Udic Moisture Regime Research Articles

Phosphorus adsorption prediction through Decision Tree Algorithm under different topographic conditions in sugarcane fields

Phosphorus availability in the soil is essential for plant growth. In Brazil, phosphorous is poorly available in the soil due to its high adsorption in the form of phosphates. This phenomenon requires much studying to assist in the nutritional management of crops. To that end, predicting the fraction of adsorbed phosphorus can be approximated by using attributes that influence soil formation and structure. This study aimed to predict soil phosphorus adsorption based on soil attributes in sugarcane crops with different relief types using data mining techniques. The experiment was carried out in sugarcane agricultural areas, experimental plots with differentiated relief (concave or convex), and identical agricultural practices. The soil was classified as an Alfisol with udic moisture (Udalf) regime and medium to clayey texture. The dataset constituted a matrix of 4580 observations. The analyzed variables corresponded to the chemical, physical, geophysical, and mineralogical attributes in the 0–0.2 m topsoil. Data analysis was carried out based on a decision tree induction model, with an 85% accuracy rate and a high level of agreement between variables. The decision tree recognized magnetic susceptibility as the attribute with the most significant influence on the prediction of soil phosphorus adsorption, validating the relation among adsorption processes and the magnetic properties of oxide minerals characteristic of Brazilian agricultural regions.

​Effect of Different Crop Sequences on Soil Nutrient Status, Nutrient Uptake and Crop Yield in Western Himalayas of India

Background: The field experiment was conducted during 2018-19 experimental farm of Department of Agronomy, College of Agriculture, CSK HPKV, Palampur (H.P.), India. The experiment comprised of ten treatments (maize-wheat, maize-wheat + gobhi sarson, dhaincha-cabbage-frenchbean, sunhemp-vegetable pea-frenchbean, maize + soybean chickpea + linseed, rice-wheat + gram, hybrid sorghum + hybrid bajra-oats + sarson (hybrid), hybrid sorghum + hybrid bajra-ryegrass + berseem, babycorn-broccoli-frenchbean and okra-turnip-tomato) which was laid out in randomized block design with three replications. Methods: The present investigation was conducted during October 2018-October 2019 (Kharif and Rabi seasons) at an elevation of 1100 m amsl at a latitude of 32°04’N and longitude of 76°35’ E at Bhadiarkar Experimental Farm, Department of Agronomy, CSK HPKV, Palampur, Kangra district of Himachal Pradesh, India. The soil of the experimental area falls in the order of Alfisols with Paleudalf as the great group as per the Udic Moisture Regime. During kharif and rabi season the crop varieties were applied with the recommended dose of N, P2O5 and K2O (kg ha-1). The source of nitrogen (N), phosphorus (P) and potassium (K) were urea, single super phosphate and muriate of potash. Result: In terms of food for human consumption, highest yield was obtained under the okra-turnip-tomato cropping sequence followed by dhaincha-cabbage-frenchbean and sunhemp-vegetable pea-frenchbean. While in terms of fodder yield, highest was obtained under hybrid sorghum + hybrid bajra-oats + sarson (hybrid) cropping sequence followed by hybrid sorghum + hybrid bajra-ryegrass + berseem. Highest maize grain equivalent yield was obtained with okra-turnip-tomato crop sequence. All other treatments remained superior in comparison to the maize-wheat crop sequence. Maize + soybean-chickpea + linseed emerged to be the best treatment with the highest benefit cost ratio. The treatment comprising okra-turnip-tomato sequence also proved to be the second-best treatment followed by hybrid sorghum + hybrid bajra-oats + sarson (hybrid). Sunhemp-vegetable pea-frenchbean recorded the highest uptake of the available nutrients from soil which was followed by babycorn-broccoli-frenchbean. There was net loss of available nutrients although the loss was less in the sequences with multiple crops during the year. The treatments had no significant effect on the pH and organic carbon content of the soil.

Soil Moisture Behavior in Relation to Topography and Land Use for Two Andean Colombian Catchments

Understanding the soil moisture behavior in relation to land use in tropical Andean mountain catchments is essential for comprehending water fluxes, ecohydrological relations and hydrological dynamics in this understudied ecosystem. Soils are a key factor of these ecosystems, especially in reference to water level regulation and anthropogenic activities that can alter the interactions, and generate physical, chemical and biological imbalances. In this study, we investigated the relationship between precipitation, soil water content (SWC) and the flow at different pedon scales, and hillslope and microcatchment scales subjected to different land uses. The results showed the relation between the soils uses, topographical conditions and soil moisture at the microcatchment scale. At the pedon scale, soil moisture is higher and with a low variability in depth; high soil moisture content throughout the study period was registered in forest > pasture > coffee agroforestry systems. The topographic wetness index (TWI), despite its adjusted interpretation of the behavior of humidity at the microcatchment scale, is a poor predictor of the behavior of soil humidity at the pedon scale. Pedon water content has a close relation with the precipitation behavior, especially in prolonged dry and humid periods. The soils studied tend to present udic moisture regimes with a dry period of approximately 67 accumulative days per year. The mean flow behavior responds to precipitation and soil moisture behavior at a monthly scale. Understanding the consequences of the land cover changes in relation to soil water behavior, as well as how soil water interacts with the different components of the hydric balance at different scales, allows an understanding of the complex interactions in natural microcatchments under different land use systems.

Genesis of an atypical Podzol in the Iberian Range: micromorphological characterization

A podzol has been described in the Iberian Range (Moncayo Natural Park), which may represent the southernmost example in Europe. The fact that it occurs at the podzol distribution limit makes its morphology atypical. The aim of this work is to identify the components and formation processes of the soil, and to determine if the processes are active or paleo-processes by a micromorphological approach. The study podzol is located in the top of a northern hillside (30% of slope), at 1600 m altitude on quartzitic sandstones, under Scots pine (<em>Pinus sylvestris</em>) with an udic moisture regime and a frigid temperature regime. We found opaque, orthic iron oxide nodules at the base of the profile (Bhs1), which is related to a current oxidation-reduction process; silt caps are also observed on the coarse elements, pedofeatures evidencing the cryoturbation process, probably also current processes. In the Bhs2 horizon, coatings and micro-laminated clay infillings are identified that are interspersed with fine silts in the holes. Many of these coatings are fragmented and mixed with the basal mass of the soil, indicating that they are paleofeature, possibly prior to the current podzolization.

Acidification Assessment after Peat Bog Drainage in the Catalan Pyrenees (NE Iberia)

The Pyrenean range (NE Iberian Peninsula) has some favourable lithological and climatic conditions (iron-rich parent materials and udic moisture regimes) for the formation of acid sulfate soils (ASS) that have not been reported on from the region until now. The analyses of a drained peat bog near València d’Àneu revealed a pH (1:2.5) of 3.7. We hypothesize that it contained sulfidic materials that were oxidized during drainage, which could have caused its acidification. The main goal of this study is to understand the characteristics and the potential acidity of these organic soils and the consequences that this could generate in the current environment. In order to do so, several profiles were described and sampled in the field for chemical and micromorphological analyses. The results show that the oxidation of the newly formed pyrite in the soil or pyrite contained in the Cambro–Ordovician parent material was responsible for the low pH and high electrical conductivity (EC). The soils still contain sulfidic materials at present, which could be oxidized in the future, with the consequent risk for water quality. The results will be useful to evaluate the risk of other peats in the Pyrenees becoming acid sulfate soils if drained.

Pedological Characterization and Fertility Assessment of Mbimba Substation Soils Under Coffee Production in Mbozi District, Tanzania

Pedological characterization was carried out on the soils of Mbimba Mbozi, Tanzania. A representative soil profile (TaCRI-P1) was identified, excavated and described using FAO (2006) Guidelines. Four disturbed soil samples and three undisturbed core samples were taken from the profile horizons for Physico-chemical laboratory analysis. The pedon developed under udic moisture and thermic temperature regimes were very deep (> 150 cm), well-drained and had dark brown to black topsoil colour over dark brown to dark reddish subsoil colour. Soil texture ranged from clay loam to clay. Soil pH was rated as very strong acid to medium (4.73 - 5.98) for all horizons. Organic carbon was low to medium; N was very low to low; CEC was medium to high and exchangeable bases ranged from low to high. Bulk densities were high (2.24 - 2.44 g/cc) for topsoil and low (0.33 - 0.91) for subsoil. Soil moisture retention properties indicated that surface horizon (0 - 5 cm) retained more water followed by intermediate (45 - 50 cm) horizon and the subsoil (95 - 100 cm) respectively. According to USDA Soil Taxonomy and World Reference Base for Soil Resources, the pedon at Mbimba was classified as Typic Palehumults and as Haplic Alisols, respectively. These taxa reflected properties that may guide on the use and management of soils. Before lime application, the upper two horizons of the pedon had total nitrogen level ranging between 0.04 - 0.17%, Phosphorus 2.91 - 4.59 mgkg-1, Potassium 2.36 - 1%, Calcium 2.36 - 2.35 cmol(+)kg-1 and Magnesium 0.71 - 1.93 cmol(+)kg-1 which were low to medium. Thus, application of inorganic (N, P, K - rich), Ca+Mg and organic fertilizers is recommended to increase nutrient availability. Use of CaMg(CO3)2 as soil amendment should be taken into consideration to raise soil pH and enhance balanced nutrient availability for coffee growth.

Insight into the source of grapevine water acquisition during key phenological stages using stable isotope analysis

Background and Aims Stable isotope analysis of grapevine water provides insight into seasonal water use trends, soil depth of active water/nutrient uptake, and the role of water in the physiological processes of grapevines. This technique identifies the sources of water utilised and the functional rooting depth for vine water uptake over the growing season to support development of efficient irrigation strategies while managing grape and wine composition. Methods and Results The hydrogen stable isotope ratio (δD) values of vine water identify rain as the principal water source during budburst and flowering/fruitset, and various combinations of rain and groundwater in summer and autumn, with an increasing proportion of groundwater in the mixture, as veraison/ripening continues and fruit maturity is achieved at harvest. The seasonal water use trend demonstrates a variable functional rooting depth for grapevine water acquisition over time, with the shallow roots utilising rain water as a main source in spring and a root system that can reach progressively deeper into the soil profile as the growing season advances. Conclusions Water acquired by grapevines during the 2015 growing season originated from various depths and was derived from a combination of meteorological sources prior to recharging the soil water reservoir. The isotopic composition of grapevine water demonstrates that the functional rooting depth for water uptake is highly variable during the different phenological stages of the grapevines. Significance of the Study The preferential vine water use allows irrigation recommendations to be made/forecasted to maximise water uptake efficiency and water conservation. This study site has an udic moisture regime, potentially providing insensitive isotopic variations due to the evenness of rainfall; thus, the success of this approach suggests that these methods will be highly effective in identifying seasonal patterns in ustic and xeric moisture regimes.

SOIL PROPERTIES OF THE ALLUVIAL PLAIN AND ITS POTENTIAL USE FOR AGRICULTURE IN DONGGALA REGION, CENTRAL SULAWESI

Agricultural lands of Donggala region are extensively distributed in alluvial plain. However, information on soil properties and fertility constraints has not been known in detail. An investigation of soil resources was conducted in September 2003 and December 2004 to characterize surface soil properties of alluvial plain and to evaluate soil fertility constraints. For this study, 55 representative soil profiles consisting of 187 soil samples were selected for physical, chemical, and mineralogical analyses. The soil profiles were classified as soil groups of Ustifluvents, Haplustepts, Eutrudepts, and Endoaquepts. All the soil physical and chemical data were calculated as weighted average based on top 30 cm soil layer analyses. The results showed that soil texture ranged from sandy loam to loam. In ustic moisture regime, the average pH was neutral (7.0-7.2), but in udic moisture regime it was slightly acid (5.5-6.2). In all soil groups, the organic carbon content was very low to low (0.58-1.44%), P retention was very low (3-18%), and soil cation exchange capacity (CEC) was very low to low (9-14 cmol(+) kg-1). In contrast, all the soil groups showed very high content of potential phosphate (81- 118 mg P2O5 100 g-1) and potassium (338-475 mg K2O 100 g-1), but the available phosphate and potassium were 16-47 mg kg-1 P and 0.18-0.35 cmol(+) kg-1, respectively, which were considered to be low to medium range. The very high P2O5 and K2O were probably derived from weathered mica-schist and granite rocks, but low exchangeable K was probably due to K fixation. The sand mineral fraction was composed of relatively high (> 20%) weatherable minerals of acid parent materials, such as orthoclase and sanidine, while the clay mineral was composed of smectite and illite. The low soil-CEC, low organic matter, and exchangeable K contents were the main soil fertility constraints. Therefore, soil management should be directed to organic matter application to increase soil carbon content, CEC, and nutrient availability. Fertilizer recommendation for wetland rice and several upland crops is suggested based on the soil properties.

SOIL PROPERTIES OF THE ALLUVIAL PLAIN AND ITS POTENTIAL USE FOR AGRICULTURE IN DONGGALA REGION, CENTRAL SULAWESI

Agricultural lands of Donggala region are extensively distributed in alluvial plain. However, information on soil properties and fertility constraints has not been known in detail. An investigation of soil resources was conducted in September 2003 and December 2004 to characterize surface soil properties of alluvial plain and to evaluate soil fertility constraints. For this study, 55 representative soil profiles consisting of 187 soil samples were selected for physical, chemical, and mineralogical analyses. The soil profiles were classified as soil groups of Ustifluvents, Haplustepts, Eutrudepts, and Endoaquepts. All the soil physical and chemical data were calculated as weighted average based on top 30 cm soil layer analyses. The results showed that soil texture ranged from sandy loam to loam. In ustic moisture regime, the average pH was neutral (7.0-7.2), but in udic moisture regime it was slightly acid (5.5-6.2). In all soil groups, the organic carbon content was very low to low (0.58-1.44%), P retention was very low (3-18%), and soil cation exchange capacity (CEC) was very low to low (9-14 cmol(+) kg-1). In contrast, all the soil groups showed very high content of potential phosphate (81- 118 mg P2O5 100 g-1) and potassium (338-475 mg K2O 100 g-1), but the available phosphate and potassium were 16-47 mg kg-1 P and 0.18-0.35 cmol(+) kg-1, respectively, which were considered to be low to medium range. The very high P2O5 and K2O were probably derived from weathered mica-schist and granite rocks, but low exchangeable K was probably due to K fixation. The sand mineral fraction was composed of relatively high (> 20%) weatherable minerals of acid parent materials, such as orthoclase and sanidine, while the clay mineral was composed of smectite and illite. The low soil-CEC, low organic matter, and exchangeable K contents were the main soil fertility constraints. Therefore, soil management should be directed to organic matter application to increase soil carbon content, CEC, and nutrient availability. Fertilizer recommendation for wetland rice and several upland crops is suggested based on the soil properties.

Using magnetic susceptibility to discriminate between soil moisture regimes in selected loess and loess-like soils in northern Iran

This study used discriminant analysis to determine the efficacy of magnetic measures for discriminating between four soil moisture regimes in northern Iran. The study area was located on loess deposits and loess-like soils containing similar parent material. Four soil moisture regimes including aridic, xeric, udic, and aquic were selected. A total of 25 soil profiles were drug from each regime and composite soil samples were collected within the moisture control section. A set of magnetic measures including magnetic susceptibility at low (χlf) and high (χhf) frequencies, frequency-dependent magnetic susceptibility (χfd), saturation isothermal remnant magnetization (SIRM), and isothermal remnant magnetization (IRM100mT, IRM 20mT) were measured in the laboratory. Dithionite citrate bicarbonate (Fed) and acid oxalate (Feo) contents of all soil samples were also determined. The lowest and highest χlf and χhf were observed in aquic and udic moisture regimes, respectively. A similar trend was obtained for Fed and Fed–Feo. The significant positive correlation between Fed and SIRM (r=0.60; P<0.01) suggested the formation of stable single domains (SSD) due to pedogenic processes. The results of discriminant analysis indicated that a combination of magnetic measures could successfully discriminate between the selected moisture regimes in the study area (average accuracy=80%). It can thus be concluded that magnetic measures could be applied as a powerful indicator for differentiation of soil moisture regimes in the study area.

A Methodology for Examining Changes in Soil Climate Geography through Time: U.S. Soil Moisture Regimes for the Period 1971–2000

Soil climate is the record of temporal patterns of soil moisture and temperature and is an important component of the structure of U.S. Soil Taxonomy. The U.S. Soil Survey has used the Newhall simulation model (NSM) for estimating soil climate from atmospheric climate records at weather stations since the 1970s. The current soil climate map of the United States was published in 1994 by using NSM runs from selected weather stations along with knowledge‐based hand‐drawn mapping procedures. We developed a revised soil climate mapping methodology using the NSM and digital soil mapping techniques. The new methodology is called grid element Newhall simulation model (GEN), where a coordinate system is used to divide geographic space into a grid, and each element or grid‐cell serves as a reference area for querying and organizing model input and for organizing and displaying model output. The GEN was used to make a soil moisture map of the conterminous United States (GEN‐CONUS). The GEN‐CONUS and the 1994 map were compared to each other and to two sets of weather station data from years 1961 to 1990 and years 1971 to 2000 (NCDC). Agreement between GEN‐CONUS and the 1994 map was 75.6%. GEN‐CONUS had higher agreement than the 1994 map with NSM output from NCDC data for 1961–1990 and 1971–2000 (k = 0.845 and 0.777). The GEN methodology was also used to generate a map of projected soil climate in the year 2080 for part of the Southern Rocky Mountains, predicting expansion of the Ustic and contraction of the Udic moisture regimes.

Soil development and microbial functional diversity: Proposal for a methodological approach

The aim of the work was to propose a new methodological approach that relates soil microbial functional diversity to soil development under different moisture regimes. As soil evolution proceeds through an increasing niche separation we expect a link between functional diversity and soil development. Shannon's (H') and Gini (D) diversity indices were calculated using eight enzyme activities (β-cellobiohydrolase, N-acetyl-β-glucosaminidase, β-glucosidase, α-glucosidase, acid phosphatase, arylsulfatase, xylosidase and butyrate esterase) in order to assess functional diversity at different scales, from soil horizons (α-diversity) to soil profiles (β-diversity) under different moisture regime (γ-diversity) and belonging to different taxonomic levels. In addition, the ratio of acid phosphatase to chitinase was calculated as a potential index of soil development. Eight soil profiles were selected: four in Northwestern Italian Alps or Northern Apennines with Udic soil moisture regimes (Typic Haplocryod, Mollic Haplocryept, Lithic Dystrudept, Lithic Cryorthent) and four in Northeastern Italy where in two cases the water table near the soil surface strongly affects the Ustic soil moisture regime, and intrazonal Aquic regime or Aquic conditions develop (Typic Haplustept, Typic Ustipsamment, Aquic Ustipsamment, Typic Psammaquent). D ranged from 50 to 95%, while the H' ranged from 3 to 2.4 in Lithic Cryorthent and Typic Psammaquent, respectively. Under Udic moisture regime an inverse relationship between soil profile development and the diversity index was observed. However the lowest the diversity in the profile, the highest the variability of the values obtained within horizons in the soil profile suggesting a link between differentiation of soil horizons and biochemical properties. The Aquic conditions interfere in establishing the relationship between soil profile development and the microbial functional diversity since H' and D increased in Typic Psammaquent with respect to Typic Haplustept (H' from 2.4 to 2.6 and D from 52.2 to 60.4). Finally, the phosphatase/chitinase ratio was related to soil development since the lowest values were obtained in the upper horizons of Typic Haplustept, Typic and Aquic Ustipsamment (from 2.0 to 4.0), while the highest values were obtained in deep horizons of Typic Haplocryod and Lithic Dystrudept (e.g. 39.2 in Bs2 and 28.0 in Bw1). In conclusion, microbial functional diversity assessed using Shannon or Gini diversity indices and phosphatase/chitinase ratio measured at different scales from soil horizons to soil profiles under different moisture regime and belonging to different taxonomic levels, may represent a new approach to establish the interrelationship between pedogenetic processes, soil development and soil microbial functions.

Regional Differences in Soil Carbon and Nitrogen Storage as Affected by Land Use and Soil Moisture Regime

Climate, particularly precipitation and to a lesser degree temperature fluctuations, and land use have often been shown to affect soil organic matter (SOM), carbon (C), and nitrogen (N) storage and cycling. Soil moisture regime has been suggested as a potentially important factor in determining soil organic C (SOC) content. However, few studies have specifically investigated soil moisture regime effects on SOM, SOC, or N storage or sequestration. The objective of this study was to evaluate potential regional differences in the effects of land use and soil moisture regime on changes in near-surface SOM, SOC, and total N (TN) contents and C:N ratio during a 6-year period in a silt-loam soil. Soil bulk density, SOM, and SOC, and TN changes during a 6-year period were measured on replicate samples collected from the top 10 cm in udic and aquic soil moisture regimes representing both managed agriculture and native grassland in the Ozark Highlands region of northwest Arkansas and in the Grand Prairie region of east central Arkansas. All treatment factors examined affected soil bulk density over time. Soil OM and SOC storage were affected by region, land use, and soil moisture regime, but SOM and SOC sequestration were unaffected by soil moisture regime. However, TN content increased by 0.03 kg m−2 over time in the aquic moisture regime in the Ozark Highlands and decreased by 0.03 kg m−2 in the Grand Prairie. Total N content also increased over time in the udic moisture regime by 0.03 kg m−2 under native prairie and decreased by 0.03 kg m−2 under agricultural land use. It is clear that the average degree of wetness a soil experiences, as indicated by soil taxonomy's soil moisture regime, directly affects N storage, cycling, and sequestration, and indirectly affects SOM and SOC cycling through effects on the soil C:N ratio. Soil moisture regime differences that may exist among sites and/or treatments should be at least examined and accounted for when necessary in future studies.

Characterization of Placic Horizons in Ironstone Soils of Louisiana, USA

Placic horizons, defined as thin, wavy, hardened layers of iron and organic matter, are rare within the United States, occurring only in Washington, Alaska, and Hawaii. While ironstone is common in many soils of the southeastern United States, it is not known to contain appreciable organic matter. As a pilot study evaluating the justification for a larger study on ironstone in Louisiana, a 40 m lateral exposure with suspected placic horizons was evaluated in Vernon Parish, Louisiana. Results of laboratory analysis show elevated levels of iron and organic matter in the suspect horizons that meet the criteria of placic horizons as defined by the Soil Survey Staff. Based on the results of this study, additional evaluation of multiple pedons with similar features is warranted. Should additional pedons demonstrate similar properties, a new great group of ‘Petrudepts’ would be needed to describe both the placic horizons in the pedon and the udic moisture regime in which they occur.

Clay accumulation and argillic-horizon development as influenced by aeolian deposition vs. local parent material on quartzite and limestone-derived alluvial fans

Where precipitation is ample (udic moisture regimes) and evidence of illuviation clear, argillic-horizon genesis is often easily understood. In drier climates (aridic to ustic), argillic horizons are often interpreted as relict features of the Pleistocene. However, in high montane, western landscapes where climate falls in between these two extremes, the role of aeolian clay inputs vs. in-situ weathering contributing to clay formation is of debate. Two mollisols, one developed in quartzite alluvium (Charkiln series — 3 pedons) and one in limestone alluvium (Troughspring series — one pedon) were examined to determine whether atmospheric dust or local geologies contribute to their development, and whether Bt horizons in both pedons were argillic horizons. We hypothesize that both soils have argillic horizons and that clays are derived from site parent materials. Thin-section specimens of Bt horizons, and sand and silt fraction grains were prepared and examined using a petrographic microscope. Regional dust XRD mineralogic data were compared to XRD rock fragment and soil mineralogic data. Clay films, while seen in all field pedons, were very few and faint in the Troughspring series. Illuviation of clays was evident in thin sections of the Charkiln pedons but not the Troughspring pedon. In the Charkiln series, illuviation is observed as clay-depleted A horizons, clay-accumulating B horizons, clay bridging, clay films on grains and in channels. In the Troughspring pedon, clay-depleted A horizons and clay-accumulating B horizons, very few clay films on grains and some pressure features in packing voids are seen, but grain bridging and coatings on channels are not observed. While local geologies influence soil mineralogy in both series, aeolian dust deposition is as significant and its affect is further enhanced by organic-acid weathering from an overlying pinyon-juniper woodland and the current ustic climate regime. While evidence of an argillic horizon is seen in the Charkiln series, excess Ca in soils is believed to be inhibiting illuviation in the Troughspring series and thus preventing argillic-horizon development.

Properties of kaolins in red Oxisols and red Ultisols in Thailand

Purified samples of kaolin group minerals [kaolins] from red Oxisols and red Ultisols from 14 sites on diverse parent materials and under various climatic conditions in Thailand were characterized using analytical transmission electron microscopy, X-ray powder diffraction and chemical analysis. The kaolins show a variety of crystal morphologies including euhedral hexagonal to subhedral platy crystals, tubes and partly rolled tubes. Tubes and partly rolled tubes occur in soils under both udic and ustic moisture regimes (i.e. Rhodic Kandiudox, Typic Kandiudox, Typic Kandiudults, Rhodic Kandiustox). The lowest kaolin HB crystallinity index (3.3–5.3) and smallest size (9–11 nm) are for kaolins consisting of anhedral plates, tubes and partly rolled tubes in a soil on basalt under very high rainfall. This kaolin has the highest specific surface area (SSA) (35–64 m 2 g − 1 ), cation exchange capacity (CEC) (16–23 cmol kg − 1 ) and Fe 2O 3 content (1.99–3.62%). The trend of increasing kaolin crystal size with associated decreasing CEC and SSA in these soils is in the sequence red Oxisols on limestone under ustic moisture regime < red Ultisols on old alluvium < red Oxisols on basalt under ustic moisture regime < red Oxisols on limestone under udic moisture regime < red Oxisols on limestone under udic moisture regime < red Ultisols on sedimentary rock under udic moisture regime.

Allophane, aluminum, and organic matter accumulation across a bioclimatic sequence of volcanic ash soils of Argentina

An investigation was conducted to study Al fractions, organic matter accumulation, and their effects on physicochemical properties in soils derived from volcanic ash at the Andinopatagonian region in SW Neuquén, Argentina. Five sites were selected in a climatic biosequence, ranging from Nothofagus forest with a udic soil moisture regime at the footslope of the Andes mountain range to grass-shrub steppe with a xeric soil moisture regime in the hills and plains. The morphological characteristics showed young pedons, containing andic, mollic, and cambic horizons. A change from low bulk density from <0.82 Mg m −3 in Andisols under a udic regime to medium density values of ∼1.1 Mg m −3 in Xerands and Xerolls was observed. This was related to a lower rate of weathering probably coinciding with a lower content of allophane and higher clay crystallization and to a decrease in total soil organic carbon (C org). The rate of soil weathering was estimated from acid oxalate extractable Al, which together with C org significantly explained the bulk density variation ( R 2=0.7091, p<0.00002). Soil acidity varied from moderately and strongly acidic in Andisols with a udic soil moisture regime to slightly acid and almost neutral in Xerands and Xerolls. The higher base concentration and low soil acidity in Xerolls were attributed to less leaching, due to lower mean annual precipitation. However, pH NaF and C org were the variables which significantly explained the pH water variation ( R 2=0.7806, p<0.0000). This showed that soil acidity was closely related to Al activity and organic matter content, rather than to base content. The lower C/N ratios, in the surface horizons of the Xerands and Xerolls versus the Andisols with a udic soil moisture regime, suggested that the rate of mineralization was faster under warmer conditions with xeric moisture regime than with udic moisture regime. There was also a remarkable difference in the humic C/fulvic C ratio in A-horizons, which may reflect the input of vegetation residues indicating a sensible contribution of the cover of grass-shrub steppe to the formation of humic substances. The acid oxalate extractable Si and Al values reflected a low rate of weathering, which decreased when mean annual precipitation decreased and a xeric soil moisture developed being also higher under Nothofagus forest than under grass-shrub steppe, which reflects the possible effect of the mean annual precipitation gradient (2000–700 mm) and vegetation types on soil weathering. The differences in type and quantity of organic matter input, with a higher organic matter content and lower humic C/fulvic C ratio under Nothofagus, indicate a more reactive organic matter which may be somewhat responsible for the weathering degree. No significant relationship between acid extractable Al and C org was found suggesting that organically bound Al is not dominant. The detection of higher allophane estimations in soils with the highest C org levels, may indicate that the anti-allophanic hypothesis probably does not apply to these soils.

Mineral neoformation in pore spaces during alteration and weathering of andesitic rocks in humid tropical Indonesia

The morphology, chemistry, and mineralogy of minerals newly formed in voids—products of weathering of andesitic rocks—were studied using optical and submicroscopic techniques on thin sections, combined with scanning electron microscopy (SEM), energy dispersion X-ray analysis (EDXRA), and X-ray diffraction analysis on subsamples. Samples were taken from the core, the outer core, and the soft outer layers of weathered andesitic boulders in the Cigudeg area, West Java, about 75 km south of Jakarta, Indonesia, with udic moisture and isohyperthermic temperature regime. The neoformed minerals observed in planar voids and cavities comprise 1:1 phyllosilicates, goethite, and gibbsite, and juxtaposed coatings of halloysite, mixed layer phyllosilicates, goethite, and gibbsite. The mineral sequences observed confirm former studies on the groundmass of the boulder: in the first weathering layer, an absolute accumulation of gibbsite takes place; further away from the core, the gibbsite is redissolved, and replaced by illuvial phyllosilicate clay. The possibility of inheritance of the 2:1 layer silicates from a hydrothermal alteration is discussed. The sharp boundaries in the juxtaposed coatings point to a stepwise, sequential—rather than a gradual—evolution of the microenvironment.

Soil Moisture Regime Changes in Tephra‐Mulched Soils

Large areas of the Canarian archipelago are catalogued as aridic according to U.S. soil taxonomy. A traditional system of cultivation, based on the application of a mulch layer of tephra, is widely practiced. The objective of this work is to compare the classification of soils with and without mulch using U. S. soil taxonomy, and illustrate the problems in estimating the soil moisture regime on the basis of meteorological data. In this study the moisture regime of a natural soil and an adjacent soil mulched with a 12‐cm layer of basaltic tephra was characterized on the basis of gravimetric moisture measurements, taken over a period of &gt;1 yr, at 10‐cm intervals to a depth of 1 m. The moisture regime of the soil was also estimated using meteorological data. Results obtained for the natural, nonmulched soil using measured values and those estimated from atmospheric data are very similar, and both indicate an aridic soil moisture regime. The difference with the soil covered with basaltic tephra is noteworthy. In the latter case, the soil remained moist throughout the year, representing a udic moisture regime. This noteworthy difference is reflected in the classification of the soils: Aridisols in the first case and Inceptisols in the second. A proposal is made to include mulching with tephra as a cultural practice along with irrigation and fallowing in the definition of the classes of soil moisture regimes in U.S. soil taxonomy. This would prevent the practice of mulching with tephra from changing the soil order placement in U.S. soil taxonomy.

PEDOGENIC AND MORPHOLOGICAL CHARACTERISTICS OF MARL-DERIVED SOILS IN THE RIDGE AND VALLEY PROVINCE, EASTERN UNITED STATES

While soils with free carbonates are rare in udic moisture regime, calcareous soils (10 to 99% CaCO 3 ) are found along drainageways in the Ridge and Valley Region (in the Great Limestone Valley portion) of the Eastern United States. These soils have developed from biogenically derived marl deposited in freshwater, ponded, settings during the late Pleistocene to the early Holocene Epochs. Pedogenesis in these marls has resulted in calcareous soils anomalous for this region; most of the adjacent upland limestone-derived soils are slightly acid and kaolinitic. Our study investigated the pedological attributes of these soils. Six transects, including four sampling pits, were examined in marl-derived map units in the Hagerstown Valley portion of the Great Limestone Valley, and chemical and physical characterization of the soils was conducted. Micro- and macromorphological investigation of carbonate forms indicated that calcic horizons were present in these soils, which is not typical in humid regions. Most of these soils possessed mollic epipedons and buried A horizons and were Mollisols. Common limnic materials in the solum were inherited from the parent material. The recent adoption of the Lma horizon designation for layers containing marl is appropriate for some of the horizons contained in these marl-derived soils.