Soil Conditions (soil + condition)

Distribution by Scientific Domains

Kinds of Soil Conditions

  • different soil condition


  • Selected Abstracts


    How does surrounding vegetation affect the course of succession: A five-year container experiment

    JOURNAL OF VEGETATION SCIENCE, Issue 4 2009
    ch Lanta
    Abstract Question: How does location and time of insertion affect the course of succession in experimental containers? Location: Bene,ov nad Lipou, ,eskomoravská vrchovina (Czech-Moravian uplands), Czech Republic Methods: We designed a 5-year container experiment in which plant succession started from scratch. Soil conditions were constant and all containers were filled with homogeneous substrate containing no propagules. We placed the containers in two contrasting habitats (meadow and floodplain) under identical climatic conditions but differing in surrounding vegetations and hence seed input. New containers were installed (and hence succession started) in two subsequent years, twice in each year (spring and autumn). We assume that the individual dates would lead to differences in propagule input and weather conditions. Results: Although both year and season of succession initiation considerably affected the initial species composition, we observed a pronounced convergence within the set of containers located in each habitat. However, the similarity of containers initiated at the same time but located in different habitats decreased over the course of succession. Final composition of the meadow and floodplain containers was therefore mostly determined by permanent seed input from their nearby neighborhood. Conclusions: This study demonstrated that propagule availability is an important determinant of the course of succession, and that differential seed input leads to different pathways of succession, even when all other environmental conditions are equal. [source]


    Comparison of critical limits for crop plant growth based on different indicators for the state of soil compaction

    JOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 4 2010
    Manfred Kaufmann
    Abstract Soil compaction affects physical soil condition, in particular aeration, soil strength, and water availability and has adverse effects on plant growth. Bulk density is the most frequently used indicator to describe the state of compaction of a soil. However, this parameter lacks a direct functional relationship with plant growth. Various indicators have been proposed to simultaneously characterize the state of compaction of agricultural soil and its suitability for plant growth. This paper examines and compares the critical limits for crop plant growth based on three of these indicators: packing density, least limiting water range, and S parameter (the latter is the slope of the soil water-retention curve in the inflexion point). In a first step, we reviewed the literature for published optimum and limiting values of bulk density and found that these values were highly dependent on clay and silt content. Converting them into corresponding values of packing density (composite index of bulk density and clay content), a value of 1.70 was found to effectively distinguish between optimum and limiting soil conditions for plant growth. In a second step, the packing density of 59 soil horizons sampled in N Switzerland was compared with the least limiting water range and the S parameter of these soil horizons (both determined by means of pedotransfer functions taken from the literature). A linear relationship between the three parameters was found, which allowed for a comparison of the published critical limits for plant growth based on these parameters. The critical limits of the three indicators, which had been postulated independently of each other in the literature, were found to agree well with each other. This means that all of them could equally be used to describe the compaction state of a soil and its physical suitability for plant growth. However, the proposed critical limits of packing density, least limiting water range, and S parameter still need further validation by field studies relating plant growth to soil compaction. [source]


    Modelling increased soil cohesion due to roots with EUROSEM

    EARTH SURFACE PROCESSES AND LANDFORMS, Issue 13 2008
    S. De Baets
    Abstract As organic root exudates cause soil particles to adhere firmly to root surfaces, roots significantly increase soil strength and therefore also increase the resistance of the topsoil to erosion by concentrated flow. This paper aims at contributing to a better prediction of the root effects on soil erosion rates in the EUROSEM model, as the input values accounting for roots, presented in the user manual, do not account for differences in root density or root architecture. Recent research indicates that small changes in root density or differences in root architecture considerably influence soil erosion rates during concentrated flow. The approach for incorporating the root effects into this model is based on a comparison of measured soil detachment rates for bare and for root-permeated topsoil samples with predicted erosion rates under the same flow conditions using the erosion equation of EUROSEM. Through backwards calculation, transport capacity efficiencies and corresponding soil cohesion values can be assessed for bare and root-permeated topsoils respectively. The results are promising and present soil cohesion values that are in accordance with reported values in the literature for the same soil type (silt loam). The results show that grass roots provide a larger increase in soil cohesion as compared with tap-rooted species and that the increase in soil cohesion is not significantly different under wet and dry soil conditions, either for fibrous root systems or for tap root systems. Power and exponential relationships are established between measured root density values and the corresponding calculated soil cohesion values, reflecting the effects of roots on the resistance of the topsoil to concentrated flow incision. These relationships enable one to incorporate the root effect into the soil erosion model EUROSEM, through adapting the soil cohesion input value. A scenario analysis shows that the contribution of roots to soil cohesion is very important for preventing soil loss and reducing runoff volume. The increase in soil shear strength due to the binding effect of roots on soil particles is two orders of magnitude lower as compared with soil reinforcement achieved when roots mobilize their tensile strength during soil shearing and root breakage. Copyright © 2008 John Wiley & Sons, Ltd. [source]


    Modelling land use changes and their impact on soil erosion and sediment supply to rivers

    EARTH SURFACE PROCESSES AND LANDFORMS, Issue 5 2002
    Anton J. J. Van Rompaey
    Abstract The potential for surface runoff and soil erosion is strongly affected by land use and cultivation. Therefore the modelling of land use changes is important with respect to the prediction of soil degradation and its on-site and off-site consequences. Land use changes during the past 250 years in the Dijle catchment (central Belgium) were analysed by comparing four historical topographic maps (1774, 1840, 1930 and 1990). A combination of land use transformation maps and biophysical land properties shows that certain decision rules are used for the conversion of forest into arable land or vice versa. During periods of increasing pressure on the land, forests were cleared mainly on areas with low slope gradients and favourable soil conditions, while in times of decreasing pressure land units with steep and unfavourable soil conditions were taken out of production. Possible future land use patterns were generated using stochastic simulations based on land use transformation probabilities. The outcome of these simulations was used to assess the soil erosion risk under different scenarios. The results indicate that even a relatively limited land use change, from forest to arable land or vice versa, has a significant effect on regional soil erosion rates and sediment supply to rivers. Copyright © 2002 John Wiley & Sons, Ltd. [source]


    The influence of groundwater on surface flow erosion processes during a rainstorm

    EARTH SURFACE PROCESSES AND LANDFORMS, Issue 5 2002
    D. L. RockwellArticle first published online: 27 MAY 200
    Abstract Surface erosion rates on a disturbed natural soil in a 10 m indoor flume increased by an order of magnitude when a water table developed at a 10 cm depth during simulated rainstorms. Erosion rate increases did not correlate well with surface hydraulic flow conditions, and all significant erosion increases began before the full soil depth was saturated, before the water table reached the soil surface, and before seepage was possible. Groundwater influenced erosion processes primarily by increasing unsaturated pore-water pressures and decreasing soil shear strength in surface rainflow, rather than through the direct entrainment of soil particles by seepage flow. There was no unique morphologic expression of the influence of groundwater during a rainstorm. Subsurface processes influencing surface erosion were detected only by appropriate subsurface instrumentation, which included micropiezometers, tensiometers and time domain reflectometry. Erosion rate increases occurred all along the slope, and were not concentrated at the base of slope due to a seepage zone. Soil depth was crucial to determining surface erosion increase. It is likely that confusing trends in surface flow erosion rates in past studies have occurred due to unrecorded groundwater development or an emphasis on seepage effects. Groundwater must be monitored along hillslopes under all moisture and soil conditions in order to avoid misleading and inconsistent conclusions derived solely from surface flow or seepage data. Copyright © 2002 John Wiley & Sons, Ltd. [source]


    Three-dimensional behavior of a spherical self-centering precast prestressed pile isolator

    EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 5 2009
    Rosita Jünemann
    Abstract A 3D analytical formulation of a precast prestressed pile (PPP) seismic isolator with top and bottom spherical rolling kinematic constraints is proposed. The PPP isolator was initially conceived as a low-cost seismic isolation (and foundation) system for housing units of low-income people. Since these structures are usually located at sites with poor soil conditions, the PPP isolator also works as a foundation pile by connecting the superstructure with more competent soil layers. The non-holonomic nature of the rolling constraint is dealt with by a structural formulation. The proposed 3D formulation is validated by numerical results obtained from a previously proposed formulation for the 2D problem, and a contact finite element model in ANSYS (www.ansys.com). Other issues associated with the dynamic response of isolated structures with the PPP are also examined, such as expected response reductions, variation in the axial force of the central prestressed cable, and torsional response amplifications. Finally, guidelines to estimate the actual 3D response using 2D analysis results are investigated. Copyright © 2009 John Wiley & Sons, Ltd. [source]


    Seismic vulnerability assessment using regional empirical data

    EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 10 2006
    Ahmet Yakut
    Abstract This article presents a procedure developed for the seismic performance assessment of low- to mid-rise reinforced concrete buildings in Turkey. The past performance of reinforced concrete buildings during major earthquakes have been compiled and analysed comprehensively using statistical procedures in order to study the empirical correlation between the significant damage inducing parameters and the observed damage. A damage database of nearly 500 representative buildings experiencing the 1999 Kocaeli and Düzce earthquakes have been used and discriminant functions expressing damage score in terms of six damage inducing parameters have been developed. In order to extrapolate the procedure to other regions that are likely to be subjected to major earthquakes a new approach that takes into account different local soil conditions, site-to-source distance and the magnitude of the earthquake has been introduced. The procedure has been applied to a pilot area in Istanbul to estimate expected damage distribution under a credible scenario earthquake. Copyright © 2006 John Wiley & Sons, Ltd. [source]


    Earthquake behavior of structures with copper energy dissipators

    EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 3 2004
    Juan C. De la Llera
    Abstract The earthquake behavior of structures with supplemental copper dampers is evaluated in this study. The investigation is divided into two parts: (i) an experimental work with seven pairs of hourglass copper dampers of different aspect ratios and side profiles; and (ii) a parametric study of 6-, 12-, and 25-story planar structures with elastic as well as inelastic behavior in the primary structure and copper dampers. The copper used in this study is electrolytic tough pitch (ETP) copper C11000; probably the most commonly used of all coppers; ductile, with a low-yield, and highly resistant to corrosion. Experimental results demonstrate that all copper plates reached stable angular distortions of the order of ,=25%, which implies transverse distortions in the devices larger than 40mm. The behavior of the devices is highly dependent on the aspect ratio of the plate, h/t, and a recommendation is made to use plates in the range 11 h/t,18. Plates beyond this range exhibit either large stress and strain concentrations in the neck of the device or a strong influence of axial deformations in their cyclic behavior. The inelastic earthquake response of structures with such devices shows that drift reduction factors of the order of 30 to 40% can be achieved with reasonably economic designs. It is also shown that the efficiency of these devices depends on the soil conditions and flexibility of the primary structure. Finally, it is concluded that supplemental copper dampers are a good alternative for drift reduction in a wide range of structural layouts, ranging from coupled shear-wall systems to moment-resisting frames, and for impulsive as well as non-impulsive ground motions. Copyright © 2003 John Wiley & Sons, Ltd. [source]


    Torsional response of symmetric buildings to incoherent and phase-delayed earthquake ground motion

    EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 7 2003
    Ernesto Heredia-Zavoni
    Abstract This paper studies the effect of coherency loss and wave passage on the seismic torsional response of three-dimensional, multi-storey, multi-span, symmetric, linear elastic buildings. A model calibrated against statistical analyses of ground motion records in Mexico City is used for the coherency function. The structural response is assessed in terms of shear forces in structural elements. Incoherence and wave passage effects are found to be significant only for columns in the ground level of stiff systems. The increase of column shears in the ground level is much higher for soft than for firm soil conditions. For the torsionally stiff systems considered, it is found that incoherent and phase-delayed ground motions do not induce a significant rotational response of the structure. The use of a code eccentricity to account for torsion due to ground motion spatial variation is assessed. On firm soil, the use of a base shear along with an accidental eccentricity results in highly overestimated shear forces; however, for soft soil conditions, code formulations may result in underestimated shear forces. Copyright © 2003 John Wiley & Sons, Ltd. [source]


    Ecological and evolutionary consequences of niche construction for its agent

    ECOLOGY LETTERS, Issue 10 2008
    Grigoris Kylafis
    Abstract Niche construction can generate ecological and evolutionary feedbacks that have been underinvestigated so far. We present an eco-evolutionary model that incorporates the process of niche construction to reveal its effects on the ecology and evolution of the niche-constructing agent. We consider a simple plant,soil nutrient ecosystem in which plants have the ability to increase the input of inorganic nutrient as an example of positive niche construction. On an ecological time scale, the model shows that niche construction allows the persistence of plants under infertile soil conditions that would otherwise lead to their extinction. This expansion of plants' niche, however, requires a high enough rate of niche construction and a high enough initial plant biomass to fuel the positive ecological feedback between plants and their soil environment. On an evolutionary time scale, we consider that the rates of niche construction and nutrient uptake coevolve in plants while a trade-off constrains their values. Different evolutionary outcomes are possible depending on the shape of the trade-off. We show that niche construction results in an evolutionary feedback between plants and their soil environment such that plants partially regulate soil nutrient content. The direct benefit accruing to plants, however, plays a crucial role in the evolutionary advantage of niche construction. [source]


    An improved force-restore method for soil temperature prediction

    EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 5 2008
    Z. Gao
    Summary The force-restore method originally developed to enable soil temperature predictions assumes that soil is uniform with depth (i.e. the vertical gradient of thermal diffusivity is zero in soil) and that thermal conduction is the only heat transfer mechanism necessary for prediction of soil temperature. These assumptions hamper the applicability of the force-restore method to many natural soil conditions. The main objective of this study is to revise the force-restore method by extending it to include the possibility of soil heterogeneity with depth (i.e. non-zero vertical gradient of thermal diffusivity in soil) and to include the possible occurrence of convective heat transfer as well as conductive heat transfer in soil. Soil temperatures calculated by the current and the revised force-restore methods for a shallow soil layer were compared with measured soil temperatures at a bare soil site in the China Loess Plateau from 22 to 26 July 2005. Results showed that the revised method improved on the current force-restore method, which overestimated either the diurnal amplitude or the phase shift for the shallow soil layer. These results indicate that the revised force-restore method is more applicable than the current force-restore method for predicting soil temperatures in naturally occurring non-uniform soil. The revised force-restore method has potential application within many land-atmosphere numerical models. [source]


    Liming upland grassland: the effects on earthworm communities and the chemical characteristics of carbon in casts

    EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 3 2008
    H. O. Bishop
    Summary Different earthworm species have different tolerances of acid soil conditions, and the application of lime to upland grassland to improve the grazing quality may therefore alter the size and diversity of the earthworm community. Altering soil properties may also affect the chemical characteristics of organic C in earthworm casts. We surveyed the earthworm community of an upland grassland in southern Scotland at the outset of annual lime applications, and after 3 years, and used 13C nuclear magnetic resonance (NMR) spectroscopy to assess the distribution of C between different functional groups in the organic matter. In addition, soil was incubated for 8 weeks with several earthworm species in the presence or absence of lime, and the earthworm casts were subsequently analysed by 13C NMR spectroscopy. Liming did not significantly affect earthworm abundance or species diversity, but it did affect the chemical composition of the casts. Casts from earthworms incubated in unlimed soil had greater ratios of alkyl-C to O,alkyl-C, indicative of more decomposed, recalcitrant C, and spectra from litter-feeding species had the greatest intensities of O,alkyl-C signals. In limed soil, the largest O,alkyl-C signal intensities were not restricted to litter-feeding species, indicating an increase in the quality of organic matter ingested by geophagous species. [source]


    Stabilization of organic matter in temperate soils: mechanisms and their relevance under different soil conditions , a review

    EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2006
    M. v. Lützow
    Summary Mechanisms for C stabilization in soils have received much interest recently due to their relevance in the global C cycle. Here we review the mechanisms that are currently, but often contradictorily or inconsistently, considered to contribute to organic matter (OM) protection against decomposition in temperate soils: (i) selective preservation due to recalcitrance of OM, including plant litter, rhizodeposits, microbial products, humic polymers, and charred OM; (ii) spatial inaccessibility of OM against decomposer organisms due to occlusion, intercalation, hydrophobicity and encapsulation; and (iii) stabilization by interaction with mineral surfaces (Fe-, Al-, Mn-oxides, phyllosilicates) and metal ions. Our goal is to assess the relevance of these mechanisms to the formation of soil OM during different stages of decomposition and under different soil conditions. The view that OM stabilization is dominated by the selective preservation of recalcitrant organic components that accumulate in proportion to their chemical properties can no longer be accepted. In contrast, our analysis of mechanisms shows that: (i) the soil biotic community is able to disintegrate any OM of natural origin; (ii) molecular recalcitrance of OM is relative, rather than absolute; (iii) recalcitrance is only important during early decomposition and in active surface soils; while (iv) during late decomposition and in the subsoil, the relevance of spatial inaccessibility and organo-mineral interactions for SOM stabilization increases. We conclude that major difficulties in the understanding and prediction of SOM dynamics originate from the simultaneous operation of several mechanisms. We discuss knowledge gaps and promising directions of future research. [source]


    Recolonisation of natural landslides in tropical mountain forests of Southern Ecuador

    FEDDES REPERTORIUM, Issue 3-4 2004
    (corresp. author) C. Ohl Dr.
    The regeneration of the vegetation of natural landslides was studied at Estación Científica San Francisco (ECSF) in a tropical mountain forest area of Southern Ecuador, north of Podocarpus National Park. The study focused on the process of regeneration on natural landslides and the vegetation change along an altitudinal gradient using space-for-time substitution. The most important plant families present on the landslides during the first stages of succession are Gleicheniaceae (Pteridophyta), Melastomataceae, Ericaceae and Orchidaceae. Species of the genus Sticherus (Gleicheniaceae) are dominant, and species composition varies with altitude and soil conditions. Colonisation of landslides is not homogeneous. Zones with bare ground, sparsely vegetated patches and densely covered areas may be present within the same slide. This small scale spatial heterogeneity is often created by local ongoing sliding processes and different distances towards undisturbed areas. Therefore, the duration of the successional process is highly variable. The initial stage of the succession is a community of non vascular plants interspersed with scattered individuals of vascular plants. By means of runner-shoots they form vegetation patches which start growing into each other. The second stage is dominated by Gleicheniaceae (species composition varying in altitude and soil chemistry). In the third stage, bushes and trees colonise, sheltered by the ferns, and a secondary forest develops with pioneer species that are not found in the primary forest vegetation. The common phenomenon of the natural landslides leads to an increase in structural and species diversity on a regional scale. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) Rekolonisation auf natürlichen Hangrutschungen in tropischen Bergwäldern Südecuadors Im tropischen Bergwald Südecuadors (nördlich des Podocarpus Nationalparks im Gebiet der Estación Científica San Francisco, ECSF) wurden Artenzusammensetzung und Rekolonisationsprozesse früher Sukzessionsstadien entlang eines Höhengradienten auf natürlichen Hangrutschungen untersucht. Besonders Gleicheniaceae, Melastomataceae, Ericaceae und Orchidaceae sind von Bedeutung. Arten der Gattung Sticherus (Gleicheniaceae) sind sehr zahlreich vertreten. Die Artenzusammensetzung wechselt entlang des Höhengradienten und in Abhängigkeit von den Bodenbedingungen. Die mosaikartige Verteilung der Vegetation auf den Rutschungen (gänzlich unbedeckte bis stark überwucherte Zonen) ist auf häufige lokale Nachrutschungen sowie auf unterschiedliche Geschwindigkeiten der Wiederbesiedlung entsprechend der Distanz zu ungestörter Vegetation zurückzuführen. Die Dauer der Sukzession ist daher sehr variabel. Das Initialstadium wird von Moosen und Flechten gebildet. Im weiteren Verlauf führt die überwiegend vegetative Ausbreitung einzelner Gefäßpflanzen zum zweiten Sukzessionsstadium. Dieses ist durch die Dominanz von Gleicheniaceae gekennzeichnet, während im dritten Stadium im Schutze der Farne erste Büsche und Bäume heranwachsen und den Pionierwald bilden. Da diese Arten nicht im Primärwald vertreten sind, kommt es regional zu einer beträchtlichen Erhöhung der Artenzahl und der strukturellen Diversität. [source]


    The life history of Salicaceae living in the active zone of floodplains

    FRESHWATER BIOLOGY, Issue 4 2002
    S. KARRENBERG
    1.,Exposed riverine sediments are difficult substrata for seedling establishment because of extremes in the microclimate, poor soil conditions and frequent habitat turnover. Various species of willows and poplars (Salicaceae) appear to be particularly successful in colonising such sediments and are often dominant in floodplain habitats throughout the northern temperate zone. 2.,In many Salicaceae regeneration seems to be adapted to regular disturbance by flooding. Efficient seed dispersal is achieved by the production of abundant seed in spring and early summer, which are dispersed by air and water. Seeds are short-lived and germinate immediately on moist surfaces. Seedling establishment is only possible if these surfaces stay moist and undisturbed for a sufficient period of time. 3.,Larger plants of Salicaceae have exceptional mechanical properties, such as high bending stability, which enable them to withstand moderate floods. If uprooted, washed away or fragmented by more powerful floods these plants re-sprout vigorously. 4.,While these life characteristics can be interpreted as adaptations to the floodplain environment, they may also cause a high genetic variability in populations of Salicaceae and predispose Salicaceae to hybridization. Thus, a feed back between adaptive life history characteristics and the evolutionary process is proposed. [source]


    Effect of seed coating on plant growth and soil conditions: A preliminary study for restoration of degraded rangeland in the Qinghai,Tibetan Plateau, China

    GRASSLAND SCIENCE, Issue 3 2010
    Yingchun Liu
    Abstract Rangeland degradation is a significant problem in the Qinghai,Tibetan Plateau, China. Restoration of the degraded rangelands through reseeding is being undermined by poor seedling growth under adverse soil moisture and nutrition conditions. Accordingly, seeds of Italian ryegrass (Lolium multiflorum) and Chinese milk vetch (Astragalus sinicus) were coated with a mixture of hygroscopic and plant-derived polysaccharide gums and alga powder (Phaeocystis sp. necolon-1), and inoculated with spores of microorganisms (Aspergillus sp. and Streptomyces sp.), serving as coating mixture decomposers, in order to improve rhizosphere moisture and nutrition. In a growth chamber simulating spring climate on the Plateau, seedling emergence of the coated seeds was 60,80 and 48,82%, respectively, for the two plant species in comparison to 38 and 24% for the uncoated seeds, which was due to moisture being supplied by the coat. In the outdoor pots with soil texture and moisture conditions similar to those of the degraded rangelands on the Plateau, dry weight of the plants from the coated seeds was 109,184 and 118,156 mg plant,1 for the respective plant species, while that of the plants from uncoated seeds was 18,20 and 10,11 mg plant,1. The number of Rhizobium sp. nodules on Chinese milk vetch plants from the coated seeds was 21,25 plant,1 while 0,2 in plants from uncoated seeds. Enhancement of plant growth was caused by increased activity of soil microbes. Plant growth on the soil after sampling plants from the coated seeds was also enhanced, indicating sustainability of improvement of soil conditions. Thus seed coating with hygroscopic nutrient-source materials and inoculation with microorganism spores as slow decomposers of the coating materials is a promising method for restoring degraded rangelands. [source]


    Neotyphodium endophyte infection affects the performance of tall fescue in temperate region Andisols

    GRASSLAND SCIENCE, Issue 1 2006
    M. Hasinur Rahman
    Abstract A pot experiment was conducted for 75 days to observe the effect of Neotyphodium coenophialum endophyte on three tall fescue (Festuca arundinacea Schreb.) ecotypes grown in two Andisols viz. Black Andisol and Red Andisol. Black Andisol with a naturally low content of P was high in other nutrients such as N, K, while Red Andisol, with a naturally high content of P, was low in other nutrients. Tiller number, plant height, chlorophyll content, shoot dry weight and agronomic efficiency of water use (WUEag) showed higher values in endophyte-infected (E+) plants than noninfected (E,) plants. Plants growing in Black Andisol performed better than those in Red Andisol. Among the three tall fescue ecotypes, one of them (ecotype Showa) had the best performance regardless of soils and endophyte infection. When considering the effect of endophyte infection in different soil conditions, higher WUEag was observed in endophyte-infected plants grown in Black Andisol. Endophyte infection significantly enhanced all plant parameters in Black Andisol but they were reduced in Red Andisol. Our results indicate that infected plants grew better in soil that was naturally low in P whereas uninfected plants had increased vegetative growth in soil that was naturally high in P. In nutrient poor soil with comparatively high P content (Red Andisol) the cost of endophyte infection may override its benefit. The presence of endophyte had a variable impact on plant performance and the effect of endophyte varied with ecotype of grass it infected into. [source]


    Using GIS and a digital elevation model to assess the effectiveness of variable grade flow diversion terraces in reducing soil erosion in northwestern New Brunswick, Canada

    HYDROLOGICAL PROCESSES, Issue 23 2009
    Qi Yang
    Abstract Flow diversion terraces (FDT) are commonly used beneficial management practice (BMP) for soil conservation on sloped terrain susceptible to water erosion. A simple GIS-based soil erosion model was designed to assess the effectiveness of the FDT system under different climatic, topographic, and soil conditions at a sub-basin level. The model was used to estimate the soil conservation support practice factor (P -factor), which inherently considered two major outcomes with its implementation, namely (1) reduced slope length, and (2) sediment deposition in terraced channels. A benchmark site, the agriculture-dominated watershed in northwestern New Brunswick (NB), was selected to test the performance of the model and estimated P -factors. The estimated P -factors ranged from 0·38,1·0 for soil conservation planning objectives and ranged from 0·001 to 0·45 in sediment yield calculations for water-quality assessment. The model estimated that the average annual sediment yield was 773 kg ha,1 yr ,1 compared with a measured value of 641 kg ha,1 yr,1. The P -factors estimated in this study were comparable with predicted values obtained with the revised universal soil loss equation (RUSLE2). The P -factors from this study have the potential to be directly used as input in hydrological models, such as the soil and water assessment tool (SWAT), or in soil conservation planning where only conventional digital elevation models (DEMs) are available. Copyright © 2009 John Wiley & Sons, Ltd. [source]


    First-year post-fire erosion rates in Bitterroot National Forest, Montana,

    HYDROLOGICAL PROCESSES, Issue 8 2007
    Kevin M. Spigel
    Abstract Accelerated runoff and erosion commonly occur following forest fires due to combustion of protective forest floor material, which results in bare soil being exposed to overland flow and raindrop impact, as well as water repellent soil conditions. After the 2000 Valley Complex Fires in the Bitterroot National Forest of west-central Montana, four sets of six hillslope plots were established to measure first-year post-wildfire erosion rates on steep slopes (greater than 50%) that had burned with high severity. Silt fences were installed at the base of each plot to trap eroded sediment from a contributing area of 100 m2. Rain gauges were installed to correlate rain event characteristics to the event sediment yield. After each sediment-producing rain event, the collected sediment was removed from the silt fence and weighed on site, and a sub-sample taken to determine dry weight, particle size distribution, organic matter content, and nutrient content of the eroded material. Rainfall intensity was the only significant factor in determining post-fire erosion rates from individual storm events. Short duration, high intensity thunderstorms with a maximum 10-min rainfall intensity of 75 mm h,1 caused the highest erosion rates (greater than 20 t ha,1). Long duration, low intensity rains produced little erosion (less than 0·01 t ha,1). Total C and N in the collected sediment varied directly with the organic matter; because the collected sediment was mostly mineral soil, the C and N content was small. Minimal amounts of Mg, Ca, and K were detected in the eroded sediments. The mean annual erosion rate predicted by Disturbed WEPP (Water Erosion Prediction Project) was 15% less than the mean annual erosion rate measured, which is within the accuracy range of the model. Published in 2007 by John Wiley & Sons, Ltd. [source]


    Simulating daily soil water under foothills fescue grazing with the soil and water assessment tool model (Alberta, Canada)

    HYDROLOGICAL PROCESSES, Issue 15 2004
    Emmanuel Mapfumo
    Abstract Grazing is common in the foothills fescue grasslands and may influence the seasonal soil-water patterns, which in turn determine range productivity. Hydrological modelling using the soil and water assessment tool (SWAT) is becoming widely adopted throughout North America especially for simulation of stream flow and runoff in small and large basins. Although applications of the SWAT model have been wide, little attention has been paid to the model's ability to simulate soil-water patterns in small watersheds. Thus a daily profile of soil water was simulated with SWAT using data collected from the Stavely Range Sub-station in the foothills of south-western Alberta, Canada. Three small watersheds were established using a combination of natural and artificial barriers in 1996,97. The watersheds were subjected to no grazing (control), heavy grazing (2·4 animal unit months (AUM) per hectare) or very heavy grazing (4·8 AUM ha,1). Soil-water measurements were conducted at four slope positions within each watershed (upper, middle, lower and 5 m close to the collector drain), every 2 weeks annually from 1998 to 2000 using a downhole CPN 503 neutron moisture meter. Calibration of the model was conducted using 1998 soil-water data and resulted in Nash,Sutcliffe coefficient (EF or R2) and regression coefficient of determination (r2) values of 0·77 and 0·85, respectively. Model graphical and statistical evaluation was conducted using the soil-water data collected in 1999 and 2000. During the evaluation period, soil water was simulated reasonably with an overall EF of 0·70, r2 of 0·72 and a root mean square error (RMSE) of 18·01. The model had a general tendency to overpredict soil water under relatively dry soil conditions, but to underpredict soil water under wet conditions. Sensitivity analysis indicated that absolute relative sensitivity indices of input parameters in soil-water simulation were in the following order; available water capacity > bulk density > runoff curve number > fraction of field capacity (FFCB) > saturated hydraulic conductivity. Thus these data were critical inputs to ensure reasonable simulation of soil-water patterns. Overall, the model performed satisfactorily in simulating soil-water patterns in all three watersheds with a daily time-step and indicates a great potential for monitoring soil-water resources in small watersheds. Copyright © 2004 John Wiley & Sons, Ltd. [source]


    Inclined load capacity of suction caissons

    INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 14 2003
    C. P. Aubeny
    Abstract A simplified method of analysis for estimating lateral load capacity of suction caisson anchors based on an upper bound plasticity formulation is presented. The simplification restricts the analysis to caissons in uniform and linearly varying undrained strength profiles; nevertheless, its computational efficiency permits quick evaluation of a number of parameters affecting load capacity. The validity and limitations of the simplified formulation are demonstrated through comparisons to more rigorous finite element solutions. A series of sensitivity studies demonstrate the effects of various soil conditions and loading parameters. Copyright © 2003 John Wiley & Sons, Ltd. [source]


    Solutions of pore pressure build up due to progressive waves

    INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 9 2001
    L. Cheng
    Abstract The analytical solution of soil pore pressure accumulations due to a progressive wave is examined in detail. First of all, the errors contained in a published analytical solution for wave-induced pore pressure accumulation are addressed, and the correct solution is presented in a more general form. The behaviour of the solution under different soil conditions is then investigated. It is found that the solution for deep soil conditions is sensitive to the soil shear stress in the top thin layer of the soil. However the solution is significantly influenced by the shear stress in the thin layer of soil near the impermeable base, for shallow and finite depth soil conditions. It is also found that a small error in the soil shear stress can lead to a large error in the accumulated pore pressure. An error analysis reveals the relationships between the accuracy of the pore pressure accumulation and the accuracy of the soil shear stress. A numerical solution to the simplified Biot consolidation equation is also developed. It is shown that the error analysis is of significant value for the numerical modelling of pore pressure buildup in marine soils. Both analytical and numerical examples are given to validate the error estimation method proposed in the present paper. Copyright © 2001 John Wiley & Sons, Ltd. [source]


    Cyst Distribution and Hatching Pattern of Chirocephalus ruffoi (Crustacea, Anostraca) in an Experimental Undisturbed Pool

    INTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 3 2005
    Graziella Mura
    Abstract The pattern of cyst distribution in the absence of turbation and their hatching behaviour were studied in an outdoor artificial pool, where just differentiated adults of the anostracan Chirocephalus ruffoi (sex ratio 1:3) lived until it dried up. The horizontal and vertical distributions of cysts in the pool bed were determined. The comparison between cyst bank estimate (Mura, 2004) and the actual number of cysts counted in the pool bed revealed an estimate error of 20.9%. Resting eggs occurred only in the upper 2.5 cm thick soil sections and decreased within this section as depth increased. Peripheral areas of the pool contained significantly larger numbers of cysts than the central area. Multiway analysis on the results recorded in hatching success (nested ANOVA) revealed that the differences were significantly affected by initial soil conditions, treatment and vertical distribution of cysts. Among these factors, vertical distribution (sections nested in cores) was the most influential. Hatching success was significantly inversely related to depth. Differences in the timing of hatching depending on the above considered factors were also noted. A nearly synchronous hatching pattern was observed only for cysts from initially dry sediment of the uppermost layers. In all successively deeper layers, hatching showed multiple peaks and was increasingly delayed and erratic (already mentioned). ANCOVA within each of the experimental conditions revealed significant differences in hatching frequencies (time as covariate) depending on sediment depth. Within any given layer, ANCOVA revealed a significant influence of initial sediment conditions and treatment on the timing of hatching. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    Assessment of the water,salinity crop production function of wheat using experimental data of the Golestan province, Iran,

    IRRIGATION AND DRAINAGE, Issue 4 2009
    A. R. Kiani
    stress hydrique; stress de salinité; fonctions de production; blé Abstract Optimisation of agricultural water management in arid and semi-arid regions requires the availability of water,salinity crop production functions. A two-year experiment was conducted in the northern Golestan province of Iran to assess the water,salinity production function of wheat. The treatments in the experiment consisted of four levels of irrigation water, i.e. 50 (W1), 75 (W2), 100 (W3) and 125 (W4) % of crop water requirement, and four levels of water salinity, respectively 1.5 (S1), 8.5 (S2), 11.5 (S3) and 14.2 (S4) dS,m,1. The plots were arranged in a randomised complete block design with three replications and water quantity as main plot treatment and water quality as subplot treatment. The data were analysed using linear, quadratic, Cobb,Douglas and transcendental functions, complemented with an economic analysis. The results indicate that for the given climate,soil conditions, transcendental functions best predict wheat yield under both water and salinity stress conditions. Yield reduction caused by a unit increase of matric potential is found to be larger than that caused by a unit increase of osmotic potential. The marginal rate of technical substitution indicates that each one of the two factors studied, namely soil salinity and water supply, can be substituted with the other in a wide range in order to achieve equal amount of yield. Copyright © 2008 John Wiley & Sons, Ltd. L'optimisation de la gestion de l'eau agricole dans les zones arides et semi-arides nécessite de savoir la relation entre l'apport d'eau selon sa salinité et la production végétale. Une expérience de deux ans a été menée dans le nord de la province du Golestan en Iran pour évaluer la fonction de production de l'eau saline sur le blé. Les traitements expérimentaux consistaient en quatre niveaux d'apports d'eau soit 50% (W1), 75% (W2), 100% (W3) et 125% (W4) des besoins en eau des cultures, et quatre niveaux de salinité de l'eau, respectivement 1.5 (S1), 8.5 (S2), 11.5 (S3) et 14.2 (S4) dS,m,1. Les parcelles ont été disposées dans un bloc de Fisher randomisé avec trois répétitions avec la quantité de l'eau comme variable principale et la qualité de l'eau comme variable secondaire. Les données ont été analysées en utilisant les fonctions linéaires, quadratiques, Cobb,Douglas et transcendantes, complétées par une analyse économique. Les résultats indiquent que, pour un climat et un état du sol donnés, les fonctions transcendantes donnent les meilleures prédictions du rendement de blé en condition de salinité et de stress hydrique. La baisse de rendement causée par une augmentation d'une unité de potentiel hydrique est plus importante que celle causée par l'augmentation d'une unité de potentiel osmotique. Le taux marginal de substitution technique indique que chacun des deux facteurs étudiés, à savoir la salinité des sols et l'apport d'eau, peuvent être largement substitués l'un à l'autre pour viser rendement identique. Copyright © 2008 John Wiley & Sons, Ltd. [source]


    Comparative Effect of Nitrogen Sources on Maize under Saline and Non-saline Conditions

    JOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 4 2008
    M. Irshad
    Abstract The main objective of this study was to compare the relationship between biomass yield and nutrient uptake in salt-stressed maize (Zea mays L.) following nitrogen (N) nutrition in a greenhouse. Three forms of N were applied, each at the rate of 100 kg ha,1: urea-N, nitrate-N, 1/2 urea-N + 1/2 nitrate-N (mixed-N) and no N application (control). Maize was grown as a test crop for 6 weeks. All N sources greatly stimulated crop growth and nutrient uptake compared with the control. The biomass (shoot and root) of maize was significantly greater in mixed-N treatment than in single sources in saline soil whereas it varied in the order of urea-N > mixed-N > nitrate-N > control in non-saline soil. Under both soil conditions, the concentration of Ca, Mg and Na in shoot was highest in nitrate-N treatments while that of K was highest in the control. Shoot nitrogen concentration was not significantly different among N sources under non-saline treatment, whereas under saline conditions, the concentration varied markedly in the order of nitrate-N > urea-N > mixed-N > control. The mineral concentrations in the shoot increased under salt treated soil when compared with non-saline soil. The ratios of Na/K, Na/Ca and Na/Mg were also higher under salt stress due to higher accumulation of Na ion in the shoot. Among N-fertilizer sources, Na/Ca and Na/Mg ratios were highest in control whereas Na/K ratio was the highest in nitrate-N treatment. The lowest cation ratios were noted in mixed-N-treated plants under both soils. Regression analysis showed that maize biomass was related to N concentration by the following equations: Y = ,4.54 + 0.97N for the non-saline soil and Y = 0.89 + 0.25N for the saline soil. Nitrogen use efficiency for non-saline soil exceeded that of saline soil by 15 %. [source]


    Relay Cropping of Sorghum and Legume Shrubs for Crop Yield Improvement and Striga Control in the Subsistence Agriculture Region of Tigray (Northern Ethiopia)

    JOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 1 2005
    F. Reda
    Abstract Striga hermonthica is a major constraint in the subsistence agriculture regions of northern Ethiopia. Low soil fertility and overall environmental degradation has contributed to the build up of the parasitic weed infestation. Improved cropping systems have to be introduced to address the interrelated problems of Striga and soil fertility decline. Thus, relay cropping of sorghum with legume shrubs was investigated at two locations representing different environments. Results showed that the output of the improved cropping system was dependent on ecological endowments. Relay cropping led to significant improvement in yield at Sheraro, at the site with relatively better weather and soil conditions. The legume shrubs resulted in significantly lower sorghum yield in a dryland location (Adibakel). Overall Striga infestation declined over the 3-year period; however, treatment differences were not apparent. Among the two legume shrubs, Sesbania sesban was better adapted to the dryland areas. Relay cropping could provide a viable option for farmers in both types of environments that are characterized by accelerated decline in natural resource base. However, it could mean compromising the yield of non-fertilized sorghum in the interest of long-term benefits of low incidence of Striga and more rewarding crop enterprise in dry areas. [source]


    Influence of plant species and soil conditions on plant,soil feedback in mixed grassland communities

    JOURNAL OF ECOLOGY, Issue 2 2010
    Kathryn A. Harrison
    Summary 1.,Our aim was to explore plant,soil feedback in mixed grassland communities and its significance for plant productivity and community composition relative to abiotic factors of soil type and fertility. 2.,We carried out a 4-year, field-based mesocosm experiment to determine the relative effects of soil type, historic management intensity and soil conditioning by a wide range of plant species of mesotrophic grassland on the productivity and evenness of subsequent mixed communities. 3.,The study consisted of an initial soil conditioning phase, whereby soil from two locations each with two levels of management intensity was conditioned with monocultures of nine grassland species, and a subsequent feedback phase, where mixed communities of the nine species were grown in conditioned soil to determine relative effects of experimental factors on the productivity and evenness of mixed communities and individual plant species performance. 4.,In the conditioning phase of the experiment, individual plant species differentially influenced soil microbial communities and nutrient availability. However, these biotic effects were much less important as drivers of soil microbial properties and nutrient availability than were abiotic factors of soil type and fertility. 5.,Significant feedback effects of conditioning were detected during the second phase of the study in terms of individual plant growth in mixed communities. These feedback effects were generally independent of soil type or fertility, and were consistently negative in nature. In most cases, individual plant species performed less well in mixed communities planted in soil that had previously supported their own species. 6.,Synthesis. These findings suggest that despite soil abiotic factors acting as major drivers of soil microbial communities and nutrient availability, biotic interactions in the form of negative feedback play a significant role in regulating individual plant performance in mixed grassland communities across a range of soil conditions. [source]


    Photon flux partitioning among species along a productivity gradient of an herbaceous plant community

    JOURNAL OF ECOLOGY, Issue 6 2006
    ANNE AAN
    Summary 1We studied light partitioning among species along the natural productivity gradient of herbaceous vegetation with an above-ground dry mass of 150,490 g m,2. The aim was to investigate how the light capturing ability per above-ground biomass and leaf nitrogen changes in an entire community and to reveal whether different species respond similarly to changes in soil conditions and competition. 2Species becoming dominant at high soil resources have intrinsically low leaf area ratios (LAR) and lower tissue nitrogen concentration, and hence relatively high nitrogen use efficiency. These traits lead to dominance when soil resources allow rapid growth so that benefits arising from the ability to locate leaves above neighbours and thereby increasing asymmetry of competition, become more crucial. 3In contrast to our expectations, above-ground efficiency of nitrogen use on the community level (aNUE) increased along the productivity gradient. Species level nitrogen use efficiency was unaffected by variation in site productivity; the increase in community aNUE was solely as a consequence of changes in species composition. 4Light absorption per unit of above-ground mass, ,M, declined significantly at the community level and also in most species, indicating that light use efficiency increased with increased site productivity and LAI. 5Light absorption per unit of leaf nitrogen, ,N, as an indicator of the ratio NUE/LUE showed no clear pattern on the community level because both NUE and LUE tend to increase with increased productivity. At the species level, ,N tends to decrease because NUE did not change with stand productivity. 6Some subordinate species responded by enlarging their LAR to increased competition. Additionally, these species were the most responsive in their leaf chlorophyll/nitrogen ratio to changes in light conditions, which shows that physiological plasticity is important for species that are unable to compete for light with the ability to position their leaves above those of other species. 7This study shows how plasticity in above-ground growth pattern and nitrogen allocation differs between species with respect to increased soil fertility and competition, leading to distinctive strategies of survival. Light partitioning analysis reveals that increased competition for light, resulting in changes in species composition, is the key factor that leads to decoupling of species and community level acclimation. [source]


    Plant species and functional group effects on abiotic and microbial soil properties and plant,soil feedback responses in two grasslands

    JOURNAL OF ECOLOGY, Issue 5 2006
    T. MARTIJN BEZEMER
    Summary 1Plant species differ in their capacity to influence soil organic matter, soil nutrient availability and the composition of soil microbial communities. Their influences on soil properties result in net positive or negative feedback effects, which influence plant performance and plant community composition. 2For two grassland systems, one on a sandy soil in the Netherlands and one on a chalk soil in the United Kingdom, we investigated how individual plant species grown in monocultures changed abiotic and biotic soil conditions. Then, we determined feedback effects of these soils to plants of the same or different species. Feedback effects were analysed at the level of plant species and plant taxonomic groups (grasses vs. forbs). 3In the sandy soils, plant species differed in their effects on soil chemical properties, in particular potassium levels, but PLFA (phospholipid fatty acid) signatures of the soil microbial community did not differ between plant species. The effects of soil chemical properties were even greater when grasses and forbs were compared, especially because potassium levels were lower in grass monocultures. 4In the chalk soil, there were no effects of plant species on soil chemical properties, but PLFA profiles differed significantly between soils from different monocultures. PLFA profiles differed between species, rather than between grasses and forbs. 5In the feedback experiment, all plant species in sandy soils grew less vigorously in soils conditioned by grasses than in soils conditioned by forbs. These effects correlated significantly with soil chemical properties. None of the seven plant species showed significant differences between performance in soil conditioned by the same vs. other plant species. 6In the chalk soil, Sanguisorba minor and in particular Briza media performed best in soil collected from conspecifics, while Bromus erectus performed best in soil from heterospecifics. There was no distinctive pattern between soils collected from forb and grass monocultures, and plant performance could not be related to soil chemical properties or PLFA signatures. 7Our study shows that mechanisms of plant,soil feedback can depend on plant species, plant taxonomic (or functional) groups and site-specific differences in abiotic and biotic soil properties. Understanding how plant species can influence their rhizosphere, and how other plant species respond to these changes, will greatly enhance our understanding of the functioning and stability of ecosystems. [source]


    Holocene pollen records from the central Arctic Foothills, northern Alaska: testing the role of substrate in the response of tundra to climate change

    JOURNAL OF ECOLOGY, Issue 6 2003
    W. Wyatt Oswald
    Summary 1To explore the role of edaphic controls in the response of arctic tundra to climate change, we analysed Holocene pollen records from lakes in northern Alaska located on glaciated surfaces with contrasting soil texture, topography and tundra communities. Using indicator taxa, pollen accumulation rates (PARs) and multivariate comparison of fossil and modern pollen assemblages, we reconstructed the vegetational changes at Upper Capsule Lake (Sagavanirktok surface) and Red Green Lake (Itkillik II surface) in response to increased effective moisture between the early and middle Holocene. 2In the Red Green record, low PARs and the continuous presence of taxa indicative of prostrate-shrub tundra (PST; Equisetum, Polypodiaceae, Thalictrum and Rosaceae) indicate that the vegetation resembled PST throughout the Holocene. During the warm, dry early Holocene (11 300,10 000 cal years BP), PST also occurred on Sagavanirktok surfaces, as evidenced by PST indicators (Bryidae, Polypodiaceae, Equisetum and Rosaceae) in this interval of the Upper Capsule record. However, PARs increased, suggesting increased vegetation cover, PST taxa declined and taxa indicative of dwarf-shrub tundra (DST; Rubus chamaemorus and Lycopodium annotinum) increased between 10 000 and 7500 cal years BP. 3We hypothesize that between the early and middle Holocene the fine-textured soils and smooth topography of Sagavanirktok surfaces led to increased soil moisture, greater vegetation cover, permafrost aggradation, anoxic and acidic soil conditions, slower decomposition and the development of a thick organic layer. In contrast, soil moisture remained low on the better-drained Itkillik II surface, and vegetational changes were minor. 4Landscape-scale substrate variations have an effect on how tundra responds to climate change, suggesting that the response of arctic ecosystems to future variability may be spatially heterogeneous. [source]