Potential Cation Exchange Capacity Research Articles

Exploiting Soil and Remote Sensing Data Archives for 3D Mapping of Multiple Soil Properties at the Swiss National Scale

Soils play a central role in ecosystem functioning, and thus, mapped soil property information is indispensable to supporting sustainable land management. Digital Soil Mapping (DSM) provides a framework to spatially estimate soil properties. However, broad-scale DSM remains challenging because of non-purposively sampled soil data, large data volumes for processing extensive soil covariates, and high model complexities due to spatially varying soil–landscape relationships. This study presents a three-dimensional DSM framework for Switzerland, targeting the soil properties of clay content (Clay), organic carbon content (SOC), pH value (pH), and potential cation exchange capacity (CECpot). The DSM approach is based on machine learning and a comprehensive exploitation of soil and remote sensing data archives. Quantile Regression Forest was applied to link the soil sample data from a national soil data base with covariates derived from a LiDAR-based elevation model, from climate raster data, and from multispectral raster time series based on satellite imagery. The covariate set comprises spatially multiscale terrain attributes, climate patterns and their temporal variation, temporarily multiscale land use features, and spectral bare soil signatures. Soil data and predictions were evaluated with respect to different landcovers and depth intervals. All reference soil data sets were found to be spatially clustered towards croplands, showing an increasing sample density from lower to upper depth intervals. According to the R2 value derived from independent data, the overall model accuracy amounts to 0.69 for Clay, 0.64 for SOC, 0.76 for pH, and 0.72 for CECpot. Reduced model accuracies were found to be accompanied by soil data sets showing limited sample sizes (e.g., CECpot), uneven statistical distributions (e.g., SOC), and low spatial sample densities (e.g., woodland subsoils). Multiscale terrain covariates were highly influential for all models; climate covariates were particularly important for the Clay model; multiscale land use covariates showed enhanced importance for modeling pH; and bare soil reflectance was a major driver in the SOC and CECpot models.

Consequences of elevated CO2 on soil acidification, cation depletion, and inorganic carbon: A column-based experimental investigation

The anthropogenic release of atmospheric CO2 affects soil nutrient cycling through varied biogeochemical processes. Cation depletion from exchange sites, carbonate mineral dissolution, and subsequent changes in organic and inorganic carbon flux are growing concerns for soil health and sustainability. Particularly, the effects of acid deposition on soil pH and soil health under changing global carbon flux is poorly understood. To estimate the magnitude and effects of pH change across different soil profiles, the depth-wise response of soil cations, pH, and soil inorganic carbon (SIC) to varying CO2 levels was investigated using column-leachate experiments. Six soils, representing acidic, neutral, and alkaline pH, were exposed to different CO2 enrichments (100%, 10%, 1%, and Control) of water percolate for 30 days. Analysis of the column leachates revealed that the base cations (Ca, Mg, Na) were higher initially than on day 30, while Si leaching increased with time. The pH in leachates tended to attain an equilibrium state with time under CO2 saturation, indicating the buffering capacity of alkaline and neutral soils. Evaluation of the soil before and after the experiments showed that the solid SIC, such as carbonate minerals and any dissolved SIC components (e.g., carbonate, bicarbonate ions) entrained in the pore space increased, whereas the potential cation exchange capacity (PCEC) decreased in all soils. This trend was especially prominent for alkaline soils at 100% CO2 enrichment. Over the short-term study, the SIC showed minimal response to varying CO2 enrichment conditions in neutral and acidic soils. The altered cation concentrations in the leachates suggest that under long-term exposure to elevated CO2, a deficiency of cationic essential plant nutrients such as Ca2+, Mg2+, and K+ is likely, especially with low buffering capacity and primary mineral content. In contrast, an increase in nutrient solubility and elemental toxicity (e.g., Al3+ Mn) can be observed in the short term. The initial soils with greater ECEC experienced an increased SIC leaching in the shorter term and suggested potential deposition in deeper layers. The resultant SIC loss might be amplified in arid to semi-arid soils with low SIC and affect soil health.

Statistical issues. Comment on “proximal sensor data fusion for tropical soil property prediction: Soil fertility properties”

dos Santos Teixeira et al. evaluated the effectiveness of three different sensors, portable X-ray fluorescence (pXRF) spectrometry, visible near-infrared (Vis-NIR), and NixProTM color sensor, in predicting six soil properties including sum of bases (SB), effective cation exchange capacity (eCEC), potential cation exchange capacity (CEC), base saturation (BS), soil organic matter (SOM) content, and soil pH, and compared their performance when used alone or in combination. Preprocessing methods and other variables were also analyzed. In this comment paper, some misuses of Kappa statistic in the original paper by dos Santos Teixeira et al. are discussed. The authors calculated Cohen's kappa coefficient to make categorical predictions for soil fertility classes. However, using Cohen's Kappa to estimate the intra-rater reliabilities (IRRs) is not appropriate on the condition of ordinal categorical variables in four or five categories in the original paper. We briefly introduce the Kappa statistic for evaluation of IRR between two raters and propose to use weighted Kappa to compute IRRs under such conditions. To conclude, we recognize that this does not significantly alter the conclusions of this paper, but it is necessary to ensure that the appropriate statistical tools are used.

Atributos químicos de um Latossolo acrescido de biocarvão de palha de café conilon

Abstract The objective of this work was to evaluate the effects of increasing rates of biochar produced with coffee straw, at two pyrolysis temperatures, on the chemical attributes of an Oxisol cultivated with conilon coffee (Coffea canephora) and on the nutrient content of coffee tree leaves. Treatments consisted of pyrolysis at two temperatures (350 and 600 °C) and of five biochar rates (0, 5, 10, 15, and 20 Mg ha-1). The following soil chemical attributes were evaluated: pH in water; P, K, Ca, Mg, Al, H+Al, Zn, Cu, Fe, and Mn contents; effective and potential cation exchange capacity (CEC); sum of bases (SB); base (V) and aluminium (m) saturation; and N, P, K, Ca, Mg, Zn, Cu, Fe, and Mn contents in the leaves. The biochar produced at 600°C, at rates of 10 and 15 Mg ha-1, promoted a greater K release into the soil. Regardless of temperature, coffee straw biochar increased K and P availability, sum of bases, base saturation, and CEC in the soil, but did not influence macro- and micronutrient contents in the leaves. The addition of increasing rates of coffee straw biochar in the soil increases P, K, Mg, SB, CEC, and V, regardless of pyrolysis temperature.

Soil formation and mineralogical changes on basaltic lava vs scoria along a hydroclimatic gradient on Santa Cruz Island, Galápagos

Climate and parent material type are important soil forming factors. On Santa Cruz Island, Galápagos, the climate shows a pronounced altitudinal zonation from arid lowlands to humid highlands, and the volcanic parent materials, although chemically rather uniform (basaltic), show pronounced differences in porosity, including dense lava flows and very vesicular scoria deposits. In this study, the effect of these two driving factors on pedogenesis was investigated. Our results show that pH and effective cation exchange capacity (CECeff) decreased, but potential cation exchange capacity (CECpot), phosphate retention, and Alo + ½Feo as well as Alp/Alo increased with increasing elevation regardless of parent material type. Conversely, topsoil bulk density (BD) and organic carbon (OC) content did not show a clear altitudinal pattern on lava but decreased (BD) or increased (OC) with increasing elevation on scoria. Clay mineralogy changed from minor (2:1-type) mixed layer phases in the low-elevation arid zone to vermiculitic (lava) or kaolinitic mineralogy (scoria) at mid-elevation (humid), whereas short-range-order (SRO) minerals (allophane and ferrihydrite) dominated in the colloidal fraction of both lava- and scoria-derived soils under very humid conditions at high elevation. The sequence of soil types developed on lava was, with increasing elevation, Cambisol → Phaeozem → Andosol, while on scoria it was Regosol → Umbrisol → Andosol. Our results show that climate is the overriding factor controlling the major mineralogical and pedogenic changes in the studied environment; however, the higher porosity of the scoria parent materials considerably accelerated weathering and pedogenic processes compared to the denser lavas. Our study highlights the importance of the parent material’s physical nature in modulating rates of chemical weathering and pedogenesis.

Precision agriculture tools for liming management in mango orchards in the Brazilian semiarid region

Optimizing the recommendation for the management of Liming Demand (LD) is essential for cost reduction and increased yield mango. Therefore, the objective of this study was to delimit management zones for the limestone recommendation in areas of irrigated mango in the Brazilian semiarid using precision agriculture techniques. The experiment was carried out in three commercial mango orchards located in the region of the San Francisco Valley, Brazil. Soil samples were collected in 0.0-0.2 m and 0.2-0.4 m depths following regular grids where the number of samples varied from 50 to 56. Soil analyses were performed. The kriging and inverse distance weighting method were used to interpolated the maps. The LD map was performed from the potential cation exchange capacity (T) and bases saturation (BS) maps. It was verified that the Mandacaru area obtained 63.42% of the field requiring liming, being subdivided into four management zones. The Sempre Verde area obtained 1.20% of the area requiring liming and the Barreiro de Santa Fé area did not present a need for the LD map. The use of precision farming techniques to delineate management zones was adequate to separate the areas into smaller and more homogeneous zones, for a more precise recommendation of liming demand.

Estimating cation exchange capacity and clay content from agricultural soil testing data

Clay content and the ability to reversibly retain cations affect many essential chemical and physical properties of soil, such as pH buffering and carbon sequestration. Cation exchange capacity (CEC) and base saturation are also commonly used as criteria in soil classification. However, determination of CEC and particle-size distribution is laborious and not included in routine soil testing. In this study, pedotransfer functions including soil test cations (STCat; Ca2+ + Mg2+ + K+), pH and soil organic carbon (SOC, %) as explanatory variables were developed for estimating CEC, titratable acidity (TA; H+ + Al3+) and clay content (clay, %). In addition, reference values for potential CEC and its components were determined for Finnish mineral and organic soils. The mean of potential CEC extracted by 1 M ammonium acetate at pH 7.0 ranged from 14 (range 6.4−25) in coarse soils to 33 (21−45) cmol(+) kg-1 in heavy clay soils, and from 42 (24−82) in mull soils to 77 (25−138) cmol(+) kg-1 in peat soils. The average CEC of clay and SOC were 27 and 160 cmol(+) kg-1, respectively. Titratable acidity occupied 53% and around 40% of the CEC sites in organic and mineral soils, respectively, evidencing that it is a prominent component of the potential CEC in these predominantly acidic soils. STCat, pH and SOC explained 96% of the variation in potential CEC. STCat and pH can be used in estimating the clay content especially for soils containing over 30% clay. In coarse textured soils, in contrast, SOC hampers the STCat based estimation of clay content.

Correction of Soil Acidity in an Organic System of Shadowed Coffee

Through sustainable agriculture it is possible to explore the coffee culture in consortium with native forests in more rugged reliefs, as coffee is a permanent crop in addition to the climatic conditions offered by the swamps that favor its development. Given the above, the present work proposes, based on the acidity results, to quantify the need for correctives in the soil to obtain a better nutritional use offered by agroforestry cultivation of organic coffee in the shade with favorable results to increase productivity and, consequently, the farmer's profit. The research was carried out at the Várzea da Onça farm, in the Yaguara Ecological Complex, located in the municipality of Taquaritinga do Norte, Borborema plateau, in the Agreste Pernambuco mesoregion. Altitude, it is necessary to adopt appropriate management techniques that guarantee production, soil conservation and biodiversity, proposing soil correction to guarantee the ideal nutritional conditions for coffee growth. For this purpose, soil samples were collected in the Top (T), Hillside (E) and Pedimento (P) ranges at depths of 0-20, 20-40 and 40-60 cm when planting shaded coffee and soil samples from Native Forest (MN) preserved and legally protected from the Brejo de Taquaritinga. Active, exchangeable and potential acidity were analyzed, as well as the sum of bases, the potential and effective cation exchange capacity, base saturation and aluminum saturation. The results obtained were subjected to analysis of variance and the means were tested at 5% by the Tukey test. A potential of the system was found with low to very low natural fertility, with a strongly acidic reaction. Thus, adequate soil management and correction techniques are necessary for the crop to absorb all the nutrients made available by the organic matter present on the surface, concluding that all slopes require liming, the slope of Hillside and Mata Nativa they also need plastering for the culture to develop properly.

Evaluating forest soil quality after deforestation and loss of ecosystem services using network analysis and factor analysis techniques

This study aimed to establish a soil quality index (SQI) using factor analysis (FA) and network analysis (NA) techniques for the assessment of soil quality after deforestation in Northern Iran. In this work, 16 soil properties from forest sites and adjacent cropland sites at two locations in the Hyrcanian forests of Northern Iran were used and analyzed. The minimum data set (MDS) indicators selected through the FA method were potential carbon mineralization (PCM), urease activity (URE), plant-available water and cation exchange capacity, which contributed to the SQI value by 39, 28, 19 and 13%, respectively. Soil quality indicators identified through the NA approach were URE, organic C (OC), PCM and microbial biomass C (MBC), contributing towards the SQI value by 34, 26, 23 and 17%, respectively. The PCM and URE, selected by both techniques, were the most significant indicators of soil quality to detect the deforestation impacts in Northern Iran. The computed SQIs were significantly correlated with OC stocks, validating the SQI models developed by both FA and NA methods. The SQI values computed through NA were more sensitive to deforestation than those computed through FA, suggesting the NA-screened SQI would represent changes in soil functions more adequately than the FA-screened SQI. Croplands were characterized by a lower value of SQI (62–79%), especially in the surface layer, indicating a loss of soil capacity to function well after deforestation for the expansion of farmlands. The current study shows that the SQI model developed by the NA approach would also be a useful, alternative technique for soil quality assessment after conversion of native forest ecosystems to agricultural lands. To conclude, our results confirmed a weighted correlation-based NA of the soil attributes can be used as a simple and robust tool for assessing soil quality following deforestation and loss of ecosystem services.

Chemical and physical attributes of five Oxisols as predictors of shoot dry mass of white oats

In no-tillage systems, oats are one of the species most used as a cover crop in the subtropical region of Brazil. This study aims is to determine a set of chemical and physical properties of five Oxisols after surface liming, and to determine whether these properties are related to the shoot dry mass production of white oat (Avena sativa L.) variety IPR Aphrodite, in order to establish a model to predict its yield.. For this purpose, a field experiment was conducted during 2015 and 2016 in Londrina County in the State of Paraná with samples of B horizon collected from five Oxisols with clay content ranging from 15-80 dag kg-1 arranged in microplots since 2004. Soil pH in CaCl2, calcium, magnesium, potassium, potential cation exchange capacity (CEC), base saturation, microporosity, total porosity, field capacity, permanent wilting point, clay and sand of the Oxisols were the parameters that most influenced the dry mass production of white oats. Oxisol extrinsic factors such as values pH and base saturation, as well as the calcium and magnesium contents, positively altered with surface liming, boosting the production of oat dry mass production.

Spatial 3D mapping of forest soil carbon stocks in Hesse, Germany

AbstractBackgroundForest soils are an important reservoir of organic carbon (OC) and a potential source or sink for atmospheric CO2. Prediction of OC stock changes under ongoing climatic and management changes requires a spatial explicit base. Knowledge of the vertical distribution of OC stocks is very important, since varying soil layers may be affected differently by environmental change.AimThree‐dimensional regionalization of OC stocks of the forest floor (FFC) and 5 cm depth increments of the mineral soil (SOC) of Hesse, Germany.MethodsDatasets of the second National Forest Soil Inventory (NFSI II) were used for parametrization of hierarchical generalized additive models (hGAM). Validation was performed by a 10 times repeated 10‐fold cross‐validation, and spatial model uncertainty was assessed.ResultsDepth‐dependent validation indicated that model performance was best between 15 and 60 cm (amount of variance explained ≈ 0.5). All covariates showed plausible partial effects. FFC stocks were predicted to be highest under coniferous forest with a high influence of N deposition. Climate and potential cation exchange capacity affected SOC stocks markedly, whereas soil class and parent material were most important for the depth distribution. Overall, average predicted OC stocks were between 78.0 and 92.5 t ha−1, amounting to 67.6 to 80.1 Mt for all forest soils of Hesse. Between 16% and 24% were stored in the forest floor. Sixty‐eight percent to 69% of predicted SOC stocks were stored in the upper 30 cm. Model uncertainty was highest at locations with high elevation or ground water influence.ConclusionsThis work provides the first spatial explicit database for OC stocks of forest soils in Hesse at an intermediate scale. Stocks can be assessed flexibly for varying depth from the forest floor down to 100 cm. Uncertainty analysis informs about locations, where the model results have to be handled with care.

Changes in Carbon and Nutrient Stocks of Secondary Forest Transformations Under Ultisol in Leyte Island, Philippines

Ultisols are old soils, inferior and acidic. However, tropical secondary forests (SF) under this soil are transformed into grasslands (GL) and forest plantations (FP) which could profoundly affect the carbon and nutrient stocks. To support efforts in conserving tropical forest, estimates of these are essential, especially in addressing climate change and carbon sequestering. This study aimed to quantify soil organic carbon (SOC), total aboveground biomass (TAGB) and nutrient stocks of SF transformations using three adjacent land-use types, namely SF, GL and FP with comparable climate, parent material, soil type and geology. Results showed that land-use mean of organic carbon, TAGB, potential cation exchange capacity, effective cation exchange capacity, exchangeable acidity, hydrogen ion, aluminum, magnesium, calcium, potassium, sodium and the base saturation decreased when SF was converted into GL and then into FP. Additionally, there was a slight increase in SOC stocks, total nitrogen, available phosphorus and pH in H2O when SF was converted into GL and then into FP. This study indicates that SF conversion into GL and FL did not affect SOC stocks and has no significant relationship with TAGB.

Carbon sequestration of forest soils is reflected by changes in physicochemical soil indicators ─ A comprehensive discussion of a long-term experiment on a detritus manipulation

The interactions of climatic and geochemical factors control soil organic carbon storage capacity and turnover. The comprehensive evaluation of the effect of long-term detritus manipulation on the soil organic carbon, soil-forming processes and the soil physical and chemical properties will help us better understand the carbon sequestration of forest soils. The long-term (19 years) effect of detrital input and removal treatments (DIRT) on physicochemical soil properties were investigated at a Central-European forest site (Síkfőkút, Hungary). In contrast to the results of similar experiments in other parts of the world, the detritus input treatments affected the soil organic carbon and almost all of the soil physicochemical indicators for the upper 15 cm layer. Soil pH, potential acidity and base saturation decreased in the litter removal plots and increased in the detritus doubling treatments. A decrease in organic matter content in the litter removal plots explained the changes in bulk density, as the stability of aggregates also decreased with the decrease of exchangeable bases and organic colloids. In this respect, compared to the other DIRT sites and other similar experiments in the world, our experimental site is considered unique, as it has the highest clay content and the driest climate. We conclude that potential cation exchange capacity and base saturation (exch. Ca) play a fundamental role in predicting the occurrence of the carbon sequestration mechanisms. We suggest to include these parameters into current SOC models.

Soil chemical and microbiological attributes under integrated production system in Oxisol of degraded pasture

The objective of this study was to evaluate the chemical attributes and quality of an Oxisol after one year of conversion of degraded pasture into integrated production system. The evaluated treatments were degraded pasture (PAST-Control); Eucalyptus, clone Urograndis 144 (Eucalyptus grandis x E. urophylla hybrid) intercropped with cor and marandu grass (Brachiaria brizantha) (integration crop-livestock-forest system - ICLFS-M); with maize and perennial horse gram (Macrotyloma axillare) (ICLFS-HG); and with maize, java and marandu grass (ICLFS-M+J); Monoculture of marandu grass (MAR) and perennial horse gram (HG); and marandu grass intercropped with Java/ perennial horse gram (H+M). Soil samples were collected in July/2015 and January/2016 in 0-5, 5-10, 10-20 and 20-30 cm soil depth layers. The soil attributes such as pH, organic matter, phosphorus, sum of bases, effective and potential cation exchange capacity and base saturation were evaluated. The implantation of ICLFS system contributed to increase of soil organic matter, sum of bases, effective and potential cation exchange capacity and soil base saturation. The soil biological activity was increased in the rainy season, and the soil microbial carbon increased in ICLFS-HG+M, ICLFS- HG, ICLFS-M and HG+M when compared to monocultures and PAST. Integrated production systems provide improved in soil quality even with a short time implementation.

Rock powder and organic fertilization in soil cultivated with black bean

The use of rock powder as a source of nutrients to plants can be an alternative or complement to mineral soluble and organic sources. Thus, the aim of this study was to evaluate the potential of different rock powder doses, associated or not with livestock manure, as a source of nutrients for bean and its effect on soil chemical attributes. The treatments consisted of the application of 0, 3, 6, 9 and 12 Mg ha-1 of rock powder, associated or not with livestock manure (17 Mg ha-1), applied on the soil surface, without incorporation. The experiment was carried out in completely randomized blocks, with three replicates, and in a factorial arrangement (5x2). The grain yield of bean, height plants and number of plants m-2 were not influenced by the treatments. On the other hand, the application of 3 Mg ha-1 of rock powder associated with livestock manure resulted in a higher number of grains per pod, and the increase in the rock powder doses affected the number of pods per plant. In the soil, only the manure application, regardless of the rock powder, resulted in effects: reduced potential acidity and potential cation exchange capacity, and increased phosphorus content and base saturation. Thus, rock powder, associated or not with livestock manure, is not effective in improving bean yield and soil chemical attributes after approximately three months of application, and the use of livestock manure, regardless of the rock powder doses, improves some chemical attributes in the soil.

Color parameters applied to pedotransfer functions in the estimation of soil attributes

Global demands for an increased food production have prompted scientists to create technological innovations in various segments of the agricultural and environmental sectors. The use of diffuse reflectance spectroscopy in soil color determination to estimate its attributes is an example of these advances. Thus, the aim of this research was to identify the potential of the three parameters of the Munsell color system (Hue, Value, and Chroma) in estimating different chemical and particle size attributes by pedotransfer functions in a Typic Hapludox in the Cerrado of Piauí State, Brazil. This soil showed a yellowish color due to the goethite and low contents of bases and organic carbon. Among the calibrated pedotransfer functions, we observed that phosphorus, aluminum, hydrogen, potential acidity, potential cation exchange capacity, and base saturation could be estimated by Hue, while clay content by Value, and Chroma used to estimate hydrogen, potential acidity, and cation exchange capacity. We conclude that the parameter color could be used to estimate soil attributes.

Soil Chemical Attributes under Crop-Livestock-Forest Integration System and in Different Land Uses in Mata dos Cocais Region

The sustainability of ecosystems is closely linked with the assessment of soil properties that estimate their quality. This work proposes to evaluate soil chemical attributes as a function of the implantation of a crop-livestock-forest integration system (ICLF) in the region of Mata dos Cocais in the state of Maranhão, Northeast Brazil. The four different land uses evaluated were native vegetation with babassu, capoeira vegetation, degraded pasture and area under ICLF system (with marandu grass, maize and eucalyptus consortium). The samples were collected up to one meter deep, comprising seven layers: 0.00-0.10, 0.10-0.20, 0.20-0.30, 0.30-0.40, 0.40-0.60, 0.60-0.80 and 0.80-1.0 m. The chemical attributes evaluated were pH, Ca, Mg, Al, P, K and Na, potential acidity, base sum, base saturation and soil cation exchange capacity (CEC). The levels of P, in the 0.00-0.10 m layer, were higher in the ICLF system than those of the native forest with babassu. The levels of K in the ICLF system and degraded pasture were higher than the other land uses up to a depth of 0.40 m, ranging from 0.92 cmolc dm-3 to 0.62 cmolc dm-3 and 1.04 cmolc dm-3 and 0.67 cmolc dm-3, respectively. Base saturation was higher in soils under ICLF system and degraded pasture than those observed in native forest and capoeira vegetation. There was an effect in chemical attributes of the soil such as a function of land use and, in general, the highest values were found in areas with degraded pasture and ICLF.

Carbon Storage and Nutrient Stocks Distribution of Three Adjacent Land Use Patterns in Lake Danao National Park, Ormoc, Leyte, Philippines

The country experienced drastic decrease of forest cover due to land use conversion, cutting of trees and doing agriculture to support food security. Secondary forests are an important component of land cover in the tropics, and when transformed or converted into another land-use, it is believed to have negative effects on some soil properties and forest ecosystem in general. A paired-area/space-for-time substitution approach was conducted to determine the changes in carbon storage: soil organic carbon (SOC) and total above ground biomass (TAGB), soil nutrient stocks and fertility status due to land use change. The study was conducted in Lake Danao National Park (LDNP), Ormoc City, Leyte, Philippines. Adjacent to the secondary forest (<1 km away), grassland and forest plantation land uses were chosen and sampled for possible changes on SOC, TAGB and nutrient stocks due to land use change. Results showed that conversion of forest to grassland and forest plantation decreased the organic carbon, exchangeable aluminum, exchangeable acidity, effective cation exchange capacity, TAGB while pH in H2O; exchangeable magnesium and potential cation exchange capacity increased when the forest was converted to grassland and forest plantation. Additionally, available P, base saturation, Ca, K, and Na increased while total N, and SOC stocks decreased when the forest was converted to grassland and forest plantation. This study indicates that conversion of forest to grassland and forest plantation greatly affected the SOC stocks, TAGB, soils nutrient stocks and fertility status. It also revealed that changes in soil properties largely depended upon the land use.

Multiple linear regression and random forest to predict and map soil properties using data from portable X-ray fluorescence spectrometer (pXRF)

ABSTRACT Determination of soil properties helps in the correct management of soil fertility. The portable X-ray fluorescence spectrometer (pXRF) has been recently adopted to determine total chemical element contents in soils, allowing soil property inferences. However, these studies are still scarce in Brazil and other countries. The objectives of this work were to predict soil properties using pXRF data, comparing stepwise multiple linear regression (SMLR) and random forest (RF) methods, as well as mapping and validating soil properties. 120 soil samples were collected at three depths and submitted to laboratory analyses. pXRF was used in the samples and total element contents were determined. From pXRF data, SMLR and RF were used to predict soil laboratory results, reflecting soil properties, and the models were validated. The best method was used to spatialize soil properties. Using SMLR, models had high values of R² (≥0.8), however the highest accuracy was obtained in RF modeling. Exchangeable Ca, Al, Mg, potential and effective cation exchange capacity, soil organic matter, pH, and base saturation had adequate adjustment and accurate predictions with RF. Eight out of the 10 soil properties predicted by RF using pXRF data had CaO as the most important variable helping predictions, followed by P2O5, Zn and Cr. Maps generated using RF from pXRF data had high accuracy for six soil properties, reaching R2 up to 0.83. pXRF in association with RF can be used to predict soil properties with high accuracy at low cost and time, besides providing variables aiding digital soil mapping.

Pedogenesis across a climatic gradient in tropical high mountains, Cordillera Blanca — Peruvian Andes

Studies in alpine environments have shown that chemical weathering and clay mineral formation are mainly controlled by climate and vegetation. However, few studies have focused specifically on pedogenesis in tropical high mountains. We evaluated pedogenic processes and weathering intensity by physical, chemical and mineralogical properties of soils under different vegetation types across a climatic gradient (east/west) in the Northern Cordillera Blanca, Peru. We established 2 catenas and sampled 10 pedons - 6 at Llanganuco valley (east-dry) and 4 at Portachuelo valley (west-wet). Pedons from both catenas are formed on colluvial deposits, gravelly and weakly developed, showing a sequence of O, A, C and C/R horizons. Lithological discontinuities in all pedons revealed sequences of buried A horizons. They also shared the same soil forming processes related to organic matter accumulation, such as humification, melanization and formation of organometallic complexes. The uppermost horizons show high values of total organic carbon and are dark colored. In general, pedons are acidic to slightly acidic, have a low base saturation, a high Al saturation and low effective and potential cation exchange capacity. Seven pedons were classified as Umbrisols, one Fluvisol, one Leptosol and one Regosol. Their similarity is attributed to environmental instability, not allowing sufficient time to develop further. However, pedons at Portachuelo valley showed higher weathering intensity revealed by crystalline iron oxide formation and transformation of phyllosilicates minerals. Among them, pedon under Polylepis forest showed the highest weathering intensity, which favored transformation of chlorite to mixed-layered minerals, suggesting that combined climate and vegetation control chemical weathering and mineral transformation.