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Studying the electrochemical behavior of colloidal particles is important for fertility management and soil conservation, since it enables the understanding of several physicochemical phenomena that occur in soils. The objective of this study was to determine the point of zero charge (PZC) and the electrochemical behavior of surface and subsurface samples of three Red-Yellow Latosols (Oxisols), with different mineralogical and textural characteristics, through potentiometric titration and ionic adsorption. The point of zero charge (PZC) and the electrochemical behavior were determined in samples from the A and B horizons of three Red-Yellow Latosols: very clayey kaolinitic (LVAcr), very clayey gibbsitic (LVAgr) and sandy loam kaolinitic (LVAcm). The analyses were conducted in soil samples with particle size smaller than 0.7 mm, with desaturation of aluminum (Al3+), and smaller than 2 mm, without desaturation. Solutions containing sodium (Na+) and nitrate (NO3−) as indifferent electrolytes were used in all methods. The LVAgr, even with higher organic matter contents, had higher PZC, indicating the importance of mineralogical composition for this characteristic. Among the two kaolinitic soils, there was higher PZC in LVAcm, with lower organic matter content; however, both soils had higher PZC in the B horizon than in the A horizon. The net electrical charge estimated by the potentiometric titration method was equivalent to the net charge estimated by the ionic adsorption method for horizons A and B of LVAgr and LVAcm. At the same time, there was underestimation of the net negative charge by the potentiometric titration method for the A and B horizons of LVAcr. [ABSTRACT FROM AUTHOR]

Copyright of Revista de la Academia Colombiana de Ciencias Exactas, Físicas y Naturales is the property of Academia Colombiana de Ciencias Exactas, Fisicas y Naturales and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The role of metal (oxy)hydroxides in sulfadiazine (SDZ) sorption is poorly understood despite their high contents in many highly weathered tropical soils. Therefore, this work evaluated soil attributes affecting SDZ sorption to several Brazilian soils having contrasting metal (oxy)hydroxide contents. Samples of 23 soils were collected from the upper soil layer (0-20 cm) in the São Paulo State, Brazil, and characterized according to their texture (silt, sand, and clay), pH-H2O, point of zero charge (PZC), organic matter (OM), exchangeable cations (Ca, Mg, K, and Al), potential acidity (H+Al), CEC, well (Fed) and poorly (Feo and Alo) crystallized Fe and Al (oxy)hydroxides, and amorphous Mn oxides (MnO), respectively. Batch sorption studies were performed and related to the soil attributes to group them according with their soil mobility. SDZ sorption coefficients were high (Kd = 15.7–24.0 L kg-1) in soils having high clay (> 500 g kg-1), OM (> 55 g kg-1), and metal (oxy)hydroxide [Fed > 150; Alo > 5; and MnO > 10.0 g kg-1] contents; but they were low (Kd = 0.7–4.9 L kg-1) in soils having low clay (< 250 g kg-1), OM (< 25 g kg-1), and metal (oxy)hydroxide (Fed < 30 and MnO < 2.0 g kg-1) contents. Kd values could be estimated by a regression equation based on CEC as well as Fe and Mn (oxy)hydroxide contents. Acidic tropical soils favor SDZ-neutral species and formation of neutral or positively charged surface sites on pedogenic (oxy)hydroxides that should favor H-bond and surface complexation. [ABSTRACT FROM AUTHOR]

This paper presents an experimental and analytical evaluation of factors affecting the interface pullout resistance of polymeric strips embedded in marginal soils, with a particular interest in supporting the partial replacement of natural sands by intensely weathered tropical soils in reinforced soil structures, which have often been considered marginal fills in design guidelines. Large-scale pullout tests were conducted to evaluate the soil-geosynthetic interface pullout resistance, which also provided quantitative insight into the local increases in vertical stresses acting on the reinforcements due to pullout. Based on the experiments, analytical models were developed and calibrated to establish the relationship between confinement and soil-geosynthetic interface pullout resistance. The relationship between actual and initial stresses could then be represented in terms of a linear model in which the angular coefficient corresponds to the ratio between the apparent and actual friction coefficients (f* / f). This analytical relationship was found to represent a useful design tool since it directly correlates with soil geotechnical properties. The use of lateritic soils to partially replace coarse-grained soils in reinforced soil structures was found to be feasible for mixtures involving up to 25% of lateritic soils, with higher fractions affecting the interface resistance significantly. • The apparent friction coefficients (f *) may not be representative of the actual stress configuration. • Actual friction coefficients (f) are largely impacted by the local increases in vertical stresses induced by the pullout of the reinforcements. • The relation between actual and initial stresses was expressed in terms of a linear equation with an angular coefficient corresponding to f* / f. • The f* / f relation can be used to predict pullout responses based on the geomechanical properties of the fill. • A lateritic soil fraction below 25% can lead to enhanced pullout performance due to a more favorable stress distribution. [ABSTRACT FROM AUTHOR]

Selenium (Se) is essential for animals and humans, and studies assessing the influence of sulfur (S) and phosphorus (P) on Se availability and biofortification in tropical soils are required. This study evaluated the adsorption of selenate (SeVI) and selenite (SeIV) in two oxidic soils with contrasting soil texture and assessed effects of phosphate and sulfate as competitive anions on Se desorption. The study also examined Se biofortification of Panicum maximum cv. Mombaça grown in Se-treated clayey soil under increasing rates of P fertilisation. In the laboratory, different Se concentrations were added to soils for adsorption studies (0, 1, 2, 4 mg L-1 for SeVI and 0, 4, 8, 16 mg L-1 for SeIV), with Se desorption performed by adding different concentrations of P (0, 2.18, 4.36, 10.90, 21.90 mg L-1) or S (0, 3.75, 7.5, 15, 30 mg L-1). Mombaça grass was grown in pots for 43 days in the clayey soil fertilised with SeVI and increasing P rates. Selenium adsorption varied depending on Se speciation, Se rate and soil texture, with SeIV showing greater adsorption than SeVI. In general, amounts of SeVI desorbed increased with increasing addition of P and (mainly) S. However, only P had a positive effect for releasing SeIV from soils. At all SeVI rates added in the clayey soil, Se contents in the shoot dry matter of Mombaça grass increased with increasing P fertilisation rate, agreeing with the desorption results. Further studies combining desorption with biofortification data are recommended for assessing the influence of P in sandy clay loam tropical soils. [ABSTRACT FROM AUTHOR]

The Brazilian Cerrado is a biodiversity hotspot characterized by a mosaic of phytophysiognomies and soil types. Arbuscular mycorrhizal fungi (AMF) are important components of biodiversity, participating in symbiotic relationships with plants and involved in ecosystem functioning. Variations in the AMF communities in Cerrado phytophysiognomies are not well understood. We collected soil samples in the dry, transition (dry to rainy), and rainy seasons to evaluate relationships between the AMF community, vegetation, and soil physicochemical parameters of three Cerrado phytophysiognomies that constitute a structural gradient (campo sujo: grassland, cerrado típico: savanna, and cerradão: forest) across seasons. The floristic similarity was high between cerrado grassland and savanna, but lower between cerrado forest and grassland and between cerrado forest and savanna. Twenty-six AMF species were identified, with genera Glomus and Acaulospora common to all phytophysiognomies. AMF communities showed low similarity between different phytophysiognomies. Spore density differed between the phytophysiognomies, increasing from grassland to cerrado forest. Seasonal distribution of precipitation affected the AMF community in cerrado savanna and forest, but not in grassland soil. Differences in edaphic factors were important drivers of AMF spore density that correlated positively with soil parameters. Except for woody plant biomass, which correlated positively with spore density in the dry and transition/rainy season, no vegetation parameters showed significant correlations with spore density in any season. Despite the high floristic similarity between cerrado grassland and savanna, similarity between AMF communities is low, highlighting the importance of the vegetation gradient and its conservation in the structuring of these fungal communities. [ABSTRACT FROM AUTHOR]

Introduction: Fine root dynamics include production, turnover and decomposition; they are crucial to forest health, affect the entire biogeochemical complex of the ecosystem, and consequently, they substantially affect carbon balance. However, the influence of environmental factors and soil nutrient limitation on fine roots presents considerable uncertainties and has not been studied in tropical forests with more than 7 000 mm annual rainfall. Objective: To measure the effect of fertilization on fine roots in the high precipitation Chocó forest. Methods: We worked in two sites of the Chocó region, Colombia (August 2014-May 2015), where rainfall exceeds 10 000 mm per year. We applied five fertilization treatments (N, P, K, NPK and Control) to two soil type plots. Soil cylinders were removed at pre-established intervals to measure roots. Results: Phosphorus applications increased fined roots; and more fine roots were produced in sandy than in loam soil. The effects of fertilization were related, but not clearly determined by edaphic conditions. Conclusions: In this Chocó forest, the production of fine roots was higher in sandy and nutrient-rich soils but belowground net primary productivity was limited by the content of edaphic Phosphorus. [ABSTRACT FROM AUTHOR]

Copyright of Terra Latinoamericana is the property of Sociedad Mexicana de la Ciencia del Suelo A.C. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Although the addition of biochar has been shown to reduce the phosphorus (P) adsorption capacity of soil, quantitative evidence of this has mainly been provided by incubation experiments and it is therefore essential to conduct long‐term field trials to draw general conclusions. It is largely unknown whether bone char has a greater effect than lignocellulosic biochar on P adsorption–desorption processes and crop yield. The aim of this study was to determine the long‐term (8 years) effect of bone char and biochar on P adsorption–desorption and crop yield in low‐input acidic soils. The results showed that bone char decreased the maximum P adsorption capacity (Qm) by 10% and increased the desorption capacity (Ds) by 150% compared with the control (i.e. without a soil amendment). The desorption ratio was highest for the bone char treatment (10.3%) and three times more than the control. Plant‐available P was seven times greater under bone char than the control. There was no variation in adsorption–desorption characteristics, desorption ratio and plant‐P available content between bone char and lignocellulosic biochar treatments. The average yield increment following the application of bone char and biochar was 1.7 and 1.4 Mg ha−1 for maize and 1.8 and 1.9 Mg ha−1 for soya bean, respectively. Despite the low application rate (4 t ha−1 year−1), these findings demonstrated that the long‐term application of bone char and biochar‐based amendments enhanced P availability in low‐input cropping systems, mainly by altering the P adsorption and desorption capacity of soils. [ABSTRACT FROM AUTHOR]

The concepts of soil security (especially relating to soil condition) provide a useful framework in building spectral libraries. Spectral libraries can be used with the purpose of assessing soil condition by measuring soil organic carbon (SOC) or increasing productivity through soil nutrient management. A spectral library was generated by measuring SOC and nutrients (nitrogen, phosphorous and potassium) and spectral reflectance data over the visible to near‐infrared range (350–2,500 nm) in soil samples collected from four production systems in Papua New Guinea (PNG). The spectral library was analysed using SpecOptim, a software tool developed at the James Hutton Institute to explore spectral pre‐processing and calibration options. From 192 model combinations of model, the best one was identified for each study area. Different combinations of data were also explored (e.g. by farm or all together). We believe that at the local‐scale, soil carbon and nitrogen variability can be captured; however, the spectrally inactive properties such as phosphorous and potassium need to have a higher variability and therefore pooling is required in order to predict properties chemometrically. The SpecOptim software is a useful tool where analysis of spectral data can be difficult to determine. Specifically, it helped improve the accuracy of predictions by 2% for C and N (except for East New Britain site) compared with previously used pre‐processing techniques and calibration models while automating identification of the optimal pre‐processing approach. We believe that we have developed research‐based evidence for using spectral libraries to fit with the soil priority areas of PNG. [ABSTRACT FROM AUTHOR]

Objective: To analyze the productive potential of taro in the state of Tabasco, Mexico, in order to suggest the edaphoclimatic zones with the best conditions for its use. Design/Methodology/Approach: The analysis was carried out using geographic information systems QGIS 3.16.1 and Arc GIS 10.2.2, to generate spatial interpolations of edaphic and climatic variables. The edaphoclimatic zoning for this crop in the state was generated through map algebra. Results: The results indicate that the edaphoclimatic conditions allow the establishment of this crop in 1 608, 565 hectares, which is equivalent to 67% of the territory of Tabasco, although the optimal surface is only 655, 632 hectares (27%). Study Limitations/Implications: The main limitations for cultivation are mainly edaphic, rather than climatic. Findings/Conclusions: From the edaphic point of view, the most suitable soils are flat, deep, with loamy or clayey textures, with slightly acidic or neutral pH. The physiographic areas of the alluvial plain, river valley and hills are the optimal ones for the cultivation of taro. The unsuitable areas are those with permanent flooding and close to the coast, as well as in the highest areas of the Sierra de Tabasco. [ABSTRACT FROM AUTHOR]

There is a need for more studies on the effects of oil palm plantations on soil organic carbon storage and on the environmental services provided by these agrosystems in Mexico. This study focused on estimating the soil organic carbon stocks in three areas within oil palm plantations (palm circle, under the frond and between palm rows), at three soil depths (20, 40 and 60 cm) and comparing the carbon storage between different land-uses: a 20-year-old pasture (GS20), a 20-year-old oil palm plantation (OP20), and a secondary forest (SF20). Our results suggest that oil palm plantations store soil organic carbon mainly under frond areas when sown in lixisols and luvisols, with lower carbon sequestration in the palm circle. Regarding the soil depth, the estimated carbon storage was 87 Mg C ha−1 and 67 Mg C ha−1 at depths of 20 and 60 cm, respectively. Regarding land-use comparison, results indicate an increase (not statistically significant) in carbon storage to 27% at 20 cm depth and 18% at 60 cm between pasture and palm plantation. The second-growth forest presented higher carbon storage compared to both other land uses. [ABSTRACT FROM AUTHOR]

This study aims to determine the concentration of potentially toxic elements (PTEs) and rare earth elements (REEs) in Brazilian sandy soils under the Cerrado at the Parnaíba–São Francisco Basin transition. We also explored the geochemical correlation between these elements and pH, cation exchange capacity (CEC), total organic carbon (TOC), sand, clay, oxides from secondary minerals, and chemical index of alteration for each basin. Mineralogical, physical, and chemical analyses were used to examine PTE and REE geochemistry in six sand soil profiles from the Brazilian Cerrado. The background concentrations of these elements are low, but soils from the Parnaíba Basin have higher concentrations of PTEs than soils from the São Francisco Basin. In soils from the Parnaíba Basin, mainly Al2O3 has relevance in the V and Cr geochemistry, as these elements increase with increasing Al2O3 content. On the other hand, the REEs have CEC as a soil attribute of higher relevance in the geochemistry of those elements is soils from the Parnaíba Basin, and this relevance divides the TOC, Fe2O3, and TiO2 minerals from the clay fraction. In soils from the São Francisco Basin, the geochemistry of PTEs is possibly associated with kaolinite, especially Cu, V, and Zn. In contrast, the Ba concentration was associated with the presence of feldspar. Unlike soils from the Parnaíba Basin, the REEs do not correlate with the studied soil attributes, except for Ho and Lu. Ho had a positive association with Al2O3. Ho and Lu are negatively related to the presence of iron oxides. [ABSTRACT FROM AUTHOR]

The objective of this study was to determine the effect of Agroforestry systems (AFS) and non-AFS of Theobroma cacao L. on soil and leaf litter quality, during rainy (RS) and dry (DS) seasons in a tropical zone. The treatments were T. cacao crop (CC), Yopo forestry (Anadenanthera peregrina L.) Speg. (YF), Acacia forestry (Acacia mangium Willd.) (AF), Agroforestry system of T. cacao + Yopo forestry (CYF), Agroforestry system of T. cacao + Acacia forestry (CAF), arranged in random design in the field. Leaf litter production was highest in CC (0.79 and 0.73 ton.ha-1) during RS and DS, respectively. CC and AFS improved soil fertility, less Mg in CC; AFS leaf litter quality, CAF in DS and CYF in both seasons, less B and S in DS. AFS can be a solution in tropical zones to solve the problems of low soil fertility.

The joint application of geophysical investigations, non-invasive methods, and geotechnical investigations, invasive methods, in order to interpret the geological features in subsurface has been increasingly accepted, however, the correlation between the values collected by the geophysical methods and the direct investigative techniques have been developed in recent years. The obtained linear relationships are site specific and complementary studies are needed to establish their validation and limitations for each site. In this study, Electrical Resistivity Tomography (ERT) was used with Standard Penetration Test (SPT) for geotechnical investigation at three hillslope sites with different tropical soil properties in Bahia, Brazil. The results from thirteen boreholes were analyzed against data from 2D inverted sections. Linear fitting successfully correlates resistivity and NSPT for one borehole. Correlations of electrical resistivity and NSPT values were also performed using soils with similar compositions and physical characteristics, which showed good results. The coefficient of correlation (R) was 0.94. In addition, results the fitting slope coefficient seems to be dependent of soil genesis (lithology, texture and clay content variation) scription obtained in SPT surveys.

Water‐extractable organic matter (WEOM) drives many fundamental functions which determine soil equilibria, acting as a useful probe to highlight the effect of land management on overall C cycling. The ecological importance of WEOM is emphasized in tropical environments characterized by humid climate and short OC turnover. The low OC concentration and the physical–chemical conditions associated to water dissolved compounds determine an analytical issue for the characterization of WEOM. The present experiment aimed to test the diffuse reflectance infrared Fourier transformation (DRIFT) spectroscopy as a rapid tool to evaluate the dynamic of WEOM in tropical soils under different soil organic matter (SOM) managements. The influence of SOM composition on WEOM fraction was evaluated in a laboratory incubation of two tropical soils treated with different organic amendments. The superficial layers of forest and sugarcane Ultisol were incubated for 1 year with 10 mg C g−1 soil of litter from either native tropical forest or sugarcane crop residues. The sugarcane residues promoted a fast increase of dissolved organic carbon (DOC) followed by a subsequent decrease in both soils, whereas the soils amended with forest litter showed DOC dynamics similar to control samples. The DRIFT analysis unveiled changes in the chemical profile of WEOM mainly reflected on the preservation of dissolved hydrophobic compounds. The results indicate the DRIFT technique as an efficient tool to monitor the chemical changes of WEOM f as related to soil use and organic inputs, and to support a comprehensive understanding of the interaction of WEOM in agro‐ecological and environmental processes. [ABSTRACT FROM AUTHOR]

Aims: The microbial dynamics associated with the decomposition of maize (Zea mays) and coconut (Cocos nucifera) residues were investigated to assess the feasibility of using them as mulch in tropical soils. Methods and Results: Phospholipid fatty‐acid (PLFA) profiling, microbial biomass (MB‐C), basal respiration, C‐cycle enzyme activities and inorganic N dynamics were monitored in a microcosm experiment incubating soil samples with plant residues for 425 days. Maize stover (MS) showed a higher decomposition, respiration rate, MB‐C, enzymes activities and shift in microbial community structure than coconut husk (CH), which was barely changed. In MS, the lower N level increased C losses and decreased N mineralization compared to the higher N level. Conclusions: Maize stover is suitable for mulching and has a high potential of increasing soil quality if the proper N fertilization level is used, avoiding excessive C mineralization and N immobilization. Coconut husk decomposition was mostly impaired, indicating that a pre‐processing is necessary to improve the benefits of this residue. Significance and Impact of the Study: Tropical soils are prone to degradation. Mulching can promote soil conservation, but depends on residue type and soil chemistry. Our study showed that MS managed under the recommended N fertilization level is suitable for mulching while CH is highly inaccessible for microbial degradation. [ABSTRACT FROM AUTHOR]

Infrastructure works require materials that are not always available. Searching for deposits near the construction site and the geotechnical study of the soils are essential. This article analyzes the geotechnical and resilient characteristics of soils originating from ten cut slopes of the Carajás Railway (EFC), between the states of Pará and Maranhão (Brazil). The occurrence of soils along this track was investigated, for application purposes in the duplication of the EFC and in future works. Consistency limits, granulometry, compaction, SEM, X-ray spectrometry and Resilience Module (MR) tests were performed, in addition to geotechnical classifications. The presence of fine sandy soils with satisfactory lateritic behavior and MR was identified, which can be used in pavement layers. [ABSTRACT FROM AUTHOR]

ABSTRACT Oxisols are the main soils in Brazil and they classically occur in stable and gentle geomorphic surfaces. However, in the south of Minas Gerais State, Oxisols have been observed under strongly undulated relief, a very rare condition for these soils in this physiographic region. Therefore, this work aimed to assess the elemental dynamics and relief enhanced with portable X-ray fluorescence (pXRF) spectrometry, associated to geomorphology, to understand such occurrence. The studied soils are located in Muzambinho municipality, Minas Gerais State, Brazil. Oxisol profiles were characterized in the upper third (P1), middle third (P2) and lower third (P3) of the hillslope. After morphological description, soil samples were collected in the A, AB and Bo horizons of the profiles. Physical, chemical and pXRF analyses of the soils were carried out in the laboratory. Ti and Fe content (pXRF) had a high correlation with the soil textural fractions. High weathering-leaching degrees were determined, although they occur on a steep slope where younger soils (Inceptisols) would be expected in this region. The altitudinal concordance of summits observed in the more elevated surrounding areas indicates a flat paleorelief, helping to explain this unusual occurrence. The soils’ weathering degree values decreased down the hillslope, indicating silica enrichment through runoff and subsuperficial water flux in the lower landscape positions. The pXRF analyses assisted the characterization of these old soils occurring in steep relief. It provided bases for confirming their high weathering degree indexes and detected evidences of the pre-weathering of the regolith of this very old landscape.

ABSTRACT: Reducing soil degradation and its impacts on the environment have been one of the main challenges of the 21st century, exacerbated by a direct link between increases in the human population and soil degradation that raises current and future food security concerns. Despite this, experiences worldwide reveal that degraded land restoration projects have either achieved little success or failed. Thus, understanding the underlying causes and devising appropriate restoration mechanisms is crucial. Soil amelioration using beneficial microorganisms, particularly arbuscular mycorrhizal fungi (AMF), is essential and pragmatic. Glomalin, a type of glycoprotein produced by arbuscular mycorrhizal fungi in the phylum Glomeromycota, contributes to the mitigation of soil degradation. Moreover, AMF and glomalin are highly correlated with other soil physico-chemical parameters and are sensitive to changes in the environment. As a result of this, they have been recommended for monitoring the recovery of degraded soil or stages of soil degradation. In this review, we discuss the role of AMF and glomalin in the restoration of degraded soils, including improvements to the soil structure and soil organic matter (SOM), microbial activity, reduction of fertility loss, bioremediation, and mitigation of the effects of drought and saline stress. We highlight the research gaps and discuss the prospects. This knowledge will improve our understanding of the ecological conduct of glomalin and AMF, stimulate future research, and be useful to sustainable restoration of degraded lands. Furthermore, we discussed the challenges and obstacles in the legislation and future perspectives on the production of inoculants based on AMF in Brazil.

Abstract Portable X-ray fluorescence (pXRF) spectrometry offers valuable information for prediction models of soil fertility attributes spatial variation, although this approach is yet scarce in tropical regions. This study aims to predict and build spatial variability maps of soil pH, remaining phosphorus (P-Rem), soil organic matter (SOM) and sum of bases (SB) using pXRF results through stepwise multiple linear regression (SMLR) and Random Forest (RF) in a highly variable tropical area. Composite samples from soil A horizon were collected at 90 points throughout the campus of the Federal University of Lavras, Minas Gerais, Brazil, for pH, P-Rem, SOM, SB and pXRF analyses. RF predictions showed the highest accuracies, especially for P-Rem and SB (R² values of 0.66 and 0.55, respectively). Attributes that showed higher R² in punctual predictions also exhibited higher R² in spatial predictions. Data obtained from pXRF in tandem with RF can be used to assist prediction models for soil fertility attributes, consequently enabling the digital mapping of such attributes and helping to improve the knowledge about the spatial variability of such attributes in soils of tropical climate. This technique can therefore assist in the identification and orientation of adequate management practices in tropical agricultural practices.

Gibbsite is a common mineral, present in several soil classes around the globe, especially in the tropical belt. It is also a key mineral in bauxite, the main natural source of aluminum. The occurrence of gibbsite in the soil greatly influences its physical and chemical characteristics. However, little is known about the important structural properties of this mineral, which determines how these characteristics will be expressed. In this work, we investigated the variation in the morphology and crystallinity of naturally occurring gibbsites from soils and bauxites. The crystallinity of the gibbsite was assessed using full width at half maximum (FWHM), mean crystallite dimensions (MCD), and deoxydylation temperature (DT) measurements. The results of these analyses were convergent, indicating a better crystallinity for gibbsites from the evaluated Amazon soils and bauxites, and worse crystallinity for the remaining soil samples. SEM analysis was used to assess the gibbsite morphology, and X-ray diffraction data were used to propose an orientation index for this mineral. The results indicated that there is little to no isomorphic substitution of Al by Fe in natural gibbsites, there is a prevalence of larger crystals, with a more laminar morphology, with orientation capability for the gibbsites of Amazon soils and bauxites, and smaller crystals tending to spherical shape for the other samples. These results suggest that natural gibbsite crystals of good crystallinity have large crystals with a laminar shape, while crystals of lower crystallinity present a smaller size and approximately an isodiametric shape.

Despite the increasing adoption of proximal sensors worldwide, rare works have coupled proximal with remotely sensed data to spatially predict soil properties. This study evaluated the contribution of proximal and remotely sensed data to predict soil texture and available contents of micronutrients using portable X-ray fluorescence (pXRF) spectrometry, magnetic susceptibility (MS), and terrain attributes (TA) via random forest algorithm. Samples were collected in Brazil from soils with high, moderate, and low weathering degrees (Oxisols, Ultisols, Inceptisols, respectively), and analyzed by pXRF and MS and for texture and available micronutrients. Seventeen TA were generated from a digital elevation model of 12.5 m spatial resolution. Predictions were made via: (i) TA; (ii) TA + pXRF; (iii) TA + MS; (iv) TA + MS + pXRF; (v) MS + pXRF; and (vi) pXRF; and validated via root mean square error (RMSE) and coefficient of determination (R2). The best predictions were achieved by: pXRF dataset alone for available Cu (R² = 0.80) and clay (R2 = 0.67) content; MS + pXRF dataset for available Fe (R2 = 0.68) and sand (R2 = 0.69) content; TA + pXRF + MS dataset for available Mn (R2 = 0.87) content. PXRF data were key to the best predictions. Soil property maps created from these predictions supported the adoption of sustainable soil management practices.

The Brazilian Atlantic Forest has undergone adverse land-use change due to deforestation for urbanization and agriculture. Numerous restoration initiatives have been taken to restore its ecosystem services. Deforested areas have been restored through active intervention or natural regeneration. Understanding the impact of those different reforestation approaches on soil quality should provide important scientific and practical conclusions on increasing forest cover in the Brazilian Atlantic Forest biome. However, studies evaluating active planting versus natural regeneration in terms of soil recovery are scarce. We evaluate soil dynamics under those two contrasting strategies at an early stage (<10 years). Reforestation was conducted simultaneously on degraded lands previously used for cattle grazing and compared to an abandoned pasture as a reference system. We examined soil physicochemical properties such as: pH, soil organic matter content, soil moisture, N, P, K, Ca, Mg, Na, Fe, Mn, Cu, Al, and soil texture. We also present the costs of both methods. We found significant differences in restored areas regarding pH, Na, Fe, Mn content, and the cost. Soil moisture was significantly higher in pasture. Our research can contribute to better decision-making about which restoration strategy to adopt to maximize restoration success regarding soil quality and ecosystem services in the tropics. [ABSTRACT FROM AUTHOR]

Land use and coverage surveys show that 30.5% of Brazil's territory was dedicated to the production of food, fibers, biofuels, and raw materials. This paper fills a gap and provides information to society and decision‐makers about the effectiveness of the adoption of conservation agriculture (CA) principles with zero tillage (ZT/CA) and integrated crop–livestock–forest (iCLF‐CA) systems as the central policies to mitigate soil erosion, the main agent of land degradation and productivity loss. The increase in CA area by 2030 was estimated using Holt's damped technique for ZT/CA and simple linear models for iCLF‐CA. The annual potential for soil erosion with intensive conventional tillage and monocropping, considering land use and cover in 2017, is 3.0 billion tons. The economic impact, based only on replacement of nutrient losses, is estimated to be 15.7 billion US$ yr−1. To control soil erosion by water, to intensify agricultural production, and mitigate the greenhouse gas emissions are the goals of the PRONASOLOS, a national program for detailed soil survey and interpretation. The annual economic impact of the adoption of CA principles by controlling soil erosion was estimated at 1.5 billion US$ for ZT/CA in 2017 and 0.5 billion US$ for iCLF‐CA in 2015. The future increase of the CA area was forecast at 34.4 and 25.4 Mha for ZT/CA and iCLF‐CA, respectively. The positive impacts of the adoption of CA principles in Brazil are the result of the determination of farmers, among many actors, and of the effectiveness of government plans and policies. [ABSTRACT FROM AUTHOR]

Soil organic carbon (SOC) plays a significant role in ecosystem protection and sustainable agriculture. The present study aims to estimate the spatial distribution of SOC using three different interpolation methods: ordinary kriging (OK), cokriging (COK), and inverse distance weighting (IDW). Sixty (n = 60) soil samples were collected from the depth of 0-30 cm and analyzed for SOC. The digital elevation model of the site was obtained from USGS explorer at 30 m spatial resolution and processed. Ten (10) terrain attributes were obtained, and a correlation matrix was conducted between SOC and terrain derivatives. The whole dataset was used to evaluate the model accuracy; root mean square error (RMSE) and mean error (ME) were the criteria adopted. Mean value of the SOC of the study area was generally low when compared to the standard rating for tropical soils (< 2%). SOC was significantly (p < 0.01) correlated with LS-factor (r = 0.34*), negatively correlated with elevation (r = -0.30*) and profile curvature (r = -0.30*). IDW performed better (RMSE = 0.75, ME = -0.004) followed by OK (RMSE= 0.78, ME = -0.004) and then COK (RMSE = 0.94, ME = -0.067). Conversely, COK produced the model with the smallest ME with terrain attributes (elevation, LS-factor, and profile curvature). The findings in the study showed that IDW is superior in SOC estimation. COK with the terrain attributes proved to have the capacity as a useful ancillary variable for improving the spatial structure of SOC maps of southeastern Nigeria. [ABSTRACT FROM AUTHOR]

Copyright of Revista de Ciencias Agricolas is the property of University of Narino, Faculty of Agricultural Sciences and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

[Display omitted] • C-, N-, and P-acquiring enzymes were higher in both preserved and restored soils. • Degradation decreases the activity of β-glucosidase, urease, and acid phosphatase. • C-, N-, and P-acquiring enzymes were influenced by organic C and microbial biomass. • The preserved soil showed higher values for both the C/P and N/P ratios. • Degraded soil, by overgrazing, in Brazilian semi-arid can be microbially P-limited. Land degradation has emerged as a significantly pressing environmental concern, contributing to the decline of soil properties in both arid and semiarid regions. Despite this, there is limited understanding of how degradation and subsequent long-term restoration efforts impact enzymatic stoichiometry in soils of the Brazilian semiarid area. Therefore, our study aimed to quantify C-, N-, and P-acquiring enzymes in soil samples from the Caatinga, a Brazilian semiarid region. We compared three different conditions: (a) Native Caatinga vegetation, primarily dominated by Fabaceae species; (b) Restored land, resulting from two decades of grazing exclusion; and (c) Degraded land due to overgrazing, characterized by high-intensity grazing practices. A total of 54 soil samples were collected at depths of 0–10 cm during both dry and rainy seasons to evaluate the levels of C-, N-, and P-acquiring enzymes and their respective stoichiometries. Our findings revealed that, overall, C- and N-enzymes showed higher and similar levels between native and restored land, whereas these enzyme levels significantly decreased (approximately 60% for C-enzymes and 80% for N-enzymes) in degraded land. Moreover, P-acquiring enzymes exhibited a notable decrease (approximately 70%) in degraded land specifically during the dry season. The degraded land exhibited a higher C/N ratio (8.5) during the rainy season compared to native land (4.8). Conversely, higher values of C/P and N/P ratios (both during rainy seasons) were observed in native land (0.3 and 0.07, respectively). Redundancy analysis showed that native and restored lands clustered with all acquiring enzymes and were notably influenced by key soil properties such as organic C, microbial biomass C, and nutrients. In contrast, degraded land showed correlations with Al3+ and Na+. Our results provide substantial evidence that Caatinga soils affected by degradation may be microbially P-limited. This underscores the necessity of integrating P-enriched amendments or fertilizers and implementing long-term restoration practices. [ABSTRACT FROM AUTHOR]

Soil acidity is the most limiting factor for agricultural yield and sustainability in acid soils. Liming is the management practice recommended for reducing soil acidity and increasing the availability of macronutrients, but it can also lead to reduction in the availability of cationic micronutrients when applied at high rates. The aim of this study was to evaluate the effect of application of high rates of limestone, incorporated in the 0–0.40 m soil layer, on nutrient availability and their relation to cumulative grain yield in an annual crop production system. Three experiments were set up in 2017 with six liming rates (0, 3, 6, 9, 12, and 15 Mg ha−1), with incorporation in the 0–0.40 m layer. Soil and leaf samples were collected for determination of macro- and micronutrient concentration in the leaves. Regression and linear correlation analyses were used to evaluate the effect of the application rates on the availability of nutrients and on cumulative yield in soybean, maize, dry bean (common bean) wheat crops over three crop years. The micronutrient that showed the greatest reduction in level in the soil through liming was Fe, in contrast with Zn, which was not affected. The concentrations of micronutrients in soybean and common bean leaves were more sensitive to the effect of deep liming than the levels in the soil, and reductions were observed in the concentrations of B, Fe, Mn, and Zn; however, they remained at suitable levels according to regional standards. Thus, even with the reductions in the availability of the micronutrients brought about by incorporation of higher doses of limestone (≥ 9 Mg ha−1), the cumulative grain yields showed an increase in accordance with liming rates, with the optimal dosage from 8.77 to 12.6 Mg ha−1, depending on the site. The main factors that had positive correlation with yield were soil pH and the macronutrients concentration in the leaves, which generally increased along with the liming rates. • Micronutrients availability to plants reduces with increasing limestone doses incorporated at 0.40 m. • The concentrations of macronutrients in the leaves increased with increasing limestone rates incorporated at 0.40 m. • There is a positive correlation with grain yield and soil pH and macronutrient concentration in leaves. • Accumulated grain yield increases with increasing limestone rates incorporated at 0.40 m. [ABSTRACT FROM AUTHOR]

This study characterized the morphological, physical and chemical attributes of sandstone-derived soils at the Cerrado of the Piauí State, Brazil, in order to identify evolutionary standards. The study was carried out with five representative soil profiles identified as P1-RY (Typical Flavic Psychotic Neosol - Aquents), P2-PA (Typical Dystrophic Yellow Argisol - Alfisol), P3-RL (Fragmentary Litholic Distrophic Neosol - Psammenit), P4-RQ (Typical Ortic Quartzenetic Neosol - Orthents) and P5-PV (Typical Dystrophic Red Argisol - Ultisol). Soil samples were submitted laboratory analysis described morphologically. In general, the soils presented high sand content, low pH, low content of exchangeable bases and low cation exchange capacity (CEC). Organic matter governed the CEC in most cases, suggesting dependence of organic matter in the supply of charges. These soils showed a low degree of weathering, but with iron of high crystallinity. Thus, the relief and the parent material are the major important soil-forming factors at the Cerrado of the Piauí State. Moreover, these soils are young, with the soils from the Piauí Formation being more evolved. However, the sandstones from the Canindé Group apparently are providing lithological secondary minerals for the soil.

Challenges facing humanity over the years include food insecurity, loss of soil and water resources and associated ecosystem disturbance. The rate of hungry people in developing world keeps on increasing and causing death and malnutrition. Food shortages, food insecurity or undernourishment has assumed a global dimension especially as climate change hits the globe with its negative impacts, with more severe cases recorded in the poor-resource African countries. Soil is the natural capital which drives the agricultural sector, being a strong-hole for crop/animal farming, apart-from being a medium for production of raw materials which powers industrial and domestic production. The inherent quality of soil is impaired by various factors including climate variability like excessive rainfall, which ends-up leaching nutrients downstream, thereby resulting in contamination of water bodies with fertilizer/agro-chemical residues. Like most tropical humid soils, the inherent quality of Nigerian soils is generally low, causing rapid degradation of applied nutrients and total crop failure in extreme cases. This has most often been exacerbated by most prevalent land use/agricultural systems, coupled with the problem of over-grazing and indiscriminate deforestation, alongside rapid population expansion with consequent urbanization and industrialization. For effective soil management, especially in the face of climate change, the need for Climate-Smart Strategy (CSS) towards agricultural production becomes imperative, inother to find a Sustainable Approach (SA) to man’s drive towards food production for effective survival. For efficient maize (Zea mays L.) production, application of mineral fertilizer becomes an important aspect for human/animal food production. Field experimentation was conducted at the Teaching and Research Farm of the Cross River University of Technology (Latitude 6° 06ꞌ N and Longitude 8° 18ꞌ E), to evaluate the potential of Nitrogen fertilizer as a Climate-Smart Approach (CSA) for sustainable maize production in the humid tropics. Maize seed variety: Ikom Local White were treated to one level of Nitrogen fertilizer at 0.078 kg ha-1. The treatment was laid out in a Randomized Complete Block Design (RCBD). The treatment were replicated four time to give a total of sixteen (16) field plots. Data collection on plant growth parameters (number of leaves and height of maize) were subjected to Analysis of Variance (ANOVA), while significant means among treatments were separated using Least Significant Difference (LSD) at 5% probability level. Result obtained showed that plots treated with 0.078 kg ha-1 of Nitrogen fertilizer (N-Fertilizer) significantly (p˂0.05) increase growth parameter of maize over the control. Outcome of the study concluded that 0.078 kg ha-1 of N-Fertilizer applied to Maize planted at 1m spacing between plants on bed increase crop growth, and acts as a CSA to remedy the rapid degradation of humid tropical soil productivity, and for environmental sustainability.

Sorption of pesticides by soils holds a major consequence for their fate in the environment. As such, sorption coefficient (Kd/Koc), which is derived from laboratory or field experiments is a fundamental parameter used in almost all screening tools to evaluate the fate or mobility of these compounds. The value of this coefficient is controlled by many soil and solute specific properties, as well as environmental variables. Soft computing techniques such as Adaptive Neuro‐Fuzzy Inference System (ANFIS) have been successfully used to predict the equilibrium partitioning of many compounds in various engineered systems. Application of these techniques to natural systems such as soils is however lacking. Here, we present the use of ANFIS in predicting the sorption per unit mass of soil, Qe, used in the calculation of Kd/Koc of compounds in soils. In a previous study, we collected data associated to the adsorption of five phenylurea herbicides in 18 tropical soils. Here, we analysed such data and based on established correlations, nine variables were selected as potential input vectors (i.e., six soil properties, two herbicides molecular descriptors and initial solute concentrations). A total of 255 ANFIS models of one to eight input vectors were elaborated under 10‐fold cross‐validation. Multiple linear regression (MLR) models were similarly developed, and compared with the ANFIS in terms of mean absolute error (MAE), root‐mean‐square error (RMSE) and coefficient of determination (R2). The best ANFIS model (M94) has an MAEtest, RMSEtest and R2test of 3.43 ± 0.43, 4.94 ± 0.80 and 0.95 ± 0.01, respectively, whereas the best MLR model (M13) returned an MAE, RMSE and R2 of 7.71 ± 0.13, 10.11 ± 1.21 and 0.81 ± 0.01, respectively. We observed that generally ANFIS performed better than MLR regarding both accuracy and interpretability. Accordingly, we recommend the use of ANFIS for predicting the sorption coefficients of phenylurea herbicides (PUHs) in soils. This article presents the application of Adaptive Neural‐based Fuzzy Inference System (ANFIS) to modelling the sorption of phenylurea herbicides by soils—from easy to obtain soil physicochemical properties, and pesticides molecular descriptors. A total of 255 ANFIS models were developed and compared with similarly developed multiple linear regressions (MLRs), using three error metrics (mean absolute error, MAE; root‐mean‐square error, RMSE, and R2). ANFIS performed better than MLRs regarding both accuracy and interpretability. Accordingly, we recommend the use of ANFIS for predicting the sorption coefficients of phenylurea herbicides (PUHs) in soils. [ABSTRACT FROM AUTHOR]

Organic phosphorus (Po) plays an important role in tropical forest nutrition on strongly-weathered soils. However, of its role in Eucalyptus nutrition little is known. For this purpose, soil P forms were determined by NaOH-Na2EDTA extraction and 31P nuclear magnetic resonance spectroscopy (31P NMR) at 10 sites of Eucalyptus plantations in Brazil. The objectives were (1) to determine the amounts and forms of soil Po; (2) to build a structural model of the soil P cycle to provide quantitative estimates of the transformation processes of soil P. Soil P was found to consist of large amounts of Monoesters-P (on average 43.7 mg kg−1) followed by Diesters-P in the form of DNA (on average 4.2 mg kg−1), as well as containing high reserves of Pi species (on average 101.6 mg kg−1 of the ortho-P; 2.7 mg kg−1 of the pyrophosphate). Thestructural model indicated that the P cycle is regulated by clay, soil organic carbon, total P and pH. High total Po concentrations (on average 48 mg kg−1) reveal a high potential of P supply to Eucalyptus trees, in which Diester-P (DNA) would be the main source P for the available P pool. The close interconnection between ortho-P, pyrophosphate, DNA and Monoester-P compounds provides evidence of a strong influence of soil biological activity on the distribution and accumulation of these P compounds and therefore on the availability of P. Thus, these results are relevant to establish soil fertility management strategies for low-fertilizer input Eucalyptus systems in soils with low fertility. [ABSTRACT FROM AUTHOR]

The heavy metal mercury (Hg) is one of the most complex and toxic pollutants. When present in soils, it may impair plant growth, but the intensity of damage depends on the physical-chemical properties of the soil such as pH, clay, and organic matter content, which in turn affects Hg sorption and bioavailability. Understanding Hg potential damage to staple food crops is of paramount relevance. Here, we evaluated the physiological effects of Hg in Phaseolus vulgaris (common bean) and Avena sativa (oat) cultivated in two Oxisols with contrasting properties: Rhodic Acrudox (RA) and Typic Hapludox (TH). We performed four independent experiments (one per species/soil combination) that lasted 30 days each. Treatments were composed by HgCl2 concentrations in soils (0 to 80 mg kg−1 Hg). At the end of the experiment, we determined the impact of Hg on photosynthesis, nutritional status, and oxidative stress. Cultivation in TH contaminated with Hg resulted in oxidative stress in common bean and decreased photosynthesis/P accumulation in oat. No deleterious effects on physiological variables were detected in both species when cultivated in the RA soil. In general, we conclude that the lower Hg sorption in the TH soil resulted in toxicity-like responses, while acclimation-like responses were observed in plants cultivated in RA, reinforcing soil physical-chemical properties as key features driving Hg toxicity in Oxisols. [ABSTRACT FROM AUTHOR]

ABSTRACT Lettuce (Lactuca sativa) is the main leafy vegetable produced in Brazil. Since its production is widespread all over the country, lettuce traceability and quality assurance is hampered. In this study, we propose a new method to identify the geographical origin of Brazilian lettuce. The method uses a powerful data mining technique called support vector machines (SVM) applied to elemental composition and soil properties of samples analyzed. We investigated lettuce produced in São Paulo and Pernambuco, two states in the southeastern and northeastern regions in Brazil, respectively. We investigated efficiency of the SVM model by comparing its results with those achieved by traditional linear discriminant analysis (LDA). The SVM models outperformed the LDA models in the two scenarios investigated, achieving an average of 98 % prediction accuracy to discriminate lettuce from both states. A feature evaluation formula, called F–score, was used to measure the discriminative power of the variables analyzed. The soil exchangeable cation capacity, soil contents of low crystalized Al and Zn content in lettuce samples were the most relevant components for differentiation. Our results reinforce the potential of data mining and machine learning techniques to support traceability strategies and authentication of leafy vegetables.

Global demand for bioenergy increases interest in biomass‐derived fuels, as ethanol from sugarcane straw. However, straw is the main carbon source to soil and its removal reduces C input, affecting active fractions (dissolved organic carbon, DOC) and C storage. To quantify the effects of straw removal on DOC and C stocks, we built lysimeter system using soil (Rhodic Kandiudox) from sugarcane field. We evaluated four soil depths (1, 20, 50 and 100 cm) and four straw removal rates: no removal NR, medium MR, high HR and total TR, leaving 12, 6, 3 and 0 Mg/ha on the soil surface, respectively. After rainfall, drainage water was collected and analysed for DOC content. Soil C stocks were determined after the 17‐month. Total DOC released at 1‐cm depth amounted to 606, 500, 441 and 157 kg/ha in NR, MR, HR and TR, respectively. Net‐DOC suggests straw as the main source of DOC. Most of DOC in NR (50%) was retained within the 1–20 cm layer, resulting in higher C stock (10 Mg/ha) in the topsoil. In HR and MR, DOC retention was higher within 20–50 cm, suggesting differences in DOC composition. DOC in TR was 40% higher at 20 cm than at 1 cm, indicating C losses from topsoil. Low concentrations of DOC were found at 100‐cm depth, but representing 30% in TR. Straw removal for bioenergy production is sustainable, but we should leave at least 3 Mg/ha of straw to ensure DOC production and soil C storage, taking account the DOC contribution to key soil functions. [ABSTRACT FROM AUTHOR]

Copyright of Anuario do Instituto de Geociencias is the property of Universidade Federal do Rio de Janeiro, Instituto de Geociencias and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Nitrous oxide (N2O) is an important greenhouse gas in which the main sources are tropical rainforest and agricultural soils. N2O is produced in soils by microbial processes, which are enhanced by the application of nitrogenous fertilizers. The soil N2O bulk isotopic composition (δ 15Nbulk and δ 18O) and the “site-specific,” or intramolecular, 15N isotopic composition, i.e., the 15N/14N ratio at the cenral (α) or terminal (β) nitrogen position, expressed in this study as δ 15N α and δ 15N β could help identify both the sources (natural and anthropogenic) and microbial pathways of N2O production and consumption prior to emission.We report new isotope measurements of soil N2O emissions and from soil air collected during the rainy season in a mature tropical forest (Tapajos National Forest, Para, Brazil) and in a tropical agricultural corn field (“Fundo Tierra Nueva,” Guárico State, Venezuela). The statistically different δ 15Nbulk emission weighted average between the mature forest (−18.0‰ ± 4.0‰, n = 6) and agricultural corn field (−34.3‰ ± 12.4‰, n = 17) suggest that theδ 15Nbulk data are useful for distinguishing N2O fluxes from fertilized agricultural and natural “background” soils. They also demonstrate that the site-specific δ 15N measurements have the potential to provide a new tool to differentiate between the production and consumption N2O microbiological processes in soils. This study further demonstrates that the observed correlations (or lack thereof) between δ 15N α,δ 15N β, and δ 18O can be used to estimate the relative proportion of N2O that would have been emitted to the air but was consumed via reduction of N2O to N2 within the soil.

ABSTRACT The water erosion process has a considerable negative effect on tropical soils, causes soil losses from arable land and reduces the capacity to support surrounding ecosystems. Estimating soil losses caused by water erosion is fundamental for evaluating the impacts of various production systems. Therefore, improving soil loss estimates via the adaptation of models for different edaphoclimatic environments is necessary for estimating local geographic and climatic differences. This study aimed to adapt, apply and evaluate the potentialities of the Potential Erosion Method for Latosols of the Hydrographic Subbasin of Caçús Stream, southern Minas Gerais State. Geological, topographic, pedological, climatic and land use and occupation data were processed via Geographic Information Systems and compared with those obtained by the Revised Universal Soil Loss Equation. The erosion intensity coefficient, Z, was 0.28, indicating weak erosion intensity, and the estimated average soil losses were 31 Mg ha-1 year-1 by the Potential Erosion Method and 36 Mg ha-1 year-1 by the Revised Universal Soil Loss Equation, which were both above the soil loss tolerance. The model results and comparisons indicated that the Potential Erosion Method has excellent performance and can be applied to estimate sediment production via water erosion in tropical soils.

Low-input cultivated pastures to feed cattle have dominated land use after forest clearing for decades in the western Brazilian Amazon. This study was undertaken to help understand the inherent nutrient supply dynamics underwriting cattle performance on three farms in the state of Acre. We assessed soil chemical and physical properties associated over time with different land uses following forest clearing. This information permitted specifying a conceptual model of nutrient stocks and flows under the observed grazing system, which produced insights about the dynamics of soil nutrient degradation. Above ground forage mass, topsoil nutrient concentrations and soil bulk density were measured. Land covers were Brachiaria spp. grasses, a grass-Pueraria phaseoloides mix, cropland and forest. Most soil nutrient parameters initially decreased after clearing, gradually recovering over time with grass-only pastures; however, 20 yr-old pastures had 20% less forage mass. Most pasture system nutrients on these farms resided in topsoil and roots, where large stocks of mature forage supported soil fertility with recycled nutrients from litter. Estimates of partial topsoil nutrient balances were negative. This suggested that corresponding nutrient stocks and the accumulation of forage mass were probably maintained primarily through the sum of inflows from cattle excreta, the subsoil, soil organic matter, and litter mineralization with scant input of commercial fertilizer. Therefore, herd management to increase animal system productivity via higher stocking rates on vegetatively younger forage requires monitoring of nutrient stocks and flows and fertilization that assures replenishment of the nutrients extracted. Otherwise, rapid depletion of soil nutrient stocks will lead to system degradation and failure.

ABSTRACT Water stored in the soil between field capacity and the permanent wilting point, is known as the available water capacity. Its availability to be effectively used by plants depends on the type of soil and its water retention characteristics. The aim of this work was to compile information about water retention curves in Latosols, and to provide a first approximation of values and most likely amplitudes for water storage and available water capacity of these soils. The database was constituted from information collected from articles, theses, dissertations and other publications. Soil water retention curves, as well as available water, were estimated for the order Latosols, and for the suborders Red Latosol (RL), Red-Yellow Latosol (RYL) and Yellow Latosol (YL). RL presented the lowest amplitude of water storage between field capacity and permanent wilting point, resulting in lower available water capacity compared to Yellow and Red-Yellow Latosols. YL presented the highest available water capacity among analyzed soils.

A 180 ha area in the headwater of Paquequer watershed, a drainage system located at the Teresópolis municipality, was selected for the evaluation of chemical weathering from collected river water samples in February and August 2013 in a granitic-gnaissic substrate free of direct anthropogenic influence for being located in a conservation unit (Serra dos ÓrgãosNational Park). The study area has a native forest cover, an altitude range of 1100-1900 m and an average annual rainfall of 2800 mm. The dissolved elements (Na, Mg, Ca, K, Si, Al) were analyzed by inductively coupled plasma spectrometries and the anions Cl and SO42-, by ion chromatography. These results, combined with the concentration data of nitrogen and phosphorus compounds (Alvim, 2016), the atmospheric deposition (Rodrigues, 2006), and the litogeochemistry (Zorita, 1979; Tupinambá, 1999; Tupinambá et al., 2012) were used to generate the dissolution model of mineral, employing the PHREEQC software. The mass balance indicate Na as the main chemical specie due to weathering. Mineralogical data show plagioclase, quartz, kfeldspar and biotite as substrate’s most abundant minerals, among which only plagioclase has sodium in its composition. According to Goldich’s series (mineral stability to weathering), plagio clase was identified as the main weathered mineral in this assemblage, being consumed at a rate of 649 mol ha-1year-1 and forming the minerals kaolinite and gibbsite, with the release of a minimum of 818 mols ha-1 year-1 and a maximum of 1490 mols ha-1 year-1 of dissolved silica in the river (measured value). Considering plagioclase as the main mineral responsible for Na flux in the basin, stoichiometric calculations in association with Si ratio, it was estimated that only from the plagioclase weathering, the soil should be composed by 14% of kaolinite and 86% of gibbsite in percentage relative of the two mineral phases. The quantitative analysis of the mineralogy (Rietveld method) confirmed the calculations, showing a soil composition 7% kaolinite e 93% gibbsite, and attested the importance of plagioclase weathering in fluvial hydrogeochemistry and soil composition.

This paper compiles experimental site characterization of an unsaturated tropical soil profile in an experimental research site in Bauru, São Paulo, Brazil. Several in situ campaigns comprised geophysical borehole tests (cross-hole, down-hole and up-hole together with the SPT), as well as mechanical tests (SPT, CPT and SDMT) have been performed. There is an unsaturated sandy soil at the studied site and, according to the MCT Classification System for tropical soils, the first 13 m depth is a colluvium with lateritic soil behavior (LA’) over the residual soil with non-lateritic behavior (NA’). The ratio between seismic (Go) and mechanical (qn, N60, ED, KD and MDMT) parameters was useful to identify the existence of microstructure and to confirm unusual soil behavior for this tropical soil site. CPT and SDMT were efficient for detailed stratigraphic logging, however, the estimative of geotechnical parameters cannot be solely been done base on just conventional correlations defined for sedimentary soil.

Natural restoration of ecosystems includes the restoration of plant-microbial associations; however, few studies had documented those changes in tropical ecosystems. With the aim to contribute to understand soil microbial changes in a natural regrowth succession of degraded pastures that were left for natural restoration, we studied changes in arbuscular mycorrhizal (AM) fungal communities. Arbuscular mycorrhizal fungi (AMF) establish a mutualistic symbiosis with plants, improving plant nutrition. Amplification of the small subunit rRNA with specific primers and subsequent Illumina sequencing were used to search soil-borne AM fungal communities in four successional natural regrowth stages in two landscapes (hill and mountain) with soil differences, located in the Andean-Amazonian transition. Molecular results corroborated the results obtained previously by spores-dependent approaches. More abundance and virtual taxa of AMF exist in the soil of degraded pastures and early natural regrowth stages than in old-growth or mature forest soils. Although changes in AM fungal communities occurred similarly over the natural regrowth chronosequence, differences in soil texture between landscapes was an important soil feature differentiating AM fungal community composition and richness. Changes in soil-borne AM fungal communities reflect some signals of environmental restoration that had not been described before, such as the reduction of Glomus dominance and the increase of Paraglomus representativeness in the AM fungal community during the natural regrowth chronosequence.

Many slope failures in residual soils have been attributed to increased soil pore pressure. During the rainy season, water infiltration occurs, which can lead the slope to rupture by increasing the pore pressure. However, some landslides have been observed with pore pressures below those required for failure. Hypotheses for such ruptures include the occurrence of creep or fatigue due to cyclic variations in the piezometric level on the slope. This paper presents a study on the effect of pore pressure on the behaviour of the residual soil of the Soberbo hillside in Rio de Janeiro, Brazil, subjected to monotonic and cyclic pore pressure. Triaxial tests that simulate the increasing piezometric level (constant shear drained—CSD tests), drained creep (DC-CSD tests) and cyclic pore pressure variation (CPP tests) in slopes were carried out. The CSD test results showed that the failure due to increasing pore pressure is essentially dilatant and confirmed the peak strength obtained from conventional drained triaxial tests. Sudden failure was observed in all CSD tests at the end of the pore pressure increase phase. The results show that the failure of the slope may occur due to drained creep and the loss of soil shear strength under cycling pore pressure. [ABSTRACT FROM AUTHOR]