Showing papers on "Silt published in 2018"

Spatial variability of soil texture fractions and pH in a flood plain (case study from eastern Iran)

Abstract: Flood plain ecosystems show significant soil spatial variability. Understanding spatial variations of soil texture fractions and pH in flood plains is necessary for ensuring proper management of these plains, because these properties influence soil structure, fertility, hydraulic conductivity, infiltration, and erosion. In the present study, the distribution of soil texture fractions and pH was investigated in a flood plain with intensive wind erosion for an area of ~ 41,000 ha in Zahak county of Sistan and Baluchestan province in eastern Iran. A random forest technique was used to link environmental variables and the studied properties. 460 soil samples were collected from 0 to 30 cm depth across a 750 m grid. 361 samples were used for training and 99 for independent validation. Results showed that the distance from the river was the most important environmental variable for predicting soil texture fractions and pH in the study area. Natural channel networks, elevation, valley depth, LS factor, NDSI, vertical distance to channel networks, slope, wind effect, NDVI, and brightness were other important variables. The maps produced indicated a higher sand content near Sistan River. Clay, silt, and pH contents increased with distance from Sistan River. Results showed that clay and pH had a similar distribution in the study area. The values of RMSE for the maps of estimated sand, silt, clay, and pH in validation data were respectively 21.40, 17.45, 6.06 and 0.45. These values of RMSE for sand, silt, clay, and pH were respectively 10.3, 10.7, 15.1, and 13.3% lower than a simple model (mean model). Results indicated that using the distance from the river and channel networks as a variable in digital soil mapping can increase the accuracy of the predictive maps of soil properties in flood plains.

Phosphorus cycling within soil aggregate fractions of a highly weathered tropical soil: A conceptual model

Abstract: Effective use of soil phosphorus (P) for crop production requires an understanding of how P pools are stabilized and cycled within soil aggregates, rather than assuming that P dynamics, particularly organic P, closely follow those of C. The main goal of this study was to compare C and N cycling with P dynamics in soil aggregate fractions under two distinct crop species, maize (Zea mays) and pigeon pea (Cajanus cajan) in a highly-weathered Lixisol. We found that while C and N follow an open cycle, whereby C and N are mineralized from microaggregates during macroaggregate turnover and partially exit the soil system as gas and leachate, P has a relatively closed cycle, where most of the mineralized and solubilized P from microaggregates is lost from the plant-available pool via sorption to the unaggregated silt and clay-sized particles (<53 μm). While the above postulated P cycling mechanisms were the same for maize and pigeon pea, P loss from microaggregates and subsequent enrichment of the silt and clay particles was significantly higher in soils under maize compared to pigeon pea (320 and 331 mg P kg−1 lost from occluded microaggregates and gained by free silt and clay particles, respectively, compared to 129 and 97 mg P kg−1 under pigeon pea). This is attributed to the significantly increased soil aggregation under pigeon pea, which led to greater accumulation of P, particularly organic P, in the free microaggregates (77 mg P kg−1 compared to 29 mg P kg−1) and slower rates of macroaggregate turnover. We conclude that increasing soil aggregation can substantially reduce organic P losses from aggregate occluded fractions and its subsequent sorption as inorganic P to silt and clay particles. Thus, P cycling can be improved in tropical cropping systems on highly-weathered soils by introducing crop species that enhance the occlusion of organic P into aggregates.

Changes in soil properties and erodibility of gully heads induced by vegetation restoration on the Loess Plateau, China

Abstract: Soil erosion on the Loess Plateau of China is effectively controlled due to the implementation of several ecological restoration projects that improve soil properties and reduce soil erodibility. However, few studies have examined the effects of vegetation restoration on soil properties and erodibility of gully head in the gully regions of the Loess Plateau. The objectives of this study were to quantify the effects of vegetation restoration on soil properties and erodibility in this region. Specifically, a control site in a slope cropland and 9 sites in 3 restored land-use types (5 sites in grassland, 3 in woodland and 1 in shrubland) in the Nanxiaohegou watershed of a typical gully region on the Loess Plateau were selected, and soil and root samples were collected to assess soil properties and root characteristics. Soil erodibility factor was calculated by the Erosion Productivity Impact Calculator method. Our results revealed that vegetation restoration increased soil sand content, soil saturated hydraulic conductivity, organic matter content and mean weight diameter of water-stable aggregate but decreased soil silt and clay contents and soil disintegration rate. A significant difference in soil erodibility was observed among different vegetation restoration patterns or land-use types. Compared with cropland, soil erodibility decreased in the restored lands by 3.99% to 21.43%. The restoration patterns of Cleistogenes caespitosa K. and Artemisia sacrorum L. in the grassland showed the lowest soil erodibility and can be considered as the optimal vegetation restoration pattern for improving soil anti-erodibility of the gully heads. Additionally, the negative linear change in soil erodibility for grassland with restoration time was faster than those of woodland and shrubland. Soil erodibility was significantly correlated with soil particle size distribution, soil disintegration rate, soil saturated hydraulic conductivity, water-stable aggregate stability, organic matter content and root characteristics (including root average diameter, root length density, root surface density and root biomass density), but it showed no association with soil bulk density and soil total porosity. These findings indicate that although vegetation destruction is a short-term process, returning the soil erodibility of cropland to the level of grassland, woodland and shrubland is a long-term process (8–50 years).

Mulching effects on erosion from steep slopes and sediment particle size distributions of gully colluvial deposits

Abstract: Mulching is an effective soil conservation practice for permanent gullies in southern China. Knowledge of the sediment characteristics that occur in mulched soils of colluvial deposits could improve the utility of mulching for soil conservation. A rainfall simulation experiment was designed to evaluate the effects of mulch on the runoff, erosion, and particle size distribution of eroded sediments. Straw mulch coverage of 0, 25, 50, 75, and 95% was tested with simulated rainfall. The effective particle size distribution of the sediment was compared with the ultimate particle size distribution to investigate the detachment and transport mechanisms involved in sediment mobilization. Mulching delayed the runoff initiation time and reduced the average runoff rate. Compared with bare soil, the increased mulch coverage decreased the soil loss rate by 13.0 to 90.3%. Moreover, the peak sediment concentration decreased from 80 to 200 g L− 1 under the different mulch coverage conditions. The optimal straw application rate was 1.5 to 3.0 Mg ha− 1 in the permanent gully's deposits. The relationship between instantaneous kinetic energy of rainfall and the proportion of effective clay- and sand-sized particles was well represented using an exponential equation. The effective clay-sized sediments under the different mulch coverage conditions were 2 to 4 times more common than those of the original soil, although there were only 13.9% sand-sized particles in the sediment when the mulch coverage was 95%. The silt-sized sediment was transported as primary particles under the different mulch coverage conditions. The effective to ultimate ratio of silt-sized particles fluctuated around 1. There were depletions of clay and silt in the colluvial deposit soil with mulch cover, and the enrichment ratios of clay and silt were larger than 1 while most of the enrichment ratios for sand were

Using laboratory Vis-NIR spectroscopy for monitoring some forest soil properties

Abstract: The development of rapid, accurate, and cost-effective methods to determine forest soil properties such as visible and near infrared (Vis-NIR) spectroscopy is important for sustainable land management. The main objective of this study was to assess the suitability of Vis-NIR spectroscopy coupled with partial least squares regression (PLSR) to determine some forest soil properties such as organic carbon (SOC), total nitrogen (TN), pH, and soil texture (sand, silt, and clay) for a representative forest area in southern Italy. Soil samples (0–20 cm depth) were collected at 267 locations, oven-dried and passed through a 2-mm sieve, and analyzed for some chemical and physical soil properties using conventional laboratory methods. Vis-NIR reflectance of each soil sample was measured in laboratory under artificial light using an ASD FieldSpec IV 350–2500 nm spectroradiometer. Partial least squares regression (PLSR) was used to develop a calibration model for SOC, TN, pH, sand, silt, and clay. Samples were split into a calibration set (187 samples) to develop the models and a validation set (80 samples) to assess the prediction accuracy of the calibration models. Results showed a good agreement between measured and predicted values with high R 2 and low root mean square error (RMSE) values. Model validation using independent data was satisfactory for all the studied soil properties. Finally, findings confirmed that laboratory Vis–NIR spectroscopy has the potential to be a non-destructive and cost-effective tool for rapid determination of many soil properties. The spectral data collected in this study could contribute to build a regional soil spectral library to be used advantageously in support to soil survey in other areas of the Calabria region (southern Italy).

Application of Lignin-Stabilized Silty Soil in Highway Subgrade: a Macroscale Laboratory Study

Abstract: Lignin is an industrial by-product, stockpiles of which are rapidly increasing worldwide due to growing demand. Highway subgrade construction has been identified as one of the viable answer...

Mineralization of organic carbon and nitrogen in semi-arid soils under organic and inorganic fertilization

Abstract: Although compost is added to soils to improve their nutritive status and properties; yet upon its decomposition, considerable amounts of CO2 might be emitted to the atmosphere causing hazardous environmental risks. Investigating the mineralization of compost applied to a sandy soil and a silty clay one of low organic-C content in the green house for 90 days under soil moisture contents of 75 or 100% of FC was considered. Efflux rate of CO2 decreased considerably for one day in the sandy soil after application of the compost; beyond which showed an almost constant rate. In the silty clay soil, the efflux rate decreased obviously to achieve non detectable value 3 days later. Even in soils amended with mineral N-fertilizer, CO2 emissions were valued while decreased with time. By the end of the incubation time, the rate of C-mineralization was significantly higher in the sandy soil compared with the silty clay one. Increasing soil moisture content from 70 to 100% of the field capacity led to further increases in rates of CO2 efflux as well as org-C mineralization. The amount of N mineralized in the sandy soil was 1.7 times higher than its content in the silt clay one at the FC and 1.1 times in case of 70% of FC. In conclusion, a reversible equilibrated process between decomposition of soil organic matter and buildup of more stable organic components might exist at the same time.

Extent and Causes of Siltation in a Headwater Stream Bed: Catchment Soil Erosion is Less Important than Internal Stream Processes

Abstract: The stream bed is a key habitat for many species, and its physicochemical properties govern important ecosystem functions. Stream bed colmation resulting from catchment erosion is considered a core problem of stream headwaters in which many species depending on coarse substrates are in decline. Here, we identify the origin of fine sediment and compare the contribution of external (i.e. catchment erosion) versus internal (i.e. in-stream carbonate precipitation and internal biomass production) sources of siltation using a case study of a pre-alpine river, the Moosach. The stream bed was dominated (51%) by fine sediment of mainly silt size. The average fine sediment thickness of 58 cm and a net deposition rate of 1.32 kg m−2 yr−1 confirmed siltation problems. Mineral analyses and mass balancing showed that still only less than 1% of the erosion input into the stream was deposited on the stream bed. Internal temperature-dependent calcite precipitation also removed less than 1% of the calcium from the water column. Thus, by far, most of the fine material from erosion and precipitation was transported and did not contribute to the deposition of fines. Since the colmation problem is governed by the sink, it cannot be solved by exclusively addressing the sources (erosion, precipitation). Despite the well-founded linkage between terrestrial and aquatic systems, this study suggests that restoration of stream bed quality must also focus on in-stream processes and flow regime management, while erosion control remains essential in its own right. Copyright © 2017 John Wiley & Sons, Ltd.

Estimation of unsaturated shear strength parameters using easily-available soil properties

Abstract: Unsaturated soil shear strength is an important parameter in soil erosion and management. Measurement of unsaturated shear strength at field scale is difficult, time-consuming, and very costly. This study was conducted to investigate the relationship between unsaturated shear strength parameters and soil properties, and to predict the unsaturated shear strength parameters (effective cohesion, c', angle of effective internal friction, φ' and angle of internal friction related to matric suction, φb) using multiple-linear regression (MLR). Direct shear tests were performed at combinations of three normal stresses of 25, 50 and 100 kPa, and four matric suctions of 0, 10, 30 and 50 kPa (i.e., 12 tests per each soil) to determine the shear strength parameters in 14 soils. Soil properties including particle size distribution (sand, silt, and clay percentages or geometric mean diameter, dg and geometric standard deviation, σg), organic matter content (OM), calcium carbonate content (CaCO3), compactness indices (bulk density, ρb and, relative bulk density, ρb-rel), and mean weight diameter of aggregates (MWDdry, MWDwet), structural stability indices (aggregate stability, AS, stability index, SI and index of crusting, Ic) were determined and used as predictors in MLR models. Strong negative correlations were found between c' and φ'. The c' positively correlated with clay content. Significant negative correlation was observed between c' and sand fractions and dg. Significant positive correlation was obtained between φ' and fractions of sand and dg. The φ' negatively correlated with clay, fine silt content (FSi), MWDdry, and AS. The φb had no significant correlation with soil properties, indicating that φb is independent of soil properties and basically is affected by matric suction. Clay, coarse sand (CS) and very fine sand (VFS) were applied in the model for predicting c'. Clay had a positive and, CS and VFS had negative effects on c'. Pedotransfer functions (PTFs) using the fine sand (FS) and VFS as predictor could estimate the φ' accurately, so that they entered to PTFs with positive signs. In addition, the φb was predicted by parameter Ic only, so that it had negative effect on φb. Overall, better prediction models were developed for φ' than for c' and φb.

Short-Term Dynamics of Soil Physical Properties as Affected by Compaction and Tillage in a Silt Loam Soil

Abstract: This study investigated short-term dynamics of soil physical properties as affected by tillage and compaction in a silt loam soil. After establishment of an autumn-sown forage oat (Avena sativa L.) crop with either NT or intensive tillage (IT), five degrees of livestock compaction (0–261 kPa) were applied in winter using a “cow treading implement.” A barley (Hordeum vulgare L.) crop was then sown following shallow cultivation of the soil in spring. After 2 yr of sheep-grazed pasture, tillage significantly improved the soil physical quality in the 0to 0.2-m layer. Compaction significantly deteriorated soil physical quality, by, for example, decreasing macroporosity, available water content, and saturated hydraulic conductivity. Compared with IT and the top 0.1-m soil layer, soil physical properties in NT and the subsurface 0.1to 0.2-m layer were more resistant to compaction. Irrespective of tillage, the topsoil (0–0.1 m) was more susceptible to physical degradation than the subsurface soil (0.1–0.2 m). Compaction and tillage effects on soil physical quality declined with time because of natural recovery and the shallow tillage used to establish the subsequent barley crop. This study demonstrated that using NT to establish an autumn-sown forage crop can mitigate the adverse impacts of livestock treading on soil physical quality during subsequent grazing. Although tillage and compaction effects were short lived, soil physical properties were significantly different between every two adjacent measurement times. This highlights the need to consider the short-term changes in soil hydraulic properties when modeling soil–crop systems.

Experimental Determination of Dispersion Coefficient in Soil

Abstract: Unsaturated soil dispersion experiment was done using three different soil samples which includes sand, clay and silt soil. The objective of the study is to determine experimentally dispersion coefficient in soil. Each sample was gradually introduced into a fabricated iron column, having a length of horizontal column 30cm and vertical part 60.96cm. A solution of silver nitrate was allowed to pass through the vertical column down to the horizontal part. Samples of soil were collected at a constant distance of 10cm and time interval of 5mins for 60mins .The concentration of nitrate was taken at a constant distance of 10cm .This was done three times for each of the soil sample. Thereafter, the dispersion coefficient was calculated, and a regression dispersion model developed as a function of permeability, average diameter of sieve, velocity of flow and time taken to flow. The model was calibrated and verified with experimental results and found to have a high correlation coefficient (r) of 0.943. Data obtained from the experiments were fitted into the two existing models and poor correlation coefficients of -0.529 and -0.524 were obtained respectively.

Effect of Pore Size Distribution on Dissociation Temperature Depression and Phase Boundary Shift of Gas Hydrate in Various Fine-Grained Sediments

Abstract: Capillarity in small, confined pores has a pronounced effect on the depression of the dissociation temperature of gas hydrates, known as the Gibbs–Thomson effect. However, this effect remains poorly understood in natural fine-grained sediments with wide pore size distributions. This study investigated the effect of pore size distributions of fine-grained sediments on the dissociation temperature of a gas hydrate. A gas hydrate was synthesized under partially water-saturated conditions in nanosized silica gels and in various natural fine-grained sediment samples, including sand, silt, diatoms, a diatom–sand mixture, and clayey sediment. The synthesized hydrate samples were thermally dissociated under isochoric conditions, while the melting temperature depression and the shifted phase boundaries were monitored. We observed a dissociation temperature depression of approximately 0.1–0.3 °C in silt, 0.2–0.4 °C in the diatom sample, and 1.2–1.5 °C in clayey silt, while no temperature depression was observed in ...

Mechanism and Implication of the Sorption of Perfluorooctanoic Acid by Varying Soil Size Fractions

Abstract: Sorption of perfluorooctanoic acid (PFOA), a toxic and persistent organic pollutant, by various size fractions of an agricultural soil at environmentally relevant concentrations was evaluated. PFOA sorption to all fractions involved both film diffusion and intraparticle diffusion with the rate-limiting step by the latter. PFOA isotherm data fitted a linear model. Organic matter (OM), cation exchange capacity, pore volume, and the Brunauer-Emmett-Teller area played key roles in PFOA sorption. The sorption capacity followed the order of humic acid > clay (0.15-4.4 mm) > fine silt (1.9-39.8 mm) > coarse silt (17.3-79.4 mm) > fine sand (45.7-316.2 mm) > coarse sand (120-724.4 mm), opposite to their contributions to overall PFOA sorption due to the influence of their percentage weight in the original soil. Percentage OM content was the dominant factor controlling the fraction contributions to overall PFOA sorption, demonstrating influence of the hydrophobic force on sorption. PFOA should be highly mobile and bioavailable in soil-crop systems due to the low log Koc values.

Technical note: Saturated hydraulic conductivity and textural heterogeneity of soils

Abstract: . Saturated hydraulic conductivity ( Ksat ) is an important soil parameter that highly depends on soil's particle size distribution (PSD). The nature of this dependency is explored in this work in two ways, (1) by using the information entropy as a heterogeneity parameter of the PSD and (2) using descriptions of PSD in forms of textural triplets, different than the usual description in terms of the triplet of sand, silt, and clay contents. The power of this parameter, as a descriptor of ln⁡Ksat , was tested on a database larger than 19 000 soils. Bootstrap analysis yielded coefficients of determination of up to 0.977 for ln⁡Ksat using a triplet that combines very coarse, coarse, medium, and fine sand as coarse particles; very fine sand, and silt as intermediate particles; and clay as fine particles. The power of the correlation was analysed for different textural classes and different triplets using a bootstrap approach. Also, it is noteworthy that soils with finer textures had worse correlations, as their hydraulic properties are not solely dependent on soil PSD. This heterogeneity parameter can lead to new descriptions of soil PSD, other than the usual clay, silt, and sand, that can describe better different soil physical properties, that are texture-dependent.