Late Glacial-Holocene genesis of Andosols from the Seaca-Tãtarca (South Gurghiu Mountains, Romania)

The purpose of the research presented here was to find an answer for the possible origin and mode of deposition of soil parent materials for Andosol formation and to link the soilscape variability to the various soil forming factors since the Last Glaciation. Soil formation was studied along a 20‐km climo‐toposequence in the Miocene Andesitic area of the South Gurghiu Mountains (Romania). Six representative soil profiles were chosen from a larger geopedological study on the western slope of the Seaca‐Tãtarca volcano. Based on the macromorphological, micromorphological and chemical properties it was possible to say that the soil profiles are composed of two major types of soil material: a relict type, with a crystalline clay fraction; and a recent type with an amorphous colloidal fraction. It was found that the present‐day distribution of the Andosols on the Seaca‐Tãtarca volcano must be related to the rejuvenation of the soil parent material by processes of aeolian input of frost‐shattered volcaniclasts and by a glacial reworking. It appears that the extension of the glaciated areas during the Pleistocene could have been larger than concluded from geomorphological studies. General Carpathian glacial features are closely related to the altitudinal distribution of the Carpathian Andosols. At the present climatic optimum, the soils of Seaca‐Tãtarca are influenced by pedogenetic processes of freeze‐thaw, oxido‐reduction, strong leaching and internal colluviation, strong accumulation of organic matter and considerable biological activity. Those Andosols that are located in special microtopographic positions with stronger water percolation tend to evolve towards Podzols.     

Applicability of ground‐penetrating radar as a tool for nondestructive soil‐depth mapping on Pleistocene periglacial slope deposits

Soil depth plays a decisive role in determining soil properties in mountainous regions for ecological site assessment. To evaluate the use of ground‐penetrating radar (GPR) for fast and high‐resolution mapping within mountainous regions, we examined the possibilities and limitations of GPR to determine soil depth over bedrock and to delineate individual substrate layers formed during the Pleistocene in a periglacial environment (Pleistocene periglacial slope deposits, PPSD). Selected catenae in representative subregions of the study area (Dill catchment, SE Rhenish Massif, Germany) have been successfully mapped using GPR. A practicable method was developed using a 400 MHz antenna to reach a mean penetration depth of 1.5 m and to map different substrates and layers of PPSD based on calibrations of the GPR at soil pits along 12 catenae. Colluvium, the three types of PPSD layers, as well as the in situ bedrock could be distinguished in most sections of the GPR surveys. Characteristic GPR facies caused by intrinsic material properties of the different substrates, such as stone content and soil moisture content, could be distinguished in different geomorphologic and lithological settings. A layer‐based velocity distribution was determined for characteristic substrate layers at soil pits enabling us to considerably enhance the accuracy of soil‐depth prediction. Compared to traditionally surveyed soil profiles, our results demonstrate an accuracy of layer thickness surveying within a standard deviation of approx. 0.1 m. It is demonstrated that the combination of GPR with conventional soil‐pit mapping is an efficient and valid method to produce high‐resolution data of substrate distribution.     

Assessment of the mineralogical status of silicate components in chernozems

An approach to assess the mineralogical status of chernozems is discussed. It is based on ten characteristics of the main groups of minerals composing the silicate part of the soil and allows us to give a comprehensive assessment of the mineralogical status of chernozems and its transformation under the impact of pedogenetic processes. The obtained data may be used for determining the soil genesis; improving soil classification; and solving various applied problems, including the assessment of the adverse effect of irrigation of chernozems on the state of their minerals, the irrigation-induced degradation of smectites and illite formation, illite formation upon the nonexchangeable fixation of potassium from fertilizers, etc. The principles of this approach may also be applied to other soils with due consideration for their mineralogical composition.     

Multivariate analysis of soils: microbial biomass,metabolic activity,and bacterial‐community structure and their relationships with soil depth and type

A multivariate statistical approach based on a large data set of abiotic and biotic variables was used to classify four contrasting‐land‐use soils. Soil samples were collected at increasing depth from a calcareous agricultural soil, a temperate upland grassland soil, a moderately acidic agricultural soil, and an acidic pine forest soil. Analytical investigations were carried out by using a combination of conventional physical, chemical, and biochemical methods coupled with denaturing gradient gel electrophoresis (DGGE) community fingerprinting of PCR‐amplified 16S rRNA gene‐coding fragments from soil‐extracted total‐community DNA. The data set of soil physical, chemical, and biochemical variables was reduced in dimensionality by means of a principal‐component‐analysis (PCA) procedure. Compositional shifts in soil bacterial‐community structure were analyzed through a clustering algorithm that allowed identifying six main bacterial‐community clusters. DGGE fingerprinting clusters were further analyzed by discriminant analysis (DA) using extracted PCA components as explanatory variables. Soil organic matter–related pools (TOC, TN) and functionally related active pools (microbial biomass C and N, K₂SO₄‐extractable C) significantly decreased with soil depth, and resulted statistically linked to one other and positively related to enzymatic activities (acid phosphatase, arylsulfatase, β‐glucosidase, dehydrogenase, hydrolysis of fluorescein diacetate) and silt content. Besides organic‐C gradients, pedogenetic‐driven physico‐chemical properties, and possibly soil thermal and moisture regimes seemed to play a key role in regulating size and energetic ecophysiological status of soil microbial communities. DGGE analysis showed that contrasting horizons were conducive to the dominance of particular bacterial ribotypes. DA revealed that the bacterial‐community structure was mainly influenced by organic matter–related variables (TOC, TN, CEC, C_flush, N_flush, Extr‐C), chemical properties such as pH, CaCO₃, and EC, together with textural properties. Results indicate that, beyond land use or plant cover, pedogenetic‐driven physico‐chemical conditions changing with soil type and depth are the key factors regulating microbial size and activity, and determining the genetic structure of bacterial community.     

Genesis of the terrae rossae of the Sierra Gádor (Andalusia, Spain)

Some aspects of the genesis of terrae rossae are still subject to controversy while others related to the genesis of the mineral fraction have been studied very little. We have studied four terrae rossae over limestone (two Chromic‐Leptic Luvisols, a Rhodi‐Leptic Luvisol and a Chromi‐Leptic Cambisol) in Sierra Gádor (Almería, southern Spain), in particular the various formation processes by (i) examination of their morphological, analytical and mineralogical characteristics (including crystallochemical parameters of the mica), (ii) examination of the insoluble residue of the gravel and rock, (iii) scanning electron microscopy (SEM) of sand and silt grains, and (iv) examination of the geochemistry of the soil solution. We have investigated the autochthonous or allochthonous nature of the soil material (fine earth and gravel) in relation to the rocky substrate, concluding that both origins are possible. Our SEM study of the morphology of the quartz grains shows that some are insoluble residue and some are probably wind blown from desert and coastal sources. The micas in the fine earth fractions are inherited from the insoluble residue. Comparison of the crystallochemical parameters of micas in the insoluble residue and the soil clay shows that the clay has more Si^IV and (Fe, Mg)^VI, and less Al^IV, Al^VI and x (layer charge) than the insoluble residue. It also has fewer polytypes 2M₁ and more 1M and has a smaller crystal size, especially in B horizons. The kaolinite is of varied origins including neoformation and inheritance from underlying rock. Some of the kaolinite and some mica has been blown in from elsewhere, probably from desert and coastal sources. The soils have undergone other typical processes of terrae rossae including dissolution of carbonate, illuviation of clay and iron oxides, and rubifaction.     

Utilizing a DUALEM‐421 and inversion modelling to map baseline soil salinity along toposequences in the Hunter Valley Wine district

In the oldest commercial wine district of Australia, the Hunter Valley, there is the threat of soil salinization because marine sediments underlie the area. To understand the risk requires information about the spatial distribution of soil properties. Electromagnetic (EM) induction instruments have been used to identify and map the spatial variation of average soil salinity to a certain depth. However, soils vary with depth dependent on soil forming factors. We collected data from a single‐frequency and multiple‐coil DUALEM‐421 along a toposequence. We inverted this data using EM4Soil software and evaluated the resultant 2‐dimensional model of true electrical conductivity (σ – mS/m) with depth against electrical conductivity of saturated soil pastes (EC_p – dS/m). Using a fitted linear regression (LR) model calibration approach and by varying the forward model (cumulative function‐CF and full solution‐FS), inversion algorithm (S1 and S2), damping factor (λ) and number of arrays, we determined a suitable electromagnetic conductivity image (EMCI), which was optimal (R² = 0.82) when using the full solution, S2, λ = 3.6 and all six coil arrays. We conducted an uncertainty analysis of the LR model used to estimate the electrical conductivity of the saturated soil‐paste extract (EC_e – dS/m). Our interpretation based on estimates of EC_e suggests the approach can identify differences in salinity, how these vary with parent material and how topography influences salt distribution. The results provide information leading to insights into how soil forming factors and agricultural practices influence salinity down a toposequence and how this can guide soil management practices.     

Characteristics of Regolith developed on basalt in Pahang,Malaysia

Abstract

The characteristics and degree of weathering in a deep regolith developed on basalt were investigated. A representative 15m deep regolith of soil‐saprolite‐rock sequence, located in Pahang state, Malaysia, was selected. The intensity of weathering in this deep regolith was assessed by various weathering indices as well as changes in the physicochemical properties and clay mineralogy of the regolith. The values of all weathering indices and other assessments gave strong evidences of intense weathering during saprolite formation. The low CËC and base cation values even in the saprolite layers were accounted By the extreme depletion of major elements such as potassium (K), sodium (Na), calcium (Ca), and magnesium (Mg), and significant enrichment of aluminum (Al), iron (Fe), titanium (Ti), copper (Cu), and niobium (Nb) occurred during saprolitization. The extreme weathering pattern of basalt differed from those described in granite and metamorphic rocks found in Peninsular Malaysia.     

Modelling long-term in situ soil profile evolution: application to the genesis of soil profiles containing stone layers

Models of soil genesis are potentially of great importance in assessing the effects of global change on ecosystems, and may also contribute to our understanding of soil genetic processes. Many quantitative models have so far focused on individual soil genetic processes and are difficult to extrapolate to the landscape scale. A few attempts have been made to model soil evolution as a whole from a pedologic perspective. This study develops a quantitative model of soil formation at the profile scale, taking into account major soil‐forming processes. These include physical and chemical weathering of primary minerals, strain processes, and bioturbation. The model allows the quantification of the evolution of the particle size, mineral composition and bulk density of the soil. The model is applied with varying values of input parameters, and is compared with actual soil genetic processes. Running the model results in the formation of stone‐layered soil profiles. Stone‐line formation by means of bioturbation, as already described in the literature, seems to be adequately simulated. Planned improvements of the model include implementation of other major soil genetic processes such as leaching, organic matter influence, etc. This model will then have to be implemented spatially considering particularly redistribution processes, to reproduce soil formation at the landscape scale.     

Genese und Klassifikation von Organomarschen der Wesermarsch

Formation and classification of humus-rich marshland soils of the Weser marshland, Germany The formation and classification of marshland soils are still controversial. To improve the knowledge on the formation of humus-rich marshland soils 11 soil profiles have been investigated. The soils mostly showed Phragmitis in the subsoil. The Gr-horizons began at low depths (40–60 cm). The clay content was often about 60% and the C_org content up to 480 g kg^?1. The amount of total sulfur was up to 29.6 g kg^?1, that of exchangeable sulfate up to 4608 mg kg^?1 and that of sulfate in the saturation extract 51.2 mg l^?1. With pH (H₂O) values between 2.0 and 7.4, Carbonate/S ratios < 3 and total sulfur contents > 7.5 g kg^?1 some soils showed “Actual Acid Sulfate Soil” (AASS) properties. The pH(per) values varied between 2.4 and 7.1, thus some profiles showed “Potential Acid Sulfate Soils” (PASS) properties. Brakish as well as marine environments with an intensive sulfur dynamics and carbonate leaching are likely within the geogenetic phase of soil development. Via the control of the water regime the pedogenetic phase is mainly of anthropogenic influence. We propose to classify humus-rich marshland soils into “Organomarsch” and “Thiomarsch” on the soil type level of the German systematics.     

Crop rotation in no‐till soils modifies the soil fatty acids signature

Analysis of whole‐soil fatty acids (WSFA ) was used to characterize no‐till productive agricultural soils associated with different crop rotation managements on the Argentinean pampas, over two sampling seasons. Crop rotation (CR ) treatment was compared with soybean monocropping (MC ). Soils from nearby natural environments (NE ) were used as reference treatments. The objective of this study was to characterize the soil lipid signature and seek putative markers of agricultural management. NE sites had greater concentration of total WSFA than agricultural sites, but no differences between CR and MC were identified. NE sites were characterized by straight chain and mono‐unsaturated fatty acids, such as 16:1 ω5c , an established biomarker for arbuscular mycorrhiza. Comparing lipid profiles using multivariate methods allowed a comprehensive comparison among treatments. The CR and NE soil samples were more alike than those of MC , with several fatty acids in common. CR soils were associated with mixed, branched and hydroxylated fatty acids. MC profiles appeared to be enriched by 16:010Me and 18:1 ω7c fatty acids, which could be potential treatment markers. Thus, use of the WSFA approach to study soil lipid signature appeared to be a sensitive method to characterize soil health and soil use and management. However, some of the fatty acids do not come from living cells but from soil organic matter, which sets a limitation on interpretation in terms of the microbial community but expands the biological origin of the soil lipid signature to any biological matter, alive or death, which is a constitutive part of the soil under study.     

Boundary line analysis of the effect of water‐filled pore space on nitrous oxide emission from cores of arable soil

The boundary line has been proposed as a model of the effects of a variable on a biological response, when this variable might limit the response in only some of a set of observations. It is proposed that the upper boundary (in some circumstances the lower boundary) represents the response function of interest. Boundary‐line analysis is a method for estimating this response function from data. The approach has been used to model the emission of N₂O from soil in response to various soil properties. However, the methods that have been used to identify the boundary are based on somewhat ad hoc partitions of the data. A statistical model that we have presented previously has not been applied to this problem in soil science, and we do so here to represent how the water‐filled pore space (WFPS) of the soil affects the rate of N₂O emission. We derive a boundary‐line response that can be shown to be a better model for the data than an unbounded alternative by statistical criteria. Furthermore, the fitted boundary‐response model is consistent with past empirical observations and modelling studies with respect to both the WFPS at which the potential emission rate is largest and the measurement error for the emission rates themselves. We show how the fitted model might be used to interpret data on soil volumetric water content with respect to seasonal changes in potential emissions, and to compare potential emissions between soil series that have contrasting physical properties.     

Mineralization of “non‐metabolizable” glucose analogues in soil: potential chemosensory mimics of glucose

Glucose is widely used to study the dynamics of easily available organics in soil. Pure culture studies have revealed that many microorganisms can sense and respond to glucose through chemosensory mechanisms that are not directly reliant on energy catabolism. However, the rapid mineralization of glucose by microorganisms makes it difficult to disentangle its energy effects from such non‐catabolic interactions. “Non‐metabolizable” glucose analogues have proven useful in mechanistic studies of glucose in pure culture, but have never been applied to complex microbial communities in soil. We sought to determine how their mineralization in soil differs from that of glucose, and whether they have potential as a new approach for investigating chemosensory mechanisms in soil microbiology. We incubated soil from an agricultural Haplic Luvisol under controlled conditions for 24 d and monitored CO₂ efflux after addition of (1) glucose, and three “non‐metabolizable” glucose analogues: (2) 2‐deoxyglucose (DG), (3) α‐methylglucoside (αMG), and (4) 3‐O‐methyl‐glucose (OMG), at three concentration levels, along with a control. All three analogues did in fact produce a large increase in soil CO₂ efflux, but the dynamics of their mineralization differed from the rapid degradation seen for glucose. At medium and high concentrations, CO₂ efflux peaked between 2.5 and 4 d after amendment with DG and αMG, and was delayed by about one week for OMG. The markedly different patterns of mineralization between glucose and OMG offer a new tool for investigating the behavior of glucose in soil. By using OMG as a glucose model, chemosensory mechanisms could be studied with limited interference from energy catabolism.     

The historic man-made soils of the Generalife garden (La Alhambra, Granada, Spain)

We studied the soils of the Patio de la Acequia garden of the Generalife, a palatial villa forming part of La Alhambra, a World Heritage Site in Granada, Spain. This garden, which is estimated to be around 700 years old, is the oldest historical garden in the Western World. The soils are man‐made cumulimollihumic‐calcaric (hypereutric, anthric) Regosols. Noteworthy amongst the main pedogenic processes, in relation to the human activities of cultivation, irrigation and tillage, are horizonation, melanization (the contents of organic carbon varied between 0.59% and 8.87%, and those of P₂0₅ extracted with citric acid between 723 mg kg⁻¹ and 7333 mg kg⁻¹, with maximae in the Ap horizons) and structure formation. The soil fabric, studied at the ultramicroscopic level using scanning electron microscopy, is of laminar and partition‐walls’ type in the lower horizons, depending on the microped zones. The partition‐walls’ fabrics found are different to those of the possible pre‐existing sedimentary fabrics. These are numerous lithological discontinuities and at least two burials, leading us to deduce that there have been two main stages of filling with materials in the formation of these soils. The first is Arabic‐Medieval (13th century), when the garden was created, its surface being some 50 cm below the level of the paved area of the present patio. In the deeper parts, the materials employed in the fill are similar to the in situ soils of the zone, unaffected by the buildings. The second stage is Christian (15th century to the present day). During this period the Medieval garden was gradually buried under a layer of materials from the nearby soils and/or sediments mixed with manure until the surface was only just below the level of the paved area of the patio. In this work we discuss the difficult classification of these relatively little studied soils. In spite of their being clearly related to human activity, they are not classified as Anthrosols in the FAO system (1998) because soil materials cannot be classified as anthropopedogenic or as anthropogeomorphic.     

Soil‐ and plant‐based nitrogen‐fertilizer recommendations in arable farming

Under‐ as well as overfertilization with nitrogen (N) will result in economic loss for the farmer due to reduced yields and quality of the products. Also from an ecological perspective, it is important that the grower makes the correct decision on how much and when to apply N for a certain crop to minimize impacts on the environment. To aggravate the situation, N is a substance that is present in many compartments in different forms (nitrate, ammonium, organic N, etc.) in the soil‐plant environment and takes part in various processes (e.g., mineralization, immobilization, leaching, denitrification, etc.). Today, many N‐recommendation systems are mainly based on yield expectation. However, yields are not stable from year to year for a given field. Also the processes that determine the N supply from other sources than fertilizer are not predictable at the start of the growing season. Different methodological approaches are reviewed that have been introduced to improve N‐fertilizer recommendations for arable crops. Many soil‐based methods have been developed to measure soil mineral N (SMN) that is available for plants at a given sampling date. Soil sampling at the start of the growing period and analyzing for the amount of NO ‐N (and NH ‐N) is a widespread approach in Europe and North America. Based on data from field calibrations, the SMN pool is filled up with fertilizer N to a recommended amount. Depending on pre‐crop, use of organic manure, or soil characteristics, the recommendation might be modified (±10–50 kg N ha^–1). Another set of soil methods has been established to estimate the amount of N that is mineralized from soil organic matter, plant residues, and/or organic manure. From the huge range of methods proposed so far, simple mild extraction procedures have gained most interest, but introduction into practical recommendation schemes has been rather limited. Plant‐analytical procedures cover the whole range from quantitative laboratory analysis to semiquantitative “quick” tests carried out in the field. The main idea is that the plant itself is the best indicator for the N supply from any source within the growth period. In‐field methods like the nitrate plant sap/petiole test and chlorophyll measurements with hand‐held devices or via remote sensing are regarded as most promising, because with these methods an adequate adjustment of the N‐fertilizer application strategy within the season is feasible. Prerequisite is a fertilization strategy that is based on several N applications and not on a one‐go approach.     

Interpretation of infrared spectra for OM characterization of soil structural surfaces of Bt‐horizons

The surfaces of macropores or aggregates can act as hot spots for biogeochemical processes and solute transport during preferential flow. For the characterization of organic matter (OM) at macropore surfaces non‐destructive methods have been applied such as diffuse reflectance infrared Fourier transform spectroscopy (DRIFT). However, effects of organic components on DRIFT signal intensities are often difficult to distinguish from those of mineral components. Here, DRIFT spectra from intact earthworm burrow walls and coated cracks were re‐evaluated to improve the interpretation of C–H and C=O bands. We compared DRIFT and transmission Fourier transform infrared (FTIR) spectra of entire samples that were from the same pedogenetic soil horizon (Bt) but different in mineral composition and texture (i.e., glacial till vs. loess). Spectra of incinerated samples were subtracted from the original spectra. Transmission FTIR and DRIFT spectra were almost identical for entire soil samples. However, the DRIFT spectra were affected by the bulk mode bands (i.e., wavenumbers 2000 to 1700 cm^?1). These bands affected spectral resolution and reproducibility. The ratios between C–H and C=O band intensities as indicator for OM quality obtained with DRIFT were smaller than those obtained from transmission FTIR. The results demonstrated that DRIFT and transmission FTIR data required separate interpretations. DRIFT spectroscopy as a non‐destructive method for analyzing OM composition at intact surfaces in structured soils could be calibrated with information obtained with the more detailed transmission FTIR and complementary methods. Spectral subtraction procedure was found useful to reduce effects of mineral absorption bands. The improved DRIFT data may be related to other soil properties (e.g., cation exchange capacity) of hot spots in structured soils.