Changes In Soil Structure Research Articles

Exploring the Soil Structure Analysis of a Subtropical Watershed by Introducing a Blanket Physico‐Hydraulic Health Index

ABSTRACTMultiple disturbed and undisturbed soil samples were collected to assess the soil structure health in support of water use and management in a subtropical watershed, which is composed of shallow Entisols, near to Canguçu, RS state—Brazil. Various physico‐hydraulic properties related to soil structure, such as bulk density, total, micro and macroporosity, saturated hydraulic conductivity, organic carbon, soil water retention curve (SWRC), and the ranges of plant available water (PAWC) and drainable porosity (DP) were measured to be analyzed. The hydraulic‐energy indices of soil aeration and water retention were determined by integrating the areas under SWRC. Combining these properties with the contents of sand and clay, a unique blanket soil physico‐hydraulic health index (BSPHI) was formulated and applied to investigate the impact of land use and management on the soils of the Ellert Creek Watershed (ECW), thereby supporting soil physical health analysis and, consequently, the analysis of water and human health. The favorable outcomes found in the ECW soils under annual crops indicated good root aeration in the surface layer due to the balance between DP and PAWC. The BSPHI results showed that only about 19% of the areas exhibited unhealthy physical health. The soil structure in pasture areas of ECW was not significantly impacted by the extensive cattle grazing, whereas lands under native forest served as a control for the natural soil quality status. The BSPHI successfully captured small changes in soil structure, regardless of land use and management, highlighting its potential as a promising tool for evaluating soil health by assessing the soil physical quality.

Impact of freeze-thaw cycles and influent C/N ratios on N2O emissions in subsurface wastewater infiltration systems

Subsurface wastewater infiltration system (SWIS) is important source of N2O emission, biological denitrification process relies on organic carbon source as electron donor, enabling denitrifying reductase (NAR, NIR, NOR, and N2OR) to reduce nitrate nitrogen to N2. However, freeze-thaw cycles cause changes in soil structure through physical and biological processes that increase organic matter availability and microbial activity, thereby accelerating upper (aerobic) organic matter degradation. This leads to carbon deficiency in the lower (anaerobic) layer, which reduces denitrification efficiency increasing N2O production and emissions. This study investigated effects of influent C/N ratios on N2O emissions from SWIS under freeze-thaw stress, and changes in denitrifying reductase and microbial communities. Results showed that as influent C/N ratio increased from 6:1–10:1, average TN removal of SWIS decreased from 89.59 % to 84.95 %, while N2O emission rate decreased from 0.106 mg·m−2·h−1 to 0.0333 mg·m−2·h−1, a reduction of 68.61 %. Meanwhile, N2OR activity increased by 29.95 % with C/N ratio increasing from 6 to 10, showing a significant reduction of N2O. High-throughput sequencing results revealed that Proteobacteria and Firmicutes showed a linear relationship with influent C/N. As C/N increased from 6 to 8 and 10, Proteobacteria relative abundance increased from 22.24 % ± 1.79–32.51 % ± 2.51 % and 39.59 % ± 3.45 %, while Firmicutes relative abundance decreased from 31.73 % ± 7.87–3.34 % ± 0.27 % and 2.19 % ± 0.07 %. These results indicated that sufficient supply of organic carbon provided abundant electron donors for denitrifying reductases in freeze-thaw-affected SWIS, promoting influent NO3--N reduction and decreasing N2O release rates. Conversely, under low C/N ratio conditions, electron acceptance capacity of N2OR was limited and N2OR activity was inhibited, resulting in N2O accumulation and emission. SynopsisThis paper shows how increasing the organic carbon supply in SWIS can reduce N2O emissions and improve nitrogen removal under freeze-thaw stress.

Nitrogen-fixing bacteria promote growth and bioactive components accumulation of Astragalus mongholicus by regulating plant metabolism and rhizosphere microbiota

BackgroundThe excessive application of chemical fertilizers in the cultivation of Astragalus mongholicus Bunge results in a reduction in the quality of the medicinal plant and compromises the sustainable productivity of the soil. PGPB inoculant is a hot topic in ecological agriculture research. In the cultivation of Astragalus mongholicus, the screened nitrogen-fixing bacteria can promote plant growth, however, whether it can promote the accumulation of main bioactive components remains unknown. In this study, mixed inoculants containing 5 strains of growth promoting bacteria (Rhizobium T16, Sinorhizobium T21, Bacillus J1, Bacillus G4 and Arthrobacter J2) were used in the field experiment. The metabolic substances in the root tissues of Astragalus mongholicus were identified during the harvest period by non-targeted metabolomics method, and the differential metabolites between groups were identified by statistical analysis. Meanwhile, high-throughput sequencing was performed to analyze the changes of rhizosphere soil and endophytic microbial community structure after mixed microbial treatment.ResultsThe results of non-targeted metabolism indicated a significant increase in the levels of 26 metabolites after treatment including 13 flavonoids, 3 saponins and 10 other components. The contents of three plant hormones (abscisic acid, salicylic acid and spermidine) also increased after treatment, which presumed to play an important role in regulating plant growth and metabolism. Studies on endosphere and rhizosphere bacterial communities showed that Rhzobiaceae, Micromonosporaceae, and Hypomicrobiaceae in endophytic, and Oxalobactereae in rhizosphere were significantly increased after treatment. These findings suggest their potential importance in plant growth promotion and secondary metabolism regulation.ConclusionsThis finding provides a basis for developing nitrogen-fixing bacteria fertilizer and improving the ecological planting efficiency of Astragalus mongholicus.

Water Management and Hydrological Characteristics of Paddy-Rice Fields under Alternate Wetting and Drying Irrigation Practice as Climate Smart Practice: A Review

Paddy-rice cultivation using the traditional continuous flooding method requires much water, up to 2500 L, to produce 1 kg of rice. Decreasing water availability is being exacerbated by climate dynamics, i.e., droughts and rainfall variability negatively affecting food security in developing regions, particularly Africa. Alternate wetting and drying (AWD) practice is a climate-smart water management strategy that, together with puddling (a critical field preparation process), significantly affects soil hydrological and physicochemical regimes, such as soil water dynamics and oxidation states in paddy fields. However, there are limited reviews on the effects and interaction of the AWD duration on hydrological conditions in the paddy-rice rhizosphere continuum under AWD practice at different rice growth stages. Our review synthesizes key scientific literature to examine water management and hydrological properties of paddy soils under AWD practice with climate change and sheds light on why farmers are skeptical in adopting the practice. To develop this paper, we reviewed scientific information from published journal articles, reliable reports, and our knowledge on paddy-rice cultivation and water management with climate change in Asia and Sub-Saharan Africa. Several studies confirm that AWD practice increases water–rice–crop productivity, yields, and reduces methane emissions. Limitations and challenges of AWD irrigation, including changes in soil structure that influence irrigation water application, variations in hydraulic conductivity caused by the duration and frequency of irrigation cycles, and frequent manual water level (WL) monitoring, are discussed. Opportunities to improve the integration of AWD strategies within government policies, irrigation schemes, and farmer acceptance due to skepticism, limited knowledge, and fear of unreliable water hindering adoption are highlighted. Future research suggestions include the following: (i) long-term measurement of water stress indices using infrared thermometers; (ii) seasonal suitability mapping using NDVI, GIS, and remote sensing; and (iii) application of smart sensors based on the Internet of Things (IoT) to address AWD challenges for precision water management in paddy fields with climate change.

Drying-wetting cycles affect soil structure by impacting soil aggregate transformations and soil organic carbon fractions

Drying-wetting (DW) cycles influence the formation and breakdown of soil aggregates and consequently impact the physical protection of soil organic carbon (SOC). However, the interaction between soil structural dynamics and SOC fraction changes driven by DW cycles is still unclear. Herein, aggregation pathways were tracked by using rare earth oxides (REOs) as tracers. The recombined soil columns were subjected to different DW frequencies (0, 1, 2, 4 and 8 cycles) and two DW intensities (low intensity, Q1; high intensity, Q2). During a 56-day incubation, aggregate distributions, mean water diameter (MWD), REO concentrations, the contents of SOC and its fractions (particulate organic carbon, POC; mineral-associated organic carbon, MOC) were measured. The results showed that MWD markedly increased with DW frequencies regardless of DW intensities and was significantly related to the relative changes of 2–0.25 mm aggregates (P < 0.05). Based on transformation paths, DW cycles stimulated the breakdown of > 0.25 mm aggregates and the aggregation of < 0.053 mm aggregates, thus leading to the increasing formation of 0.25–0.053 mm aggregates. Soil aggregate turnover time was affected by DW intensities and extended with DW frequencies (P < 0.05). Soil aggregate turnover time was displayed in the order of < 0.25 mm aggregates < 2–0.25 mm aggregates < 5–2 mm aggregates. MOC concentration exhibited an increasing trend with DW frequencies. A higher loss of SOC under high DW intensity resulted from more exposure of POC through soil aggregate breakdown. POC concentration was sensitive most to the 2–0.25 mm aggregates turnover time. The structural equation model (SEM) revealed that DW cycles exerted remarkable effects on MWD by impacting SOC fractions and soil aggregate transformations. Overall, our findings suggested that soil aggregate breakdown and formation processes, rather than aggregate size distributions, were more of a concern when evaluating the effects of DW cycles on soil structural stability.

Effects of Salt Content and Freeze-Thaw Conditions on Dynamic characteristics and its microscopic mechanism of Chloride Silty Clay

Generally, artificial ground freezing (AGF) technology is utilized to guarantee tunnel safety during construction. However, the soil structure changes significantly after freeze-thaw, resulting in uneven deformation of the tunnel under traffic loading from subway vibration. To solve this problem effectively, it is necessary to consider the combined impact of freeze-thaw, salt, and traffic loading damage that marine soft soil must withstand simultaneously. For this reason, cyclic triaxial test and NMR test were performed on the silty clay saturated with NaCl solution in this study. The influence of three main factors on dynamic properties has been thoroughly investigated, namely freeze-thaw, salt content, and confining pressure. According to cyclic triaxial test, the shape of the hysteresis loop of the specimens after freeze-thaw changed more significantly with increasing loading cycles. The dynamic elastic modulus was weakened by freeze-thaw, while improved by the addition of NaCl. Damping ratio was consistent with the dynamic elastic modulus law. It was worth noting that the different freezing temperatures (−10 °C, −20 °C and − 30 °C) had only a slight impact on dynamic elastic modulus, as well as damping ratio. Mathematical models were proposed to forecast the dynamic elastic modulus and damping ratio regarding marine soft clay. NMR test indicated that the addition of salt made the internal pore environment of the specimens tend to be consistent and enhanced the water-solid interaction. The increase in porosity resulted in the decrease in dynamic elastic modulus. The results have provided valuable insights into the mechanical characteristics of marine soft clay when AGF technology is applied.

Conservative farming systems and their effects on soil organic carbon and structural quality

Pesticides-free integrated farming systems emerge as a viable option to promote environmental protection, due to the diversification of the agroecosystem, making the soil productive and resilient. However, there is a lack of information about the influence of integration farming systems on the relationship between soil physical quality and organic matter. The objective was to determine soil organic carbon fractions, and soil structural attributes in conservative single and integrated farming systems, to verify the potential of these farming systems to increase soil organic carbon stocks and improve soil structural quality. The experiment was carried out at a pesticide-free agricultural systems. Soil samples were collected in three layers (0–0.05, 0.05–0.10, and 0.10–0.20 m) of five farming systems (Cropland - C, Livestock - L, Forestry - F, Livestock-Forestry – LF, and Crop-Livestock-Forestry - CLF) in the randomized block design. Sampling was carried out in two transects of 25 m each, collecting five samples per transect, totaling 10 samples per layer. The following soil attributes were determined: soil organic carbon (SOC), particulate organic carbon (POC), mineral-associated organic carbon (MAOC), soil organic carbon stocks (Cst), visual evaluation of soil structure (VESS), tensile strength of aggregates (TS), soil friability, weighted mean diameter (WMD), geometric mean diameter (GMD) and the aggregate stability index (ASI). At 0–0.05 m, the SOC content was up to 12% higher in the Cropland system compared to other farming systems, while at 0.05–0.10 m and 0.10–0.20 m of depth, the difference was higher, around 27% between Cropland and other farming systems. For the VESS, Cropland had the lowest score (1.35), while the higher scores were in the Forestry, and CLF systems (2.25, 2.24, respectively). Both soil organic carbon and soil physical quality were greater in all farming systems. The particulate organic carbon and weighted mean diameter were efficiently to promote changes in soil carbon inputs and structural changes. The single and integrated farming systems promoted an increase in soil organic carbon, by a rate of 3.02, 1.81, 2.17, 1.78, and 2.01 Mg ha−1 yr−1, respectively for Cropland, Livestock, Forestry, LF, and CLF. The pesticide-free farming systems, under conservative practices, were very promising in showing the increase of SOC, POC and MAOC, supporting the soil physical quality, and cooperating with the soil health.

Spatial variation characteristics and influencing factors of sediment connectivity in the black soil region of northeast China

Connectivity has become an important indicator of the sediment transfer potential through sediment sources to catchment sinks. Connectivity plays a vital role in investigating the rate of soil erosion caused by runoff and sediment output across the watershed landscape. However, there have been few quantitative studies on the spatial variations in sediment connectivity in the black soil region of Northeast China. Seven classic watersheds in the northeast black soil region were selected to discover spatial variations in sediment connectivity and their influencing factors. The connectivity index (IC) was used to study the spatial variation of sediment connectivity, and the weight of IC was calculated using the vegetation cover management factor (C), which reflected the influence of human activities on the soil erosion process caused by cultivated land expansion and encroachment of forest grassland. The redundancy analysis method (RDA) was used to determine the main factors affecting the spatial variation of IC. The results showed that IC decreased from north (0.45) to south (0.12). The spatial variations of watersheds in sediment connectivity showed significant spatial heterogeneity. IC was correlated with topographic, climatic, and artificial management characteristics at 0.01 or 0.05 levels except soil structural index; RDA results showed that topography and human activities were the main factors affecting sediment connectivity. Topographic and climatic factors explained more sediment connectivity changes in the southern watersheds than in the northern watersheds, while the human activities factor explanation was the opposite of topographic factors. Human activities refer to changes in vegetation cover and soil structure and properties resulting from human logging and farming that affect sediment connectivity.

An Exploration of Forest Fires and Post-Disaster Recovery

This study aims to explore the ecological impact of forest fires and the theoretical framework for post-disaster recovery. It focuses on analyzing the mechanisms of fire-induced damage to forest ecosystems and the critical factors in the recovery process. By systematically reviewing relevant domestic and international literature and integrating perspectives from ecology, environmental science, and sociology, this paper employs a literature review and theoretical analysis to delve into the causes of forest fires, their multifaceted impacts on ecosystems, and theoretical pathways for post-disaster recovery. The study begins with a review of ecological theories related to forest fires, examining the role and function of fire in ecosystem dynamics. It then explores the comprehensive effects of fires on biodiversity, soil structure, water resources, and climate change. Combining these insights with ecological restoration theories, the paper proposes key steps and strategies for post-disaster recovery, including vegetation restoration, soil repair, water resource management, and biodiversity protection. the findings indicate that forest fires cause direct damage to ecosystems and affect their long-term stability and sustainability by altering ecosystem structure and function. Effective post-disaster recovery requires consideration of the complexity and diversity of ecosystems, implementing multi-level and multi-dimensional strategies to achieve comprehensive ecosystem restoration and sustainable development. This study provides theoretical support and practical guidance for the ecological management and post-disaster recovery of forest fires, emphasizing the importance of scientific management and multi-stakeholder collaboration, aiming to promote the healthy development of forest ecosystems and ecological civilization construction.

Soil Cover Modifications in Vicinity of Disappearing Lakes as a Result of Climate Change

Abstract Disappearance of lakes is one of the most dangerous processes affecting the entire natural environment, including soil. This phenomenon is considered natural, resulting from climate change, however in recent decades, a significant acceleration of this process has been observed due to the direct impact of human activity. In areas directly adjacent to lakes, organic soils usually predominate. Unfortunately, wetlands are increasingly being drained and used for agricultural purposes. Under such circumstances, changes in the physical and chemical properties of these soils are often irreversible, causing their degradation. As an effect of increased mineralization, a number of typical modifications occur in soils, such as carbon loss, increased degree of peat decomposition, and changes in soil structure. Long-term dehydration has led to muck formation. Additionally, lowering of lake water uncovers previously flooded areas and increases the intensity of soil-forming processes. However, the presence of the Subaquatic qualifier in the World Reference Base for Soil Resources (WRB) suggests that sediments in shallow water bodies no more than 200 cm deep can also be classified as soils. The progressive disappearance of lakes observed all over the world is therefore a process affecting not only the reduction of water bodies, but also changes in the properties and typology of soils and vegetation cover.

High salinity prolongs water processes required for soil structure stability during drying–wetting cycles

AbstractClimate events, such as drought and rainfall, can lead to a cycle of drying and wetting that may cause changes in soil structure, leading to deteriorations in the health of saline soils. However, little is known about the extent and behavior of soil structure degradation under the combined influences of salinity and drying–wetting (D‐W) cycles. Thus, we systematically investigated the effects of salinity (0, 5, 30, and 100 g/L, labeled as CK, T5, T30, and T100) and D‐W cycles on soil structure by determining soil volume, shrinkage, and swelling potentials along with soil pore character obtained from soil shrinkage characteristics curve, intending to explore how D‐W cycles and salinity affect soil structure. The results showed that soil deformation behaviors in saline and non‐saline soils varied with the number of D‐W cycles. Irreversible deformation of the soil was observed during continual D‐W cycles. The soil volume increased by 3.75%–15.73% after three D‐W cycles. In vertical direction, the maximum expansion magnitude for each treatment was reached with the value of 29.03%, 23.42%, 34.23%, and 35.87% in CK, T5, T30, and T100, respectively. The magnitudes of shrinkage and expansion were equal in the horizontal direction since the soil samples consistently returned to their original dimensions. Furthermore, the decrease was observed in the micropores and capillary pores affected by salinity, with values of 50%, 58.6%, and 70.4% in CK, T5, T30, and T100, respectively. However, the D‐W cycles primarily affected large pores. High salinity levels enhanced swelling potential and inhabit shrinkage potential, prolonging the water processes required for the soil structure to achieve stability. The results of this study underscore the necessity of understanding the hysteresis of soil volume change and elucidate the mechanisms of soil structure deterioration driven by salinity and D‐W cycles. These findings provide a valuable reference for healthier soil management.

A field investigation on the soil management practices in a productive vineyard considering C sequestration and water resistance of soil structure

AbstractOptimal soil structure is linked to soil organic matter (SOM). Different soil management practice alternates SOM but the storing C to soil structure formation in vineyard soils is not sufficiently studied. In addition, understanding the impact of soil management practices in vineyard on changes in SOM and soil structure is crucial for sustainable viticulture. In this study conducted in a productive vineyard near Nitra city, Slovakia, we investigated the dynamics of individual size-fractions of water-stable aggregates (WSA) as results of changes in soil organic matter (SOM) under different soil management practices. Five distinct management practices – Intensive tillage system (T); Intensive tillage system with poultry manure (T + M); Strip grass (G); Fertilization in lower rates of NPK (NPK 1) to grass strips; and Fertilization in higher level of NPK (NPK 2) to grass strips were adopted to to be tested. The results have shown that the highest content of soil organic carbon (SOC) 20.3 ± 3.68 g kg−1, labile carbon (CL) 2.71 ± 0.78 g kg−1, and the most favor soil structure were identified in NPK 1, however, the most effectively improved soil structure and C sequestration (SOC: 19.9 ± 3.88 g kg−1; CL: 2.53 ± 0.83 g kg−1) was under G treatment. SOC had a more significant influence on the content of water-stable aggregates than CL. Intense changes in SOM took place in larger size-fractions of water-stable macroaggregates (WSAma) above 2 mm, while smaller WSAma below 2 mm and water-stable microaggregates were more stable.

Experimental study on the water and heat dynamic characteristics of silty clay at different depths under temperature gradient

Soil properties play a crucial role in the stability of engineering foundations, particularly in cold regions where temperature gradients impact water migration and soil conditions. This study utilized MRI-Cryogenic Soil-Moisture Analyzer (MRI-CSMA) to conduct indoor freeze-thaw experiments on silty clay specimens with varying initial water contents (12.0 %, 16.8 %, and 21.1 %). Dynamic changes in water content and temperature at different soil depths were analyzed. The results revealed distinct stage decrease characteristics in both temperature and water content as freezing progressed, with more pronounced changes closer to the cold end. Conversely, during thawing, temperatures and water content gradually increased as the boundary temperature rose. Notably, after the freeze-thaw cycle, the frozen zone consistently retained higher water content than the unfrozen zone, indicating water redistribution, regardless of initial water content levels. Furthermore, in three soil samples with different initial water contents, the water migration flux in the unfrozen soil layer decreased exponentially as freezing time increased. This phenomenon can be attributed to the combined effects of water boundary conditions, temperature gradients, and soil structure changes during soil freezing. These findings are likely to have significant implications for understanding water-heat dynamics in cold region soils as well as ensuring the stability of engineering projects.

Understanding Salinity-Driven Modulation of Microbial Interactions: Rhizosphere versus Edaphic Microbiome Dynamics.

Soil salinization poses a global threat to terrestrial ecosystems. Soil microorganisms, crucial for maintaining ecosystem services, are sensitive to changes in soil structure and properties, particularly salinity. In this study, contrasting dynamics within the rhizosphere and bulk soil were focused on exploring the effects of heightened salinity on soil microbial communities, evaluating the influences shaping their composition in saline environments. This study observed a general decrease in bacterial alpha diversity with increasing salinity, along with shifts in community structure in terms of taxa relative abundance. The size and stability of bacterial co-occurrence networks declined under salt stress, indicating functional and resilience losses. An increased proportion of heterogeneous selection in bacterial community assembly suggested salinity's critical role in shaping bacterial communities. Stochasticity dominated fungal community assembly, suggesting their relatively lower sensitivity to soil salinity. However, bipartite network analysis revealed that fungi played a more significant role than bacteria in intensified microbial interactions in the rhizosphere under salinity stress compared to the bulk soil. Therefore, microbial cross-domain interactions might play a key role in bacterial resilience under salt stress in the rhizosphere.

Changes in the degree of lateral root trait plasticity and trade-offs of maize under long-term no tillage.

While no tillage (NT) can significantly influence soil structure stratification compared to conventional tillage (CT), a comprehensive understanding of the degree of root trait plasticity and trade-offs of lateral roots of crops at various growth stages along a deep soil profile in response to NT remains elusive. This knowledge gap is important for understanding soil resource acquisition strategies and yield of crops. We systematically investigated the traits of lateral roots at jointing and flowering stages in a long-term (12 years) experiment in Northeast China where maize (Zea mays) has been continuously planted under CT and NT with or without maize residue mulch on soil surface. We also measured soil penetration resistance and bulk density. Soil penetration resistance was reduced at the jointing stage, and was increased at the flowering stage under NT especially at a depth of 10 - 40 cm. Root length density decreased under NT across the two growth stages by on average 22%. In contrast, specific root length and diameter showed greater plasticity, ranging from -14% to 20% and from -11% to 8%, respectively, relative to those under CT. These responses could be attributed to changes in root length proportions with different diameters associated with differences in soil penetration resistance between tillage practices. The negative relationships between root traits were stronger under CT than NT, and became weaker from the jointing stage to the flowering stage. To the best of our knowledge, for the first time, our study provides empirical evidence for pivotal root trait plasticity and trade-offs across growth stages as key indicators of changes in soil structure and resources in response to NT. These insights contribute to a better understanding of soil resource acquisition strategies of crops under NT.

Modeling Tillage Effects on Plant-Available Water by Considering Changes in Soil Structure

Highlights No-tillage improved plant-available water (PAW) as compared to conventional tillage, especially in dry years. Soil structure showed 4.5 times higher impact on PAW than surface disturbance due to tillage. Consideration of changes in soil structure is important in modeling the effects of soil management. PALMS was found to be an effective model to assess the effects of changes in soil management on soil water. Abstract. Management practices such as no-tillage (NT) have the potential to provide many benefits, such as reduced runoff and soil erosion and increased infiltration and soil water holding capacity. Most hydrological models that are used to simulate the effects of soil management are built based on empirical relationships between management and hydrology outcomes, and they tend to ignore or oversimplify the effects of soil structure. However, soil structure is management dependent and is a driver of water movement and storage in soil. The goal of this study was to better understand the effects of differences in soil structure between NT and conventional tillage (CT) on field-scale hydrology and plant available water (PAW). This study employed in-field measurements of soil structure in NT and CT fields in the Texas Blackland Prairies and used the Precision Agricultural-Landscape Modeling System (PALMS), which can simulate the effects of differences in soil structure. Regression analysis was performed on simulated soil water to understand the relative contributions of variations in surface roughness and macropore properties due to tillage on PAW. Results from this study showed that NT accumulated 44.8, 20.4, and 5.7 cm more PAW than CT in the top 150 cm of the soil profile during the summer growing season in the years 2006, 2008, and 2011, respectively, all of which encountered considerable dry spells. It was also found that the changes of soil structure due to tillage had about 4.5 times more impact on PAW than surface roughness. This study highlights the benefits of adopting NT over CT and showcases the importance of considering soil structure in modeling the effects of soil management on PAW. Keywords: Macropores, No-till, Preferential flow, Surface disturbance, Surface roughness, Texas Blackland Prairies.

Distribution characteristics of soil microplastics and their impact on soil physicochemical properties in agricultural areas of the North China plain.

Microplastic (MPs) pollution has become a global issue, with particular concern regarding MPs in soil. To determine the characteristics of MPs in agricultural production areas and their impact on soil physicochemical properties, soil samples were collected from different land use types in the North China Plain. Layered sampling was conducted and the soil physicochemical properties were determined. A novel image recognition method based on fluorescence staining was proposed for the batch analysis of MPs in the study area. Together with the results of the soil physicochemical properties, the impact of MPs on soil physicochemical properties was analyzed and evaluated. The results showed that the soil MPs abundance in this agricultural area was moderate to low compared to other agricultural areas, with a larger proportion of particle-type and fragment-type MPs smaller than 10 μm. The soil MPs were predominantly composed of polyvinyl chloride (PVC) and polypropylene (PP). MPs abundance was higher in farmland and forest land than in vegetable fields. The impact of MPs on soil physicochemical properties was mainly manifested in the changes in soil structure due to the different MPs characteristics. Apart from abundance, the type of MPs was found to be the main factor affecting soil bulk density, with particle size and shape influencing the soil aggregate structure. MPs may effect the pH values of sandy and loamy soils, primarily by altering the soil porosity and water holding capacity, but also by increasing the area and duration of contact between the soil medium and external water sources. This study revealed the MPs characteristics in agricultural areas as well as the pathways by which they can impact soil physicochemical properties.

Numerical implementation of the hypoplastic model for SPH analysis of soil structure development in extremely large deformation

The extremely large deformation of soil is a significant challenge due to the dynamic changes in soil structure, but it is poorly understood owing to inadequate effective numerical methods. This paper presents a numerical method for analysing the responses of sand-like granular soil undergoing extremely large deformation. The proposed method utilizes the Smoothed Particle Hydrodynamics (SPH) technique, which is a meshfree particle-based approach capable of circumventing the computational difficulties associated with mesh distortion. The Gudehus-Bauer (G-B) hypoplastic model, which can capture the pressure- and density- dependent mechanical behaviour of granular soil, is implemented into the in-house developed SPH code. Concerning the characteristics of large deformation, the Green-Naghdi rate is applied in this study to achieve objective stress integration. An adaptive explicit stress integration scheme, termed Modified Euler automatic Substepping with Error Control (M-E-SEC) is utilized to handle the time integration of the SPH equation system. Additionally, a stability correction method is introduced to suppress the breakdown problem that occurs at low-stress states. The effectiveness of the proposed method is validated by experimental data. Furthermore, several numerical examples are presented to elucidate the evolution of shear band structures in granular soils subject to extremely large deformation levels.

Biochar modifies soil physical properties mostly through changes in soil structure rather than through its internal porosity

AbstractBesides its carbon sequestration potential, biochar application generally improves soil physical properties, but the magnitude of its impact and the underlying mechanisms remain debated and depend on soil type, biochar application rate, and age. The objective was therefore to determine the effect of biochar application rate and age on physical properties of agricultural soils in a temperate climate. On a silt loam and a sandy loam soils, we compared the physical properties of fresh biochar (1% and 2% w/w) or century‐old biochar (0.5%–1% w/w; 19th‐century kiln sites)‐enriched soil samples with biochar‐free soil samples. Biochar pore network characteristics were determined using helium pycnometry, mercury intrusion porosimetry, scanning electron microscopy observation, and electron dispersive X‐ray spectrometry, whereas location of biochar particles within soil structure was analyzed using optical microscopy observations. Fresh biochar application decreased bulk density by 16.8% and increased saturated water content by 16.0% and macroporosity by 78.8%. These effects were attributed to soil structure improvement rather than to biochar porosity. Soil type and biochar application rate had a limited impact. In the long‐term, biochar effects were mostly nonsignificant, which might result from its fairly low content in kiln sites and from the clogging of its internal porosity by clay particles. Biochar was thus able to improve some soil physical properties in the short‐term, but these effects could no longer be detected in the very long‐term. Further investigating the time rate of change in soil physical properties over several decades following biochar additions to soil would therefore seem particularly relevant.

Nanosized spent coffee grounds can increase soil clay dispersibility

The application of spent coffee grounds (SCGs) to soil has been widely encouraged because of the agronomic benefits of SCGs. However, the negative impacts of this practice are not fully understood. This study aims to present the effect of nanosized SCGs (nSCGs) on the dispersibility/transportability of soil clay. An nSCG sample with an average hydrodynamic size of ∼260 nm was extracted from SCG waste, and its effects on the dispersibility of clay were tracked over a pH range of ∼3 to ∼9 and an ionic strength range of 0.001–0.1 N by using dynamic light scattering techniques and a test tube-based method. nSCGs were found to carry negative charges (zeta potential, ζ, varying from −2 to −30 mV), and the presence of nSCGs in clay suspensions resulted in decreases in the surface charge (towards more negative charge) of the clay suspensions, particularly at pH < 6. By providing more negative charges to the clay system, nSCGs stimulated and favoured clay dispersal. The edge surface of clays and Fe oxides may play a central role in promoting soil particles association, but this effect was likely weakened in the presence of nSCGs. In general, it can be inferred that the utilization of SCGs may have adverse impacts such as soil/clay losses or soil structural changes, and these impacts need to be considered.