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Soil Structure (soil + structure)

Distribution by Scientific Domains

Earth and Environmental Science	60%
Life Sciences	23%
Engineering	10%
2 Other Domains	7%

Selected Abstracts

Soil structure and pedotransfer functions

EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 3 2003
Y.A. Pachepsky
Summary Accurate estimates of soil hydraulic properties from other soil characteristics using pedotransfer functions (PTFs) are in demand in many applications, and soil structural characteristics are natural candidates for improving PTFs. Soil survey provides mostly categorical data about soil structure. Many available characteristics such as bulk density, aggregate distribution, and penetration resistance reflect not only structural but also other soil properties. Our objective here is to provoke a discussion of the value of structural information in modelling water transport in soils. Two case studies are presented. Data from the US National Pedon Characterization database are used to estimate soil water retention from categorical field-determined structural and textural classes. Regression-tree estimates have the same accuracy as those from textural class as determined in the laboratory. Grade of structure appears to be a strong predictor of water retention at ,33 kPa and ,1500 kPa. Data from the UNSODA database are used to compare field and laboratory soil water retention. The field-measured retention is significantly less than that measured in the laboratory for soils with a sand content of less than 50%. This could be explained by Rieu and Sposito's theory of scaling in soil structure. Our results suggest a close relationship between structure observed at the soil horizon scale and structure at finer scales affecting water retention of soil clods. Finally we indicate research needs, including (i) quantitative characterization of the field soil structure, (ii) an across-scale modelling of soil structure to use fine-scale data for coarse-scale PTFs, (iii) the need to understand the effects of soil structure on the performance of various methods available to measure soil hydraulic properties, and (iv) further studies of ways to use soil,landscape relationships to estimate variations of soil hydraulic properties across large areas of land. [source]

Mineral soil surface crusts and wind and water erosion

EARTH SURFACE PROCESSES AND LANDFORMS, Issue 9 2004
Michael J. Singer
Abstract The ,rst few millimetres of soil largely control the soil's response to the eroding forces of wind and water. The tendency of soils to form surface seals and crusts in,uences the processes of wind and water erosion differently. For wind, dry particle size distribution and particle organization determine the shear strength and threshold wind velocity necessary to initiate particle movement. In loams and clay loams, seals and crusts decrease roughness but increase surface soil strength, generally decreasing wind erosion. Conversely, in sand and sandy loams, loose erodible sandy material may either deposit on the crust and is subject to erosion or it may disrupt the crust, accelerating the erosion process. For water erosion, particle size distribution and structure determine in,ltration rate, time to ponding, and energy required for soil particle detachment. Seals and crusts tend to decrease in,ltration rate and time to ponding thus increasing overland ,ow and soil erosion. This paper brie,y reviews how permanent and time-dependent soil properties in,uence surface seals and crusts and how these affect soil erosion by wind and water. The tendency of a soil to form a seal and crust depends to some degree on the time-dependent property of soil structural stability, which tends to increase with increasing clay content and smectitic mineralogy which are permanent properties. These permanent properties and their effect on structure are variable depending on dynamic properties of exchangeable sodium percentage and soil solution electrical conductivity. Antecedent water content prior to irrigation or rainfall, rate of wetting before an erosive event and aging, the time between wetting and an erosive event, greatly in,uence the response of soil structure to raindrop impact. The effect of these dynamic processes is further in,uenced by the static and dynamic properties of the soil. Weak structure will be less in,uenced by wetting rate than will a soil with strong structure. Process-based models of wind and water erosion need to consider the details of the interactions between soil static and dynamic properties and the dynamic processes that occur prior to erosive events. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Waterponding: Reclamation technique for scalded duplex soils in western New South Wales rangelands

ECOLOGICAL MANAGEMENT & RESTORATION, Issue 3 2008
Ray Thompson
Summary Building on previous trials initiated in the 1960s, a demonstration programme involving 18 landholders was established at Nyngan, New South Wales Australia; in the mid-1980s to refine ,waterponding' techniques used to rehabilitate scalded claypans. The waterponding technique involves building horseshoe shaped banks (about 240 m in length) to create ponds of about 0.4 ha each. Each pond retains up to 10 cm of water after rain which leaches soluble salts from the scald surface. This improves the remaining soil structure, inducing surface cracking, better water penetration and allows entrapment of wind-blown seed. Consequently, niches are formed for the germination of this (and any sown) seed and recovery of a range of chenopod native pasture species occurs on the sites, which can be supplemented by direct seeding. What started as a project continues now as a standard rangeland rehabilitation process for reclaiming bare, scalded semi-arid areas of New South Wales and turning them back into biodiverse and productive rangelands. Since 1985, further modifications have been made to the method and the ongoing programme has surveyed, marked out and built approximately 56 700 waterponds within the Marra Creek waterponding district. [source]

Adaptation to nickel spiking of bacterial communities in neocaledonian soils

ENVIRONMENTAL MICROBIOLOGY, Issue 1 2003
Marina Héry
Summary Adaptation to nickel of bacterial communities of two extreme neocaledonian soils (an ultramafic soil and an acidic soil) was investigated by nickel spiking and compared with adaptation in a non-neocaledonian soil used as reference. Soil microcosms were amended with nickel chloride (NiCl2), and bacterial community structure was analysed with the ribosomal intergenic spacer analysis (RISA) technique. Then, bacterial populations that respond to nickel stress were identified by cloning and sequencing. In the ultramafic soil, a shift occurred on day zero on the assay profiles and consisted of the emergence of a bacterial group closely related to the Ralstonia/Oxalobacter/Burkholderia group. It is hypothesized that NiCl2 had a physico-chemical impact on soil structure. Fourteen days after nickel spiking, another shift occurred in the two soils that concerned a bacterial group belonging to the Actinomycete group. Only a few changes occurred in the bacterial community structure of the neocaledonian soils compared with those of the reference soil, which is more affected by nickel spiking. These results suggest that neocaledonian soil bacteria are particularly well adapted to nickel. [source]

Quantifying the relationship between soil organic carbon and soil physical properties using shrinkage modelling

EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 2 2009
P. Boivin
Summary Changes in soil organic carbon (SOC) may strongly affect soil structure and soil physical properties, which in turn may have feedback effects on the soil microbial activity and SOC dynamics. Such interactions are still not quantitatively described and accounted for in SOC dynamics modelling. The objective of this study was to test the hypothesis that soil shrinkage curve (ShC) analysis allows the establishment of close relationships between soil physical properties and SOC. We sampled a rice-cropped vertisol, a cambisol under conventional tillage and no-tillage and a restored cambisol. Soil samples were analysed for clay and SOC content, bulk volume, hydro-structural stability and plasma and structural pore volumes changes on the full water content range using ShC analysis. Although the soils behaved differently according to their constituents and history, changes in SOC linearly affected most of the soil physical properties, with stronger effects than changes in clay content. The observed effects of increasing SOC, such as increasing hydro-structural stability, specific bulk volume and water retention, agreed well with previously reported results. However, using ShC measurement and modelling allowed the observation of all these different effects simultaneously for small changes in SOC, and in a single measurement. Moreover, the relation between SOC changes and physical properties could be quantified. ShC analysis may, therefore, be used to account for the effect of changes in SOC on soil physical properties. [source]

Changes in shrinkage of restored soil caused by compaction beneath heavy agricultural machinery

EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2008
B. Schäffer
Summary Compaction is a major cause of soil degradation. It affects not only the porosity of the soil, but also the soil's hydrostructural stability. Soil that is restored after temporary removal is particularly sensitive to compaction. We investigated the effects of trafficking with a heavy combine harvester on the shrinkage behaviour of a restored soil that had been gently cultivated for several years. We tested the hypothesis that compaction decreases the hydrostructural stability of restored soil by analysing simultaneously measured shrinkage and water retention curves of undisturbed soil samples. Shrinkage strongly depended on clay and organic carbon content. Taking account of this influence and normalizing the shrinkage parameters with respect to these soil properties, we found pronounced effects of trafficking on shrinkage. Ten passes with the combine harvester decreased the structural porosity by about 40% at maximum swelling and by about 30% at the shrinkage limit and increased the bulk density by 8% at maximum swelling and by 10% at the shrinkage limit, but did not significantly affect the porosity of the soil plasma. Moreover, trafficking modified shrinkage, increasing the slopes of the shrinkage curve in the basic and structural shrinkage domains by about 30% and more than 150% after 10 passes, respectively. Evidently the aggregate structure was strongly destabilized. The results indicate that the hydrostructural stability of the soil was still very sensitive to compaction by trafficking even 5 years after restoration. The analysis of shrinkage seemed well suited for the assessment of compaction effects on soil structure. [source]

Shrinkage of initially very wet soil blocks, cores and clods from a range of European Andosol horizons

EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 2 2007
F. Bartoli
Summary In advanced stages of volcanic ash soil formation, when more clay is formed, soil porosity values and soil water retention capacities are large and the soils show pronounced shrinkage on drying. Soil shrinkage is a key issue in volcanic soil environments because it often occurs irreversibly when topsoils dry out after changes from permanent grassland or forest to agriculture. European Andosols have developed in a wide range of climatic conditions, leading to a wide range in intensity of both weathering and organo-mineral interactions. The question arises as to whether these differences affect their shrinkage properties. We aimed to identify common physically based shrinkage laws which could be derived from soil structure, the analysis of soil constituents, the selected sampling size and the drying procedure. We found that the final volumetric shrinkage of the initially field-wet (56,86% of total porosity) or capillary-wet (87,100% of total porosity) undisturbed soil samples was negatively related to initial bulk density and positively related to initial capillary porosity (volumetric soil water content of soil cores after capillary rise). These relationships were linear for the soil clods of 3,8 cm3, with final shrinkage ranging from 21.2 to 52.2%. For soil blocks of 240 cm3 and soil cores of 28.6 cm3 we found polynomial and exponential relationships, respectively, with thresholds separating shrinkage and nearly non-shrinkage domains, and larger shrinkage values for the soil cores than for the soil blocks. For a given sample size, shrinkage was more pronounced in the most weathered and most porous Andosol horizons, rich in Al-humus, than in the less weathered and less porous Andosol horizons, poor in Al-humus. The Bw horizons, being more weathered and more porous, shrank more than the Ah horizons. We showed that the structural approach combining drying kinetics under vacuum, soil water analysis and mercury porosimetry is useful for relating water loss and shrinkage to soil structure and its dynamics. We also found that the more shrinkage that occurred in the Andosol horizon, the more pronounced was its irreversible mechanical change. [source]

Simulation of water flow and solute transport in free-drainage lysimeters and field soils with heterogeneous structures

EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 2 2004
H. M. Abdou
Summary Lysimeters are valuable for studying the fate and transport of chemicals in soil. Large-scale field lysimeters are used to assess pesticide behaviour and radionuclide transport, and are assumed to represent natural field conditions better than laboratory columns. Field lysimeters are usually characterized by a free-draining lower boundary. As a result, the hydraulic gradient is disrupted, and leachate cannot be collected until the bottom of the lysimeter becomes saturated. We compared heterogeneously structured, free-drainage lysimeters and field soils with respect to water flow and solute transport. Numerical simulations were carried out in a two-dimensional heterogeneous sandy soil under unsaturated water flow conditions with the CHAIN_2D code. Three different soil structures (isotropic, horizontal, and vertical) were generated, and Miller,Miller similitude was used to scale the hydraulic properties of the soil. The results showed that ponding occurs at the bottom of the lysimeter for the three soil structures and that it occurred faster and was more pronounced with the vertical structure (preferential flow effect). Breakthrough curves of a conservative solute (bromide) showed that solutes are moving faster in the field than in the lysimeters. Fewer differences between lysimeters and field soils were found with the horizontal soil structure than with the isotropic and vertical structures. [source]

Soil structure and pedotransfer functions

Effect of root mucilage and modelled root exudates on soil structure

EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2000
O. Traoré
Summary Plant roots release in the rhizosphere diverse organic materials which may have different effects on soil structure. We have evaluated the effect of natural and modelled root-released materials on soil aggregates and the biodegradation of carbon from roots in the soil. The effects of root mucilage from maize and of a modelled soluble exudate were compared with those of simple compounds (glucose, polygalacturonic acid). For all treatments, soil was amended with 2 g C kg,1 soil and incubated for 30 days at 25°C. The biodegradation of mucilage was similar to that of polygalacturonic acid, and slower than the decomposition of modelled exudates and glucose. Addition of all substrates increased the stability of aggregates, but the duration of this effect depended on the chemical nature of the material. Compared with the control, the proportion of stable aggregates after 30 days of incubation was multiplied by 3.8 for root mucilage, by 4.2 for modelled soluble exudates, by 2.5 for polygalacturonic acid and by 2.0 for glucose. The different fractions of root exudates in the rhizosphere evidently affected the aggregate stability. [source]

Biodiversity and ecosystem function in soil

FUNCTIONAL ECOLOGY, Issue 3 2005
A. H. FITTER
Summary 1Soils are one of the last great frontiers for biodiversity research and are home to an extraordinary range of microbial and animal groups. Biological activities in soils drive many of the key ecosystem processes that govern the global system, especially in the cycling of elements such as carbon, nitrogen and phosphorus. 2We cannot currently make firm statements about the scale of biodiversity in soils, or about the roles played by soil organisms in the transformations of organic materials that underlie those cycles. The recent UK Soil Biodiversity Programme (SBP) has brought a unique concentration of researchers to bear on a single soil in Scotland, and has generated a large amount of data concerning biodiversity, carbon flux and resilience in the soil ecosystem. 3One of the key discoveries of the SBP was the extreme diversity of small organisms: researchers in the programme identified over 100 species of bacteria, 350 protozoa, 140 nematodes and 24 distinct types of arbuscular mycorrhizal fungi. Statistical analysis of these results suggests a much greater ,hidden diversity'. In contrast, there was no unusual richness in other organisms, such as higher fungi, mites, collembola and annelids. 4Stable-isotope (13C) technology was used to measure carbon fluxes and map the path of carbon through the food web. A novel finding was the rapidity with which carbon moves through the soil biota, revealing an extraordinarily dynamic soil ecosystem. 5The combination of taxonomic diversity and rapid carbon flux makes the soil ecosystem highly resistant to perturbation through either changing soil structure or removing selected groups of organisms. [source]

Elevated carbon dioxide and irrigation effects on water stable aggregates in a Sorghum field: a possible role for arbuscular mycorrhizal fungi

GLOBAL CHANGE BIOLOGY, Issue 3 2001
Matthias C. Rillig
Summary While soil biota and processes are becoming increasingly appreciated as important parameters for consideration in global change studies, the fundamental characteristic of soil structure is a neglected area of research. In a sorghum [Sorghum bicolor (L.) Moench] field experiment in which CO2[supplied using free-air CO2 enrichment (FACE) technology] was crossed factorially with an irrigation treatment, soil aggregate (1,2 mm) water stability increased in response to elevated CO2. Aggregate water stability was increased by 40% and 20% in response to CO2, at ample and limited water supply treatments, respectively. Soil hyphal lengths of arbuscular mycorrhizal fungi (AMF) increased strongly (with a threefold increase in the dry treatment) in response to CO2, and the concentrations of one fraction (easily extractable glomalin, EEG) of the AMF-produced protein glomalin were also increased. Two fractions of glomalin, and AMF hyphal lengths were all positively correlated with soil aggregate water stability. The present results further support the hypothesis that AMF can become important in global change scenarios. Although in this field study a causal relationship between hyphal length, glomalin and aggregate stability cannot be demonstrated, the present data do suggest that AMF could mediate changes in soil structure under elevated CO2. This could be of great importance in agricultural systems threatened by erosional soil loss. [source]

Using a pore-scale model to quantify the effect of particle re-arrangement on pore structure and hydraulic properties

HYDROLOGICAL PROCESSES, Issue 8 2007
Oagile Dikinya
Abstract A pore-scale model based on measured particle size distributions has been used to quantify the changes in pore space geometry of packed soil columns resulting from a dilution in electrolyte concentration from 500 to 1 mmol l,1 NaCl during leaching. This was applied to examine the effects of particle release and re-deposition on pore structure and hydraulic properties. Two different soils, an agricultural soil and a mining residue, were investigated with respect to the change in hydraulic properties. The mining residue was much more affected by this process with the water saturated hydraulic conductivity decreasing to 0·4% of the initial value and the air-entry value changing from 20 to 50 cm. For agricultural soil, there was little detectable shift in the water retention curve but the saturated hydraulic conductivity decreased to 8·5% of the initial value. This was attributed to localized pore clogging (similar to a surface seal) affecting hydraulic conductivity, but not the microscopically measured pore-size distribution or water retention. We modelled the soil structure at the pore scale to explain the different responses of the two soils to the experimental conditions. The size of the pores was determined as a function of deposited clay particles. The modal pore size of the agricultural soil as indicated by the constant water retention curve was 45 µm and was not affected by the leaching process. In the case of the mining residue, the mode changed from 75 to 45 µm. This reduction of pore size corresponds to an increase of capillary forces that is related to the measured shift of the water retention curve. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Parentage analysis in Gabonese colonies of soil-feeding termites belonging to the Cubitermes sp. affinis subarquatus complex of species (Termitidae: Termitinae)

INSECT SCIENCE, Issue 2 2010
Virginie Roy
Abstract,Cubitermes spp. are widely distributed soil-feeding termite species in sub-Saharan Africa which play a fundamental role in soil structure and fertility. A complex of at least four cryptic species (i.e., Cubitermes sp. affinis subarquatus complex of species) has been recently described using molecular markers. In order to investigate the breeding system of these species, five microsatellite markers were used to carry out parentage and relatedness analyses in 15 Gabonese colonies. Monogamy was confirmed as the predominant reproductive organization in Cubitermes spp. (76% of the colonies). Within 30% of these monogamous colonies, a high relatedness between reproductives was shown, suggesting that mating between related individuals occurs. However, Cubitermes colonies can deviate from monogamy. Indeed, parental contributions by at least two related reproductives of the same sex were revealed in four colonies and polyandry was demonstrated in two of them. Infiltration of reproductives in the colony is the most plausible explanation for such cases of polygamy in Cubitermes spp. [source]

An analytical solution of one-dimensional consolidation for soft sensitive soil ground

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 9 2004
Yun-Min Chen
Abstract An analytical solution of one-dimensional consolidation for soft sensitive soil ground is presented. The moving boundary is introduced to indicate the notable change of consolidation behaviour of sensitive soil with the increase of stress level. It is assumed that the soil structure of the upper subsoil gradually destroys downwards with the dissipation of pore pressure, and the coefficient of consolidation as well as the coefficient of permeability of the upper subsoil become small, which hinders the dissipation of pore pressure of the lower subsoil. The consolidation degree curve obtained from the present solution is found to lie between the two curves obtained from Terzaghi one-dimensional consolidation solution with the parameters of the undisturbed soil and the remolded soil. The calculated results provide a new explanation for a general phenomenon in the consolidation of soft sensitive soil ground, as that for high loadings the consolidation is longer than for small ones. It should be pointed out from this study that both the deep mixing method and the long vertical drains methods are effective techniques for improving deep sensitive soil ground. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Stabilization of soft clay in irrigation projects,

IRRIGATION AND DRAINAGE, Issue 2 2005
M. M. Mubeen
stabilisation de chaux; utilisation d'argile molle; déchet de pierre pulvérisée; ouvrage d'irrigation Abstract Clay,lime improvement is an effective means to improve soft clay soil. Lime stabilization especially improves the strength and the workability of the clay soil. In addition, lime improvement provides more resistance to the soil structure and to the effect of weather on the soil structure. This study has investigated lime stabilization of soft clay and the possibility of utilizing waste rock powder produced in crusher plants as a supplemental material for lime stabilization in order to increase the strength of the soil structure. The purpose of the study was to apply the results especially in irrigation projects in order to avoid the problems of soft clay on irrigation structures in Sri Lanka. However, the results and conclusions can be considered for other regions, where the same type of soft clay problems exists. The Dutch Oostvaardersplassen (OVP) soft clay, which has a high plasticity, low shear strength and high natural water content, was chosen for the investigations. The results of unconfined compressive strength for different water contents of clay and also for different lime and waste rock powder contents show an excellent increase in strength and workability. The waste rock powder proved to increase the effect of lime stabilization. The strength improvement caused by waste rock powder is more significant for those soils which have a low clay content. Since in irrigation projects a wide range of clay soils exist, this investigation may be useful to utilize waste rock powder in order to improve the quality and the durability of the foundation of irrigation structures in the long run. Therefore the application of lime and rock material improvement on soft clay in irrigation projects may be a useful approach to stabilize soft soils and improve medium-scale shallow foundation irrigation structures and road and canal embankments, including repairing canal leaks. It has also been found that by applying this method in irrigation projects in Sri Lanka, the stabilization cost for structures on soft clay can be significantly reduced compared to other methods. Copyright © 2005 John Wiley & Sons, Ltd. L'amélioration de l'argile avec de la chaux est une moyenne effective pour améliorer la terre de l'argile molle. Spécialement la stabilisation de chaux améliore la force et la maniabilité de la terre argileuse. De plus l'amélioration de chaux fournit plus de résistance à la structure de la terre avec l'effet du temps sur la structure de la terre pendant les conditions atmosphériques différentes. Dans cette étude on a examiné la stabilisation de chaux dans l'argile molle et la possibilité de utiliser des déchets de pierre pulvérisée, obtenus par pulvériser des usines, comme une matérielle supplémentaire pour la stabilisation de chaux afin que la force de la structure de la terre s'améliore. L'objective de cette étude était d'appliquer les résultats spécialement dans des projets d'irrigation pour éviter des problèmes de l'argile molle dans des structures d'irrigation en Sri Lanka. Les résultats et les conclusions peuvent être considérés pour d'autres régions, ayant le même problème de l'argile molle. Les Oostvaarderplassen (OVP) en Hollande ont de l'argile molle ayant une plasticité haute, une résistance au cisaillement basse et un haut pourcentage de l'eau naturelle. C'est pour ça les Oostvaardersplassen ont été choisis pour accomplir la recherche. Les résultats de la force de pression indéfinie pour des teneurs en eau différents dans l'argile, aussi pour les teneurs en chaux différents et des déchets de pierres pulvérisées montrent une augmentation excellente de la force et de la maniabilité. Les déchets de pierre pulvérisée se révèlent d'augmenter l'effet de la stabilisation de chaux. L'amélioration de la force, causée par les déchets de pierre pulvérisée, est plus significative pour ces terres ayant un teneur d'argile bas. Parce que les projets d'irrigation ont beaucoup de la terre d'argile cette recherche peut être utile pour user des déchets de pierre pulvérisée pour améliorer la qualité et la durabilité de la fondation des structures d'irrigation à long terme. C'est pourquoi l'application du matériel de chaux et de pierre sur de l'argile molle dans des projets d'irrigation peut être une approche utile pour stabiliser des terres molles et peut améliorer des structures de fondations d'irrigation dans des eaux pas profondes, dans des remblais de chemins et de canaux, inclus dans des réparations des fuites de canaux. Aussi on a révélé qu'en appliquant ce méthode dans des projets d'irrigation en Sri Lanka les coûts de la stabilisation des structures sur de l'argile molle peuvent être réduits d'une manière importante comparée avec d'autres méthodes. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Arbuscular mycorrhizal propagule densities respond rapidly to ponderosa pine restoration treatments

JOURNAL OF APPLIED ECOLOGY, Issue 1 2003
Julie E. Korb
Summary 1Mycorrhizae form a critical link between above-ground plants and the soil system by influencing plant nutrition, nutrient cycling and soil structure. Understanding how mycorrhizae respond to disturbances may lead to important advances in interpreting above-ground plant recovery. 2The inoculum potential for arbuscular mycorrhizae (AM) and ectomycorrhizal (EM) fungi was investigated in thinned-only, thinned and prescribed burned (both restoration treatments) and unthinned and unburned control stands in northern Arizona ponderosa pine forests. The relationships between mycorrhizal fungal propagule densities and plant community and soil properties were quantified. 3The relative amount of infective propagules of AM fungi was significantly higher in samples collected from both restoration treatments than their paired controls (unthinned and unburned stands). In contrast, the same restoration treatments had no significant effect on the relative amount of infective propagules of EM fungi. 4The relative amount of infective propagules of AM fungi was significantly positively correlated with graminoid cover and herbaceous understorey species richness and negatively correlated with overstorey tree canopy cover and litter cover. 5Synthesis and applications. These results indicate that population densities of AM fungi can rapidly increase following restoration treatments in northern Arizona ponderosa pine forests. This has important implications for restoring the herbaceous understorey of these forests because most understorey plants depend on AM associations for normal growth. These results also can be applied to other ecosystems that are in a state of restoration or where the role of fire is just beginning to be understood. [source]

Fluid biomulching based on poly(vinyl alcohol) and fillers from renewable resources

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008
E. Chiellini
Abstract This article reports on the results obtained in an investigation on the application of biodegradable polymeric materials in the agricultural practice of mulching. Particular attention has been devoted to the effect of biobased mulching films generated in situ by low-pressure spraying of polymeric water dispersions on the various cultivars. In a field trial, the effectiveness of the hydromulching (liquid-mulching) technique was assessed by the monitoring of the growth and yield of lettuce and corn, which were used as reference plants. Conventional plastic films and straw mulching (SM) were compared with liquid-mulching treatments based on poly(vinyl alcohol) and natural fillers derived from agroindustrial wastes (sugar cane bagasse, wheat flour, saw dust, and wheat straw). An improvement of the biomass yield of the two selected plants with respect to conventional polyethylene mulching was attained in various liquid-mulching formulations with positive effects on the maintenance of soil structure. Alternative fluid-mulching treatments based on biodegradable components were effective in preserving soil aggregates and improving some crop growth parameters. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

Quantification of soil structural changes induced by cereal anchorage failure: Image analysis of thin sections

JOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 3 2007
Sacha J. Mooney
Abstract Cereal anchorage failure, or lodging, is the permanent displacement of a crop from the vertical and results in significant annual yield losses globally. Several factors have been identified as contributors to this phenomenon but the precise mechanisms of failure are still largely unknown because of difficulties in observing these processes as they occur in situ. To identify potential soil management practices to minimize losses associated with cereal root failure, an understanding of the nature of root-soil interactions attributed to lodging is needed. An experiment was conducted that involved field impregnation and subsequent thin sectioning of lodged and unlodged root-soil complexes from contrasting soils, cereal crops, and management practices to elucidate the effects of lodging on soil structure and porous architecture. Using image analysis, size and distribution of pores in soils were quantified at both meso- (100,30 ,m) and microscales (<30 ,m). A significant effect of lodging on porosity was recorded whereby lodging reduced total porosity through compaction created by movement of the stem base, although this was variable among soil types. Pore-size distributions comprehensively supported these trends since alteration in the relative frequency of pores within specific size classes was clearly observed. The effects of lodging were more pronounced at the mesoscale because the data were more susceptible to variations created by natural soil heterogeneity at the microscale. These data suggested that sideways movement of the subterranean stem within the soil is a significant factor which is likely to affect the propensity for a cereal plant to lodge, indicating soil strength in the upper part of the soil profile is crucial. [source]

Soil-aggregate formation as influenced by clay content and organic-matter amendment

JOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 1 2007
Stephen Wagner
Abstract Naturally occurring wetting-and-drying cycles often enhance aggregation and give rise to a stable soil structure. In comparatively dry regions, such as large areas of Australia, organic-matter (OM) contents in topsoils of arable land are usually small. Therefore, the effects of wetting and drying are almost solely reliant on the clay content. To investigate the relations between wetting-and-drying cycles, aggregation, clay content, and OM in the Australian environment, an experiment was set up to determine the relative influence of both clay content (23%, 31%, 34%, and 38%) and OM amendments of barley straw (equivalent to 3.1,t,ha,1, 6.2,t,ha,1, and 12.4,t,ha,1) on the development of water-stable aggregates in agricultural soil. The aggregate stability of each of the sixteen composite soils was determined after one, three, and six wet/dry cycles and subsequent fast and slow prewetting and was then compared to the aggregate stabilities of all other composite soils. While a single wet/dry cycle initiated soil structural evolution in all composite soils, enhancing macroaggregation, the incorporation of barley straw was most effective for the development of water-stable aggregates in those soils with 34% and 38% clay. Repeated wetting-and-drying events revealed that soil aggregation is primarily based on the clay content of the soil, but that large straw additions also tend to enhance soil aggregation. Relative to untreated soil, straw additions equivalent to 3.1,t,ha,1 and 12.4,t,ha,1 increased soil aggregation by about 100% and 250%, respectively, after three wet/dry cycles and fast prewetting, but were of less influence with subsequent wet/dry cycles. Straw additions were even more effective in aggregating soil when combined with slow prewetting; after three wet/dry cycles, the mean weight diameters of aggregates were increased by 70% and 140% with the same OM additions and by 160% and 290% after six wet/dry cycles, compared to samples without organic amendments. We suggest that in arable soils poor in OM and with a field texture grade of clay loam or finer, the addition of straw, which is often available from preceding crops, may be useful for improving aggregation. For a satisfactory degree of aggregate stability and an improved soil structural form, we found that straw additions of at least 6.2,t,ha,1 were required. However, rapid wetting of straw-amended soil will disrupt newly formed aggregates, and straw has only a limited ability to sustain structural improvement. [source]

Effect of water and nitrogen management on aggregate size and carbon enrichment of soil in rice-wheat cropping system,

JOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 2 2004
Rojalin Tripathy
Abstract A study was carried out on a silty clay loam soil (Typic Haplustept) to evaluate the effect of farmyard manure (FYM) vis-à-vis fertilizer and irrigation application on the soil organic C content and soil structure. The fertilizer treatments comprised of eight different combinations of N and FYM and three water regimes. The results indicated that the application of FYM and increasing N rate increased soil organic carbon (SOC) content. Addition of FYM also increased the percentage of large sized water stable aggregates (> 5,mm) and reduced the percentage of smaller size aggregates. This was reflected in an increase in the mean weight diameter (MWD) and improved soil structure. The organic carbon content in macroaggregates (> 1,mm) was greater compared to microaggregates, and it declined with decrease in size of microaggregates. This difference in organic C content between macro- and microaggregates was more with higher N dose and FYM treated plots. The effect of residual FYM on MWD and organic C content of the soil after wheat harvest was not significant. The effect was less in deeper layers compared to surface layers of the soil. MWD was significantly correlated with the SOC content for the top two layers. [source]

The influence of multi-scale environmental variables on the distribution of terricolous lichens in a fog desert

JOURNAL OF VEGETATION SCIENCE, Issue 6 2006
Jennifer S. Lalley
Abstract Question: How do environmental variables in a hyper-arid fog desert influence the distribution patterns of terricolous lichens on both macro- and micro-scales? Location: Namib Desert, Namibia. Methods: Sites with varying lichen species cover were sampled for environmental variables on a macro-scale (elevation, slope degree, aspect, proximity to river channels, and fog deposition) and on a micro-scale (soil structure and chemistry). Macro-scale and micro-scale variables were analysed separately for associations with lichen species cover using constrained ordination (DCCA) and unconstrained ordination (DCA). Explanatory variables that dominated the first two axes of the constrained ordinations were tested against a lichen cover gradient. Results: Elevation and proximity to river channels were the most significant drivers of lichen species cover in the macro-scale DCCA, but results of the DCA suggest that a considerable percentage of variation in lichen species cover is unexplained by these variables. On a micro-scale, sediment particle size explained a majority of lichen community variations, followed by soil pH. When both macro and micro-scale variables were tested along a lichen cover gradient, soil pH was the only variable to show a significant relationship to lichen cover. Conclusion: The findings suggest that landscape variables contribute to variations in lichen species cover, but that stronger links occur between lichen growth and small-scale variations in soil characteristics, supporting the need for multi-scale approaches in the management of threatened biological soil crust communities and related ecosystem functions. [source]

Carbon sequestration in soils of central Asia,

LAND DEGRADATION AND DEVELOPMENT, Issue 6 2004
R. Lal
Abstract Problems of frequent drought stress, low soil organic carbon (SOC) concentration, low aggregation, susceptibility to compaction, salinization and accelerated soil erosion in dry regions are accentuated by removal of crop residues, mechanical methods of seedbed preparation, summer clean fallowing and overgrazing, and excessive irrigation. The attendant soil degradation and desertification lead to depletion of SOC, decline in biomass production, eutrophication/pollution of waters and emission of greenhouse gases. Adoption of conservation agriculture, based on the use of crop residue mulch and no till farming, can conserve water, reduce soil erosion, improve soil structure, enhance SOC concentration, and reduce the rate of enrichment of atmospheric CO2. The rate of SOC sequestration with conversion to conservation agriculture, elimination of summer fallowing and growing forages/cover crops may be 100 to 200,kg,ha,1,y,1 in coarse-textured soils of semiarid regions and 150 to 300,kg,ha,1,y,1 in heavy-textured soils of the subhumid regions. The potential of soil C sequestration in central Asia is 10 to 22,Tg,C,y,1 (16±8,Tg,C,y,1) for about 50 years, and it represents 20,per,cent of the CO2 emissions by fossil fuel combustion. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Semiarid land rehabilitation by direct drilling in the South Island, New Zealand,plant species and establishment technology

LAND DEGRADATION AND DEVELOPMENT, Issue 5 2004
B. J. Wills
Abstract Large areas of the east coast and inland basins of the South Island, New Zealand, are affected by periodic drought and/or semiarid climatic conditions, particularly during cyclic El Niño climatic events. The severity of these environmental conditions places great stress on introduced and native pasture species and frequently results in poor establishment of new pastures using standard drilling techniques. The objective of this study was to determine effective, practical means of rehabilitating semiarid land (about 470,mm annual rainfall) on a site in Central Otago. A comparison of two direct drilling methods, a novel strip-seeder drill and a standard hoe-coulter drill, was conducted in a trial initiated during spring 1998. Five drought-tolerant forage species were established: wheatgrass (Thinopyron intermedium), tall oat grass (Arrhenatherum elatius), birdsfoot trefoil (Lotus corniculatus), hairy dorycnium (Dorycnium hirsutum) and bluebush (Kochia prostrata). For the 2000/2001 growing season, species established with the strip-seeder drill had an overall mean herbage biomass of 235,g,m,,2,, three-times that for the hoe-coulter drill (77,g,m,,2,, P,<,0·001). Differences in herbage biomass between species were observed, with hairy dorycnium (mean 328,g,m,,2,) producing significantly (P,<,0·001) more herbage biomass than the other species. After the third spring, the percentage ground cover recorded from transects across the strip-seeder drill plots (cf. the hoe-coulter drill) was: wheatgrass,41,per,cent (10,per,cent); tall oat grass,44,per,cent (25,per,cent); birdsfoot trefoil,25,per,cent (5,per,cent); hairy dorycnium,50,per,cent (19,per,cent); and bluebush,4,per,cent (0,per,cent). The native plant content of the resident vegetation was reduced as a result of the drilling treatments and also when fertilizer was added to undistrubed pasture. The strip-seeder drill is capable of providing superior plant growth on dryland sites even during adverse drought conditions. It produces a furrow approximately 16,cm wider than the hoe-coulter drill, exerts a greater shattering effect on the soil structure and places fertilizer at depth. It is suggested that this assists plant establishment by providing good seedling protection from wind and sun, and subsequent plant growth by allowing easier root penetration to the subsoil where nutrients and moisture are available. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Labyrinthula terrestris: a new pathogen of cool-season turfgrasses

MOLECULAR PLANT PATHOLOGY, Issue 6 2007
MARY W. OLSEN
ABSTRACT A new disease of turfgrass known as rapid blight is caused by Labyrinthula terrestris, a newly described member of the Labyrinthulids. This unusual group of microorganisms previously has been found in marine systems, and L. terrestris is the only member of the genus Labyrinthula known to be a pathogen of terrestrial plants. Members of this genus are defined by the formation of ectoplasmic networks in which the unicellular somatic cells move or ,glide'. Infections of cool-season turfgrasses occur most commonly when they are irrigated with suboptimal irrigation water with elevated salinity. Disease has been observed in 11 states in the United States and in the United Kingdom. A phylogenetic study indicates that isolates from turfgrass in the United States fall firmly within a clade containing other Labyrinthula spp. and that they came from a common lineage. Its rapid emergence as a turfgrass pathogen may coincide with increased use of relatively high-salinity water or reclaimed water for irrigation. L. terrestris is a potential problem in susceptible turfgrass varieties wherever soil salinity is allowed to accumulate as a result of poor soil structure or suboptimal quality irrigation water is used for irrigation. [source]

The transient layer: implications for geocryology and climate-change science

PERMAFROST AND PERIGLACIAL PROCESSES, Issue 1 2005
Yuri Shur
Abstract Research treating permafrost-climate interactions is traditionally based on a two-layer conceptual model involving a seasonally frozen active layer and underlying perennially frozen materials. This conceptualization is inadequate to explain the behaviour of the active-layer/permafrost system over long periods, particularly in ice-rich terrain. Recent research in North America supports earlier Russian conclusions about the existence of a transition zone that alternates in status between seasonally frozen ground and permafrost over sub-decadal to centennial time scales. The transition zone is ice-enriched, and functions as a buffer between the active layer and long-term permafrost by increasing the latent heat required for thaw. The existence of the transition zone has an impact on the formation of a cryogenic soil structure, and imparts stability to permafrost under low-amplitude or random climatic fluctuations. Despite its importance, the transition zone has been the focus of relatively little research. The impacts of possible global warming in permafrost regions cannot be understood fully without consideration of a more realistic three-layer model. The extensive data set under development within the Circumpolar Active Layer Monitoring (CALM) program will provide a significant source of information about the development, characteristics, behaviour, and extent of the transition zone. This paper is focused on the uppermost part of the transition zone, which joins the active layer at sub-decadal to multi-centennial time scales. This upper part of the transition zone is known as the transient layer. Copyright © 2005 John Wiley & Sons, Ltd. [source]