deforestation, making this region susceptible to desertification and reducing the productive capacity of soils (
Changes in the environmental landscape and land use in the semi-arid region are also associated with agricultural expansion. Several studies showed that the agricultural uses in this region have caused soil degradation (
The impact on forest resources in the Araripe region has led to the use of strategic alternatives to contain deforestation (
In this study, we hypothesized that the deforestation of Caatinga for cultivation of cassava monoculture or eucalyptus plantations for use as biomass energy may be the cause of environmental degradation in different soil properties responsible for maintaining the quality and sustainability of the environment.
Recently, soil degradation in dry environment has expanded in the Chapada do Araripe region, mainly due to the intense exploitation of native vegetation, thus making it essential to study the physical and chemical aspects of soil quality. In this study, we meant to answer the following questions: (i) which soil properties are being most impacted by deforestation? (ii) What is the influence of subsistence family farming (cassava cultivation) on soil properties? (iii) Can the establishment of alternative energy crops, such as eucalyptus, affect soil properties and reduce its quality?
The study was carried out in top areas of Chapada do Araripe (07° 27′ 32″ S and 40° 24′ 55″ W), located in the extreme west of the state of Pernambuco, in the municipality of Araripina, in an area of gypsum mining and production. According to the classification of Koppen (
The native vegetation of the top areas of Chapada do Araripe includes the following dominant species:
The study was carried out in four distinct though adjacent areas: (i) preserved native vegetation area (PNV); (ii) degraded native vegetation area, with low natural regeneration (DNV); (iii) cassava conventional cultivation area (CCC), with plantations established 46 years ago; and (iv) eucalyptus agro-energetic cultivation area (EAC), aged only 11 years (
The number of samples needed to accurately represent each soil property (sample adequacy) was calculated as follows (
where
Sampling for determination of the physical properties was performed at the four vertices and in the center of a 100 × 100 m square plot located in the center of each study area, at depths of 0-10 cm and 10-20 cm, totaling ten samples per area (40 samples in total). Samples were collected in volumetric rings with 5 × 5 cm (height × diameter) without structure deformation. The
The properties analyzed were total porosity (TP), macroporosity (MaP), microporosity (MiP), field capacity moisture content (FC), wilting point moisture content (WP), soil resistance penetration (SRP) and bulk density (BD). Available water (AW) content was calculated by the difference between FC and WP. A preliminary analysis revealed small and negligible variation in soil texture and particle size distribution among the different areas (Tab. S2 in Supplementary material).
Samples were saturated for 24 h for determination of TP, MaP and MiP. After the saturation period, samples were submitted to the tension of 6 KPa using a tension table for MiP determination. MaP was obtained by the difference between TP and MiP. To determine BD, samples were placed in an oven at 105 °C until constant weight. To obtain the FC, samples were placed on the tension table at 10 KPa, and to obtain the WP, samples were placed in a Richards extractor at 1.500 KPa (
Sampling for determination of chemical properties, TOC and SOM fractions was performed within the 100 × 100 m square plot in the center of each study area. Twenty-five samples were collected within each plot, spaced 25 × 25 m at depths of 0-5 cm, 5-10 cm and 10-20 cm, totaling 75 samples per area (300 samples in total). Samples were collected with a Dutch type auger with a deformed structure. The
The collection of undisturbed samples to evaluate the physical properties of the soil was carried out on the side of a small soil profile by introducing a volumetric ring of 5 cm in diameter. In this case, soil sampling was carried out at depths 0-10 cm (topsoil) and 10-20 cm (subsoil), as there was not enough space to collect samples at the same depths used for the evaluation of soil chemical properties (0-5 cm; 5-10 cm; and 10-20 cm - see above). Additionally, we sampled the entire A horizon and a fraction of the AB horizon, as the most effective absorption capacity of the root system is up to 20 cm deep.
The following chemical properties were determined on soil samples: pH in H2O; exchangeable Ca2+; Mg2+; K+; Al3+; potential acidity (H+Al); and available P. The pH was measured with a glass electrode in a 1:2.5 ratio of the soil solution in distilled water. The Ca2+, Mg2+ and Al3+ were extracted with KCl 1.0 mol L-1. Ions Ca2+ and Mg2+ were measured by atomic absorption spectroscopy and Al3+ was measured by titration in the presence of the blue bromothymol indicator and titrated with NaOH (0.025 mol L-1). Available P and K+ were estimation with Mehlich-1 extraction. P concentration was dosed by colorimetry and K+ content was dosed by flame photometry. The (H+Al) was extracted with 0.5 mol L-1 calcium acetate and titrated with NaOH and phenolphthalein as indicator. All chemical protocols were taken from
The following indexes derived from the above chemical properties were obtained: sum of bases (SB); potential cation exchange capacity (CECp); saturation by bases (V) and saturation by aluminum (Al saturation).
TOC was determined by oxidation of the organic matter by potassium dichromate (K2Cr2O7) 0.020 mol L-1 and titrated with ammonium ferrous sulphate (Mohr’s salt) 0.005 mol L-1, according to
Chemical fractionation of SOM was based on different solubilities of fulvic acid (FA-C), humic acid (HA-C) and humin (HU-C) fractions in acid and alkaline media, according to
Data from physical and chemical properties, TOC and SOM fractions were submitted to analysis of variance by the F test (p<0.05). When there was a significant effect of the different land uses on these properties, the Scott-Knott’s mean test (p<0.05) was applied.
Data were also analyzed by multivariate statistics, through principal component analysis (PCA) and cluster analysis (CA) to select properties that were most influenced by different land uses and to identify similar groups (
Data were centralized and normalized to mean zero and variance one to ensure that all properties equally contributed to the multivariate models used (
Different land uses had an effect on MaP, TP and BD in the soil surface layer (topsoil: 0-10 cm) and on SRP in both soil layers. The soil physical properties FC, WP AW were only influenced by different land uses in the subsurface layer (subsoil: 10-20 cm -
The DNV area in the topsoil had the lowest values of MaP and TP and the highest values of BD and SRP. The DNV area presented the highest SRP value, being 207, 300 and 221% higher than the PNV, CCC and EAC areas. The PNV, CCC and EAC areas presented MaP values above 0.10 m3 m-3. The DNV area at both depths and EAC at the subsurface layer showed SRP values greater than 2.0 MPa (
The physical properties that better accounted for data variation were MaP, TP, BD and SRP in topsoil, which were significantly correlated with PC1, showing the influence of the different soil uses on these properties. Regarding PC2, MiP, FC and AW showed the highest and significant correlation values with this axis (
Regarding the 10-20 cm depth layer (subsoil), the first two PC axes explained 91.90% of the total variance in physical properties among the 4 different land uses. PC1 a 54.10% and presented a high correlation with TP, SRP, BD and WP, while PC2 accountd for 37.80% of the variability and showed a high correlation with MiP, FC and AW (
In the derived PC biplots (
The different land uses sampled were distributed in different quadrants of the biplots in both layer of the soil, forming 4 distinct groups (
Cluster analysis based on soil physical attributes highlighted the existence of three groups of land uses, according to the different types of land use and soil depth (
Deforestation and different land uses altered soil chemical properties at all depths (
Exchangeable bases (Ca2+, Mg2+ and K+) had the highest levels in the EAC area at all soil depths, with the exception of Ca2+ in the 10-20 cm depth layer, where the highest content was found in the CCC area. These results reflected in the increment of SB, CECp and V of the soil (
In general, we found low soil fertility in all the different land uses. The exchangeable bases, available P and pH were low, and Al saturation was high. CCC or EAC contributed to raise fertility levels and reduce acidity indicators, but the CECp of the PNV area was higher than the areas of cultivation (CCC and EAC). Further, the inappropriate exploitation of the DNV area degraded the soil, reducing its fertility and increasing acidity.
Deforestation and different land use affected TOC (all depths) and the humic fractions of organic matter HA-C (all depths), HU-C at 0-5 cm depth and HS-C at 0-5 cm and 10-20 cm depths (
The HA-C fractions in the PNV and EAC areas were also higher than in the CCC and DNV areas in the superficial layers (0-5 and 5-10 cm), but the PNV area had the highest C content in the HA-C fraction in the subsurface layer (10-20 cm). The C of the HU-C fraction in the CCC area showed a reduction of 24% in relation to the more preserved area (PNV) at 0-5 cm depth. In the CCC and DNV areas, there was a reduction of the C content on the HS-C fraction in layers of 0-5 cm and 10-20 cm depth (
In general, a low level of humification (<45%) was observed in the soil of all land uses, as organic C of the HU-C fraction represented on average 43%, 29% and 26% of TOC at 0-5 cm, 5-10 cm and 10-20 cm depths, respectively (
TOC reduction with depth ranged from 41% to 47% between the 0-5 cm and 10-20 cm depth layers, with the EAC area showing the greatest reduction (
The first two components of the PCA carried out on soil chemical properties accounted for 96% of the total variation in the 0-5 cm depth layer. PC1 was associated with most of the chemical properties (pH, P, K+, Ca2+, Mg2+, Al3+, SB and Al saturation) and all humic fractions of SOM (TOC, HA-C, FA-C, HU-C, HS-C and HA-C/FA-C), with the exception of HS-C/TOC, while PC2 was associated with properties (H+Al) and V (
Regarding the 5-10 cm depth layer, the first two components explained 94.5% (PC1: 65.20%, PC2: 29.30%) of the variance in soil chemical properties and humic fractions of SOM. With the exception of (H+Al), HU-C, HA-C/FA-C and HS-C/TOC, all other properties were correlated with PC1, while PC2 was associated with (H+Al), HU-C and HS-C/TOC (
In the 10-20 cm depth layer, PC1 and PC2 were responsible for 94.30% of the total variance (63.30% and 31.00%, respectively). Soil chemical properties and the SOM fractions that most correlated with PC1 were: pH, P, K+, Ca2+, Mg2+, Al3+, SB, CECp, Al saturation, V, TOC, HA-C, FA-C and HS-C. The soil property (H + Al) and SOM fractions HU-C and HS-C/TOC were those showing the stronger association with PC2 (
The acidity indicators Al3+ and Al saturation correlated negatively with pH, SB (except for K+), V and P in all soil layers (
The TOC and humic fractions of SOM were positively correlated. However, their correlation is stronger in the superficial layer and becomes weaker in depth, with TOC showing greater association with FA-C in the layer 10-20 cm. Moreover, the vector of the parameter HU-C in
The chemical properties pH, P, Ca2+, Mg2+ and V reached their largest values in the soil of EAC and CCC plots. The PNV areas were associated with TOC and humic fractions of SOM. The DNV area was more influenced by acidic properties Al3+ and Al saturation (
The dendrogram of similarity between different land uses based on soil chemical properties (
The soils of areas with different land uses showed comparable texture at the studied depths (
We found that the increase in BD in DNV was explained by reduction in soil porosity (mainly MaP), agreeing with the findings of
The MaP little varied in the subsurface layer, indicating that different land uses weakly affect this physical property. Indeed, soil macroporosity may reflect the contribution of plant roots and plant residues, which occur mainly on the soil surface (
The degradation of soil physical properties in the DNV area can be favored by the reduced vegetation cover and the consequent higher exposure to rainfall (
The highest values of BD and SRP in DNV were also related with the lower TOC content in this area in the 0-5 and 10-20 cm layers, promoting lower root content and microbial action as SOM improves structuring and porosity (
The strong association between the MiP, FC and AW soil properties in the CCC area may be explained by the greater homogenization due to tillage applied for crop cultivation, thus reducing pores and increases water retention (
The highest values of pH in cultivated areas (CCC and EAC) can be attributed to liming and fertilization practices that increased the number of exchangeable bases and soil pH (
The high acidification of the DNV area may be related to the reduction of exchangeable bases due to surface erosion and leaching during periods of higher rainfall, as a consequence of the removal of native vegetation leaving the soil exposed (
The high amounts of exchangeable bases in the soil of planted forests such as eucalyptus cultivation may be associated with fertilization and liming practices in these areas and to the contribution of plant material to the soil surface. According to
The amount of exchangeable bases in areas of preserved vegetation are naturally low (
The high P availability in the soil of these dry ecosystems is due to chemical fertilization. However, in areas with preserved vegetation, it can be promoted by the organic material contribution, which reduces the adsorption and precipitation of P (
The similarity of TOC contents between PNV and EAC areas in the soil surface layer showed that increase in TOC content is favored by continuous deposition of litter and by the presence of more developed root systems on the surface (
The increase of HA-C in PNV and EAC areas reveals that the management that maintains soil coverage, adequate humidity and minimal or no anthropic action may promote microbial action and humic fraction production, and more developed root systems as well (
The higher proportion of HU-C in relation to HA-C and FA-C in the topsoil of different land uses is due to its molecule size which determines a higher chemical affinity to colloids (
Low biomass production and low organic matter input to soil are common in semi-arid regions (
The humification degree (HS-C/TOC) varying from 72 to 87% in all areas under different land uses indicates that most of TOC is in humic fractions, suggesting a high level of humification.
We found that P, Ca2+ and TOC, SB and Al saturation were the most important chemical properties to explain data variation, in addition to the HA-C fraction of SOM, which strongly discriminate areas under different land uses.
The negative correlation of Al3+ with pH, nutrient availability and humic fractions of SOM suggests a complexation of Al3+ by humic substances (
The close association of FA-C with TOC in the subsurface may be due to characteristics of the FA, which is highly soluble and mobile in the soil, and thus its content incraeses with depth (
We found that the differences in soil chemical properties between DNV and the other land uses become weaker in the subsurface layer, and this may reflect the low capacity of the different land uses to improve chemical quality and SOM at the lower soil depths in these dry habitats. The higher recalcitrance of the eucalyptus plant material (
The clustering of CCC and EAC areas in soil subsurface indicated that cultivation practices adopted in these areas did not affect the soil chemical properties and SOM fractions. The low capacity of eucalyptus to improve soil conditions at lower depth (
SOM preservation and transformation processes in different land uses has the greatest importance and has to be studied in detail. However, it has been widely questioned whether the traditional chemical fractionation involving extraction with strong alkali can provide information on SOM dynamics and turnover in soils (
Finally, the improvement of soil properties in the surface layer by the EAC does not prove the hypothesis tested.
The physical and chemical properties that best described the soil quality of different land uses in Chapada do Araripe were MaP, BD, SRP, SB (mainly Ca2+), available P and Al saturation. The TOC and the HA-C fraction of SOM were also important in improving soil quality. The DNV area showed degradation of both chemicals and physical properties, resulting in the reduction of soil quality. Improvement of these properties in the EAC area was limited to the surface layer. Grouping obtained by cluster analysis showed that DNV (degraded native vegetation) and PNV (preserved native vegetation) areas are different from the cultivated areas (EAC and CCC) in terms of soil physical and chemical parameters, though EAC and CCC areas approach the PNV area in the soil surface layers, while DNV showed a strong reduction in soil quality.
Our study suggests that the disordered cutting of native vegetation causes land degradation in Chapada do Araripe, which results in the reduction of soil quality. Crops that allow the input of biomass and keep the soil covered, protecting it from weathering, can maintain or improve soil properties and functions, although this improvement has not been observed below the soil surface (>10 cm depth).
JSR: investigation, methodology, formal analysis and writing the original draft; FJF; conceptualization, funding acquisition, supervision, writing review and editing; JCAF: resources, methodology and data curation; MBGSF: resources, methodology and visualization; BGA: formal analysis, data curation and visualization; LRCS: formal analysis and data curation.
The authors thank the Experimental Station of Araripina of the Agronomic Institute of Pernambuco (IPA), Brazil for the logistic and operational support. The study was supported by Pernambuco State Science and Technology Support Foundation (FACEPE) and by the National Council for Scientific and Technological Development (CNPq), project no. APQ-0729-5.01/14 “
The studied sites. (a) Preserved native vegetation (PNV); (b) degraded native vegetation (DNV); (c) Cassava conventional cultivation (CCC); (d) Eucalyptus agro-energy cultivation (EAC).
Biplots of the soil physical properties. (a) Topsoil (0-10 cm) and (b) subsoil (10-20 cm). (PNV): Preserved native vegetation; (DNV): Degraded native vegetation; (CCC): Cassava conventional cultivation; (EAC): Eucalyptus agro-energy cultivation. Soil physical attributes: (MaP) macroporosity; (MiP) microporosity; (TP) total porosity; (BD) bulk density; (SRP) soil resistance penetration; (FC) field capacity moisture content; (WP) wilting point moisture content; (AW) available water. The arrow represents the direction of high weighting (maximum variation) of soil physical properties along the principal components. PC1 and PC2 of topsoil (a) explain 95.7% of the variation, while PC1 and PC2 of subsoil (b) explain 91.9% of the total variation.
Dendrograms of the different land uses analyzed according to the soil physical properties. (a) Topsoil (0-10 cm) and (b) subsoil (10-20 cm).(PNV): preserved native vegetation; (DNV): degraded native vegetation; (CCC): Cassava conventional cultivation; (EAC): Eucalyptus agro-energy cultivation.
Biplots of the soil chemical properties and humic fractions of the organic matter. (a) topsoil (0-5 cm), (b) subsoil 1 (5-10 cm) and (c) subsoil 2 (10-20 cm). (PNV): preserved native vegetation; (DNV): degraded native vegetation; (CCC): Cassava conventional cultivation; (EAC): Eucalyptus agro-energy cultivation; (pH): hydrogen potential (H2O/1:2.5); (P): available phosphorus; (K): exchangeable potassium; (Ca): exchangeable calcium; (Mg): exchangeable magnesium; (Al): exchangeable aluminum; (H+Al): potential Acidity; (SB): sum of bases; (CECp): cations exchange capacity potential; (V): base saturation; (Al saturation): saturation by aluminum; (TOC): total organic carbon; (HA-C): humic acid fraction; (FA-C): fulvic acid fraction; (HU-C): humin fraction; (HS-C): humic substances fractions; (HA-C/FA-C): humic acid fraction/fulvic acid fraction; (HS-C/TOC): humic substances fractions/total organic carbon. The arrows represent the directions of the high weighting of soil chemical properties and humic fractions of the organic matter along the first (PC1) and second (PC2) principal components. PC1 and PC2 of topsoil explained 96.00% of the total variation, while they accounted for 94.50% and 94.30% of the variation is soil chemical parameters in subsoil 1 (5-10 cm) and subsoil 2 (10-20 cm), respectively.
Dendrograms of the different land uses according to the soil chemical properties and humic fractions of the organic matter. (a) topsoil (0-5 cm); (b) subsoil 1 (5-10 cm); (c) subsoil 2 (10-20 cm). (PNV): preserved native vegetation; (DNV): degraded native vegetation; (CCC): Cassava conventional cultivation; (EAC): Eucalyptus agro-energy cultivation.
Soil physical attributes of topsoil (0-10 cm) and subsoil (10-20 cm) under forest, deforested, cropland and agro-energy sites. (PNV): preserved native vegetation; (DNV): degraded native vegetation; (CCC): Cassava conventional cultivation; (EAC): Eucalyptus agro-energy cultivation; (MaP): macroporosity; (MiP): microporosity; (TP): total porosity; (BD): bulk density; (SRP): soil resistance penetration; (FC): field capacity moisture content; (WP): wilting point moisture content; (AW): available water. Mean values and standard deviation are displayed. Values in columns with similar letters are not significantly different (p>0.05); (ns): not significant.
SoilDepth | Site | MaP(m-3 m-3) | MiP(m-3 m-3) | TP(m-3 m-3) | BD(Mg m-3) | SRP(Mpa) | FC(m-3 m-3) | WP(m-3 m-3) | AW(m-3 m-3) |
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0-10 cm | PNV | 0.17 ± 0.03 a | 0.31 ± 0.01 a | 0.48 ± 0.02 a | 1.27 ± 0.06 b | 1.12 ± 0.22 b | 0.30 ± 0.01 a | 0.09 ± 0.01 a | 0.21 ± 0.02 a |
DNV | 0.08 ± 0.01 b | 0.33 ± 0.01 a | 0.41 ± 0.02 b | 1.51 ± 0.07 a | 3.44 ± 0.69 a | 0.33 ± 0.01 a | 0.10 ± 0.01 a | 0.22 ± 0.02 a | |
CCC | 0.13 ± 0.02 a | 0.36 ± 0.02 a | 0.49 ± 0.02 a | 1.34 ± 0.06 b | 0.86 ± 0.17 b | 0.36 ± 0.02 a | 0.10 ± 0.01 a | 0.25 ± 0.02 a | |
EAC | 0.16 ± 0.03 a | 0.33 ± 0.01 a | 0.49 ± 0.02 a | 1.30 ± 0.06 b | 1.07 ± 0.21 b | 0.32 ± 0.01 a | 0.10 ± 0.01 a | 0.22 ± 0.02 a | |
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10-20 cm | PNV | 0.12 ± 0.02 a | 0.33 ± 0.01 a | 0.45 ± 0.01 a | 1.34 ± 0.02 a | 0.93 ± 0.14 b | 0.33 ± 0.01 b | 0.07 ± 0.003 b | 0.25 ± 0.01 a |
DNV | 0.08 ± 0.01 a | 0.35 ± 0.01 a | 0.43 ± 0.01 a | 1.43 ± 0.02 a | 2.05 ± 0.30 a | 0.35 ± 0.01 a | 0.10 ± 0.004 a | 0.25 ± 0.01 a | |
CCC | 0.10 ± 0.02 a | 0.36 ± 0.01 a | 0.47 ± 0.01 a | 1.41 ± 0.02 a | 1.46 ± 0.22 b | 0.36 ± 0.01 a | 0.10 ± 0.004 a | 0.27 ± 0.02 a | |
EAC | 0.10 ± 0.02 a | 0.33 ± 0.01 a | 0.42 ± 0.01 a | 1.42 ± 0.02 a | 2.69 ± 0.40 a | 0.32 ± 0.01 b | 0.10 ± 0.004 a | 0.21 ± 0.01 b | |
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Correlation between principal components (PC1, PC2) and soil physical attributes of topsoil (0-10 cm) and subsoil (10-20 cm). (MaP): macroporosity; (MiP): microporosity; (TP): total porosity; (BD): bulk density; (SRP): soil resistance penetration; (FC): field capacity moisture content; (WP): wilting point moisture content; (AW): available water; (*): p<0.05.
Attribute | 0-10 cm | 10-20 cm | ||
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PC1 | PC2 | PC1 | PC2 | |
MaP | -0.983* | 0.027 | -0.647 | -0.568 |
MiP | 0.365 | 0.930* | -0.258 | 0.966* |
TP | -0.834* | 0.525 | -0.735* | 0.548 |
BD | 0.991* | -0.124 | 0.816* | 0.427 |
SRP | 0.851* | -0.520 | 0.997* | -0.074 |
FC | 0.487 | 0.864* | -0.252 | 0.959* |
WP | 0.692 | 0.530 | 0.935* | 0.276 |
AW | 0.234 | 0.955* | -0.695 | 0.713* |
Absolute variance (%) | 54.80 | 40.90 | 54.10 | 37.80 |
Cumulated variance (%) | 54.80 | 95.70 | 54.10 | 91.90 |
Soil chemical attributes of topsoil (0-5 cm) and subsoil (5-10 and 10-20 cm) under forest, deforested, cropland and agro-energy sites. (PNV): preserved native vegetation; (DNV): degraded native vegetation; (CCC): Cassava conventional cultivation; (EAC): Eucalyptus agro-energy cultivation. Soil chemical attibutes: (pH) hydrogen potential (H2O/1:2.5); (P) available phosphorus; (K+) exchangeable potassium; (Ca2+) exchangeable calcium; (Mg2+) exchangeable magnesium; (Al3+) exchangeable aluminum; (H+Al) potential acidity; (SB) sum of bases; (CECp) cations exchange capacity potential; (V) base saturation; (Al saturation) saturation by aluminum. Mean values and standard deviation are reported. Values in columns with similar letters are not significantly different (p>0.05).
Depth | Site | pH | P(mg dm-3) | K+(cmolc dm-3) | Ca2+(cmolc dm-3) | Mg2+(cmolc dm-3) | Al3+(cmolc dm-3) | H+Al(cmolc dm-3) | SB(cmolc dm-3) | CECp(cmolc dm-3) | V(%) | Alsaturation(%) |
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0-5 cm | PNV | 4.83±0.25b | 1.26±0.63b | 0.14±0.03a | 0.65±0.02b | 0.18±0.08b | .0.51±0.13b | 6.68±1.87a | 0.97±0.29c | 7.66±1.98a | 13.36±4.80b | 35.19±9.04b |
DNV | 4.49±0.20c | 0.95±0.68c | 0.06±0.01c | 0.36±0.05c | 0.07±0.02c | 0.66±0.12a | 4.15±1.05c | 0.52±0.08d | 4.67±1.04d | 11.70±3.25b | 55.70±6.03a | |
CCC | 4.96±0.38b | 2.10±0.63a | 0.10±0.03b | 0.98±0.19a | 0.18±0.06b | 0.38±0.09c | 4.27±1.14c | 1.29±0.25b | 5.57±1.14c | 24.17±6.67a | 23.23±7.23c | |
EAC | 5.42±0.51a | 2.59±0.89a | 0.14±0.07a | 1.04±0.38a | 0.32±0.18a | 0.33±0.17c | 4.78±0.79a | 1.53±0.57a | 6.31±0.79b | 24.19±8.51a | 19.94±13.43d | |
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5-10 cm | PNV | 5.00±0.21b | 1.26±0.62b | 0.07±0.02b | 0.80±0.21b | 0.15±0.05b | 0.53±0.11b | 6.60±1.59a | 1.03±0.27b | 7.63±1.33a | 13.67±2.91b | 34.71±7.01b |
DNV | 4.72±0.12c | 0.81±0.66c | 0.03±0.01d | 0.45±0.06c | 0.04±0.01c | 0.60±0.10a | 4.48±0.94b | 0.53±0.07c | 5.02±0.97c | 10.93±1.99c | 52.78±5.02a | |
CCC | 5.23±0.32a | 2.04±0.69a | 0.05±0.01c | 1.04±0.21a | 0.18±0.08b | 0.36±0.11c | 4.98±1.29b | 1.29±0.24a | 6.27±1.33b | 21.16±4.85a | 22.37±8.01c | |
EAC | 5.22±0.46a | 1.78±0.91a | 0.09±0.05a | 1.00±0.37a | 0.28±0.11a | 0.36±0.16c | 5.16±1.00b | 1.39±0.56a | 6.55±1.05b | 21.37±7.76a | 22.82±12.90c | |
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10-20 cm | PNV | 4.83±0.18b | 0.56±0.59a | 0.06±0.01b | 0.28±0.12c | 0.15±0.05b | 0.59±0.09b | 5.41±1.35a | 0.49±0.18b | 5.91±1.44a | 8.39±2.85c | 55.90±10.8b |
DNV | 4.70±0.15b | 0.11±0.18b | 0.02±0.01d | 0.07±0.03d | 0.04±0.01c | 0.66±0.09a | 4.36±1.25b | 0.14±0.05c | 4.50±1.24b | 3.51±1.79d | 82.51±5.32a | |
CCC | 4.93±0.29a | 0.90±0.59a | 0.05±0.01c | 0.64±0.33a | 0.17±0.05b | 0.48±0.10c | 4.17±1.09b | 0.86±0.38a | 5.03±1.13b | 17.61±8.96a | 38.08±13.08c | |
EAC | 5.04±0.43a | 0.79±0.52a | 0.08±0.01a | 0.45±0.32b | 0.25±0.05a | 0.51±0.17c | 5.15±1.37a | 0.79±0.51a | 5.95±1.63a | 13.11±6.17b | 43.17±18.09c | |
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Total organic carbon and humic fractions of the organic matter of topsoil (0-5 cm) and subsoil (5-10 and 10-20 cm) under forest, deforested, cropland and agro-energy. (PNV): preserved native vegetation; (DNV): degraded native vegetation; (CCC): Cassava conventional cultivation; (EAC): Eucalyptus agro-energy cultivation. (TOC): total organic carbon; (HA-C): humic acid fraction; (FA-C): fulvic acid fraction; (HU-C): humin fraction; (HS-C): humic substances fractions; (HA-C/FA-C): humic acid fraction/fulvic acid fraction; (HS-C/TOC): humic substances fractions/total organic carbon. Mean values and standard deviation are reported. Values in columns with similar letter are not significantly different (p>0.05). (ns): not significant.
SoilDepth | Site | TOC(g kg-1) | HA-C(g kg-1) | FA-C(g kg-1) | HU-C(g kg-1) | HS-C(g kg-1) | HA-C/FA-C(g kg-1) | HS-C/TOC(g kg-1) |
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0-5 cm | PNV | 14.16 ± 2.23 a | 3.21 ± 1.73 a | 2.82 ± 2.05 a | 6.34 ± 1.73 a | 12.37 ± 2.88 a | 1.14 ± 0.51 a | 0.87 ± 0.26 a |
DNV | 11.26 ± 3.00 c | 1.97 ± 1.43 b | 2.56 ± 1.59 a | 4.81 ± 2.73 b | 9.34 ± 3.55 b | 0.77 ± 0.34 b | 0.83 ± 0.39 a | |
CCC | 12.78 ± 2.56 b | 2.33 ± 1.75 b | 2.88 ± 1.72 a | 5.67 ± 1.80 a | 10.88 ± 3.06 b | 0.81 ± 0.36 b | 0.85 ± 0.30 a | |
EAC | 14.31 ± 2.72 a | 3.67 ± 2.47 a | 2.84 ± 1.28 a | 5.75 ± 2.01 a | 12.26 ± 3.48 a | 1.29 ± 0.58 a | 0.86 ± 0.28 a | |
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5-10 cm | PNV | 12.17 ± 2.19 a | 3.06 ± 0.82 a | 2.92 ± 0.95 a | 3.59 ± 2.23 a | 9.57 ± 2.96 a | 1.04 ± 0.68 a | 0.79 ± 0.36 a |
DNV | 9.48 ± 1.70 b | 1.93 ± 0.52 b | 2.51 ± 0.73 a | 3.11 ± 1.93 a | 7.55 ± 2.84 a | 0.77 ± 0.80 b | 0.80 ± 0.41 a | |
CCC | 11.16 ± 2.00 a | 2.04 ± 0.55 b | 2.83 ± 0.97 a | 3.19 ± 1.79 a | 8.06 ± 2.66 a | 0.72 ± 0.54 b | 0.72 ± 0.34 a | |
EAC | 12.00 ± 2.16 a | 3.07 ± 0.83 a | 3.05 ± 1.13 a | 3.23 ± 2.24 a | 9.35 ± 4.62 a | 1.01 ± 0.67 a | 0.78 ± 0.36 a | |
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10-20 cm | PNV | 7.73 ± 2.08 a | 1.90 ± 1.25 a | 2.85 ± 1.38 a | 1.98 ± 0.95 a | 6.73 ± 2.21 a | 0.67 ± 0.51 a | 0.87 ± 0.35 a |
DNV | 6.03 ± 1.28 b | 0.66 ± 0.80 b | 2.20 ± 1.73 a | 1.81 ± 0.89 a | 4.67 ± 2.01 b | 0.30 ± 0.44 b | 0.77 ± 0.36 a | |
CCC | 7.49 ± 2.07 a | 1.11 ± 0.75 b | 2.61 ± 1.53 a | 1.83 ± 0.84 a | 5.55 ± 1.74 b | 0.43 ± 0.86 b | 0.74 ± 0.41 a | |
EAC | 7.61 ± 1.73 a | 1.24 ± 0.94 b | 2.89 ± 2.22 a | 1.86 ± 1.02 a | 5.99 ± 2.40 a | 0.43 ± 0.44 b | 0.79 ± 0.33 a | |
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Correlation between each principal component (PC) and soil chemical attributes and humic fractions of the organic matter in topsoil (0-5 cm) and subsoil (5-10 cm and 10-20 cm). (pH): hydrogen potential (H2O/1:2.5); (P): available phosphorus; (K+): exchangeable potassium; (Ca2+): exchangeable calcium; (Mg2+): exchangeable magnesium; (Al3+): exchangeable aluminum; (H+Al): potential Acidity; (SB): sum of bases; (CECp): cations exchange capacity potential; (V): base saturation; (Al saturation): saturation by aluminum; (TOC): total organic carbon; (HA-C): humic acid fraction; (FA-C): fulvic acid fraction; (HU-C): humin fraction; (HS-C): humic substances fractions; (HA-C/FA-C): humic acid fraction/fulvic acid fraction; (HS-C/TOC): humic substances fractions/total organic carbon. (*): p<0.05.
Attribute | 0-5 cm | 5-10 cm | 10-20 cm | |||
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PC1 | PC2 | PC1 | PC2 | PC1 | PC2 | |
pH | 0.931* | -0.325 | 0.847* | -0.508 | 0.870* | -0.393 |
P | 0.794* | -0.606 | 0.703* | -0.671 | 0.887* | -0.430 |
K+ | 0.941* | 0.332 | 0.949* | 0.151 | 0.881* | 0.192 |
Ca2+ | 0.832* | -0.509 | 0.852* | -0.473 | 0.746* | -0.614 |
Mg2+ | 0.960* | -0.195 | 0.934* | -0.288 | 0.935* | -0.204 |
Al3+ | -0.879* | 0.454 | -0.727* | 0.687 | -0.798* | 0.592 |
(H+Al) | 0.410 | 0.884* | 0.563 | 0.701* | 0.553 | 0.766* |
SB | 0.904* | -0.416 | 0.914* | -0.400 | 0.858* | -0.506 |
CECp | 0.694 | 0.677 | 0.742* | 0.606 | 0.875* | 0.421 |
Al saturation | -0.890* | 0.370 | -0.865* | 0.469 | -0.903* | 0.402 |
V | 0.659 | -0.737* | 0.718* | -0.696 | 0.733* | -0.633 |
TOC | 0.954* | 0.294 | 0.936* | 0.340 | 0.981* | 0.094 |
HA-C | 0.924* | 0.277 | 0.819* | 0.532 | 0.717* | 0.645 |
FA-C | 0.952* | 0.233 | 0.999* | 0.010 | 0.966* | 0.236 |
HU-C | 0.798* | 0.587 | 0.498 | 0.750* | 0.513 | 0.826* |
HS-C | 0.921* | 0.386 | 0.861* | 0.506 | 0.826* | 0.545 |
HA-C /FA-C | 0.873* | 0.294 | 0.679 | 0.683 | 0.639 | 0.684 |
HS-C /TOC | 0.696 | 0.658 | 0.650 | 0.725* | 0.253 | 0.964* |
Absolute variance (%) | 71.60 | 24.40 | 65.20 | 29.30 | 63.30 | 31.00 |
Cumulated variance (%) | 71.60 | 96.00 | 65.20 | 94.50 | 63.30 | 94.30 |
Tab. S1 - The background history of the studied areas.
Tab. S2 - Particle size distribution in the studied areas.
Appendix 1 - Description of soil profiles.