Basaltic Parent Material Research Articles

VARIATION OF DEHIDROGENASE ENZYME AKTIVITY AND DIFFERENT PEDOGENETIC DEVELOPMENT ON WEATHERED BASALTIC TOPOSEQUENCES

Enzymes play the most important role in the decomposition and deterioration of organic matter inthe soil. Most of the microbial activity in the soil is determined by measuring the activities of theenzymes. The aim of this study is to examine the changes in dehydrogenase enzyme activity indifferent pedological development soils formed on the same parent material, but with differentslopes, land cover and land use under semihumid climatic conditions. It was carried out on the soilformed on the basaltic parent material in different topographical positions within the Dağköy area ofEngiz district, which is located at the south of the Samsun-Bafra Highway. In this study,dehydrogenase enzyme activity was assessed in order to reveal the biological properties of the soilof the study area and it was investigated the dehydrogenase enzyme activity in terms of soilbiological property. For this aim, six soil profiles formed on weathered basaltic parent material andlocated on toposequence of north-south transect were described according to genetic horizon andclassified as Lithic Ustorthent, Vertic Haplustept, Typic Haplustept and Typic Haplustert. I

Experimental shock metamorphism of terrestrial basalts: Agglutinate‐like particle formation, petrology, and magnetism

AbstractHypervelocity impacts occur on bodies throughout our solar system, and play an important role in altering the mineralogy, texture, and magnetic properties in target rocks at nanometer to planetary scales. Here we present the results of hypervelocity impact experiments conducted using a two‐stage light‐gas gun with 5 mm spherical copper projectiles accelerated toward basalt targets with ~6 km s−1 impact velocities. Four different types of magnetite‐ and titanomagnetite‐bearing basalts were used as targets for seven independent experiments. These laboratory impacts resulted in the formation of agglutinate‐like particles similar in texture to lunar agglutinates, which are an important fraction of lunar soil. Materials recovered from the impacts were examined using a suite of complementary techniques, including optical and scanning electron microscopy, micro‐Raman spectroscopy, and high‐ and low‐temperature magnetometry, to investigate the texture, chemistry, and magnetic properties of newly formed agglutinate‐like particles and were compared to unshocked basaltic parent materials. The use of Cu‐projectiles, rather than Fe‐ and Ni‐projectiles, avoids magnetic contamination in the final shock products and enables a clearer view of the magnetic properties of impact‐generated agglutinates. Agglutinate‐like particles show shock features, such as melting and planar deformation features, and demonstrate shock‐induced magnetic hardening (two‐ to seven‐fold increases in the coercivity of remanence Bcr compared to the initial target materials) and decreases in low‐field magnetic susceptibility and saturation magnetization.

Keterkaitan parameter nilai pH, C-organik, N-Total, C/N dan alofan pada beberapa Andisols di Jawa Barat

The correlation of chemical parameters and soil mineralogy one to another in Andisols were interesting to be studied, to increase the understanding of soil reactions, nutrient availability and soil mineral content. Andisols from three locations and derived from three different volcanic eruptions namely G. Tangkuban Parahu, G. Patuha and G. Tilu, with andesite, andesite-basalt and basalt parent materials respectively, were examined the correlation of several soil parameters. The values of pH, organic carbon, total nitrogen, C/N and allophane content were obtained from the soil analysis of every horizon of the soil profiles at each site. Correlation analyses were used to see the relationship of the parameters. The results showed a negative correlation between pH and organic carbon (r = -590 *). The soil pH values were positively correlated with the amount of allophane (r = 0.687 *). The pH values were correlated positively with imogolite content (r = 0.356 *). The pH values were negatively correlated with organic carbon (r = -0.590 *). The organic carbon content was negatively correlated with depth (r = - 0.582 *). The organic carbon content was negatively correlated with allophane (r = 0.707 *). Total nitrogen values were negatively correlated with increasing depth (r = -0.531 *).Keywords: Mt. Tangkuban Parahu, Mt. Patuha, Mt. Tilu, andesit, andesit-basalan, alophane

Soil types influence predictions of soil carbon stock recovery in tropical secondary forests

Tropical forests are major sinks of terrestrial carbon (C) both above- and below-ground. As a consequence their destruction and degradation is considered the second largest anthropogenic source of carbon dioxide to the atmosphere. Also contributing to the changing dynamics of the global carbon cycle is the widespread and significant expansion of secondary forest. Secondary forests that colonise abandoned agricultural lands can potentially recover above-ground C stocks to historical levels in a few decades. However, the dynamics of below-ground C stored as soil C stocks are unaccounted for in several tropical regions. Similarly, although parent materials are known to differ in chemical and physical properties, little is known about the relationships of soil C stocks with environmental predictors and whether they interact with soil types during natural forest regeneration. We investigated whether soil organic carbon (SOC) stocks change with secondary forest age in two contrasting soil types (derived from either basalt or granite). Soil and vegetation parameters were analysed to determine the best predictors of SOC stock changes in secondary forests. SOC stocks from 24 secondary forests (up to 69years since pasture abandonment) were compared with those from active pastures and mature forests. We found that clay-rich soils (originating from basalt parent material) store higher amounts of SOC, although these stocks remain unchanged as secondary forests matured. In contrast, SOC stocks in granite soils tend to be lower in young secondary forests and increase rapidly to levels comparable to mature forests. Moreover, our analysis indicated that soil pH and woody plant diversity are strong candidates as predictors of SOC stock variations, yet it appears this is within the context of soil type. Our results support the contention that models predicting SOC stocks during forest succession should not rely only on secondary forest age. Instead, predictions of SOC stocks can be improved with the inclusion of basic information on vegetation cover and soil type (especially soil texture).

Productivity and Suitability Evaluation of Orange (Citrus reticulata)-Growing Soils of Hot and Semi-Arid Region of Rajasthan (AESR 5.2)

Fourteen pedons were evaluated for their productivity and suitability on the basis of variation in physiography, parent materials, soils and productivity of orange in Jhalawar district of Rajasthan. The pedons were developed by sandstone and shale (P1-P6) and basalt parent materials (P7–14) in Vindhyan and Malwa region, respectively and classified as Vertisols (P3, P5, P7-P13) and Inceptisols (P1, P2, P4, P6 and P14). In general, sand silt and clay contents ranged from 3.4 to 48.1, 27.8 to 71.0 and 18.6 to 60.9% in different horizons, respectively. The soils were calcareous and moderately alkaline to strongly alkaline in reaction and sub-soil sodicity is just arising mostly in soils of Malwa region (P3, P9 and P12). The organic carbon ranged from 0.36 to 9.13 g kg−1 and cation exchange capacity from 22.5 to 62.5 cmol(p+)kg−1 soil. The soils were low to optimum in available N and K and low to excess in available P. The Riquier productivity index appears to be more reliable as compared to Storie index and these ratings are not in reliance with the Sys and proposed suitability criteria and yield of orange realized. On computation of the existing limitations, a new criterion has been proposed (against Sys suitability criteria for citrus species) which indicated that P2, P3, P7, P9, P10, P11 and P12 were moderately suitable, P1, P4-P6, P8, P13 and P14 were suitable for orange production.

Molybdenum isotope fractionation in soils: Influence of redox conditions, organic matter, and atmospheric inputs

Molybdenum isotope fractionation accompanying soil development is studied across three pedogenic gradients encompassing a range of controlling factors. These factors include variable redox conditions, organic matter content, Fe and Mn oxy(hydr)oxide content, mineral composition, degree of weathering, pH, type and amount of atmospheric inputs, age, climate, and underlying rock type. Soil profiles from the island of Maui (Hawaii) along a precipitation gradient ranging from 850 to 5050mm mean annual precipitation show a decrease in average soil δ98Mo from −0.04±0.11‰ at the driest, most oxic site, which is indistinguishable from the basalt parent material (−0.09±0.08‰), to −0.33±0.10‰ at the wettest, most reducing site. A suite of 6 Icelandic soils display a broad trend with heavier δ98Mo values (up to +1.50±0.09‰) in soil horizons that are more weathered and have higher organic matter content. Selective extractions of Mo from different soil components indicate that the association with organic matter and silicate or Ti-oxide residue dominates retention of Mo in these soils, with adsorption on Fe and Mn oxy(hydr)oxides playing a lesser role. Across all basaltic soils, δ98Mo values are lighter in soils that exhibit the most net Mo loss relative to the parent material, and δ98Mo values are heavier in soils that exhibit net Mo gains. A well-drained regolith profile in the Luquillo Mountains of Puerto Rico developed on quartz diorite shows heavier δ98Mo values than the parent material (up to +0.71±0.10‰ with an integrated profile average of +0.28±0.10‰) in soil and shallower saprolite, despite overall moderate loss of 28% of Mo relative to the bedrock. However, the deeper saprolite is unfractionated from bedrock (−0.01±0.10‰, quartz diorite bedrock) indicating that rock weathering dissolution processes and secondary clay formation do not fractionate Mo isotopes. Our data suggest that the Mo mass balance and isotope composition of soils are controlled by redox conditions, organic matter, and atmospheric inputs. In this way Mo isotopes have the potential to react to and record climate driven changes in the weathering environment. The presence of both isotopically light and heavy Mo (relative to parent material) across all sites and within individual soil profiles suggests that it is normal for multiple fractionation mechanisms to operate under the open-system conditions of soils.

English

Characterization of soils is helpful in the appraisal of soil productivity. The study investigated detailed physico-chemical characterize of the soils developed on basaltic parent materials on the Jos plateau, Nigeria. The aim was to assess appropriate management practice for their sustainability in agricultural production. Four profiles pits were dug and studied, soil samples collected from pedogenetic horizons were analysed for particle size distribution, pH, fertility related properties. Results indicated that the soils were deep, clayey and reddish in colour (2.5YR 3/3-5YR 3/4). In terms of chemical characteristic, the soils are acidic (pH ranged between 4.6 and 5.6) with low to high CEC values (between 4.3 and 14.8 cmol (+) kg-1) and generally low in organic matter on the average (<1.5%) and exchangeable bases. The four profiles developed on basaltic parent materials on the Jos Plateau of Nigeria were characterized and classified as Typic Haplustusts and Andic Haplustepts. All the soils were well drained in spite of high percent clay above 40% and silt fraction of 20 to 30%, which is apparently kaolinitic, with moderate to high aluminium saturation. Higher agricultural productivity of these soils is constraint by low nutrient-holding capacities and strong acidity. Ways to ameliorate these problems include; to raise the exchangeable Al3+ above toxicity and to supply Ca and Mg contents besides improving soil physical conditions.      Key words: Basaltic, typic haplustusts, andic haplustepts, kaolinitic, aluminium toxicity. &nbsp

Magnetic mineralogy of a weathered tropical basalt, Hainan Island, South China

Numerous studies have shown that mineral magnetic properties are sensitive indicators of weathering and soil formation (pedogenesis). However, the formation pathways and subsequent alteration mechanisms of specific weathering products are poorly constrained. We report a detailed magnetic investigation through a basalt profile that has been weathered under tropical conditions in South China. The rock magnetic analyses show that hot and humid conditions led to the neoformation of fine-grained magnetite and promoted mineral transformations in the form of maghemitization and hematization. Thus, although the basaltic parent material is rich in titanomagnetite, the final products of the weathering process are maghemite and hematite. Magnetic grain-size varies through the profile, with a combination of pseudo-single domain and single-domain particles at the base, with fining to single-domain in the middle and a mixture of superparamagnetic and single-domain particles in the uppermost profile. Importantly, the magnetic mineral assemblage through the profile is influenced by the mobilization and migration of iron through the sequence. This process is illustrated by concentration-dependent magnetic parameters, which reach maxima at the assembly depth of major and trace elements and minima at the oxic front where Fe content is its lowest.

Moisture Release Behaviour of Orange-Growing Soils Developed from Different Parent Materials in Jhalawar District of Rajasthan

Variation in water retention characteristics has been evaluated in soils developed on Vindhyan scarplands and Malwa plateau from sandstone and shale with band of limestone and basaltic parent materials, respectively. Six typifying pedons from Vindhyan scarplands and eight from Malwa plateau representing dominant landforms have been studied for their physicochemical properties and water retention at various suctions. The higher values of water retention (0.69 and 0.38 m3 m−3) at 0.03 and 1.5 MPa were recorded in soils of basaltic origin (P12), whereas the corresponding values were very low (0.32 and 0.13 m3 m−3) in soils of sandstone and shale with band of limestone (P6 and P5). The variability in water retention at various suctions (0.03, 0.1, 0.3, 0.5, 1.0 and 1.5 MPa) was governed by clay content and associated soil properties. In general, water retention increased down the depth of profile in the pedons, which have increasing pattern of clay content in both the parent materials, at lower and higher suction pressures. The available water content ranged from 0.15 to 0.29 m3 m−3 with mean value of 0.20 m3 m−3 in soils of sandstone and shale with band of limestone, while in basaltic soils it varied from 0.14 to 0.31 m3 m−3 with mean content of 0.20 m3 m−3.

Understanding the combined effect of soil properties on gully erosion using quantile regression

The individual effects of soil properties on soil erodibility are well understood. It is also known that various interactions between these properties exist, which creates the need for unique investigations into how soil properties influence soil stability. Quantile regression was used in this paper to determine which soil properties control gully erosion in a catchment in Lesotho. Samples of typical soil forms found in the catchment were analysed for properties related to soil erosion. Dispersion ratio had the best correlation with areas of severe gully erosion. No strong correlation was found for a single soil property with dispersion ratio. Quantile regression showed that a combination of effective cation exchange capacity (CEC), total carbon, exchangeable sodium percentage (ESP) and free iron influenced soil dispersion. When the aggregating agents (effective CEC, total carbon and free iron) are deficient in the soil sample, very small amounts of a dispersing agent (ESP > 0.67%) will lead to above-average dispersion. Soils with an increased amount of basaltic parent material tended to be more stable.

Magnesium Isotope Fractionation During Arid Pedogenesis on the Island of Hawaii (USA)

We combines Mg isotopic analyses with soil characterization methods to determine Mg isotopic compositions of bulk soils, basalts, and carbonate fractions at an arid (∼30cm MAP) soil chronosequence on the Island of Hawaii. This chronosequence is developed on Pololu (350 ka) and Hawi (170 ka) lava flows. Both profiles contain pedogenic carbonates and secondary alumino- silicate and sequioxide phases. Bulk soil horizons at these sites range in δ26Mg from -0.21±0.31 ‰ to -1.75±0.22 ‰ for the Hawi and -0.01±0.31 ‰ to -0.21±0.31 ‰ for the Pololu. Basalts underlying the soil profiles have average δ26Mg values of - 0.25±0.06 ‰. Pedogenic carbonate δ26Mg values at these sites vary from -1.05±0.22‰ to -2.31±0.22‰. Integrating the soils as a whole yields bulk soil isotopic compositions of -1.35±0.16 ‰ for the Hawi and -0.12±0.12 ‰ for the Pololu. These differences in overall δ26Mg between total soils may be explained by the relative abundance of Mg in carbonate; in the Hawi soil 69±11% of Mg is hosted by carbonate phases, while in the Pololu soil 16±2% of Mg is in carbonate phases. Estimates of Mg input to the soils through time, through rainfall estimates as well as rock weathering estimates provided by the immobile index element Zr, allows the calculation of the δ26Mg of Mg exported from these systems. The isotopic composition Mg exported from the Hawi soil is not tightly constrained but must be significantly isotopically heavier than the basalt parent material. The Pololu soil is much better constrained and has exported Mg with a δ26Mg of -0.36±0.26 ‰, close to the weighted mean value of inputs to the soil from weathering and atmospheric deposition. The evolution of the soil mineralogy and morphology during progressive development of the weathering profile result in significant changes in the isotopic composition of Mg exported through time.

Fractionation of yttrium and holmium during basaltic soil weathering

The anomalously low affinity of yttrium (Y) for iron (Fe) (oxyhydr)oxides relative to lanthanides with similar ionic radius (e.g., Ho) has been demonstrated in experiments with isolated Fe minerals and in a variety of marine systems that contain high concentrations of solid phase Fe. However, it has not previously been demonstrated to occur during soil genesis, despite the common observation that many soils become enriched in Fe over time. We hypothesized that Y would become progressively depleted in soils relative to Ho with increased weathering. Since, trivalent Y has an anomalously low Misono softness relative to other trivalent ions included in the rare earth element and yttrium group (REY3+), we also investigated whether soil REY fractionation reflects variation in Misono softness. To test this, we measured trends in total REY concentrations for Hawaiian soils derived from basaltic parent materials aged 0.3–4100ky, and measured REYs released from the same samples during short-time (3h) dissolution experiments conducted as part of a previous investigation linking dissolution with surface charge properties (Chorover et al., 2004). The chondrite-normalized Y/Ho ratios in the parent Hawaiian basalt (Chond[Y/Ho]=0.998) and continental dust (Chond[Y/Ho]=0.994) inputs are remarkably similar, and thus we can interpret deviations from Chond[Y/Ho]∼1.0 to result from soil biogeochemical processes and not source mixing. Between 0.3 and 20ky, the Chond[Y/Ho] ratio of the subsurface soils decreased from 0.96±0.07(2σ) to 0.71±0.05, and then remained unchanged across the rest of the weathering sequence. In contrast, the Chond[Y/Ho] ratio of the surface soils decreased from 0.99±0.07 to 0.76±0.05 at 150ky and then, most likely due to continued dust inputs, increased to 1.04±0.07 in the oldest soils. Analysis of the short-time dissolution experiments revealed preferential release of Y relative to Ho (and also La relative Pr) at intermediate pH where aqueous REY concentrations are governed by proton competition for adsorption sites. Proton-competition-control over REY release is bounded at high pH by the onset of colloidal dispersion—represented by the point of minimum dissolution (p.m.d.) of Al—and at low pH by the soil’s point of zero net charge (p.z.n.c.) and/or when proton-promoted dissolution of REY-containing solids, including Fe-(oxyhydr)oxides, control REY release. Results of our dissolution experiments suggest that complexation of REYs by dissolved organic matter (DOM) does not drive Y–Ho fractionation during pedogenesis, but rather may suppress it. Synthesis of these field and laboratory experiments suggests the Y/Ho ratio decreases early in soil development (<20ky) when weathering rates are high and competitive proton adsorption affects REY fractionation. Given that Fe-(oxyhydr)oxide sorbents exhibit greater affinity for Ho relative to Y, their prevalent neo-formation during incipient pedogenesis likely plays a central role in Y–Ho fractionation in these soils. Persistence of low Chond[Y/Ho] ratios in the subsurface soils even at 4100ky suggests Y–Ho fractionation continues, albeit at a slower rate, as weathering proceeds.

Selected soil properties as indicators of soil water regime in the Cathedral Peak VI catchment of KwaZulu-Natal, South Africa

The morphological features and physicochemical properties of 14 soil profiles, representing the major soil types, were studied in the Cathedral Peak VI catchment of KwaZulu-Natal, South Africa. The soils are characterised by a high organic carbon content in the topsoil, red and yellow freely drained subsoils, and some signs of water saturation in the deep subsoil and saprolite. The lack of variability in the morphology of the soils is probably a result of deep weathering of the chemically homogeneous basaltic parent material. Shelving controls the development of return flow on the slopes, feeding into the two prominent wetlands. The freely drained nature of the subsoil horizons are reflected in the red colour and low pH values of these horizons. The iron and manganese redoximorphic features, occurring in the lower horizons, are indicative of periodic short periods of water saturation.

Redistributions of 137Cs and soil components on cultivated hill slopes with hedgerows as conservation measures

137Cs tracing technique combined with soil composition characterization was used to investigate the mechanism and effectiveness of conservation measures for cultivated hill slopes of strongly weathered acidic Acrisol. The results of analysis of 66 soil samples taken across six plots showed much lower losses of 137Cs, soil organic carbon (SOC), and nutrients in the four treatments of alley cropping with hedgerows compared to the two control treatments of bare land and without conservation measures. No-tillage cultivation combined with vetiver grass hedgerows was most effective in securing high levels of 137Cs, SOC, N, P, K, and CEC while reducing considerably the contents of dissolved cations and anions. Within the plots of alley cropping, 137Cs, SOC, nutrients, dissolved ions, and sand were accumulated in the areas immediately upslope of the hedgerows, whereas the clay content and bulk density were highest downslope of the hedgerows. SOC inversely correlates with clay in concurrence with observations for the soils derived from basaltic parent materials, in which clay minerals are predominated by kaolinite. The correlations of 137Cs with dissolved Ca, Mg, and P indicate that in the highly leaching Acrisol 137Cs may partly occur in the soil solution that is susceptible to leaching and loss. The interrelationships among soil components were interpreted as being driven by the redistribution of soil aggregates which were fractionated in situ according to their sizes and specific densities by erosion forces combined with tillage and conservation measures (hedgerows).

Relações solo-paisagem em topossequência de origem basáltica

Variações nos atributos do solo dependem da posição do solo na paisagem e processos de drenagem, erosão e deposição. Este estudo objetivou avaliar os atributos físicos e químicos do solo, em uma topossequência de origem basáltica, na região de Batatais (SP). A área possui relevo aplanado e altitude oscilando entre 740 m e 610 m, em região dominada por basaltos. Foi estabelecido caminhamento de 3.000 m, a partir do espigão da vertente, no seu declive mais suave. As superfícies geomórficas foram identificadas e delimitadas conforme critérios topográficos e estratigráficos, com base em intensas investigações detalhadas de campo. Foram coletadas amostras laterais aos perfis modais representativos das diversas superfícies geomórficas (S.G.) da topossequência (S.G. I = topo; S.G. II = meia encosta e sopé de transporte; S.G. III = ombro e sopé de deposição), totalizando 142 amostras. Além disto, foram abertas trincheiras, nos segmentos de vertente inseridos nas superfícies geomórficas mapeadas. As amostras coletadas foram analisadas quanto à densidade do solo, textura, bases trocáveis (Ca2+, K+ e Mg2+), soma de bases, capacidade de troca catiônica, saturação por bases, pH (água e KCl), SiO2, Al2O3, Fe2O3 (ataque por H2SO4), óxidos de Fe livres extraídos com ditionito-citrato-bicarbonato e Fe mal cristalizado extraído com oxalato de amônio. Os resultados revelaram que os solos oriundos de basalto apresentaram atributos físicos e químicos com comportamento dependente das formas do relevo. Com o uso de técnicas estatísticas multivariadas, foi possível distinguir três diferentes ambientes, que equivalem às três superfícies geomórficas.

Long‐term carbon storage through retention of dissolved aromatic acids by reactive particles in soil

AbstractSoils retain large quantities of carbon, thereby slowing its return to the atmosphere. The mechanisms governing organic carbon sequestration in soil remain poorly understood, yet are integral to understanding soil‐climate feedbacks. We evaluated the biochemistry of dissolved and solid organic carbon in potential source and sink horizons across a chronosequence of volcanic soils in Hawai'i. The soils are derived from similar basaltic parent material on gently sloping volcanic shield surfaces, support the same vegetation assemblage, and yet exhibit strong shifts in soil mineralogy and soil carbon content as a function of volcanic substrate age. Solid‐state13carbon nuclear magnetic resonance spectra indicate that the most persistent mineral‐bound carbon is comprised of partially oxidized aromatic compounds with strong chemical resemblance to dissolved organic matter derived from plant litter. A molecular mixing model indicates that protein, lipid, carbohydrate, and char content decreased whereas oxidized lignin and carboxyl/carbonyl content increased with increasing short‐range order mineral content. When solutions rich in dissolved organic matter were passed through Bw‐horizon mineral cores, aromatic compounds were preferentially sorbed with the greatest retention occurring in horizons containing the greatest amount of short‐range ordered minerals. These minerals are reactive metastable nanocrystals that are most common in volcanic soils, but exist in smaller amounts in nearly all major soil classes. Our results indicate that long‐term carbon storage in short‐range ordered minerals occurs via chemical retention with dissolved aromatic acids derived from plant litter and carried along preferential flow‐paths to deeper B horizons.

Mineral magnetic properties of a weathering sequence of soils derived from basalt in Eastern China

Abstract The magnetic properties and magnetic mineralogy of a weathering sequence of soils developed on basalt parent material from eastern China, were studied by rock magnetism, X-ray diffraction and soil chemical analyses to establish the connection between mineral magnetic properties and pedogenic development in a subtropical region. The magnetic susceptibility of soils formed on basalt varied greatly and did not increase with the degree of pedogenic development. The frequency-dependent susceptibility (χfd) values of soils ranged from 1.0 to 11.1% and increased with the pedogenic development. Highly significant linear relationship was found between the frequency-dependent susceptibility and the Fed content (R2 = 0.683) and Fed/Fet ratio (R2 = 0.780) in soils, indicating that pedogenic SP ferrimagnetic grains were associated with enrichment of the secondary iron oxide minerals in the weathering process of soil. Rock magnetism analysis showed that the major magnetic carriers in the weakly weathered soil profiles are magnetite and/or maghemite, and the highly developed soil profiles are generally enriched in magnetite/maghemite grains of pedogenic origin and the magnetically hard haematite, indicating that the magnetic component was transformed from a ferrimagnetic phase (magnetite) to antiferromagnetic phase (hematite) during pedogenic development. Results indicated that some of the magnetic parameters of soils, in this case χfd, can be useful for pedogenic comparisons and age correlations in the weathering sequence of soil. It is thus suggested that multiparameter rock magnetic investigations represent a more powerful approach for pedogenesis.

Influence of soil fertility on the distribution of tree species in a deciduous forest in the Triângulo Mineiro region of Brazil

Dry semideciduous and deciduous forests occur only on calcium-rich soils and occupy almost 20% of the 200 million ha of the cerrado region of central Brazil. Other savanna physiognomies of woodlands and grasslands, and gallery forests generally occur on acid soils with low calcium levels. The literature on phytosociological aspects of such cerrado physiognomies is quite abundant whereas there is very little information on deciduous forests. Also lacking is information on soil fertility and its influence on species distribution. The objective of the present study was to study the distribution of native species within a dry deciduous forest in the Araguari river valley, Uberlândia, Minas Gerais as related to soil properties. A 1-ha sampling area, with no apparent difference in physiognomy, was divided into fifty 10 m × 20 m plots arrayed in 10 × 5 grid and all trees with a minimum circumference of 15 cm at 1.30 m height were surveyed. A composite soil sample was collected from 0 to 10 cm depth in each plot and soil pH, organic C and nutrient availability were determined. Cluster analysis based on soil chemical properties showed the existence of two distinct groups of plots. Further field examinations revealed that the forest was situated in an area of transition between mica schist and basalt parent materials, without any apparent difference in the forest physiognomy. The basalt-derived soil in 23 plots had significantly higher availability of Ca (47.0 cmol(+) kg−1 soil), Mg (2.59), and K (0.96) than the mica schist derived soil (Ca—18.4, Mg—1.29, and K—0.66) in the remaining 27 plots, though both soils would be classified as eutrophic. A total of 59 species belonging to 27 families were encountered in the area as a whole, of which 36 were common to both soils. In total, 16 species occurred exclusively on the mica schist soil and 7 on the basaltic soil. Myracrodruon urundeuva Allem. (Anacardiaceae) and Tabebuia roseo-alba (Ridl.) Sandwith (Bignoniaceae) were species with high importance values in the forest as a whole. Though there was no significant difference in the diversity index between the two soils, the importance values of these species was larger in the basalt-derived soil with higher nutrient availability.

Distribution of Total and DTPA‐Extractable Zinc, Copper, Manganese, and Iron in Vertisols of India

Vertisols of India are developed over isohyets of 600 to 1500 mm, and their chemical cycles are set by drainage, landforms, and particle size, which results in variable pedogenic development within the otherwise homogeneous soils. The purpose of this study was to identify pedogenic processes in the distribution of total and DTPA‐extractable zinc (Zn), copper (Cu), manganese (Mn), and iron (Fe). The soils are developed over basaltic parent material of Cretaceous age. Soil samples were drawn from genetic horizons of the 13 benchmark profiles and analyzed by using HF–HClO4 acid for total and DTPA extraction. Correlation coefficients were calculated taking all samples together. The total concentration varied from 24 to 102 mg kg−1 for Zn, 21 to 148 mg kg−1 for Cu, 387 to 1396 mg kg−1 for Mn, and 2.36 to 9.50% for Fe. Their variability was proisotropic and haplodized, and their concentrations increased with advancing isohyets. Within the isohyets, hindrance in drainage caused retention of Zn and Cu but loss of Fe. The piedmont soils had more Fe than alluvium soils. The spatial distribution of total contents of Zn, Cu, and Fe was influenced by the pedogenic processes associated with Haplusterts but not with provenance materials. Surface concentrations of the elements by biotic lifting and/or harvest removal were negated by the pedoturbation that further contributed to the irregular distribution of the elements in the profiles. Total Zn and total Cu had positive coefficients of correlations with coarse clay, whereas total Mn and total Fe were positively correlated with fine clay. The DTPA‐extractable forms were functions of isohyets and drainage and showed association with organic carbon content and coarse clay.

An evaluation of the Olsen test as a measure of plant-available phosphorus in grassland soils derived from basalt parent material

Abstract. Anecdotal and circumstantial evidence have suggested that the Olsen test underestimates plant-available phosphorus (P) in basaltic soils in Northern Ireland. Therefore, the ability of this test to predict plant-available P in basaltic (and non-basaltic) soils was investigated by regressing Olsen-P data against herbage P indices calculated from plant tissue test data using the diagnosis and recommendation integrated system. The average Olsen-P concentration for a range of fields situated on basaltic soils was considerably lower than the average Olsen-P concentration for a range of fields situated on non-basaltic soils, and yet mean sward P status, as given by the herbage P indices, was similar for both groups of fields. Herbage P indices were also much better correlated with Olsen-P measurements in non-basaltic soils than in basaltic soils. Furthermore, at low Olsen-P values (≶9mgPL−1) some swards on basaltic soils were genuinely deficient in P, while others were sufficient or even in surplus for this nutrient. The results confirm that Olsen-P is inadequate as a predictor of plant-available P in basaltic soils. It is concluded that an alternative soil test is needed to provide a reliable assessment of plant-available P in basaltic soils, to prevent overuse of fertilizer and manure P and to minimize the amounts of P entering local watercourses.