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Purpose: Organic amendment applications have been proposed as important agricultural management practices for the maintenance of soil health. Weathered coal (WC), biochar (BC), and grass peat (GP) have been used widely and globally for a long time. However, the differences in soil physical properties following the application of these amendments have rarely been evaluated under the same field conditions. Methods: In this study, the changes in the physical properties of loamy clay soil after applying WC, BC, and GP (3%, w:w) were investigated under field conditions after 375 days. Results: Relative to unamended soil, the WC, BC, and GP applications increased the total porosity and decreased the bulk density of amended soils (P < 0.05). The soil water content increased by 23.8% following the BC application, whereas it was decreased by 10.5% following the GP application (P < 0.05). The application of all the amendments increased the soil average temperature by 0.71 °C (GP), 0.41 °C (WC), and 0.18 °C (BC) (P < 0.05). Additionally, the WC application increased the fraction of aggregates of 1–2 mm in size (by 47.6%) and of 2–5 mm in size (by 65.8%), and the stability of soil aggregates (P < 0.05). All the amendments increased the soil pores (> 300 and 30–300 µm) of amended soils, but the saturated hydraulic conductivity of these soils was not significantly improved. Conclusion: The application of WC can improve the formation and stability of soil aggregates to reduce the risk of soil erosion. BC is suitable for use in drought-prone areas with low rainfall and strong evaporation because it can increase the retention capacity of soil water. GP should be applied with caution, considering that its decomposition after extraction leads to the severe loss of organic carbon to the atmosphere. Overall, the selection of organic amendments in agricultural management practices should take into account the local environmental conditions. [ABSTRACT FROM AUTHOR]

Purpose: Biochar amendment is considered as a soil management practice worldwide for the sustainable agricultural production by improving soil physical property, fertility, and microbial activity. However, the change of soil structure and hydraulic conductivity over time after applying biochar to expansive clayey soil under field conditions are unclear. Materials and methods: In this study, biochar was applied to soil at the rates of 0% (CK), 1% (BC1), and 3% (BC3) (w/w) to assess the variation in soil physical properties after day 10, day 193, and day 375, respectively. Results and discussion: The results showed that the total soil porosity estimated based on bulk density and the average particle density of 2.65 g cm−3 was significantly higher than the total porosity as measured by water retention curve (P < 0.05). Compared with day 10, the measured total porosity at days 193 and 375 significantly decreased by 5.09% and 7.38%, respectively, under CK; however, that significantly increased by 2.14%/2.60% and 1.85%/3.60%, respectively, under BC1/BC3 (P < 0.05). The average bulk density in 1 year was significantly lower 3.30%/6.99% under BC1/BC3 than CK (P < 0.05). Compared with CK, soil pores (5–30 μm) significantly increased by 12.71% under BC3 and soil pores (> 300 μm) significantly increased by 114.25%/164.58% under BC1/BC3 after 375 days (P < 0.05). There were no significant differences in the saturated hydraulic conductivity among all treatments after 1 year (P < 0.05). Conclusions: Our findings indicate that the estimated total porosity is not suitable for evaluating the change of soil porosity over time after biochar application. Biochar in size less than 2 mm can improve soil structure in expansive clayey soil under field conditions. However, these positive changes may be insufficient to facilitate the improvement of saturated hydraulic conductivity after 1 year at the biochar application rates of 1% and 3%. Our findings provide insights into the application of biochar as a soil amendment for management practices in expansive clayey soil. [ABSTRACT FROM AUTHOR]

Intense mechanization during forest harvesting and timber extraction degrades soil structure and affects pore functioning, but no studies have clearly distinguished the response of composition and functional soil properties to pine harvest in a subtropical environment. This paper describes the effect of mechanized harvesting of Pinus taeda L. on compaction and pore functioning of two subtropical Alfisols intensively used for commercial forest production in southern Brazil. The study was conducted in a 17-year old commercial forest of P. taeda on clay and sandy clay Hapludalf soils. Soil conditions tested were a control, i.e., before harvesting (BH); after tree felling (AF) in the full tree system; after timber dragging with one skidder pass (A1P); after timber dragging with three skidder passes (A3P); and after timber removal from stocking yard (TY). We evaluated composition (bulk density, degree-of-compactness, total porosity, and macroporosity) and functional (saturated hydraulic conductivity, precompression stress, compressibility coefficient, and penetration resistance) soil properties. The results show the upper soil layer is the most vulnerable to compaction, which significantly impairs pore functioning. Nevertheless, machine wheeling may affect subsurface layers (down to at least 0.40 m, as tested herein) depending on soil type, moisture and structure. Three passes of the skidder resulted in greatest degree-of-compactness, high bulk density, low macroporosity (below the critical level), reduced hydraulic conductivity (nearly water impermeable), and increased resistance to penetration (above the critical limit of 2 MPa). Pine harvest residues (9.8–15.6 Mg ha −1 , corresponding to 7.3–8.2 cm height) were insufficient to dissipate stress applied by skidder intense wheeling. We show planning of harvesting activities must consider reducing traffic intensity and/or establishing permanent traffic routes to ensure minimum damage on forest soils, particularly on their functional soil properties. [ABSTRACT FROM AUTHOR]

Studies of the volume change behaviour of saturated and unsaturated fine-grained soils upon exposure to various types of fluid are of significant interest while dealing with contaminated soils. In this study, the one-dimensional volume change behaviour of two clays (Spergau kaolin and Calcigel bentonite) with dominant minerals as kaolinite and montmorillonite was studied by inundating several initially unsaturated and saturated clay specimens with water and a non-polar organic liquid (heptane). For both cases, applied vertical pressures of 25 and 100 kPa were considered under oedometric conditions. The magnitude of compression and swelling deformations of the clays were found to be strongly dependent upon the mineralogy of clays, dielectric properties of the pore-fluid, initial compaction conditions, and applied stress during the wetting process. The test results indicated distinct interactions between unsaturated clays and water. Specimens of Spergau kaolin exhibited compression with water, whereas specimens of Calcigel bentonite exhibited swelling. Compression and swelling deformations of the clays with heptane as the inundating liquid remained within about ±1.0% for both clays indicating a very minor interaction between unsaturated clays and molecules of this non-polar organic liquid. The test results emphasized the significance of attractive and repulsive forces and their impact on the volume change behaviour of clays of different mineralogy. [ABSTRACT FROM AUTHOR]

Biochar amendment can change the soil pore architecture and improve soil physical and hydraulic properties. In this study, two clayey soils were selected and treated with or without biochar amendment (four treatments). Synchrotron-based X-ray micro-computed tomography (SR-mCT) was used to characterize pore structures of the selected aggregates from the treatments. Based on the high-resolution soil pore structure information, the three-dimensional lattice Boltzmann (LB) method was used to simulate water flow in pores. The highresolution soil pore structures were also used to define the internal boundary conditions in the LB method that was accelerated by graphics processing unit parallel computing. Results showed that biochar amendment increased soil permeability by at least one order of magnitude, reduced tortuosity by 20 to 30%, and resulted in more uniformly distributed pore water velocities, which was attributed to the change in soil pore geometry. This study is the first physically based modeling effort to assess the effect of biochar amendment on hydraulic properties of soil aggregates. The SR-mCT method and modeling approach developed in the research play an important role in understanding the mechanisms of water and nutrient transport in soil at the pore scale. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A review of the McNeal clay swelling model, including its underpinning assumptions and the method for determining its parameters, was undertaken. Limitations of the model include model parameter identification, the fixed threshold exchangeable sodium percentage level at which hydraulic conductivity begins to decline, and the assumption that the expanding clay will always be 10% of the soil. To overcome these problems, an improved form of the model that accommodates a range of clay content is proposed. The modified model was used to estimate the reduction in saturated hydraulic conductivity in the three McNeal groups of soils containing different percentages of expanding clay. The model produced good agreement between the observed and estimated saturated hydraulic conductivities over the entire range of irrigation salinity (3-200 mmolc/L) and sodicity used for the original swelling model. The modified model was also successfully validated against three new sets of relative hydraulic conductivity data. The generalization of interlayer clay swelling in the modified model is more appropriately described as determining the dispersive potential of a given solution, rather than physical interlayer swelling. Consequently, this modified model more accurately predicts the reduction in saturated hydraulic conductivity as a function of the sodicity and salinity of the applied water. [ABSTRACT FROM AUTHOR]

Vegetated buffer zones ( BZs) between arable fields and bodies of water are commonly established to reduce erosion and run-off of particle-bound nutrients. Functioning of a BZ depends on soil structure, as it is important for water infiltration. Therefore, it is vital to understand how varying management practices affect soils of BZs. We studied the structural and hydraulic properties of three differently managed BZs established in a boreal Vertic Stagnic Cambisol (clay, 51%). The three management practices for vegetation were as follows: natural with no treatment, harvested yearly and grazed by cattle. We used bulk density and macroporosity, together with a pore geometry index (air permeability per unit air-filled porosity), to describe the soil structural properties. Hydraulic properties were measured at different length scales by means of an aggregate sorptivity test, saturated hydraulic conductivity of the core samples and field-saturated hydraulic conductivity. Vegetation management markedly affected the physical properties in the top 5 cm of the soil. Properties were least favourable for infiltration at the grazed site, with the greatest bulk density, least macroporosity and hydraulic conductivity or greatest pore tortuosity. In general, spatial variation in zones with restricted and good hydraulic conductivity together with reduced aggregate sorptivity in the deeper horizons made the soil prone to preferential flow when initially dry. Prolonged wetness, on the other hand, reduced saturated hydraulic conductivity significantly, resulting in surface run-off. Harvesting was considered the best management practice due to its inherent capacity for reducing the soil nutrient content and because it has minor implications for soil physical properties. [ABSTRACT FROM AUTHOR]

Abstract: Water infiltration is a crucial process for functioning of vegetated buffer zones (BZ). Structure of a clayey surface soil of three differently managed BZs, i.e., 1) natural with no treatment, 2) harvested once a year and 3) grazed by cattle was investigated in this study. Soil macro pores (>50μm) were characterized by qualitative description and quantitative image analysis of soil thin sections in order to assess their capability to water infiltration. Less than 10% of the macro pores consisted of rounded and irregular pores smaller than 300μm indicating root activity. Instead, macro porosity was clearly dominated by elongated pores characterized by irregularity, expressing the complexity of the pore system. This pore pattern appeared in thin sections as weak or moderate ped separation suggesting good water infiltration when initially dry. Partial accommodation of pores may result in decrease of hydraulic conductivity, as these pores tend to close upon wetting and swelling. In the grazed site a platy structure was observed due to hoof pressure, which may further impair the hydraulic properties of soil. Moisture and temperature related processes (shrink–swell, freeze–thaw, and water saturation) are thought to be conducive to the aggregation and rearrangement of soil structure around the year, resulting in a complex pore system with low intra-aggregate porosity. In addition, wet periods typical of boreal soils result in clay dispersion and formation of aggregate-related pedofeatures of dense infillings, described as fine clay intrusions. [Copyright &y& Elsevier]

An experiment was mounted under a heavy clay soil in order to define the place for the application of stripe tillage either in row or in the inter-row space according to the physical soil properties. Structure factor FE, aggregate stability AE and permeability index K was evaluated. It was found that: the FE in row at 0 to 20 cm showed significant different respect to both depths of inter-row space in 1,2 and 2% respectively, also in row at 20 to 40 cm in regard to the same depth of inter-row in 1.3%; in other side It was found significant difference in AE in the row at 0-20 cm in respect to both depth of the inter-row in 3.6 and 5.4% respectively and between the row and the inter-row at 20 to 40 cm in 3,1% too. The values of K to the row at 0 to 20 cm showed significant difference in regard to the other depth of that zone and both depth of the inter-row in 0,07, 0,08 and 0,14 respectively, and also among the row at 20 to 40 cm and the inter-row at 0 to 20 and from 20 to 40 cm of the last one in 0,06 approximately. The tilling located is recommended in the row of sugar cane. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The aim of this study was to evaluate the compacting effect of rubber tracked tractors in comparison to that of the traditional wheeled tractors. Macroporosity, pore shape and size distribution, bulk density, penetration resistance and saturated hydraulic conductivity were analysed in a clay soil (Vertic Cambisol) near Rome (Italy) following one and four passes on the same track of rubber tracked and wheeled tractors of medium power. The soil structure attributes were evaluated by characterising porosity by means of image analysis of soil thin sections prepared from undisturbed samples. Macroporosity decreased in the 0–10 cm layer of compacted soil, particularly after four tractor passes, due to a large reduction in the proportion of elongated pores and in their vertical continuity. The rubber tracked tractor had a more pronounced compaction effect in the surface layer (0–10 cm) than the wheeled tractor both after one and four passes; the latter treatment producing the lowest soil porosity. The same trend was observed for hydraulic conductivity, which showed a highly significant correlation with elongated pores. In the 10–20 cm layer the porosity was significantly decreased following traffic, apart from in the soil under one pass of the rubber tracked tractor. Again in this layer, the lowest values of porosity were found in soil after four passes of the rubber tracked tractor. Single and multiple passes made by the two tractors induced different effects regarding soil penetration resistance and bulk density. Increment ratio of penetration resistance after tractor passes with respect to the control was: 12.5 and 49.9% with the wheeled and 34.4 and 39.8% with the tracked after one and four passes, respectively. Increment ratio of dry bulk density values after tractor passes with respect to the control was 7.9 and 11.7% with the wheeled and 7.5 and 8.3% with the tracked after one and four passes, respectively. The tractor passes transformed the initial subangular blocky structure into a massive structure with sometimes a platy structure in the upper few centimetres. The results indicated that soil compaction following traffic with the rubber tracked tractor was generally the more pronounced. However the compacting effect of this tractor after one pass seemed to be limited to the surface layer only. [Copyright &y& Elsevier]

Even though the most prominent soil degradation processes are observed at arable lands, natural soils are also prone to deterioration processes, and in a greater extent over the recent years, due to global climate change, that accelerates soil erosion and the salinization processes. The observed soil degradation processes included: (1) soil salinization that is seen as salt crusts at the soil surface (Figure 2); (2) soil compaction (Figure 3), and soil erosion (Figure 4). [Extracted from the article]