Sandstone Soils Research Articles

Erodibility of soils of varying land utilization types and lithologic materials in central southeastern Nigeria


 
 
 Land use and parent materials influence behaviour of soils including responsiveness to erosion forces. The study investigated some soil properties related to erodibility in Abia and Imo States of Nigeria. Soil sampling was guided by geology and land use type. Random sampling technique was adopted in field studies. Two parent materials and three land use types were chosen for the study. In each parent material, three land use types were studied and in each land use, three soil profiles were sunk, described, and sampled using FAO procedure. Soil samples were subjected to laboratory analyses and data generated were analyzed using descriptive and inferential statistical tools. Results showed that sand sized particles ranged from 533.10 to 778.80 g kg–1 and this distribution differed significantly between parent materials. Silt content ranged from 141.70 g kg–1 in soils derived from false-bedded sandstone to 202.20 g kg–1 in shale-derived soils. Clay-sized particles ranged from 77.30 g kg–1 in soils derived from false-bedded sandstone to 264.70 g kg–1 in shale-derived soils, respectively. Water-stable aggregate ranged from 19.38% in false-bedded sandstone to 29.23% in shale-derived soils. The DR (dispersion ratio) mean values ranged between 4.26 in shale and 8.46 in false-bedded sandstone, while the CDI (clay dispersion index) mean values ranged between 2.17 in shale and 8.41 in false-bedded sandstone, respectively. The forest soils had the lowest values of both DR (6.89) and CDI (6.40) for soils of the false-bedded sandstone, 3.85 and 1.59 for those derived from shale. The clay flocculation index (CFI) had mean of 2.16 in false-bedded sandstone and 7.83 in shale. In soils of the varying land use types, the mean soil pH (H2O) ranged from 4.28 to 4.64 in soils derived from false-bedded sandstone and 4.27-5.57 in those derived from Shale. From the results, parent material and land use influenced soil erodibility parameters (water-stable aggregates, mean-weight diameter, DR, CDI, and CFI) and other soil properties such as organic carbon, bulk density, and moisture content.
 
 

Analysis of complex erosion models and their implication in the transport of Pisha sandstone sediments

Coarse sediment of the Yellow River in the complex erosion area of the Pisha sandstone region of the Ordos Plateau is deposited on the downstream riverbed, posing a threat to the flood control safety of the river. The objectives of the present study were to analyze the mechanisms of combined erosion and sediment yield under the synergistic action of multiple dynamics, employing the indoor artificial rainfall-wind-freezing-thawing cycle solid model test to explore the temporal and spatial variation of the coarse sediment production and the transportation process. In this study, complex erosion indoor tests were carried out through the artificial rainfall-wind-freezing-thawing cycle solid model. The enrichment rate (ER), fractal dimension, and median diameter (d50) of soil particles were used to quantify the size distribution characteristics of sediment particles under different erosion dynamics. The coarse sediment was first transported in the process of soil erosion because of the special texture and terrain characteristics of Pisha sandstone soil. Moreover, the degree of heterogeneity of sediment under complex erosion was larger than that under water erosion. The effect of wind could aggravate the instability of the erosion dynamic system. Under the combined action of freezing-thawing, wind, and water, the particle size composition changed greatly, and the erosion energy was extremely unstable. The effect of complex erosion created conditions for the coarse sediment transportation. Under the freezing-thawing-wind-water combined action, the particle size of eroded sediment was the coarsest, and that of water erosion was the smallest. We concluded that the reason why the Pisha sandstone area has become the core area of the concentrated source of coarse sediment in the Yellow River is related not only to the special nature of the Pisha sandstone soil itself but also to the effect of complex erosion.

Experimental research on applicability of weathered red sandstone soil to roadbed filling

The weathered red sandstone soil is seen with extreme strength reduction after encountering water. With an aim to evaluate the long-term stability of the weathered red sandstone soil as the roadbed filler, laboratory experiments are carried out for soil stabilised with cement dosages of 0%, 3%, 4%, and 5%, respectively. Meanwhile, the compressive rebound modulus and the unconfined compressive strength of the cement-stabilised soil are measured after 0–7 cycles of wetting and drying, respectively. Besides, scanning electron microscope (SEM) is used to observation and quantitative analyse. The testing results shows that the strength attenuation laws of stabilised soils with different cement dosages after wetting and drying cycles. Moreover, this study proposes the technical standard for cement-stabilised red sandstone soil used as roadbed filler.

Effects of a compound microbial agent and plants on soil properties, enzyme activities, and bacterial composition of Pisha sandstone.

The objective of this study was to investigate the effects of the microbial agent on the improvement of Pisha sandstone soil and find out an effective measure for the control of soil erosion in the Pisha sandstone area. Pisha sandstone containing the microbial agent composed of Bacillus halotolerans P75, Sinorhizobium meliloti D10, Bacillus megaterium H3, Bacillus subtilis HB01, and organic substrate was utilized to be the soil matrix for pot experiment, and then alfalfa, ryegrass, and caragana were planted, respectively. Effects of the microbial agent plus plants on the soil properties of Pisha sandstone were evaluated, and the results showed that the microbial agent plus plants significantly increased the organic matter content, alkali hydrolyzed nitrogen content, available phosphorus content, available potassium content, invertase activity, and urease activity. Meanwhile, inoculation with the microbial agent significantly promoted the growth of alfalfa, ryegrass, and caragana and also influenced the number of soil bacteria and the relative abundance of Proteobacteria, Bacteroidetes, Actinobacteria, and others. However, the effects of the microbial agent plus different plants on the soil properties and bacterial composition of Pisha sandstone were different, while the growth of different plants showed differences, suggesting that there was a different interaction between microbes and different plants in Pisha sandstone soil. In conclusion, the microbial agent plus plants could improve Pisha sandstone soil which could provide some theoretical and experimental references for soil erosion control in the Pisha sandstone area.

Impacts of residue quality and soil texture on soil aggregation pathways by using rare earth oxides as tracers

Rare earth oxides (REOs) as tracers track aggregate formation and breakdown pathways. However, investigations on the impacts of residue quality and soil texture on aggregation pathways are lacking. In this study, easily, moderately and slowly decomposable residues with different qualities (milk vetch, C/N = 16.7; maize, C/N = 35.5; and decomposed maize, C/N = 30.8) were applied to four types of red soils (Red clay, Basalt, Sandstone and Granite) with a range of soil textures. Aggregate fractions of each soil were labelled by different REOs. The soil respiration (CO2), mean weight diameter (MWD) and REOs concentrations were measured after 0, 7, 14, 28 and 56 days of incubation. The results showed that except for Basalt soil, the incorporation of organic residues increased the formation but decreased the breakdown of macroaggregates in the order of milk vetch > maize > decomposed maize in the first two weeks, thus leading to a greater standardized MWD in higher-quality residue-incorporated soils. In the mid-to-late incubation time (28–56 d), the standardized MWD and relative formation of macroaggregates in the milk vetch and maize treatments converged regardless of soil types. An exponential relation between the standardized MWD and accumulated CO2 (P < 0.05) indicated that the residue quality-dependent MWD dynamics were further driven by microbial activity. The two coarse-textured soils (Sandstone and Granite) presented a more rapid response of aggregation to microbial activity than the two fine-textured soils (Red clay and Basalt) did. The relative formation of 2–5 mm aggregates was significantly greater in Sandstone soil at a given residue incorporation, thus leading to a faster increase in the standardized MWD compared with fine-textured soils. However, a similar result was not observed in Granite soil. A positive linear relationship between the standardized MWD and 2–5 mm aggregate formation in all investigated soils (P < 0.001) suggested that MWD dynamics mainly depended on the newly formed large macroaggregate rate. Our study demonstrates that the dynamics of soil aggregation are closely related to microbial activity and newly formed macroaggregates, beyond the impacts of residue quality and soil texture on soil aggregation.

Weathering sequence of soils along a basalt-sandstone toposequence in the Brazilian Cerrado

Despite a multitude of studies on fertility and physics of tropical soils, the effect of soil parent material on their genesis, chemical and mineralogical composition is not yet fully understood. Here, we studied a toposequence of four deep, well-developed soils along a basalt-sandstone transition, comprising two Ferralsols and one Luvisol on the summit and midslopes of a basalt plateau, and one Cambisol at a lower sandstone plateau. Basalt soils had high (42–77%) clay contents, and were mostly comprised by gibbsite, Fe oxides, and poorly crystalline kaolinite, whereas the sandstone soil had < 20% clay and kaolinitic clay. The studied Ferralsols were moderately to highly fertile, presented pH values 6.4–7.2 and blocky instead of the common granular structure, contrasting with most gibbsitic Ferralsols in tropical Brazil. The Luvisol showed very high base nutrient contents but lower pH (5.5–6.0), and the sandy Cambisol was also relatively fertile. All soils had no exchangeable Al3+, which was also unusual for Cerrado soils, which are mostly very acidic and nutrient-poor. Most likely these unusual features result from the formation of an interstratified clay mineral complex between kaolinite and mica, which occurred as a major phase in the Luvisol and as traces in Ferralsols. Micromorphological analysis showed that celadonite, a green-colored inclusion probably comprised by muscovite/paragonite micas, was a major component of the basalt and the last mineral to weather within the Luvisol. Thus, the toposequence ranged from the less developed, high-activity clay Luvisol to extremely weathered, gibbsitic Ferralsols, with the sandstone Cambisol in an intermediate stage of development.

Investigation on labile organic carbons in soils developed from limestone and sandstone in karst areas of southwest China

Although labile soil organic carbons (LSOC) represent only a small part of soil organic carbon (SOC), they are an important source of energy for the belowground portion of the ecosystem and play a crucial role regarding changes in the quality of soil organic matter (SOM). This study measured and compared the content of LSOC and SOC in limestone soil (developed from limestone) and sandstone soil (developed from sandstone) in the karstic area of southwest China to better understand the impacts of different soil types on LSOC (water-extractable and readily oxidizable organic carbon) and evaluate the existence of a possible relationship between LSOC and SOC in the soil. The results demonstrated that the amounts of SOC, soil readily oxidizable carbon (SROC), and soil water-extractable organic carbon (WEOC) (hot-water extractable organic carbon (hot-WEOC) and cold-water extractable organic carbon (cold-WEOC)) were the highest in the surface soil and decreased with increasing depth in both types of soil profiles. In addition, the content of SOC and LSOC were significantly higher in the limestone soil profiles than those in the sandstone soil profiles. This may be as a result of the occurrence of higher pH values and higher content of calcium, magnesium, and clay minerals in the limestone soil than in the sandstone soil. The proportions of WEOC in total SOC extracted at 25°C and 70°C in the sandstone soil profiles displayed higher average values of 0.040% and 0.527%, respectively, whereas the limestone soil profiles displayed lower average values of 0.015% and 0.255% for the WEOC extracted at 25°C and 70°C, respectively. Regarding the SROC content, both soil profiles showed higher values than WEOC content, ranging from 39.4%–55.2%. The results also showed that for the two types of soils significant correlations were found between samples of SROC, WEOC, and SOC (P < 0.01). Among the LSOC, the hot-WEOC showed clear differences between different soil types, and significant relationships were observed for not only SOC but also SROC. The correlation coefficients between hot-WEOC and SOC or SROC were higher than those between cold-WEOC and SOC or SROC. This study, therefore, suggests that hot-WEOC could be a useful indicator of changes in the quality of SOM in different soil types.

On the controls of preferential flow in soils of different hillslope position and lithological origin

AbstractSoils derived from different lithologies and their controls on preferential flow remain underexplored in forested landscapes. In the same lithology, the propensity for preferential flow occurrence at different hillslope positions also remains largely elusive. By utilizing a soil moisture response time method, we compared preferential flow occurrence between a shale site (Shale Hills, silt loam soils) and a sandstone site (Garner Run, sandy loam soils) at four hillslope positions: ridge‐top, North‐ and South‐facing mid‐slopes and toe slope, for over 2 years. The catchments are neighbouring and covered by temperate forest. For the four hillslope positions, Shale Hills had higher preferential flow frequencies compared to Garner Run. Between these two catchments, the South‐facing mid‐slope sites showed the highest contrasts in preferential flow frequency (33.5% of events at Shale Hills vs. 8.8% at Garner Run) while the ridge‐top sites showed the lowest contrasts (18.7 vs. 13.2%). Additionally, over the unfrozen period, for seven out of eight monitoring sites, drier antecedent conditions tended to be more favourable for preferential flows to occur, with significant (p &lt; .01) relationships at two sites. Except for the South‐facing mid‐slope sites, both Shale Hills and Garner Run had two preferential flow pathways. The characteristic preferential flow pathways at Shale Hills were the Bwand C horizons, and for Garner Run, preferential flow moved from the E/AE horizon to the Bwhorizon. This study shows that shale‐derived soils tended to have higher preferential flow occurrence than sandstone soils, but hillslope positions exhibit different levels of contrasts. More effort should be paid to study the impact of lithology on preferential flows in the context of land surface modelling and biogeochemical reactions to improve ecosystem services of headwater catchments.

Manganese hyperaccumulation capacity of Ilex paraguariensis A. St. Hil. and occurrence of interveinal chlorosis induced by transient toxicity

Manganese (Mn) toxicity is common in plants grown on very acid soils. However, some plants species that grow in this condition can take up high amounts of Mn and are referred to as hyperaccumulating species. In this study, we evaluated the capacity of Ilex paraguariensis to accumulate Mn and the effect of excessive concentrations on plant growth and nutrition. For this, a container experiment was conducted using soils from different parent materials (basalt and sandstone), with and without liming, and at six doses of applied Mn (0, 30, 90, 270, 540 and 1,080 mg kg−1). Clonal plants grown for 203 days were harvested to evaluate yield, and leaf tissue samples were evaluated for Mn and other elements. Without liming and with high Mn doses, leaf Mn concentrations reached 13,452 and 12,127 mg kg−1 in sandstone and basalt soils, respectively; concentrations in excess of 10,000 mg kg−1 are characteristic of hyperaccumulating plants. Liming reduced these values to 7203 and 8030 mg kg−1. More plant growth accompanied increased Mn leaf concentrations, with a growth reduction noted at the highest dose in unlimed soils. Elemental distribution showed Mn presence in the mesophyll, primarily in vascular bundles, without high Mn precipitates. Interveinal chlorosis of young leaves associated with high Mn concentration and lower Fe concentrations was observed, especially in sandstone soil without liming. However, the occurrence of this symptom was not associated with decreased plant growth.

Experimental study of sediment transport processes and size selectivity of eroded sediment on steep Pisha sandstone slopes

The Pisha sandstone area on the Ordos Plateau of China is the primary source of coarse sediment (with a particle size d > 0.05 mm) of the Yellow River. Sediment size distribution and selectivity greatly affect sediment transport and deposition. Hence, sediment transport processes and size selectivity by overland flow on Pisha sandstone slopes were investigated in this study. Experiments were run with Pisha sandstone soil (bulk density of 1.35 g cm−3) under rainfall intensities of 87 and 133 mm h−1 with a 25° slope gradient, and the duration of simulated rainfall was 1 h. Sediment and runoff were sampled at 2-min intervals to examine the size distribution change of the eroded sediment. The particle composition, enrichment rate, fractal dimension, and time distribution characteristics of median grain size (d50) of eroded sediment were comprehensively analyzed. Statistical analyses showed that Pisha sandstone slope generated a large amount of coarse sediment during the erosion. >40% of eroded sediment particles were coarse sediment, which will become the main sediment in the lower reaches of the Yellow River bed. The particle size of eroded sediment tended to gradually decrease with the continuous rainfall but remained larger than the initial value of Pisha sandstone soil after refinement. The fractal dimension was positively correlated with the slope flow velocity, while the d50 was negatively correlated with the slope flow velocity. Overall, these findings indicates that the selectivity and transportation of sediment particles on the Pisha sandstone slopes is mainly influenced by the hydrodynamic parameters of overland flow. The reason for the large amount of coarse sediment generated during the erosion in Pisha sandstone area is not only related to the large porosity and a small cohesive force of sand, but also related to the hydraulic conditions of the Pisha sandstone slopes. In the Pisha sandstone area, we should control soil erosion mainly by reducing the initial erosion dynamics, such as reducing splash erosion, increasing soil infiltration and surface resistance. This study provides a methodology and data references for studying the particle selectivity characteristics of eroded sediment and provides a scientific basis for revealing the mechanism of erosion and sediment yield in the Pisha sandstone area of China.

Study on the rainfall change in Pisha stone area

Rainfall and raindrop characteristics have an important impact on the erosion of sandstone soil. The LPM laser raindrop spectrometer is used to analyze the rainfall characteristics of the Ordos City in the Yellow River Basin, including the distribution characteristics of the velocity and size of a natural rainfall raindrop. Statistical analysis shows that with the gradual strengthening of rainfall intensity, the number of raindrops per unit time, the size and speed of raindrops will increase parabolically. However, the natural rainfall process finds that the diameter and velocity of the raindrop are relatively scattered. During this measurement, the velocity of raindrops is mainly distributed between 1-3.4m / s, and most raindrops are distributed at 1-1.8m / s. The diameter of the raindrops is mainly distributed in the range of 0.125-0.5 mm. The raindrops with a diameter of 0.125mm are mainly distributed between 0.8-3.4m / s, the raindrops with a diameter of 0.25mm are mainly distributed between 1-2.6m / s, and the raindrops with a diameter of 0.375mm are mainly distributed between 1.0-2.2 m/s, and the diameter of 0.5 mm is mainly distributed in the range of 2.2-2.6 m / s.

A simple calibration of Hobo 4 channel analogue dataloggers for use with Watermark 253–L soil water potential sensors

The combination of granular matrix sensors with a Hobo 4 analogue channel datalogger provides a relatively inexpensive continuous soil water monitoring system. However, the datalogger excites all 4 channels concomitantly as it reads the sensor measurement of each channel in sequence. This results in localised electrolysis causing measurement bias error in Channels 2, 3 and 4. To evaluate this channel bias, Watermark granular matrix sensors were connected to Hobo 4 channel dataloggers to measure electrical conductance of the soil. This study formed part of a larger study aimed at understanding water use by Eucalyptus plantations at different soil depths. The measured soil conductivity was calibrated against the gravimetric method in soil derived from Natal Group Sandstone and Dwyka Tillite that occur in southern KwaZulu-Natal. The channels of a Hobo 4 channel datalogger were successfully calibrated against the gravimetric method for both soil types (R2 &gt; 0.92). The voltage measurements of each channel increased in the order 1 &lt; 2 &lt; 3 &lt; 4 for both soil types at a soil water content range of 12 to 44% and 6 to 46% for Dwyka Tillite and Natal Group Sandstone soils, respectively. Channel measurements were similar at soil water content ranges below 12 and 6% for tillite and sandstone soils, respectively. The study showed that Channels 2, 3 and 4 of the Hobo 4 channel datalogger are affected by electrolysis. If this analogue datalogger is used with these types of sensors, these channels need to be calibrated back to Channel 1.

Variation of Leaf Carbon Isotope in Plants in Different Lithological Habitats in a Karst Area

Drought is the major factor that limits vegetation recovery in rocky desertification areas. The leaf carbon isotope (δ13C) value is related to plant water-use efficiency (WUE) and is of great significance in revealing the WUE characteristics of species in karst areas. Measurements of the δ13C value in plant leaves and the nutrient and water contents of lithologic soils were obtained for six woody species (cypress, Cupressus funebris Endl.; mansur shrub, Coriaria nepalensis Wall.; camphor, Cinnamomum bodinieri Levl.; birch, Betula luminifera H. Winkl.; alder, Alnus cremastogyne Burk. and dyetree, Platycarya longipes Wu.) planted in three different lithologic soil types (dolomite, dolomite sandstone, limestone) in the karst area of Guizhou Province. The results showed that C. funebris in the dolomite sandstone soil had the highest δ13C value (−27.19‰), whereas C. bodinieri in the limestone soil had the lowest δ13C value (−31.50‰). In terms of lithology, the average leaf δ13C values were −28.66‰ (dolomitic sandstone), −28.83‰ (dolomite), and −29.46‰ (limestone). The δ13C values of C. funebris and A. cremastogyne were significantly lower in the limestone soil than in the dolomite and dolomite sandstone soil, indicating that the WUE of some tree species is affected by soil conditions under different lithological development processes. Moreover, the relationship between the δ13C value in the leaves and the comprehensive soil conditions varied among the species, and the δ13C value was negatively correlated with the soil water content in all three soil types. Our study provides basic data on the composition characteristics of the δ13C value of tree species, which is beneficial for the selection of tree species for vegetation restoration and afforestation in karst areas.

Nutritional evaluation of Brachiaria brizantha cv. Marandu cultivated in soils developed from basalt and sandstone in the state of Paraná

Determining the nutritional composition of a pasture is necessary to evaluate its quality, aiming to meet the requirements of feeding animals and guarantee good performance. The quality of the forage biomass produced depends directly on the fertility and type of soil, environmental conditions, and management. In this scenario, the aim was to evaluate the chemical composition, in vitro digestibility of dry matter, and macro- and micronutrient contents of Brachiaria brizantha cv. Marandu cultivated in soils developed from basalt and sandstone in the state of Paraná. A total of 120 forage samples were collected in a soil developed from basalt and 116 in soil developed from sandstone. Forage harvesting occurred in autumn and spring for basalt soil (season effect), and in spring (soil effect) for sandstone soil. Soil samples (0–20 cm) were collected in the spring season, at the same forage collection sites, to obtain a greater sample representativity regarding climate–soil–plant relationships. Forage samples were separated in leaf blade and stem + sheath, and analyses of dry matter (DM), mineral matter (MM), crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), lignin, cellulose, hemicellulose, in vitro dry matter digestibility (IVDMD), total digestible nutrients (TDN), nitrogen, and macro- and micronutrient contents were performed. In soil samples, the contents of P, K, Ca, Mg, Mn, and Zn were analyzed. There were season and soil-type effects on the chemical composition of the cultivar studied. The highest levels of protein, NDF, ADF, lignin, and cellulose were obtained in autumn. In samples from soil developed from basalt, higher levels of hemicellulose, IVDMD, and TDN were obtained in the spring. K, P, Mn, and Zn presented levels within the range recommended for the studied forage, but the values of Ca and Mg in autumn and N in the three studied periods remained below the level considered adequate. Soil nutrient contents were influenced (P &lt; 0.05) by the soil source material, and the highest levels of K, Ca, Mg, Mn, and Zn were observed in soil developed from basalt. Forage cultivated in spring in the soil area developed from basalt, was nutritionally superior in relation to forage cultivated in the soil developed from sandstone.

Volatile profiling of Arnicão (Lychnophora salicifolia mart.), a wild medicinal species from Brazilian Cerrado

The Cerrado is a diverse Brazilian savanna with more than 12,000 species. Arnicão (Lychnophora salicifolia Mart – Compositae) is an endemic species occurring in central and southeast Brazil, at higher altitudes, in sandstone and quartzite soils. Lychnophora species have been reported for anti-inflammatory, antioxidant and UV protectant effects. Local communities use it to prepare traditional remedies (i.e. ointments or creams). The aim of this work was (1) to characterize the qualitative composition of L. salicifolia volatile fraction; (2) to evaluate the influence of the environmental conditions on the volatile fraction composition, by investigating plants harvested both in areas under stress conditions and protected from human interference; (3) optimizing a non-separative method for routine in-field analyses. Separative (HS-SPME-GC-MS) and non-separative (HS-SPME-MS) approach combined with PCA are proposed to discriminate between plant populations of L. salicifolia from two distinct areas. Forty-eight individuals were randomly collected from four populations. A clear separation between populations from protected and non-protected areas was observed, with an important presence of caryophyllene derivatives in populations from non-protected areas, usually with compounds associated to plant defense. Both analytical approaches gave the same results, confirming HS-SPME a useful approach for rapid in-field analysis of samples of wild populations.

Experimental research on dynamic response of red sandstone soil under impact loads

The cycling impact test of red sandstone soil under different axial pressure and different impact loads are conducted to reveal the mechanical properties and energy consumption mechanism of red sandstone soil with static-dynamic coupling loading. The results show that: Under the action of different axial pressure and different impact loads, the peak stress of the specimen increases, and then tends to be stable with the times of impact. With the increase of impact times, the specific energy absorption value of the red sandstone soil specimen is increased first and then gentle development trend. When the impact loads are certain, the larger the axial pressure is, the smaller the peak value of energy absorption, which indicates that the energy utilization rate is not high under the condition of large axial pressure. Through the analysis of energy utilization, it is found that the smaller the impact load, the higher the energy utilization rate. The greater the axial pressure, the lower the energy utilization rate. when the axial pressure is large, the impact loads corresponding to the maximum values of reflectivity, transmissivity and absorptivity are the same. The relationship between reflectivity and transmissivity is negatively correlated.

Cover crop and deep tillage on sandstone soil structure and microbial biomass

ABSTRACTThe aim of this study was to evaluate and quantify structural volumes of dystrophic Red-Yellow Latosol, submitted to localized deep soil tillage in sugarcane crop after cultivation of millet and crotalaria, and verify the effect of these managements on microbial biomass. Three management systems were evaluated: localized deep soil tillage (without cover crop), localized deep soil tillage and millet cover crop, and localized deep soil tillage and crotalaria cover crop. For each management three trenches were dug for crop profile description and carbon and nitrogen of microbial biomass were evaluated. Non-utilized profiles of covering plant submitted to localized deep soil tillage presented soil volumes with more morphologically compact structure and smaller porosity than millet and crotalaria profiles. These structures occupied 53.3% of total area of localized deep soil tillage profiles, which presented roots with a more flattened and tortuous aspect. A higher content of microbial biomass carbon (285 mg kg−1 soil) was found in the volume of cracked soil inlocalized deep soil tillage and millet management while lower contents of microbial biomass carbon (23 mg kg−1 soil) and microbial biomass nitrogen (4 mg kg−1 soil) were obtained in localized deep soil tillage compact and laminar structure. Despite covering plant utilization before localized deep soil tillage, the effect of this practice had consequences to the functionality of sandstone soil.

Landslide analysis of unsaturated soil slopes based on rainfall and matric suction data

Shallow slope failures that occur as a result of a decrease in matric suction after water infiltration from intense rains (unsaturated soil conditions) are the main causes of slope instability in tropical and subtropical regions. This study analyzes the occurrence of shallow landslides in a highway cutting of residual soil originating from aeolian sandstone. Characterization of failure mechanisms and stability analyses have been carried out in different scenarios and supported by surface and subsurface investigations, instrumentation and monitoring of rainfall, matric suction, and water level, field tests, and laboratory tests. The results indicate that the reduction in matric suction induced by rainwater infiltration is the triggering mechanism of slope failure. Conventional slope stability analyses and analyses incorporating unsaturated seepage models present results compatible with the hydrological and geotechnical data collected in the study. On the basis of these analyses, and considering the frequent rainfall events in the study area, a critical geometric configuration is proposed for the triggering of landslides in highway cutting slopes of residual soils of aeolian sandstone.

A hybrid method for reconstruction of three-dimensional heterogeneous porous media from two-dimensional images

The heterogeneous pore space of porous media strongly affects the storage and migration of oil and gas in the reservoir. To accurately reproduce complex pore structure validated with experiment data, a hybrid method which combines the CCSIM-TSS method (the cross correlation based simulation-three step sampling method) with the optimization method is proposed to reconstruct stochastically 3D models of the heterogeneous porous media based on 2D images and some constrain conditions. Moreover, the new system in the hybrid method is generated by exchanging the objective points and boundary points of pore and matrix based on two algorithms. Then the hybrid method are tested on the two typical samples (carbonate rock, tight sandstone samples with micro-nanopores). Quantitative comparison is made by computing various statistical and petrophysical properties for the reconstructed models, as well as the original samples. It was found that the hybrid method generates an ensemble of stochastic realization that honor the constrain conditions (permeability data, pore-size distributions and the connectivity). Generating realization of tight sandstones that match the experimental data based on 2D SEM image shows that this method may be then used for more accurate characterization of tight sandstones oil reservoir and analysis of their pore network.

The effect of organic acids on wettability of sandstone and carbonate rocks

This paper examines the role of crude oil's organic acid surface active compounds (SAC) in determining the reservoir wettability over a range of salinities and temperatures. To isolate the effects of individual SACs, this project used model oil mixtures of pure decane and single SACs to represent the oleic phase. Due to the large number of experiments in this study, we used wettability measurement method by the modified flotation technique (MFT) to produce fast, reliable, and quantitative results. The results showed that oil wetting by decane increased with temperature for carbonate rocks. Sandstones oil wetting showed little temperature dependency. The presence of long-chained acids in decane increased oil wetting in sandstone and carbonate rocks as salinity was lowered, while the short-chained acid increased water wetting under the same conditions. The effect of organic acids on wettability was slightly enhanced with increasing temperature for all rock types.