Similar Parent Material Research Articles

Geochemistry of Soils and Streams on Surfaces of Varying Ages in Arctic Alaska

ABSTRACTClimate change may bring about geochemical changes in arctic regions as a result of increasing thaw depth. In order to better understand current watershed geochemistry and mineral weathering and provide a basis for predicting the geochemical effects of active-layer thickness increase, we examined elemental chemistry and 87Sr/86Sr of streams and sequential and total digests of soils, permafrost, and soil parent materials from seven glacial deposit surfaces of varying geomorphic ages in arctic Alaska in the vicinity of the Philip Smith Mountains quadrangle (69°N, 150°W). We found overall greater exchangeable K concentrations, exchangeable and acid digestible P and Ca concentrations, acid digestible and total Ca/Na and Ca/Sr, and lower acid digestible 87Sr/86Sr in permafrost than in active-layer mineral soil. Of the surfaces with similar parent material, stream and soil data suggest that weathering has progressively depleted calcium carbonate in the active layer with increasing surface age. Our results suggest that increasing thaw depth will lead to increasing carbonate and Ca supply to soils and streams, as well as spatially variable increases in P and K supply. Geochemical differences between active-layer soil and permafrost suggest the possibility of using stream geochemistry to detect changes in active-layer thickness in watersheds.

Halloysite versus gibbsite: Silicon cycling as a pedogenetic process in two lowland neotropical rain forest soils of La Selva, Costa Rica

Halloysite and gibbsite, although known to require quite different conditions for their formation, commonly occur together in the same horizon in oxisols derived from andesitic parent materials in tropical Costa Rica. We selected two soils of similar parent material, but of different ages and soil moisture regimes to identify possible clues to the coexistence of these two minerals. We employed selective dissolution procedures, X-ray fluorescence analysis and X-ray diffraction on field moist and air dry bulk soil samples to investigate how mineralogy changes with depth. We further separated the size fraction < 2 μm by means of sedimentation after organic matter and iron oxide removal to obtain more specific information on the phyllosilicate mineralogy of the clay size fraction. We found both soils to be depleted of primary minerals and pedogenesis to have progressed to advanced weathering stages particularly in the subsoils. Gibbsite XRD signal intensities were linearly and significantly related to weathering indices, corroborating the residual nature of gibbsite as an endproduct of weathering processes. The Si-bearing quartz and kaolinite-group minerals were enriched in the topsoils, indicating (i) their independence from a primary mineral Si source and (ii) the existence of a mechanism capable of protecting them against the continuous tropical weathering pressure. As we found no indications for retrospective additions of soil material through mass movement or aeolian additions, we believe a vegetation dependent, biological pumping mechanism to be the most plausible explanation for the presence of silica bearing minerals in the La Selva topsoils. The vertical distribution of 1.0 nm halloysite and its accumulation in the lower reaches of the wetter alluvial soil suggest that this metastable mineral forms as a result of Si enrichment where the residence time of the pore water is long enough to allow for Si concentrations to exceed the halloysite precipitation threshold. Taken together, our evidence indicates gibbsite in the La Selva soils to be the endproduct of intense tropical weathering, while the presence of hydrated halloysite seems to have mainly kinetic reasons and is most probably coupled to the contemporary soil moisture regime.

Roxolany and Novaya Etuliya—key sections in the western Black Sea loess area: Magnetostratigraphy, rock magnetism, and paleopedology

Loess/paleosol sequences in the western Black sea area at Roxolany (48 m thick) and Novaya Etuliya (30 m thick) were studied using paleo- and rock-magnetic methods in conjunction with micromorphology and Mössbauer investigations. Although seemingly complete, the sites show variability in the type and number of loess/paleosol cycles, and inconsistency of the Matuyama/Brunhes boundary (MBB) stratigraphic position. At Roxolany, nine pedocomplexes (PK) and several incipient paleosols, alternating with thick loesses, were observed with the MBB being located between PK 6 and PK 7. At Novaya Etuliya, 13 PKs occur upon terrace XII with Khapry fauna and with the MBB in the upper part of PK 7 and the Jaramillo subchron within the lower part of PK 8. The depth functions of rock magnetic properties, organic carbon content C org, both for bulk samples and for clay extracts, along with micromorphology and Mössbauer spectra, allowed objective identification of individual soils within PKs, and maximizing the resolution of paleopedological reconstructions of global climatic stages. The Mössbauer studies demonstrate that paleosols are basically enriched in ferric montmorillonite. Oxidized magnetite, ultrafine iron hydroxides and hematite are intimately associated with clay minerals. In contrast, Fe-compounds in loess consist mainly of ferrous silicates. These data indicate that the paleosol magnetism is basically of bio-chemogenic origin and is related to pedogenic transformation of Fe-compounds in a changing environment, while loess magnetism is primarily detrital. Pedogenic magnetically “soft” and partly oxidized magnetite may also originate during or even after burial. This ensuing transformation of Fe minerals in paleosols seems to be crucial for the understanding of the timing of natural remanent magnetization (NRM) in subaerial sediments. Given that paleosols formed on the similar parent material (loess), their typological variability seems to depend on climate and/or chronology. Hence, the different paleosol types from Roxolany and Novaya Etuliya provide key information for intra- and inter-regional correlation of loess/soil sequences, and represent valid paleoclimatic proxies.

Soils and Geomorphology in the Oregon Cascades: A Comparative Study of Illinoian-Aged and Wisconsin-Aged Moraines

Catena approaches to soil chronosequence studies in the Oregon Cascades are lacking in the literature. Here we compare pedogenesis with slope position on two different aged moraines. The younger Suttle Lake moraine (11 to 20 ka B.P.) contains a sequence of pyroclastic teprhas overlying glacial till and subsequently a series of buried soils. The older Jack Creek moraine (120 to 200 ka B.P.) is predominantly uniform in its parent material, glacial till. Both moraines show evidence of upslope erosion and down-slope deposition, being more active on the younger Suttle Lake moraine. Major differences in soil properties between the two moraines are associated with texture. Pyroclastic parent material is much coarser, with textures of sand and gravel, while older glacial till parent material typically displays a texture of loamy sand. Percent organic matter is higher in the finer glacial till. Harden's Profile Development Index values (i.e., PDI) were used to compare B-horizons of similar glacial till parent material. The PDI is of limited use in this study due to volcanism and glaciations producing alternating layers of parent material. However, B-horizons of similar parent material did obtain higher values on the older Jack Creek moraine. The index was also useful in identifying a much older buried B-horizon at the toeslope of the Suttle Lake moraine, possibly comparable to that of pre-Bull Lake-aged deposits in the Rocky Mountains. The use of soils as relative age indicators is cautioned for future work in the Oregon Cascades due to the complexity associated with an active volcanic landscape.

Nature and Properties of Some Cultivated Entisols Under Peach Orchards

Entisols have developed from Quaternary deposits in northwestern Turkey under xeric moisture and thermic temperature regimes. The morphological features and physico-chemical properties of ten soil profiles representing the major Entisols under Mediterranean climate in northwestern Turkey were studied. These soils show a similar variation in morphological, physical, and chemical properties as a result of similar parent material, topography, climate, and vegetation. Entisols were developed in the 700 mm precipitation zone. These soils occur in nearly flat areas and are characterized by being dry in summers and moist in winter months. It is believed that present agricultural practices are degrading Entisols in this area.

A comparison of plant and microbial biomarkers in grassland soils from the Prairie Ecozone of Canada

Free and bound lipids and CuO oxidation products from four grassland soils that developed from similar parent materials, vegetation, relief, and time but under different climatic conditions were analyzed using solvent extraction, chemolysis and gas chromatography–mass spectrometry (GC–MS) to assess the stage of soil organic matter (SOM) decomposition. In general, the more northern soils (Black Chernozems) yielded less free and bound lipids and CuO products than those in the southern region (Brown Chernozems). The solvent extracts contained a series of long-chain aliphatic lipids, steroids, and triterpenoids. Most of the free lipids were typical constituents of higher plant waxes while biomarkers for microbes represented minor components. A series of aliphatic lipids and several phenols were detected in the soils after base hydrolysis. The predominant long-chain ω-hydroxyalkanoic and α,ω-alkanedioic acids are typical biomarkers for suberin and indicate a major input of root-biomass to the soils. Cutin-derived short-chain hydroxyacids (C 16, C 18) and phenols originating from suberin and ligno-cellulose were also detected. The CuO oxidation products comprised benzyls, lignin phenols and short-chain diacids and hydroxy acids. The lignin composition with equal proportions of vanillyl, syringyl, and cinnamyl units reflect its origin from non-woody angiosperms. The similar composition of free and bound lipids and lignin degradation products in all soils analyzed is consistent with the same type of overlying vegetation (prairie grasses). Different stages of SOM degradation in the Brown and Black Chernozems are indicated by the extract yields and degradation parameters of lignin and cutin/suberin. Lower yields of recognizable products of SOM biodegradation and parameters indicating a higher stage of degradation while exhibiting higher C contents were observed in the Black Chernozems. The results suggest that the plant-derived biomolecules in the Black Chernozems are altered into less biodegradable structures (“humification”) and are accumulated in the SOM. The observations are in accordance with the formation of the soils in this climosequence and imply that there are large reserves of recalcitrant components in the northern part of the Prairie Ecozone.

Average variograms to guide soil sampling

To manage land in a site-specific way for agriculture requires detailed maps of the variation in the soil properties of interest. To predict accurately for mapping, the interval at which the soil is sampled should relate to the scale of spatial variation. A variogram can be used to guide sampling in two ways. A sampling interval of less than half the range of spatial dependence can be used, or the variogram can be used with the kriging equations to determine an optimal sampling interval to achieve a given tolerable error. A variogram might not be available for the site, but if the variograms of several soil properties were available on a similar parent material and or particular topographic positions an average variogram could be calculated from these. Averages of the variogram ranges and standardized average variograms from four different parent materials in southern England were used to suggest suitable sampling intervals for future surveys in similar pedological settings based on half the variogram range. The standardized average variograms were also used to determine optimal sampling intervals using the kriging equations. Similar sampling intervals were suggested by each method and the maps of predictions based on data at different grid spacings were evaluated for the different parent materials. Variograms of loss on ignition (LOI) taken from the literature for other sites in southern England with similar parent materials had ranges close to the average for a given parent material showing the possible wider application of such averages to guide sampling.

Soil Phosphorus Fractionation and Phosphorus-Use Efficiency of a Bornean Tropical Montane Rain Forest During Soil Aging With Podozolization

We compared phosphorus (P) dynamics and plant productivity in two montane tropical rain forests (Mount Kinabalu, Borneo) that derived from similar parent materials (largely sedimentary rocks) and had similar climates but differed in terms of soil age. The younger site originated from Quaternary colluvial deposits, whereas the older site had Tertiary-age material. The older site had a distinctive spodic horizon, reduced levels of labile inorganic soil P, higher concentrations of recalcitrant organic soil P, and lower rates of net soil N mineralization. P fertilization led to soil nitrogen (N) immobilization in the P-deficient soil, indicating that soil N mineralization was limited by P at the P-deficient older site. Mean foliar nutrient concentration (on both a weight and an area basis) was similar at the two sites for all elements except P, which was lower at the older site. Aboveground net primary production (ANPP) was lower at the older site than at the younger one; this difference could be explained by the reduced availability of P and N (as down-regulated by P) at the older site. The relatively ample allocation of P and N to leaves, despite the reduced availability at the P-deficient old site, was attributable to its high resorption efficiency. High resorption resulted in lower concentrations of elements in leaf litter—that is, less decomposable low-quality litter. On the other hand, the concentration of leaf litter lignin was considerably lower at the older site; this appeared to be a de facto adaptive mechanism to avoid retarding litter decomposition.

Effect of land degradation on soil microbial biomass in a hilly area of south Sumatra, Indonesia

We investigated the impact of land-use changes on the soil biomass at several soil sites in Indonesia under different types of land-use (primary forest, secondary forest, coffee plantation, traditional orchard, and deforested area), located within a small geographical area with similar parent material and climatic conditions. Various parameters of soil microbial biomass (biomass C, biomass N, content of anthrone-reactive carbohydrate carbon, and soil ergosterol content) were examined. Our results suggested that the removal of the natural plant cover did not cause any appreciable decrease in the amount of microbial biomass; on the contrary it led to a short-time increase in the amount of microbial biomass which may be due to the availability of readily decomposable dead roots and higher sensitivity to the decomposition of residual litter in recently deforested soils. However, the amount of microbial biomass tended to decrease in proportion to the duration of the land history in coffee plantation soils. This may be ascribed to the effect of the loss of available substrates associated with soil erosion in the long term. Lower ergosterol contents in recently deforested areas reflected a reduction in the amount of fungal biomass which may be due to the destruction of the hyphal network by the slash and burn practice. On the other hand, the higher soil ergosterol content at the sites under bush regrowth indicated that microbial biomass was able to recover rapidly with the occurrence of a new plant cover.

Air–surface exchange of mercury in natural and anthropogenically impacted landscapes in Atlantic Canada

Understanding the relative importance of various sources of mercury within ecosystems and their subsequent impact on biota requires a thorough understanding of the biogeochemical cycling of mercury. An important component of the biogeochemical mercury cycle involves the exchange of gas-phase mercury between the atmosphere and various landscape surfaces. This study examines air–surface exchange (flux) of gaseous elemental mercury in selected undisturbed and anthropogenically impacted aquatic and terrestrial landscape settings. The objective of this study was to quantify air–surface mercury exchange rates in these contrasting landscape settings, to put constraints on these rates and provide insight into physical processes controlling mercury flux. Mean daily mercury flux was typically low over natural forest soils varying from −0.4 (net deposition) to 2.2 ng m −2 h −1 (net evasion). Minimum and maximum flux rates measured at these sites over the diurnal cycle ranged from a minimum of −1.3 to a maximum of 5.7 ng m −2 h −1 . Low flux rates from forest soils was partially due to poor light penetration through the forest canopy. Average daily mercury flux over undisturbed glacial till soil at an open field site with full sun exposure was also low (0.9 ng m −2 h −1 ) compared to the same soil mixed over a depth of 2 m (8.0 ng m −2 h −1 ). Mean daily mercury flux rates measured over pristine freshwater lake surfaces were also low (0.7–6.5 ng m −2 h −1 ), although the overall range in flux varied more widely (−0.3 to 44 ng m −2 h −1 ). Total mercury concentrations in marine water at a moderately polluted coastal harbour site (mean c. 0.8 ng l −1 ) and mean daily mercury flux rates over salt water (0.7 ng m −2 h −1 ) were similar to those measured over freshwater lakes. The highest daily average and diurnal range in mercury flux rates were measured at two abandoned gold mine tailings sites (130 and 237 ng m −2 h −1 ). The abandoned mine sites comprised tailings high in mercury content due to the past use of the mercury amalgamation process in gold extraction from the ore. Flux rates from tailings were two orders of magnitude higher than those observed over undisturbed native soils of similar parent material. Higher flux rates at the mine tailings sites were accompanied by ambient air concentrations 5–10 times background levels at 20 cm above the tailings. Mercury flux from vegetation has not been widely considered. A preliminary study of mercury flux from a white pine tree ( Pinus strobus ) indicated that actively growing trees might play a role in the atmospheric mercury cycle.

The influence of mineralogy on weathering rates and processes in an acid-sensitive granitic catchment

Weathering in an upland catchment on granitic parent material has been studied by chemical and mineralogical analyses of soils. Long-term weathering rates for base cations, calculated from chemical analyses of the mineral horizons from soil profiles using Zr as an internal, immobile, index element, are among the smallest recorded for Scottish soils (1.7–3.1 meq m−2 a−1), indicating that these soils are susceptible to acid deposition. Sodium is the base cation lost to the greatest extent from the soils, due to weathering of plagioclase feldspar, mainly in the coarse size-fractions. Calcium is lost not only from plagioclase feldspar, but also from hornblende, grains of which show dissolution etch pits and denticulate surface features when examined by scanning electron microscopy. Weathering of hornblende, present in basic inclusions in the granite, is a significant weathering process in these soils. A range of values for 87Sr/86Sr ratios in stream-waters confirms the spatial variability of the material supplying Ca to the streams. The current weathering rate, calculated from input–output budgets to be 28.9 meq m−2 a−1, is much greater than the long-term weathering rate, but small compared to other catchments on similar parent material.

Solubility and Potential Mobility of Heavy Metals in Two Contaminated Urban Soils from Stockholm, Sweden

The solubility and potential mobility of heavy metals (Cd, Cu,Hg, Pb and Zn) in two urban soils were studied by sequential andleaching extractions (rainwater). Compared to rural (arable) soils on similar parent material, the urban soils were highlycontaminated with Hg and Pb and to a lesser extent also with Cd,Cu and Zn. Metal concentrations in rainwater leachates were related to sequential extractions and metal levels reported fromStockholm groundwater. Cadmium and Zn in the soils were mainly recovered in easily extractable fractions, whereas Cu and Pb were complex bound. Concentrations of Pb in the residual fractionwere between two- and eightfold those in arable soils, indicatingthat the sequential extraction scheme did not reflect the solidphases affected by anthropogenic inputs. Cadmium and Zn conc. inthe rainwater leachates were within the range detected in Stockholm groundwater, while Cu and Pb conc. were higher, whichsuggests that Cu and Pb released from the surface soil were immobilised in deeper soil layers. In a soil highly contaminatedwith Hg, the Hg conc. in the leachate was above the median concentration, but still 50 times lower than the max concentration found in groundwater, indicating the possibilityof other sources. In conclusion, it proved difficult to quantitatively predict the mobility of metals in soils by sequential extractions.

Relações material de origem / solo e pedogênese em uma seqüência de solos predominantemente argilosos e Latossólicos sobre psamitos na depressão periférica Paulista: Paulo State Peripheral Depression, southeastern Brazil

Na região da Depressão Periférica Paulista, estudaram-se os solos em uma encosta representativa das baixas colinas com relevo suave ondulado e lançantes longos do baixo vale do rio Piracicaba. Após intensas observações de campo, foram amostrados cinco pedons, assentados em rochas psamíticas da formação Itararé (Carbonífero-Permiano). Quatro apresentaram características latossólicas e textura argilosa e um, interposto na porção superior da meia encosta, textura média e B textural. Com observações de campo, estratigráficas, macro e micromorfológicas e da mineralogia da argila, concluiu-se que grande parte do material de origem dos pedons Latossólicos argilosos proveio do retrabalhamento de um sedimento neocenozóico argiloso, previamente bastante intemperizado, com remanescentes semelhantes, hoje ocupando preferencialmente as superfícies cimeiras locais, e sem aparente filiação com as rochas psamíticas subjacentes. Deduziu-se que as características latossólicas dos solos da meia encosta e do sopé foram herdadas de idêntico material. No terço inferior da encosta, ocorreu um Bt, relativamente pouco espesso, interpretado como produto de transformação do transportado Bw, principalmente por mecanismos de argiluviação que coalescem os antigos microagregados tipicamente Latossólicos. O mais provável material de origem do Podzólico Vermelho-Amarelo Latossólico textura média/argilosa no terço superior da meia encosta, foi considerado como derivado, em grande parte, de sedimento correlativo a um antigo e elevado depósito aluvial correspondente a um nível de terraço do rio Piracicaba, hoje quase totalmente reafeiçoado.

Management versus inherent soil properties effects on bulk density and relative compaction

Bulk density ( D b) is a soil physical parameter used extensively to quantify soil compactness. The D b varies with management as well as with inherent soil properties. Because of its dependence on inherent soil properties, measurements of D b are of limited value as a measure of the effect of management on soil compaction when soils with different inherent characteristics are compared. Researchers have used the concept of relative compaction or relative bulk density, ( D b-rel), the ratio of the D b of a soil to the D b under some standard compaction treatment ( D b-ref), in order to compare the response of different soils to stresses arising from management. This research was conducted to determine D b, D b-ref and D b-rel across a range of soils under different tillage practices and to assess the relative importance of texture, organic matter content and management on these parameters. Thirty-six paired sampling sites were located along two parallel transects in a side by side comparison of no-tillage and conventional tillage treatments. The transects crossed three soil types: Aquic Hapludalfs, Psammentic Hapludalfs, and Typic Hapludalfs. Clay content (CLAY) varied from 5.8 to 42.3%, and organic matter (OM) varied from 1.4 to 11.6%. Multiple regression analyses showed that D b was related ( R 2 = 0.83) with CLAY, OM, tillage, position, and the interactions OM∗CLAY and tillage∗position, whereas the D b-ref was related ( R 2 = 0.86) with OM, CLAY, and tillage. Normalizing D b with respect to D b-ref, effectively eliminated the influence of CLAY, OM and their interaction on D b-rel. The analyses indicated that it is possible to quantify the separate effects of inherent soil properties and management on D b, when soils derived from similar parent materials and under similar climatic conditions are considered, either by using multiple regression analyses to describe D b, or by normalizing D b with respect to D b-ref.

Urban soils as pollutant sinks — a case study from Aberdeen, Scotland

The chemical composition of soils from 80 sites within the city of Aberdeen in north-east Scotland have been determined by aqua-regia digestion and inductively coupled plasma emission spectroscopy. Within the urban dataset soils from roadside locations show enhanced contents of Pb, Zn, Ba and Cu and can be readily distinguished from those obtained from city parks. However, comparison of the composition of the urban soils with rural soils, derived from similar parent material, show that chemically these 2 groups of soils now have little in common.

Early postharvest succession in relation to site type in the southern boreal forest of Quebec

Early vegetation development following harvest was evaluated for nine common site types in the southern clay belt of northwestern Quebec. Stocking of broadleaf tree and high shrub stems less than 1 m tall was either stable or declined on all sites over a period of 8 years following harvest, whereas stocking of stems over 1 m displayed increases on all but mesic clay sites. These latter sites had the lowest broadleaf and high shrub stocking but a high cover of raspberry (Rubusidaeus L.), low shrubs, and herbs. Mesic to hydric clays and hydric organic site types had considerably higher cover of ruderal and introduced species than sand and till sites, TWINSPAN indicator species analysis was used to explore phytosociological associations of postharvest vegetation. The distribution of 11 phytosociological groups among the nine site types was analysed using contingency analysis to test the specificity of species groups to site types and the floristic amplitude of the latter. With the exception of one phytosociological group that displayed a broad spectrum of site type occupation, these groups tended to be associated with sites of similar soil moisture regimes and (or) parent material types. While site type may be improved upon as a stratifier by integrating other environmental, biotic, and operational variables, it does appear to provide a good initial basis for stratification in studies of postdisturbance vegetation dynamics.

Spatial and Temporal Variations in the Chemical Weathering of Basaltic Pyroclastic Materials

AbstractThe spatial and temporal distributions of 17 elements in basaltic pyroclastic materials originating from Mt. Fuji, Japan, were investigated. The relatedness of the profiles was established tephrochronologically, which then allowed a comparison of the chemical compositions of the various weathered pyroclastic materials in terms of their spatial (distance away from the volcano) and temporal (older to younger deposits) relations. The distributions of mobile elements (e.g., Ca, Mg, Na, and Sr) and resistant elements (e.g., Ti) are strongly affected by the extent of weathering, which increases with time and increases with distance from the volcano (the effects of the thickness and specific surface area of parent material). The application of a few weathering indices based on chemical composition was successful. Furthermore, a principal component analysis statistically extracted the expected dominance of the element mobility‐resistance, which accounts for 43% of the field‐scale variability of the distribution of the 17 elements. The second principal component explained 21% of variability, and discriminated soils developed from similar parent materials but different weathering‐soil‐formation factors (agricultural activities and the impact of a river).

Decade-scale changes of soil carbon, nitrogen and exchangeable cations under chaparral and pine

Four large lysimeters on the San Dimas Experimental Forest, each filled with similar parent material and planted with monocultures of native species in 1946, provide a unique opportunity to quantify short-term effects of plant species on soil properties. The four species under which soils were investigated are scrub oak ( Quercus dumosa Nutt.), chamise ( Adenostoma fasciculatum Hook. and Arn.), ceanothus ( Ceanothus crassifolia Torr.), and Coulter pine ( Pinus coulteri B. Don). A mass-balance approach was used to measure changes in C, N, exchangeable base cations, and exchangeable acidity to a depth of 1 m in the mineral soils over a 41-year period. The C content increased in all of the soils, but the greatest change was in the soil under oak (3.7 kg m −3 more than doubling the original amount. Since the source of C in these soils is the photosynthetic fixation of atmospheric CO 2, the mass of C accumulated reflects the magnitude of the CO 2 sink provided by chapatral soils in their initial stages of formation. The calculated rate of soil C accumulation is as much as 0.09 kg M −3 yr 1̄ The increase in N was highest in the soil under ceanothus (0.12 kg m −3 the only N 2-fixing species in this study. Exchangeable Ca increased by 25.7 mol m −3 in the soil under oak, while the maximum increase in exchangeable Mg was 5.5 mol m −3 also under oak. Exchangeable Na was leached from all of the soils (a maximum of 2.4 mol m −3 lost from under chamise and ceanothus) and K was slightly depleted.

The soil condition of adjacent bio‐dynamic and conventionally managed dairy pastures in Victoria, Australia

Abstract. Physical and chemical properties were compared during 1992 in adjacent bio‐dynamic and conventionally managed Haploxeralfs under improved, summer‐irrigated pastures in the Goulburn Valley of N.E. Victoria. Intensive dairy production has been practised on both the farms since the early 1950s, and aspects of the bio‐dynamic method have been practised on one farm for the past 18 years. Particle‐size analysis showed that the soil profiles of each field are derived from similar parent materials. The bio‐dynamic soil had greater macro‐porosity to a depth of at least 420 mm, lesser soil strength at 60, 120 and 200 mm, smaller dry bulk density values between 120 and 200 mm and larger organic matter content in the upper 50 mm. Volumetric soil water content measured along three transects to a depth of 1.4 m in the summer showed that the bio‐dynamic field was drier at depths greater than 200 mm. After heavy rains during the winter, the conventionally managed soil had an air‐filled porosity unfavourable for plant roots (2%) at 200 mm depth, whereas the bio‐dynamic soil was marginal for root growth (7%). The more favourable physical and chemical properties in the bio‐dynamic soil may be attributed to less grazing pressure, longer intervals between irrigations, use of the bio‐dynamic horn‐manure preparation, intermittent compost applications, less tractor traffic and the encouragement of taller pasture growth.

Vertical distribution of roots along a soil toposequence in the New Jersey Pinelands

Root biomass was determined for four sites on each of two toposequences in the New Jersey Pinelands. The sites have similar plant species composition, disturbance histories, and soil parent materials; the soils at the different topographic positions vary principally in the thickness of the organic horizon. Each toposequence consisted of lowland, transition, and upland sites, plus a site in the pygmy pine stands found on exposed topographic rises within the region. Root biomass was determined for three depths (organic horizon, 0–10 cm and 10–20 cm mineral soil) and three size classes (&lt;1, 1–5, and &gt;5 mm). Total, fine, and intermediate root biomass was greatest at lowland sites and least at sites in the pygmy pine stands. Total and fine root biomass in both the forest floor and also the upper mineral layer was linearly related to thickness of the organic horizon. The percent allocation of roots among soil layers, and the percentage of roots in different size classes within each soil depth interval, were similar for lowland, transition, and upland sites. The pygmy pine stands, in contrast, had higher relative quantities of total and fine roots in the mineral soil than in the organic horizon. In the organic horizons at all topographic positions, 50–100% of the roots are fine roots, whereas only 10–20% of the roots in the mineral layers are fine roots. Although root biomass per unit area varies &gt;2-fold from lowland to pygmy sites, biomass per unit volume of organic material does not vary among topographic positions. Volumes of organic matter are more densely filled with roots than are comparable volumes of mineral soil. Implications for the role of roots in nutrient cycling in different soil horizons are discussed.