Aggregation Of Soil Particles Research Articles

Strength and dilatancy of an unsaturated expansive soil at high suction levels

A series of suction-controlled triaxial tests was conducted on Nanyang expansive clay to investigate the effects of dry density and suction on dilatancy and strength. The suction of the soil samples was controlled using a vapour equilibrium technique, with four suction levels ranging from 3.29 MPa to 198.14 MPa, where water retention is dominated by adsorption. The experimental results show that the tested soil exhibits a brittle failure mode under high suction, significantly distinguishing the hydro-mechanical behaviour of the soil at high suction from that observed at low suction. This brittle failure mode significantly increases the contribution of suction to peak strength compared to residual strength, causes the soil to fail before reaching the critical state, a phenomenon not observed in soils under high suction, and results in dilatancy caused by damage to the soil particle aggregates rather than particle rearrangement. The dilatancy data obtained from the triaxial tests reveal that significant soil dilatancy occurs during shear after reaching peak strength, with the maximum dilatancy angle increasing with suction and decreasing with confining pressure. However, the initial dry density has a negligible impact on the soil's dilatancy under high suction levels. This observation further supports that, for unsaturated soils under high suction levels, dilatancy is attributed to damage to soil particle aggregates rather than the rearrangement of soil particles.

Fe oxides simultaneously improve stability of Cd and carbon in paddy soil：The underlying influence at aggregate level

Iron (Fe) oxides have a strong adsorption affinity for Cd and organic carbon (SOC). However, under alternate wet-dry (IF) condition,the influences of Fe oxides on the speciation and disrtribution of Cd and SOC in soil aggregates are unkown. In the present study, soils untreated (S), removed (S-Fe) or added (S+Fe) Fe oxide soils were blended with cadmium chloride solution and cultivated for 56 days under different moisture management practices. Compared with the S-Fe soil, the IF treatment increased the contents of Fe oxide-bound SOC (Fe-OC) and Fe/Mn oxide-bound Cd (Fe/Mn-Cd) by 18.5–29.8-fold and 1.45–2.45-fold, repectively, in the S and S+Fe soils, corresponding to a 36 %−42 % increase in the recalcitrant C pool (RCP) and a 53 %−87 % decrease in the exchangeable Cd content. These results could be attributed to soil particle aggregation and Fe redistribution. Fe addition promoted the transfer of Cd/SOC accumulated in microaggregates to macroaggregates and increased the variable negative charge content in macroaggregates and the adsorption capacity of macroaggregates for Cd/SOC. More Cd/SOC accumulated in macroaggregates in Fe oxide-bound form, which reduced the risk of Cd migration and Cd availability and increased the physical protection of SOC. Therefore, Fe oxide has great potential to simultaneously reduce carbon emissions and cadmium toxicity in paddy soil.

Assessment of Soil Particle Distribution and Primary Nutrient Status in the Groundnut-Producing Areas of Nalgonda, Telangana, India

The current research involved a thorough field survey to assess particle size distribution and the availability of primary nutrients in rabi-grown groundnut soils (2022-2023) across three productivity regions: high (2497.15-3006.47 kg ha-1), medium (1987.82-2497.15 kg ha-1), and low (up to 1987.82 kg ha-1) in Nalgonda district, Telangana. A total of 150 surface soil samples (0 - 15 cm depth), with 50 samples from each productivity region, were collected before the sowing of rabi groundnut crop using a stratified random sampling method. These collected soil samples are further processed and analysed for soil texture, available nitrogen (N), phosphorus (P) and potassium (K). The objective of this research is to know the status of texture and primary nutrients in groundnut growing areas of Nalgonda district. The sand, silt and clay content in high, medium and low productivity regions averaged 72.90%, 71.29%, 67.56%; 6.82%, 8.35%, 10.16% and 20.27%, 20.36%, 22.27% respectively. The respective available N, P and K showed mean values of 257.29 kg ha-1, 189.40 kg ha-1 and 138.99 kg ha-1; 48.025 kg h IJPSS_116978a-1, 44.512 kg ha-1, 27.09 kg ha-1 and 251.91 kg ha-1, 236.48 kg ha-1, 174.86 kg ha-1 in high, medium and low productivity regions. In regions characterized by high productivity, there was a pronounced prevalence of sand content, significantly influencing soil particle aggregation. Notably, silt content exhibited considerable variation, particularly within areas of medium and low productivity, whereas clay content displayed the most variability in regions of low productivity. The availability of nitrogen decreased sequentially from high to medium productivity areas, and further from medium to low productivity regions. This same pattern was observed for available phosphorus and potassium, with substantial variations across the three productivity categories, declining consistently from high productivity regions to low productivity ones. Variations in available phosphorus (P) and potassium (K) exhibited extensive dispersion within every productivity category, as evidenced by the significant standard deviation and coefficient of variation values across these regions. This is particularly notable for potassium, highlighting the necessity of considering diverse soil conditions and factors affecting potassium availability when formulating fertilization plans.

New insights into the parameterization of the dry surface layer and its hydrogeochemical mechanism: An experimental study

Knowledge of the parameterization of the dry surface layer (DSL) is essential for evaluating near-surface water flow and water balance in arid and semi-arid areas. Existing studies have parameterized DSL thickness and vapor flow as functions of the soil moisture content (SMC) in the surface layer to predict soil evaporation. However, hydrochemical processes related to DSL development have been ignored, including changes in hydrochemistry, the underlying hydrochemical mechanism, and the role of dissolved substances in the DSL development. Herein, we performed a series of soil evaporation experiments for 260 days and explored the factors influencing DSL development (e.g., soil texture, atmospheric temperature, SMC, solutes). Evaporation experiments were performed using silty loess, sandy loess, and fine sand with a 60-cm water table. Results showed that the cumulative evaporation of silty loess, sandy loess, and fine sand over the experimental period were 1,391.52, 460.10, and 185.53 mm, respectively, which determined by the maximum height of liquid flow continuity. The content of total dissolved solids (TDS) and major ions at the surface soil were significantly higher than the values at deep depths of 5‒55 cm, which largely depend on evaporative water loss. Evolutionary trends of chemical facies in sand media along the liquid water migration were from HCO3-Ca type to SO4·Cl-Na type. This was attributed to mineral dissolution at a depth of 5–55 cm and their transport with liquid water, resulting in the precipitation of salt crystals at the surface soil. Furthermore, a consolidated DSL with a thickness of 3.0–3.5 cm in the sandy loess and a loose DSL with a thickness of 1.5–2.0 cm in fine sand were observed at the end of the experiments. The accumulation of solutes at the surface leads to a reduction in effective porosity and the aggregation of soil particles during continuous drying, which facilitates the consolidation of DSL in sandy loess. This overestimated the DSL thickness, resulting in a difference between the experimental and predicted evaporation rates by Fick's law. Overall, these results highlight the limitations of considering DSL thickness as a function of SMC only, providing new insights into hydrochemical processes and dissolved solutes involving DSL parameterization during continuous soil drying.

Assessment of Soil Particle Distribution, Primary Nutrient Status and Their Response to Environmental Factors Across the Bengal Gram Productive Regions of Sangareddy, Telangana

The present study was carried out to know the fertility status of rabi grown bengal gram soils of Sanga Reddy district, Telangana state by thorough field survey during the year 2022-2023. Total of 150 soil samples (50 samples from each productivity regions) from soil surface (0 - 15 cm depth) across three productivity regions high (592-613 kg acre-1), medium (571-592 kg/acre) and low (<571 kg acre-1) were collected from the study area before sowing of the crop and analyzed for the soil particle size distribution, available Nitrogen(N), Phosphorous(P) and Potassium(K). Their status was quantified and analytical data was interpreted and statistical parameters like range, mean, standard deviation and coefficient of variation were calculated. The sand, silt and clay content in high, medium and low productivity regions averaged 32.1 %, 26.7%, 41.1 %; 33.7 %, 26.1 %, 40.1 % and 37.4 %, 25.1 %, 37.2 % respectively. The soil available N, P and K showed mean values of 224.3 kg ha-1, 209.4 kg ha-1 and 204.0 kg ha-1; 32.0 kg ha-1, 28.4 kg ha-1, 24.8 kg ha-1 and 316.4 kg ha-1, 311.0 kg ha-1, 306.1 kg ha-1 in high, medium and low productivity regions. Low productivity areas had the largest mean sand concentration, which influenced soil particle aggregation. Silt content varied greatly, particularly in medium and low productivity zones, whereas clay content varied the most in high productivity regions. Available N decreased from high to medium and medium to low production areas. Fluctuations in available P and K showed a wide distribution within each category, as evidenced by large standard deviation and coefficient of variation values across productivity regions, particularly for potassium, emphasising the importance of considering diverse soil conditions and factors influencing potassium availability when developing fertilisation strategies.

Simultaneous stabilization of particulate and bioavailable arsenic in soils from the realgar mining area by polyacrylamide, nano-SiO2, and ferrihydrite composite materials

Arsenic (As) contamination in realgar mining areas poses a severe environmental and health risk, highlighting the critical need for effective strategies to manage As migration, particularly in its particulate and bioavailable states. Soil erosion and water leaching serve as significant pathways for spreading As, emphasizing the imperative to curtail its mobility. In the present study, we proposed an effective strategy that combines the utilization of polyacrylamide (PAM), nano-SiO2 (NS), and ferrihydrite (Fh) to elevate the stability of As in soils from a realgar mining area. The results show that this composite material demonstrates the capability to concurrently regulate soil erosion and mitigate the leaching of bioavailable As. The combination of the three materials in the proportion of 0.5 % PAM +0.1 % NS + 1.0 % Fh can reduce the soil particulate and bioavailable As content by 99.11 % and 93.98 %, respectively. The unconfined compressive strength of the soil can be increased by about 30 % under this condition. The SEM analyses show that the addition of PAM and NS can significantly enhance the aggregation of soil particles and then reduce the soil erosion rate. These findings highlight the significant potential of the proposed approach in mitigating As contamination in soil within mining environments. The approach offers a sustainable and comprehensive solution to address the transport of heavy metal contaminants in both particulate and bioavailable states in mining areas.

Effect of Different Mulch Materials on the Growth and Yield of Maize (Zea Mays) on Coastal Plain Sand in Southern Nigeria

The presence of residue mulches in farm has been known to effectively save the soil surface, prevent soil erosion on slopes, help reduce soil moisture loss through evapotranspiration and insulates soil, protect roots from extreme temperature, improve soil biology, aeration, aggregation of soil particles and reduce drainage over-time, improve soil fertility as certain mulch type decompose, inhibit plant diseases, give planting beds a uniform and provide favourable preservation of ecological stability. This experiment was conducted in Teaching and research farm of Akwa ibom State University, Obio Akpa Campus to assess the effect of sawdust, calopogonium leaves, and siam weed on microbial, physicochemical properties and performance of White Maize (Zea mays) on a coastal plain sand of Obio Akpa in Southern Nigeria. Results showed that soil mulches with calopogonium mucunoides recorded highest in the following parameters measured; ECEC 10.35%, Cmol and AV.P323mg/kg-1,% base saturation (91.11),100% seed emergence and less leaf area, the highest moisture(35%) was obtain in the soil mulched with saw dust. The highest moisture content in Zea mays ,(5.63%) crude fibre (3.91), lipid (4.71), Total Ash(4.42) and carbohydrates (61.98%) were obtained in the soil mulched calopogonium mucunoides while the highest bacterial count 37x105cful/g-1 and fungi counts 5.1x103cfu/g_1 which gives rise to typical adult characteristics of soil derived from coastal plain sand.

Exploration of Soil Particle Size Diversity and Primary Nutrient Status Across the Rice Productivity Regions of Mahabubnagar, Telangana, India

The current study involved a thorough field survey to assess particle size distribution and the availability of primary nutrients in rabi - grown rice soils (2022 - 2023) across three productivity regions: high (5923 - 6052 kg ha-1), medium (5793 - 5923 kg ha-1), and low (<5793 kg ha-1) in Mahabubnagar district, Telangana. A total of 225 surface soil samples (0 - 15 cm depth), with 75 samples from each productivity region, were collected before the transplanting of rabi rice crop using a stratified random sampling method and are further processed and analysed for soil texture, available nitrogen (Avl. N) available phosphorus (Avl. P) and available potassium (Avl. K). The sand, silt and clay content in high, medium and low productivity regions averaged 52.37%, 55.75%, 57.41%; 17.77%, 15.47%, 16.96% and 29.86%, 28.79%, 25.63% respectively. Low productivity areas had the highest mean sand content, negatively impacting soil particle aggregation thus affecting their rice productivity. Silt and clay content varied in three productivity regions, with the highest variation of clay content in high productivity regions. The respective Avl. N, Avl. P and Avl. K showed mean values of 257.88 kg ha-1, 253.61 kg ha-1 and 240.13 kg ha-1; 59.13 kg ha-1, 55.40 kg ha-1, 54.49 kg ha-1 and 304.96 kg ha-1, 301.25 kg ha-1, 300.19 kg ha-1 in high, medium and low productivity regions. Available N declined from high to medium and medium to low productivity regions. Fluctuations in available P and K showed wide distribution within each category, particularly in case of potassium emphasizing the inclusion of diverse soil conditions and factors influencing potassium availability. This variability study helped in identifying the fertility levels of three regions across the productivity regions.

Self-weighting of the overlying soil horizon catalyzed by freeze–thaw cycles leads to silt particle enrichment in the soil profile

Freeze–thaw cycles, as a strong weathering effect, can cause changes in the soil particle size and content, which can affect changes in the geological environment of the soil. A zone of silt enrichment was found at certain depths in the soil profile of the study regions. To understand and analyze the causes of this substratum phenomenon, a unidirectional freeze–thaw test on soil under static loading was designed and simulated in the laboratory in accordance with actual field conditions to investigate the process of changes in the physical index parameters after freeze–thaw cycles when the soil is under pressure. The changes in the parameters in the upper, middle and lower parts of the test soil column after 6, 10, 20, 40 and 50 freeze–thaw cycles were measured for the three regions. The test results show that the mechanical composition of the soil changes significantly after freeze–thaw cycles, the sand content decreases significantly, the clay and silt contents increase, and the particle frequency curve moves in the direction of particle size reduction. The freeze–thaw process is always accompanied by the fragmentation and aggregation of soil particles, and the fractal dimension is used to describe the distribution width of the soil particle population and to compare the clay content. The larger the fractal dimension is, the higher the clay content in the sample. Kvar(Coefficient of granulometric variation) decreases as the number of freeze–thaw cycles increases, the soil particles change from high-intensity to low-intensity variation, and the soil particles gradually transition to silt particles. The occurrence of silt-rich zones is the result of a combination of freeze–thaw action and static loading. This study can provide a new reference and vision for the freeze–thaw evolution process and tectonic development of soil in middle- and high-latitude cold regions.

Soil moisture dynamics regulates the release rates and lability of copper in contaminated paddy soils

The climate changes have caused more extreme precipitation and drought events in the field and have exacerbated the severity of wet-dry events in soils, which will inevitably lead to severe fluctuations in soil moisture content. Soil moisture content has been recognized to influence the distribution of heavy metals, but how temporal changes of soil moisture dynamics affect the release rates and lability of heavy metals is still poorly understood, which precludes accurate prediction of environmental behavior and environmental risk of heavy metals in the field. In this study, we combined experimental and modeling approaches to quantify copper release rates and labile copper fractions in two paddy soils from southern China under different moisture conditions. Our kinetic data and models showed that the release rates and lability of copper were highly associated with the soil moisture contents, in which, surprisingly, high soil moisture contents effectively reduced the release rates of copper even with little changes in the reactive portions of copper in soils. A suite of comprehensive characterization on soil solid and solution components along the incubation suggested that soil microbes may regulate soil copper lability through forming microbially derived organic matter that sequestered copper and by increasing soil particle aggregation for protecting copper from release. This study highlights the importance of incorporating soil moisture dynamics into future environmental models. The experimental and modeling approaches in this study have provided basis for further developing predictive models applicable to paddy soils with varying soil moisture under the impact of climate change.

Mechanism of the variation in axial strain of sand subjected to undrained cyclic triaxial loading explained by DEM with non-spherical particles

The mechanical response of sand is affected by the axial strain accumulated during undrained cyclic triaxial loading tests. However, the large deformation that occurs during the post-liquefaction stage is difficult to measure using testing apparatus. To address this limitation, this research utilizes the numerical method of DEM with non-spherical particles to simulate the undrained cyclic triaxial loading test on clean sand material. The validity of DEM is confirmed through laboratory test. A four-stage scheme for the development of axial strain in the liquefaction process is proposed and verified by analyzing the deformation features of sand specimens with different densities. Meanwhile, the macroscopic behavior is also described in conjunction with microscopic characteristics of sand particles, such as coordination number, force chain network and anisotropy degree of contact normal, which are calculated using DEM. In addition, the central value of variating axial strain at each cycle is analyzed to determine its variation feature via loading cycle. Due to the capability of DEM in describing the microscopic behavior of soil particle aggregation, it is found that the difference in the proposed four-stage scheme between compression and extension sides is the main cause of the central value of axial strain shifting monotonically.

Cover crops on soil quality and yield of cowpea under no-tillage in the Amazon savanna

Conservation practices such as no-tillage are necessary to maintain, and/or improve agricultural soil quality. However, straw formation and maintenance in tropical regions is a limiting factor to adopting this system. In this sense, this research aimed to study the effect of cover crops on straw formation, soil quality indicators, and cowpea yield under no-tillage in the Amazon savanna. Two experiments were carried out in consecutive years, on a Latossolo Amarelo. The treatments consisted of the straw of cover crops in a single (S) and intercrop (I) system, as follows: Urochloa brizantha (UBS), Pennisetum glaucum (PGS), Crotalaria juncea (CJS), Canavalia ensiformis (CES), Mucuna aterrima (MAS), U. brizantha and C. juncea (UBCJI), U. brizantha and C. ensiformis (UBCEI), P. glaucum and C. juncea (PGCJI), P. glaucum and C. ensiformis (PGCEI), and spontaneous vegetation (SV). Cowpea was cultivated after desiccation of the cover crops. Most of the straw favored soil particle aggregation, except for C. juncea and SV, which negatively influenced this variable. Basal soil respiration, organic carbon content, potassium, base saturation, geometric mean diameter, macroaggregates, and macroporosity at layer of 0-0.10 m were the most sensitive indicators for improving soil quality in a savanna environment. UBS, UBCJI, and UBCEI were superior to the other treatments in improving soil quality. Almost all treatments increased cowpea yield by up to 29%, except for CJS and SV.

Change in glomalin-related soil protein along latitudinal gradient encompassing subtropical and temperate blue carbon zones

Glomalin-related soil protein (GRSP), an abundant and eco-friendly bioproduct associated with arbuscular mycorrhizal fungi (AMF), contributes significantly to the soil particle aggregation and carbon sequestration. Although much research has been conducted on the storage of GRSP at different spatio-temporal scales in terrestrial ecosystems. However, the deposition of GRSP in large-scale coastal environments has not been revealed, which hinders an in-depth understanding of GRSP storage patterns and environmental controls, and this knowledge gap has become one of the key uncertainties in understanding the ecological functions of GRSP as blue carbon components in coastal environments. Therefore, we conducted large-scale experiments (spanning subtropical and warm temperate climate zones, coastlines over 2500 km) to test the relative contributions of environmental drivers that shape unique GRSP storage. In salt marshes of China, we found that the abundance of GRSP ranges from 0.29 mg g−1 to 1.10 mg g−1, and its concentration decreases with increasing latitude (R2 = 0.30, p < 0.01). The GRSP-C/SOC of salt marshes ranged from 4 % to 43 % and increased with the increase in latitude (R2 = 0.13, p < 0.05). The carbon contribution of GRSP does not follow the trend of increasing abundance, but is limited by the total amount of background organic carbon. In salt marsh wetlands, precipitation, clay content and pH are the main factors influencing GRSP storage. GRSP is positively correlated with precipitation (R2 = 0.42, p < 0.01) and clay content (R2 = 0.59, p < 0.01), but negatively correlated with pH (R2 = 0.48, p < 0.01). The relative contributions of the main factors to the GRSP differed across climatic zones. Soil properties, such as clay content and pH, explained 19.8 % of the GRSP in subtropical salt marshes (20°N < 34°N), however, in warm temperate salt marshes (34°N < 40°N), precipitation explained 18.9 % of the GRSP variation. Our study provides insight into the distribution and function of GRSP in coastal environments.

Leaching Test Protocols to Evaluate Contaminant Response of Nano-Calcium Silicate–Treated Tropical Soils

The current study deals with the interaction of toxic metals with soils by conducting a series of leaching tests on four kaolinitic soils procured from locations with varying pollution levels, such as a pristine location, vicinity of steel mill works, battery works unit, and an abandoned municipal waste dump site. The procured soils were spiked with 3,000 mg/kg of toxic metals, lead (Pb), and nickel (Ni) to understand the contaminant transport. An innovative amendment, such as synthesized nano-calcium silicate (NCS), was also mixed with the soils for toxic metal immobilization. Leaching tests. such as the toxicity characteristic leaching procedure (TCLP), extended TCLP, and caged TCLP, were conducted on soil samples. These tests were successful in predicting the interactive behavior of the composite mix containing soil, NCS, and toxic metals, comprehensively. The vulnerability of soils based on TCLP can be expressed in the order of Soil C > Soil D > Soil B > Soil A. These results were concurrent with extended TCLP, wherein the response of these composites at various pH levels was presented. Caged TCLP quantified the leaching rate for different mixtures, and it was found that the leaching rate for virgin soils reduced from 1.3 to 0.075 cm/yr after the NCS amendment. The addition of NCS resulted in the agglomeration and aggregation of soil particles. This increased the density and reduced the void spaces of the soil–nano mix, thereby encapsulating the toxic metals permanently within its interstices. The highest attenuation was observed for Pb2+ compared with Ni2+ for all the mixtures considered. Thus, leaching tests can be considered a prospective short-term technique for monitoring polluted soil media compared with tedious and time-dependent column studies.

The role of bromelain extraction waste product application for intensive land management practice

An intensive land management practice, especially, when related to long-live perennial crops such as pineapples, may lead to acute soil organic matter content depletion. However, incorporation of organic matter into soil in the middle of the planting season is not possible due to massive plant density. The application of bromelain extraction waste product as resistant organic matter resources might answer the problem. A set of experiments consisting of 0, 20, 40, 60, and 80 tons/ha of bromelain waste, based on a case study at PT Great Giant Pineapple Plantation, Lampung, has been done to indicate its role in increasing soil physical quality. After being incubated for 5 months, the application of bromelain showed more stable soil particle aggregation through the slake test. Soil aggregate stability is getting better with the higher rate of bromelain waste application. Soil shear strength is negatively correlated to the rate of bromelain waste, where the higher rate of bromelain waste application, the lower the soil shear strength. Soil sensitivity is carried out to determine the potential loss of soil strength because of remoulding. It indicates a decrease in shear sensitivity following the increasing rate of bromelain waste.

Frost heave mitigation of silt clay using nonionic polyacrylamide

Frost heave occurs frequently in high-latitude or high-altitude areas in many parts of the world, and it is a common challenge for geotechnical engineers in road construction. In order to solve the excessive frost heave induced frost damage to geotechnical engineering in cold regions, frost heave susceptible soil from the Tibetan Plateau (the seasonal frozen area) is modified by nonionic polyacrylamide (NPAM) and then used for frost heave testing. Moreover, cohesion test, permeability test, scanning electron microscopy (SEM) test, and Fourier transform infrared spectroscopy (FTIR) analysis are carried out on the NPAM modified soil to gain more insight into the frost heave mitigation mechanism. The impact of NPAM on soil frost heave and its physicochemical mechanism for frost heave mitigation are subsequently investigated. Our results demonstrate that NPAM is physically adsorbed on the surface of soil particles through hydrogen bonding. The increase of NPAM content does not only increase the viscosity of the solution, but it also enhances the aggregation of fine soil particles. In addition, the permeability of the modified soil decreases with increasing NPAM content, thus implying an increase in the water migration resistance. NPAM can be effectively used to reduce the frost heave susceptibility of soil. Our results show that 0.3 wt% of NPAM can significantly convert a strong frost heave soil to a weak frost heave soil. Our results reveal the mechanism of frost heave mitigation using NPAM and provides engineers and researchers with a new physicochemical method for the treatment of frost heave susceptible soil in railway and road construction in cold regions.

Soil particle aggregation and aggregate stability associated with ion specificity and organic matter content

Soil aggregate formation and stability are profoundly influenced by soil organic matter (SOM) content and electrolyte conditions by altering particle interactions during soil particle aggregation and aggregate breakdown. However, the effect of the ion-interface reaction, especially the newly discovered asymmetric hybridization of counterions, and its coupling with SOM on particle interactions and accordingly the particle aggregation and aggregate breakdown remain unclear. In this study, four black soils with different SOM contents were adopted to examine the particle aggregation kinetics using dynamic laser scattering method and aggregate stability using aggregate breakdown intensity in Li+, Na+, and K+ solutions with different concentrations. Combining experimental results with theoretical calculation of particle interactions, it found that different patterns of asymmetric hybridization between the three counterions produce ion specificity and lead to an ion sequence of Li+ < Na+ < K+ in promoting soil particle aggregation and reducing soil aggregate breakdown by decreasing the electrostatic repulsive force between soil particles. An increase in SOM, particularly its dissolvable fraction, increases the electrostatic repulsive force and steric repulsion and then inhibits soil particle aggregation, which is contrary to the effect of the ion sequence. The effects of ion specificity and SOM on particle aggregation could cancel each other in some specific cases of ion species and SOM contents. Moreover, similar to the above ion sequence, the increase in SOM also reduces soil aggregate breakdown and improves soil aggregate stability, because SOM greatly increases the van der Waals attractive force and short-range bonding interactions but rarely changes the electrostatic repulsive force between particles in soil aggregates.

Fine soil particle aggregation in ultra-fine bubble irrigated paddy fields

Abstract The flotation method of ultra-fine bubbles (UFB) aims to address pollution and has been used for combating the undesirable water conditions of contaminated soils. Hence, water containing UFB is gaining increasing attention for potential agricultural applications. Although certain hypotheses have been proposed, such as the collection of ions in water through the electrical characteristic of UFB, no clear experimental data have been provided. We found that improvement in turbidity may cause the adsorption of fine soil particles in the water by the UFB, thereby improving the quality of the water. The data from the paddy field showed that a decrease in turbidity (below 2 nephelometric turbidity units) occurred over a short period of time (3 days). UFB concentration is directly related to turbidity with a coefficient of determination of 0.93. This phenomenon was also observed through the distribution of bubbles and soil particles, where the average particle size increased because of the aggregation of soil particles and the decrease in turbidity in the paddy field, indicating that UFB collect soil particles and thereby improve water quality. Therefore, UFB are highly effective in cleaning rice field water and will be a preferred method for purifying the environment in the future.

Study on the geometry characteristics of soil primary mineral particles under cryogenic action

Repeated freeze–thaw causes the fragmentation and aggregation of soil particles, which affect particle shape (aspect ratio, roundness, etc.), and this process is a cryogenic weathering process. Changes in soil particle morphology record information about freeze–thaw processes and have the unique characteristics of freeze–thaw traces. To prove this conjecture, four soil specimens were selected in the experiment, and each specimen was studied after 0, 5, 10, 50 and 100 freeze–thaw cycles. The test results show that: Freeze–thaw will change the aspect ratio of particles, and the aspect ratio of particles is mainly distributed between 1 and 4. The particles with aspect ratio of 1.26 are stable and not easy to fragment, and the particles with aspect ratio more than 4 are easy to fragment. The freeze–thaw effect leads to changes in particle roundness, with different manners of change for the four specimens, but all undergo repeated freeze–thaw fragmenting and rounding process. Repeated freezing and thawing can not only lead to fragmentation particle edges and increased particle roundness, but also to fragmentation large-size particles and reduced particle roundness. Compared with the roundness before freeze–thaw and after 100 cycles of freeze–thaw, the coarse sand grains increased the most in roundness, indicating that the large grain size grains showed the most rounding. This study helps to understand the geometric characteristics of soil primary mineral particles under the action of cryogenic environments, and also helps to discern whether the particles have experienced the action of cryogenic environments, which is important for the study of cryogenic soil in cold environments.

Biofilm producing Bacillus vallismortis TR01K from tea rhizosphere acting as plant growth promoting agent

Microbial biofilms are an aggregation of single or multi-species bacteria that acquires the capacity to adhere to any surface where they can act like a wholesome system chemically “speaking with” each other through quorum sensing. This synergism is very prominently noticed in the rhizospheric regions of plant roots subsequently forming a dome which can protect the root-rhizospheric niche from various biotic and abiotic stress. The bacterial EPS have a number of roles like adhesion, cohesion and aggregation of soil particles, retaining water molecules, acts as a potential barrier on the rhizospheric regions, facilitating ionic and genetic information exchange within the matrix component, enhanced production of plant readily available nutrients etc. Keeping this scenario in mind, this study was formulated on to isolate and explore novel rhizobacteria with colossal biofilm forming ability showing great potential as a source of lignocellulolytic plant growth promoting agent.The crop chosen for this study was tea or Camellia sinensis, a quintessential beverage that is consumed across the globe. The rhizospheric region of a woody plant like tea, acts as a hub for lignocellulosic enzyme producing bacteria. The novel rhizobacteria isolated from cultivated tea soil, Bacillus vallismortis TR01K [NCBI Genbank Accession Number MT672714], was found to have an immense biofilm forming potential that ranged approximately 40x times higher than normal standard bacterial biofilm forming potentials when tested under laboratory conditions. Further in vitro characterizations of the novel strain showed it's immense potential to make plant nutrient available, to produce plant growth hormones (IAA, GA3, Cytokinin) and produce plant stress mitigating hormone (ACC deaminase). Lignocellulolytic enzymes are a vital part of lignocellulosic biomass degradation-a sustainable biotechnological approach for enzymes, organic acids, feed and biofuel production. The selected bacteria was tested elaborately for the family of lignocellulolytic enzymes (cellulase, laccase, lignin peroxidase, pectinase, amylase, chitinase, beta glucanase etc.) which showed promising results. Thus, proving the entire set of experiments in compliance with the aforementioned hypothesis that the novel bacterial isolate from tea rhizosphere has a significant biofilm forming potential with a colossal potency for being lignocellulolytic plant growth promoting agent.