Soil Structural Properties Research Articles

Land-use change and its impact on physical and mechanical properties of Archaeological Black Earth in the Amazon rainforest

The intense pressure of anthropic actions to change the use and management can promote the degradation of anthropogenic soils with high natural fertility and high content of organic matter such as the Archaeological Black Earths of the Brazilian Amazon. Therefore, this study aimed to quantify the impact of land use and occupation in the Amazon biome on the physical and mechanical properties of Archaeological Black Earth. The research was carried out in the municipality of Novo Aripuanã, in the south of Amazonas State (Brazil), in a Chromic, Pretic, Acrisol with native forest, pasture, and pigeon pea. The soil properties of bulk density, mean weighted diameter, soil resistance to penetration, macroporosity, microporosity, particle size distribution (sand, silt, and clay), water-dispersible clay, flocculation index, total organic carbon, and preconsolidation pressure were assessed in the 0.0–0.1 and 0.1–0.2 m soil layers. Archaeological black earth under native forest showed better soil structural properties such as greater macroporosity and lower bulk density and resistance to penetration. The conversion to other uses promotes soil compaction and increases the resistance to compression. However, the greatest negative impacts on soil properties occurred when the land-use change was for pasture than for pigeon pea. The pigeon pea crop promoted the increase of soil total organic carbon in the 0.0–0.1 m layer. The soil mechanical behavior showed a greater load-bearing capacity in the native forest area for the surface layer than the subsurface layer. The preconsolidation pressure allowed to determine that the pasture land-use has a greater occurrence of compaction and might suffer additional compaction if the applied pressures on the soil during grazing are larger than the higher limit of the confidence interval of load-bearing capacity models when compared to the pigeon pea land-use.

Impact of Dairy Wastewater Irrigation and Manure Application on Soil Structural and Water-Holding Properties

HighlightsQuantitative evaluation was performed of dairy waste on soil water-holding capacity.Considering the soil variability on a farm is significant for management practices.Soil aggregate structure plays a pivotal role in studying the impact of waste reuse.Abstract. The livestock sector contributes about 40% of global agricultural output and uses over 30% of total feed-crop land. The sector’s continuing growth has led to increased technology and larger-scale, commercialized agriculture, and it correlates to growth in by-products and waste, which can compromise the environment and human health. Although organic manure is an excellent soil fertilizer whose nutrient content increases crop yield, untreated and/or overapplied manure pollutes local water resources and can alter soil aggregate structure, potentially affecting soil health and available water. Proper livestock waste management is essential for sustainable food production. Waste reuse strategies exist, with goals such as minimizing freshwater consumption, improving food production, and contributing to energy production, However, each strategy has tradeoffs in environmental, energy, or monetary costs. This study provides a quantitative approach to evaluating waste impact on soil health and helps to better manage irrigation practices and water supply gaps in arid and semi-arid areas by better understanding how management practices affect physical soil health. The TypoSoil apparatus was used to measure and analyze the hydrostructural parameters (water-holding capacity and soil structure) of fine sandy loam (A horizon) and sandy clay (B horizon). Soils from the Texas A&M AgriLife Research Dairy (Stephenville, Texas) were collected and compared with control (untouched) soils. Waste (manure, bedding materials, wash water) was separated into liquid (passed through a natural lagoon treatment process) and solid components (applied as fertilizer). Approximately half the wastewater was reused as wash water, the remainder for irrigation. Although the soil varied substantially between sample locations, a statistically significant difference existed between the control and manure/wastewater applications in both the A and B horizons. Both applications improved plant-available water (AW) in the A horizon (40% and 30%, respectively) but deteriorated AW in the B horizon (25% and 30%). Thus, dairy farm waste is a viable source for agricultural use. Keywords: Available water capacity, Pedostructure, Soil health, Soil shrinkage curve, Soil water characteristic curve.

Investigating the effect of inoculation of chickpea with rhizobium and mycorrhizal fungi (Funneliformis mosseae) on soil mechanical and physical behavior

Symbiosis with plants by mycorrhiza and rhizobium (bio-fertilizers) is effective in improving soil structure and increasing the stability of aggregates against compression. In addition to soil deformation, soil structural properties should be included for the assessment of compaction. The purpose of this study was to investigate the effect of application of rhizobium and mycorrhizae on plant yield, some soil physical properties, and the confined compression curve and its characteristics, which have not been reported in any research so far. Experiments were conducted in a completely randomized design with three replications in the field and glasshouse. Mycorrhizal fungi (Funneliformis mosseae), rhizobium (Mesorhizobium), mycorrhiza - rhizobium and control (no inoculation) were the treatments of the field experiment. Sterilized mycorrhiza background material and non-plant-non-inoculation were the two additional treatments of the glasshouse experiment. The plant cultivated in this experiment was chickpea. Mycorrhizal and rhizobium treatments increased the stability of aggregates compared to non-plant-non-inoculation treatment. Mycorrhiza and rhizobium increased the macroporosity and near-saturation water content. The smallest total yield was found in the sterilized mycorrhiza background material and control treatments. Mycorrhiza and rhizobium increased the void ratio at different compression stresses by 9–16% and 19–25%, respectively, compared to non-inoculation treatments under the glasshouse experiment. Pre-compression stress was increased by 84.3% in the control treatment with plant compared to the mycorrhiza treatment in the glasshouse experiment, but did not change significantly in the field experiment. Symbiosis of mycorrhiza and rhizobium as a sustainable biological method improved the physical and mechanical properties of the soil by affecting plant yield and root exudates.

Dielectric Spectroscopy and Application of Mixing Models Describing Dielectric Dispersion in Clay Minerals and Clayey Soils.

The number of sensors, ground-based and remote, exploiting the relationship between soil dielectric response and soil water content continues to grow. Empirical expressions for this relationship generally work well in coarse-textured soils but can break down for high-surface area and intricate materials such as clayey soils. Dielectric mixing models are helpful for exploring mechanisms and developing new understanding of the dielectric response in porous media that do not conform to a simple empirical approach, such as clayey soils. Here, we explore the dielectric response of clay minerals and clayey soils using the mixing model approach in the frequency domain. Our modeling focuses on the use of mixing models to explore geometrical effects. New spectroscopic data are presented for clay minerals (talc, kaolinite, illite and montmorillonite) and soils dominated by these clay minerals in the 1 MHz–6 GHz bandwidth. We also present a new typology for the way water is held in soils that we hope will act as a framework for furthering discussion on sensor design. We found that the frequency-domain response can be mostly accounted for by adjusting model structural parameters, which needs to be conducted to describe the Maxwell–Wagner (MW) relaxation effects. The work supports the importance of accounting for soil structural properties to understand and predict soil dielectric response and ultimately to find models that can describe the dielectric–water content relationship in fine-textured soils measured with sensors.

Seedbed consolidation and surface sealing for soils of different texture and soil organic carbon contents

The soil structure near the surface of agricultural soils changes with season mainly by land management together with climatic and biological factors. Quantitative analysis of post-tillage changes in soil structure and related hydraulic properties are necessary for evaluating and improving models of soil hydrological and transport processes. The objectives of this study were to quantify changes in soil seedbed structure induced by rainfall and drainage and to estimate the eff ;ects of soil texture and SOC on these changes. We collected samples from the harrowed layer of twenty-six fine to coarse textured Swedish mineral soils. Air-dried soil was placed in cylinders (5 cm high, diameter 5 cm) and exposed to simulated rainfall (5 mm h−1 for 4 h) and drainage (−50 cm pressure potential) cycles in the laboratory. We used X-ray tomography to quantify changes in pore networks in a thin surface layer and in the whole cylinder. Infiltration rates at -5 cm pressure potential were measured using a mini disc tension infiltrometer on replicate air-dried samples and on the samples included in the consolidation experiments at the final state. Total imaged specific pore volumes generally decreased from initial to final state and pore size distributions were shifted towards larger proportions of below image resolution pores (< 80 μm). There was a strong positive correlation between clay content and changes (i.e. final state-initial state) in the specific volume of pores <80 μm. Soils with high clay content and soil organic carbon (SOC) content often have strong aggregates that resist changes. Nevertheless, both clay and SOC contents were negatively correlated with the changes in specific imaged pore volume. These results highlight the importance of swelling, which is largely controlled by clay content, for seedbed consolidation. In line with previous studies, when excluding coarse textured soil, the changes in surface porosity were negatively correlated with silt content. Changes in infiltration capacity were not significantly correlated with any basic soil properties. Our results suggest that shrinking-swelling should be a central part in any model for seedbed consolidation.

Soil mixing with organic matter amendment improves Albic soil physicochemical properties and crop yield in Heilongjiang province, China.

Crop productivity in Albic soil is poor, owing to poor soil physicochemical properties. Mixing of Aw layers, representing Albic soil, with B layers, could improve the physicochemical properties of Albic soil, which is characterized by poor humus on the topsoil and high penetration resistance. The objective of the present study conducted in 2015-2016 in an Albic soil region in Heilongjiang province, China, was to explore the effects of different soil mixing strategies on the physicochemical properties of Albic soil and crop yield. There were four soil mixing treatments: conventional subsoiler (CS), three-stage subsoil mixing plough (TSMP), four-stage subsoil mixing plough (FSMP), and three-stage subsoil interval mixing plough (TSIMP). Our results demonstrated that the Aw layer bulk density of Albic soil under TSMP, FSMP, and TSIMP decreased significantly compared to that under CS. In addition, the total porosity of the soil under these treatments increased significantly in 2 years. Compared to the water holding capacity under the CS treatment, other treatments increased significantly in the Aw layer. Furthermore, soil penetration resistance of the Aw layer decreased following Aw and B layer mixing. All three soil mixing treatments also increased soil aggregate stability and cation exchange capacity but reduced soil organic carbon content in the Aw layer. Soil mixing increased soybean and maize seed yield. Overall, Aw and B layer mixing improved Albic soil structure and physiochemical properties and increased crop yield; thus, this mixing is a feasible approach for Albic soil improvement, with optimal improvements observed under the FMSP strategy, which also added organic substances to the Aw layer.

Estimating the overconsolidation ratio in uniform cohesive soil with cone penetrometer tests considering soil structure and index properties

A basic empirical approach to estimate the preconsolidation stress and overconsolidation ratio, OCR, in uniform cohesive soils using cone penetration and piezocone tests uses a correlation factor, kc, that is equal to the preconsolidation stress divided by the net tip stress referenced to the soil plasticity index. An adaptation of the “stress history and normalized soil engineering properties” (SHANSEP) format extends this basic approach by organizing the data into normally consolidated and overconsolidated components. The SHANSEP-based approach is improved in this paper by applying an empirical method to identify structured and unstructured soil behavior and to develop a separate empirical correlation for each type of soil structure. Overconsolidated structured soils are shown to exhibit kc values less than the normally consolidated kc and the m exponent in the SHANSEP relationship is greater than 1. In unstructured overconsolidated soils, the kc value is greater than the normally consolidated kc value and the SHANSEP m exponent is less than 1. The proposed method to identify structured vs. unstructured behavior is an important improvement in the approach and helps illustrate why some mCPTu values are less than 1 and others are greater than 1. Site characterization efforts are significantly improved when structured soil behavior is identified and included in the assessment of OCR.

Three-dimensional fractal characteristics of soil pore structure and their relationships with hydraulic parameters in biochar-amended saline soil

Due to poor soil quality, coastal saline soil limits soil productivity. Therefore, it is of great importance to find appropriate and efficient methods to improve the quality of coastal saline soil. Biochar has been widely used as a soil amendment to improve soil properties, but the effects of biochar amendment on soil pore structure and soil hydraulic properties are unclear. In recent years, with the development of fractal theory and computer technology, fractal geometry based on image analysis has been employed for quantitatively characterizing the structure and heterogeneity of soil pores. In this study, field experiments were established with three proportions of straw biochar (0, 2 and 5 %, w/w) to study the biochar amendment effects on soil structure and soil hydraulic properties. Three replicates were set for each treatment. The results showed that the addition of biochar to saline soil improved soil pore structures and soil hydraulic characteristics. The biochar amendment led to the strong pore spatial variation, complex pore structure and irregular pore shape. The biochar-amended saline soil had a high considerable water retention capacity (θS, AWC). Biochar had a long-term effect on saline soil improvement. For multifractal analysis, it is better to use the ΔD and Δα values to analyze the multifractal characteristics of soil. The heterogeneity of the soil pore distribution became stronger after biochar amendment. Multifractal parameters had significant changes with the time of biochar amendment. The changes of soil pore structure resulted in the improvement of soil hydraulic characteristics. The Ks value improved as the pore connectivity increased. The strong pore spatial variation, complex pore structure and irregular pore shape aided in increasing the θs value. The available water content value was improved as the number of soil pores, especially the micropores, increased. In response, this study proposes a new approach to analyzing soil pore structure to explain the association between the soil pore structure and soil hydraulic characteristics in biochar-amended saline soil.

Retração do solo e relação com as propriedades físicas e matéria orgânica de Latossolos e Nitossolos do Sul do Brasil

Estudos recentes apontaram que o principal fator de origem do caráter retrátil, observado em Latossolos e Nitossolos, não é a mineralogia. Com isso formulou-se a hipótese de que a retração do solo em Latossolos e Nitossolos tem origem em fatores estruturais do solo, portanto podem ser investigados indiretamente através das propriedades físicas da estrutura do solo. Sendo assim o objetivo deste trabalho foi relacionar a retração com propriedades físicas e a matéria orgânica do solo, investigando de maneira indireta o processo de retração do solo. Foram selecionados seis perfis coletados nos Estados de Santa Catarina e no Rio Grande do Sul que apresentam caráter retrátil e um Vertissolo Ebânico no Rio Grande do Sul. Foram avaliados: granulometria, limites de consistência, densidade do solo e de partículas, porosidade total, microporos e macroporos, área superficial específica, índice de retração, matéria orgânica do solo e retenção de água no solo. A relação entre as propriedades foi realizada através de análise de componentes principais (ACP). Adicionalmente, para analisar o efeito da estrutura e da matéria orgânica no índice de retração, e amostras foram coletadas nos horizontes A, AB, BA, Bt1, Bt2, Bt3 do Nitossolo Bruno de Painel, o qual possui um gradiente natural de decréscimo de matéria orgânica no perfil. Neste, as determinações da curva de retenção e índice de retração foram realizadas com amostras de estrutura preservada e alterada. A ACP indicou o índice plasticidade com maior relação com a retração do solo, indicando que a redução do teor de água cria meniscos entre as partículas assim a tensão superficial aumenta, causando uma curvatura do menisco, na interface entre água e ar aproximando as partículas, causando assim a retração do solo. A matéria orgânica tem efeito direto no processo de retração, no entanto, a intensidade da retração é dependente da estruturação do solo.

KEYLINK: towards a more integrative soil representation for inclusion in ecosystem scale models. I. review and model concept.

The relatively poor simulation of the below-ground processes is a severe drawback for many ecosystem models, especially when predicting responses to climate change and management. For a meaningful estimation of ecosystem production and the cycling of water, energy, nutrients and carbon, the integration of soil processes and the exchanges at the surface is crucial. It is increasingly recognized that soil biota play an important role in soil organic carbon and nutrient cycling, shaping soil structure and hydrological properties through their activity, and in water and nutrient uptake by plants through mycorrhizal processes. In this article, we review the main soil biological actors (microbiota, fauna and roots) and their effects on soil functioning. We review to what extent they have been included in soil models and propose which of them could be included in ecosystem models. We show that the model representation of the soil food web, the impact of soil ecosystem engineers on soil structure and the related effects on hydrology and soil organic matter (SOM) stabilization are key issues in improving ecosystem-scale soil representation in models. Finally, we describe a new core model concept (KEYLINK) that integrates insights from SOM models, structural models and food web models to simulate the living soil at an ecosystem scale.

Experimental study and numerical simulation on dynamic soil‐structure interaction under earthquake excitations

Soil-structure interaction (SSI) phenomena subjected to seismic loadings are investigated in this study. Firstly, shaking table tests on dynamic soil‐structure interaction subjected to seismic loadings are carried out, and SSI effects are analyzed through a comparative study between the soil-structure system and the rigid foundation condition. Then, a corresponding numerical model on the SSI tests is presented. In the finite element model, a bounding surface plasticity model and an equivalent linear method are separately used for simulating the nonlinear behavior of soil. It turns out that the calculated results by the bounding surface plasticity model agree much better with the experimental results. Finally, the effects of different soil types and structural properties on soil-structure interaction are discussed by numerical parametric study. The results show that SSI effects noticeably mitigate the dynamic response of structure, and the closer the frequency of superstructure to the soil frequency, the more obvious the effect of soil-structure interaction. With increased shear wave velocity of soil, the impact of soil-structure interaction weakens. It is important for studying the impact of SSI on structural responses and practical engineering design purposes.

Effect of salinity on soil structure and soil hydraulic characteristics

Revealing the influences of soil salinity on soil structure and hydraulic properties contributes to understanding the mechanism of salinity restraining rehabilitation of saline sodic soil in coastal area. After being passed through a 1 mm sieve, silt loam and silty clay were irrigated with saline water to achieve different soil salinities to highlight the effect of irrigation salinity on aggregate formation from primary particles. Three irrigation events with different saline water were conducted in the same 2 mo interval in soil columns; the soil columns were subjected to natural evaporation during the interval. The soil salinity, soil structure, soil–water characteristic curve, and saturated hydraulic conductivity (Ks) results were determined after the end of the third drying subprocess. The results showed that the proportion of water-stable macroaggregates (0.25–2 mm) in the silt loam and silty clay increased as the soil salt content (SSC) increased. Under the same matric suction, the retention capacity and plant-available water capacity (PAWC) of the silt loam first increased and then decreased, with the SSC increasing to a maximum of approximately 14.5 g kg−1. The retention capacity of the silty clay increased with the SSC, whereas the PAWC decreased with the SSC. The Ksof the silt loam increased with SSC. This study reveals the effects of soil salinity on aggregate formation from primary particles in wetting–drying cycles and describes the corresponding changes in hydraulic properties, which influence the rehabilitation of saline sodic soils in coastal areas.

Studying the soil pore physical resistance and resilience of a shallow volcanic ash soil subjected to pure cyclic loading

In the last 250 years the Aquands (depth-limited and waterlogged-volcanic ash soils) in southern Chile were exposed to an intensive land use change inducing physical degradation of these fragile soils. The aim of this work was to evaluate the effect of cyclic loading on soil structural properties and the resilience capacity after simulating one event of soil waterlogging as usually occurs in the field. In undisturbed soil samples, collected from two horizons (2−5 cm, Hz1 [A1] and 20−23 cm, Hz2 [Bs1]) of a Duric Histic Placaquand under secondary native forest (sNF) and naturalized grassland (NG), the precompression stress (Pc), deformation and recovery indices derived from cyclic loading tests (20, 80 and 200 kPa) were determined. The air permeability (Ka) and soil volume changes were measured during the entire test. The land use change from sNF to NG increased the rigidity of the pore system due to plastic deformation. However, the cyclic loading provokes changes in the pore system (e.g. increase in bulk density as well as decrease in wide coarse pores, which finally induce a decrease in air permeability: 1.89 to -0.17 log μm2 and 1.03 to 0.37 log μm2 in Hz1 of aNF and NG, respectively) even at loads lower than Pc highlighting the fragility of the soils. As the applied load increases to levels higher than Pc, the plastic deformation induces an increase in pore water pressure and mechanical strength, affecting the pore network and in turn the air permeability of the soil. After one event of ten days of waterlogging conditions, the resilience capacity of the pore system was low. CT-images show that the soil under sNF recovered apart of the deformed porosity allowing an increase in Ka (0.55 ± 0.15 log μm2) after waterlogging conditions, however, no changes were identified for the soil under NG (final Ka = 0.57 ± 0.26 log μm2). Therefore, both land use change and increasing loads on these fragile soils imply the loss of their resilience capacity generating a further soil settlement.

The impacts of ditch-buried straw layers on the interface soil physicochemical and microbial properties in a rice-wheat rotation system

Ditch-buried straw return (DB-SR) is a novel soil tillage and fertility-building practice, which may allow for the formation of a straw layer structure in rice–wheat rotation systems. However, it is presently unknown how the straw layer affects soil physicochemical and microbial processes in the interface between straw layer and bulk soils. Thus, we conducted a field experiment from 2008 to 2014 to determine whether there were changes in soil structure, temperature, available nitrogen, and microbial properties in the soil layer close to the straw layers (± 5 cm). Three treatments were included: control with no-till and straw removal (CK), ditch-buried straw return to a depth of 20 cm (DB-SR-20), and ditch-buried straw return to a depth of 40 cm (DB-SR-40). Our results showed that soil macroaggregate formation was increased with the duration of straw return in the soils 5 cm below the straw layers under DB-SR-20 and above the straw layers under DB-SR-40. The straw layers could significantly increase soil temperature below the straw layers, but a larger increase was observed for DB-SR-40 than DB-SR-20. We also found that DB-SR-20 largely increased the NH4+ concentration in both the soil layers above and below the straw layers, but DB-SR-40 only increased NO3− in the soils above the straw layers. In addition, the catabolic profile of soil microbial communities was largely affected by the straw layers, but the effects decreased with the duration of the treatment. These findings suggest that the straw layer largely alters the spatio-temporal processes of physicochemical and microbial properties in the interface soils after long-term implementation of ditch-buried straw return. Some of the positive alterations may cascade to facilitate crop growth and enhance the productivity of rice-wheat rotation systems.

Effects of subsoiling depth, period interval and combined tillage practice on soil properties and yield in the Huang-Huai-Hai Plain, China

Compaction layers are widely distributed in the Huang-Huai-Hai Plain, China, which restrict root growth and reduce yields. The adoption of subsoiling has been recommended to disrupt compacted soil layers and create a reasonable soil structure for crop development. In this paper, the effects of subsoiling depth (30, 35 and 40 cm), period interval (2 or 3 years) and combined pre-sowing tillage practice (rotary cultivation or ploughing) on soil condition improvement was studied on a tidal soil in the Huang-Huai-Hai Plain. Seven tillage patterns were designed by combining different subsoiling depths, period intervals and pre-sowing. The evaluation indicators for soil condition improvement were as follows: thickness of the plough layer and hard pan, soil bulk density, cone index, soil three-phase R values, alkali nitrogen content, crop yield, and economic benefits. The results showed that subsoiling can significantly improve the soil structure and physical properties. In all subsoiling treatments, the depth of 35 or 40 cm at a 2-year interval was the most significant. The thickness of the plough layer increased from 13.67 cm before the test to 21.54–23.45 cm in 2018. The thickness of the hard pan decreased from 17.68 cm before the test to 12.09–12.76 cm in 2018, a decrease of about 40.07%. However, the subsoiling combined pre-sowing tillage practice, that is, rotary cultivation or ploughing, was not significant for soil structure and physical properties. For all subsoiling treatments, the soil bulk density, cone index and soil three-phase R values of the 15–25 cm soil layer were significantly lower compared to single rotary cultivation. Subsoiling was observed to increase the soil alkaline nitrogen and water contents. The tillage patterns that had subsoiling at the depth of 35–40 cm at a 2-year interval combined with rotary cultivation had the highest alkali nitrogen and water contents, which increased by 31.08–34.23% compared with that of the single rotary cultivation. Subsoiling can significantly increase the yield both of wheat and corn, as well as the economic benefits. The treatment of subsoiling at the depth of 35 cm at an interval of 2 years combined with rotary cultivation had the highest annual yield and economic benefits. For this treatment, the annual yield and economic benefits increased by 14.55 and 62.87% in 2018, respectively. In conclusion, the tillage patterns that involved subsoiling at a depth of 35 cm at a 2-year interval along with rotary cultivation are suitable for the Huang-Huai-Hai Plain.

The effects of freeze-thaw cycles at different initial soil water contents on soil erodibility in Chinese Mollisol region

Freeze-thaw action is a common natural phenomenon in cold regions, which affects soil erodibility by changing soil structure and mechanical properties. However, quantifying the impacts of freeze-thaw cycles (FTCs) at different initial soil water contents (ISWCs) on soil erodibility is challenging due to the complex interactive soil mechanical responses. In this study, direct shear strength and soil disintegration tests were conducted to quantify soil erodibility indices. Seven FTCs (0, 1, 3, 5, 7, 10 and 13) and three ISWCs (16.5, 24.8 and 33.0%) were employed to investigate soil shear behavior and disintegration properties for two Mollisol soils. Results showed that repeated FTCs had cumulative impacts on soil mechanical properties, and the 10th FTCs might be the threshold number for influencing soil erodibility. The soil shear strengths decreased by 1.1–15.1% and 9.2–30.5% under four normal stresses at the first and 13th FTCs, respectively, for these two soils. Soil cohesion generally decreased with the increase of FTCs. Soil internal friction angle showed no trend with FTCs at the 16.5% and 24.8% water contents but a decreasing trend at the 33.0% water content. Soil disintegration rate increased with FTC and reached a maximum value at the 10th cycle but decreased with the increase of ISWC. Soil disintegration of the two Mollisols showed a sharp disintegration of about 60% in 133 s. This study provides a new understanding of the response of erodibility to freeze-thaw conditions for two Mollisols.

Assessment of subsidence and consolidation of dredger fill area based on SBAS-InSAR and laboratory tests

Abstract. With the development of economy, land reclamation by dredger fill has become an effective measure to alleviate the shortage of land resources. However, the accompanying subsidence has always been a challenge to the safe use of soil in dredger fill area. In this study, Chongming East Shoal, China, where dredger filling activities are going on in recent years was selected as the study area. SBAS-InSAR was applied to monitor the variation of land subsidence and deformation in the recent two years. Furthermore, a total of 25 undisturbed soil samples including dredger fill and underlying soil were collected from 5 boreholes (maximum depth 55 m), and the land at each borehole had different a formation time. The physical properties and compressibility were tested by laboratory tests. Results show that for the current state, fast to slow subsidence velocity was observed in the reclamation area close to the coastline, which is controlled by building load and geological features of soil layers. The building load is the main factor affecting the land subsidence and special attention should be paid. It is the poor drainage condition of the soil layer in the offshore area resulting in slow subsidence. Consolidation degree and final settlement of soil can be obtained from monitoring data of land subsidence. Based on the settlement-time curve obtained by SBAS-InSAR, the estimated final settlement of typical settlement area is −27.03 to −38.96 mm, and the corresponding consolidation degree is 58.95 % on average. It still takes a long time to achieve stability. In conclusion, land subsidence is essentially the macro-accumulation of drainage consolidation of all the soil layers, so it is controlled by soil structure and engineering geological properties of both dredger fill and underlying soil layer. The research combined with field investigation, laboratory testing can provide a mechanism explanation for monitoring results. Future research will focus on longer monitoring time and a higher sampling frequency to enrich and improve the research.

Impacts of conservation agriculture on soil structure and hydraulic properties of Malawian agricultural systems

Sub-Saharan Africa (SSA) faces climate change and food insecurity challenges, which require action to create resilient farming systems. Conservation agriculture (CA) is widely promoted across SSA but the impacts on key soil physical properties and functions such as soil structure and hydraulic properties that govern water storage and transmission are not well understood. The aim of this study was to assess the impacts of long term (10–12 years) maize-based CA on soil hydraulic conductivity, water retention and pore size distribution. Root zone (0–30 cm depth) soil total porosity, pore size distribution, saturated hydraulic conductivity (Ksat) and plant available water capacity (PAWC) of conventional maize monocrop farming systems (CP) are compared with those of adjacent CA trials with either sole maize or maize intercrop/rotation with cowpea (Vigna unguiculata L.), pigeon pea (Cajanus cajan L.) or velvet bean (Mucuna pruriens L) in trial locations across central and southern Malawi. Results show that maize-based CA systems result in significant changes to soil hydraulic properties that correlate with improved soil structure. Results demonstrate increases of 5–15 % in total porosity, 0.06−0.22 cm/min in Ksat, 3–7 % in fine pores for water storage and 3–6 % in PAWC. Maize monocrop CA had similar effect on the hydraulic properties as the maize-legume associations. The values of Ksat for CA systems were within optimum levels (0.03–0.3 cm/min) whereas PAWC was below optimum (<20 %). There was no significant build-up in soil organic matter (OM) in the CA systems. The results lead to a recommendation that crop residue management should be more pro-actively pursued in CA guidance from agricultural extension staff to increase soil OM levels, increase yields and enhance climate resilience of sub-Saharan African farming systems.

The assessment of soil chemical, physical, and structural properties as landslide predisposing factors in the Serra do Mar mountain range (Caraguatatuba, Brazil)

Landslides have environmental, social, and economic impact in the Brazilian Atlantic coast (Serra do Mar). In addition to meteorological, geological, and geomorphological settings, mineralogical and pore space heterogeneities in soil covers are considered important characteristics that can influence landslide occurrence. Since soil covers are very clayey, the evaluation of macro- and micromorphological soil features (soil structures, soil materials, and pores) resulted by mass movement during slope instability is difficult. This field of investigation practically does not exist in the Serra do Mar. The objective of this paper is to analyze the soil cover in a toposequence to identify macro- and microscopic soil features resulted from landslide processes, and assess the role of pedogenesis on landslide development. Macro- and micromorphological approaches were used to study the architecture of the soil cover and soil was sampled to determine chemical and mineralogical composition by XRF and XRD. Undisturbed clods were used to determine pore size and pore compartment by mercury porosimetry. It was recognized a brecciated and an undulating parallel-striated fabric. Both features were generated from mass movement and were unclear in the clayey horizons in the bottom of the toposequence. In this level, the occurrence of mottles suggesting short-term soil saturation and the presence of micropores < 1000 nm in soil could be the factors that drive soil movement downslope.

Use of X‐ray microcomputed tomography for characterizing earthworm‐derived belowground soil aggregates

AbstractSoil structure is closely linked to biological activities. However, identifying, describing and quantifying soil aggregates remain challenging. X‐ray micro computed tomography (X‐ray μCT) provides a detailed view of the physical structure at a spatial resolution of a few microns. It could be a useful tool to discriminate soil aggregates, their origin and their formation processes for a better comprehension of soil structure properties and genesis. Our study aims to (a) determine different X‐ray μCT‐based aggregate parameters for differentiating earthworm casts belowground (earthworm aggregates) from aggregates that are not formed by earthworms (non‐earthworm aggregates), and (b) to evaluate if these parameters can also serve as specific “tomographic signatures” for the studied earthworm species. For this purpose, we set up a microcosm experiment under controlled conditions during 8 weeks, including three species of earthworms tested separately: the epigeic Lumbricus rubellus, the anecic Lumbricus terrestris and the endogeic Allolobophora chlorotica. Our results show that X‐ray μCT analysis helps distinguish earthworm aggregates from non‐earthworm ones using (a) the relative volume of the components within aggregates and (b) the volumetric mass of aggregates and their global volume. In particular, the volume ratio of mineral grains within the aggregates is significantly different according to earthworm species. So, X‐ray μCT is a powerful and promising tool for studying the composition of earthworm casts and their formation. However, future research is needed to take into account the shapes and spatial distribution of the aggregates' components, in particular the different states of organic matter decomposition.Highlights Can earthworm belowground casts be differentiated from other soil aggregates using X‐ray μCT? The use of X‐ray μCT for characterizing soil aggregates at a spatial resolution of a few microns. A combination of X‐ray μCT variables discriminates earthworm casts from non‐earthworm aggregates. X‐ray μCT, used alone, is relevant for defining species‐specific signatures of earthworm casts.