Soil Retention Capacity Research Articles

Effects of Different Land Uses and Slope on Runoff and Soil Loss on the Loess Plateau of China

ABSTRACTThe Loess Plateau has one of the most serious areas of soil erosion in China; therefore, studying the effect of soil and water conservation measures on the erosion of loess soil slopes is important for land management and agricultural development. This study is based on 5 years of field runoff observations and rainfall data from 2015 to 2019. Correlation and regression analyses were used to study the runoff and sediment production of loess soil and its relationship with rainfall, slope and land use. The results show that > 80% of the erosive rainfall occurs mainly in July to August in the area. Runoff and soil loss from the plots differed substantially, depending on land use, soil conservation measures and slope degree. Bare plots experienced the highest soil loss rate of over 27 t/ha with higher runoff depth, followed by cultivated plots (4.55 t/ha), grass plots (0.43 t/ha), shrub plots (0.35 t/ha) and forest plots (0.13 t/ha). Among the four soil and water conservation measures, the runoff and sediment reduction benefits of forest and shrub plots were the highest. The runoff reduction benefit fluctuated at approximately 0.8, and the benefit of sediment reduction was ≈1. The overall performance was forest > shrubland > grassland > cultivated land > bare land, and the benefits of sediment reduction were greater than those of runoff reduction. Forests had the highest soil retention capacity on slopes from 5° to 25°, and forests on gentle slopes had the best water storage capacity. Shrub plots had the best water storage capacity when they were on steep slopes. Rainfall erosion forces were significantly and positively correlated (p < 0.01) with runoff depth and soil loss, making it the most significant rainfall indicator of sediment production. Under the same rainfall conditions, soil and water conservation measures are still required on bare slopes, land use is the main control factor for slope sediment production, and appropriate land use can greatly reduce the threat of slopes in terms of soil erosion. This study shows that soil and water conservation measures are imperative to prevent runoff and soil loss, especially for bare land without any measures; on steep slopes, a vegetation combination primarily featuring shrubs is expected to achieve greater benefits in reducing runoff and sediment. This study can provide a scientific basis for the management of vegetation measures and the implementation of soil and water conservation measures on loess soil slopes.

Soil-water retention capacity of expansive soil improved through enzyme induced carbonate precipitation-eggshell powder

Enzyme Induced Carbonate Precipitation (EICP) has been extensively investigated as a promising approach to improve engineering properties of soil, while Eggshell Powder (ESP) is an agricultural waste that effectively fills soil pores. The ESP provides abundant nucleation at sites for the EICP process, further promoting the effective precipitation of calcium carbonate. The research presented in this paper investigated the Soil Water Characteristic Curves (SWCC), permeability coefficient, and microstructure of expansive soil before and after EICP and EICP+ESP modification. A series of laboratory experiments were conducted, including soil water characteristic tests, permeability tests and Scanning Electron Microscopy (SEM). The results proved that the addition of EICP and EICP+ESP into natural expansive soil resulted in a gradual decline in air entry value, residual water content, and permeability coefficient, indicating an increase in water retention capacity and a decrease in permeability. Furthermore, with the intrusion of EICP and EICP+ESP, the contact between particles becomes smoother, and the soil pores become more equally distributed. Ultimately, there was an enhancement in water retention capacity of the natural expansive soil. This study emphasizes the synergistic potential of combining EICP and EICP+ESP as stabilizing additives to enhance the water retention capacity of expansive soil. Moreover, the reuse of ESP provides a sustainable solution for the resource utilization of agricultural waste and the improvement of expansive soil using bio-inspired methods.

Solid fraction of digestate from olive pomace modulates abiotic and biotic processes in soil: Retention of agrochemicals and inhibition of fungal pathogens

A new type of solid digestate (DG) obtained exclusively from two-phase olive pomace was characterised and evaluated for physicochemical and biological properties. In slurry-type experiments, the adsorption of the fungicide boscalid and the herbicide oxyfluorfen on non-amended loam soil (SOIL) and on soil amended with DG at doses of 1 % (SOIL-DG1), 3 % (SOIL-DG3) and 6 % (SOIL-DG6) (w/w) was quantified and modelled. The DG showed a remarkable and stable capacity to adsorb the compounds over a temperature range of 5–40 °C. Based on the data of the adsorption isotherms conducted at 20 °C, the distribution coefficients of SOIL, SOIL-DG1, SOIL-DG3 and SOIL-DG6 were, respectively, 1.3, 2.2, 2.2 and 3.4 mg kg-1 for boscalid and 2.0, 2.1, 2.2 and 5.9 mg kg-1 for oxyfluorfen, which suggested a significant increase in soil retention capacity after the addition of DG, especially at the highest dose. The desorption of both compounds from all treatments, especially from SOIL-DG6, was slower than adsorption and incomplete (hysteresis coefficient < 1), thus indicating a prolonged permanence of the molecules on the soil. In lab-scale experiments, the phytopathogenic fungi Armillaria mellea, Fusarium culmorum and Verticillium dahliae were exposed to 0.02, 0.1, 0.5 and 1 % (w/w) DG alone, and 0.02 and 0.1 % DG preliminary interacted with 100 mg l-1 of soil humic acid (HA-DG). Fungal response was clearly influenced by the species, the treatment and the dosage adopted. In general, all treatments did not significantly modify the growth rate of A. mellea and V. dahliae, whereas all DG treatments, especially HA-DG, caused evident suppressive effects on F. culmorum. Based on the results of this study, it can be concluded that the addition of DG to the soil can regulate the bioavailability of agrochemicals in pore water and exert an inhibitory or irrelevant action depending on the phytopathogenic fungus.

Soil fertility and plant nutrition in an organic olive orchard after 5 years of amendment with compost, biochar or their blend

The agronomic use of compost and biochar as soil amendments may exhibit contrasting results in terms of soil fertility and plant nutrition. The effects of the biennial application of biochar, compost and a blend of compost:biochar (90:10; % dw:dw) on the agronomical performance of an organically managed and well established 25-year-old olive orchard was assessed 5 years after the initial application. The agronomical evaluation was based on the assessment of the soil physical, chemical, and biological characteristics, and the assessment of the soil fertility by both crop production and nutritional status of the orchard, and the bioassay with olive plantlets. Biochar mainly benefited the physical properties (bulk density, total porosity, aeration, water retention capacity) of soil, especially in the top 0–5 cm. Compost and its blend with biochar improved microbial activity, soil nutritional status (increasing the content of soluble organic C, N, and P) and favoured the formation of aggregates in soil. The bioassay conducted with young plantlets confirmed the enhanced soil fertility status in the three amended treatments, particularly in the case of biochar and its blend with compost. However, this effect was not significantly observed in the adult plants after 5 years of application, reflecting the slow response of adult olive trees to changes in fertilization. Based on these results, alongside the desirable long-residence time of biochar in soil and the ready availability of compost, the blend of biochar with compost assayed in this study is defined as a valid strategy for preparing high quality soil organic amendments.

Properties of biochars derived from different straw at 500℃ pyrolytic temperature: Implications for their use to improving acidic soil water retention

Climate change cause extreme weather effects with temperature increases and drops in humidity, such as drought and heatwaves, which will lead to more evaporation in arid and semi-arid lands. The application of biochar made from crop straw without burning to farmland can effectively improve the water retention capacity of soil. A testing program has been carried out in a climate simulation laboratory to study the effects of different straw biochars on the cracking and evaporation of soils due to drying. Biochar from wheat straw (WS), corn straw (CS) and rice straw (RS) is produced at a pyrolysis temperature of 500℃. Thermogravimetric analysis and elemental analysis are carried out to obtain the properties of the biochar. Five percent of WS, CS and RS biochar by weight is added to acidic soil. Digital camera and digital image processing technology are used to analyze the crack morphology of the samples during evaporation. The results indicate that the RS biochar has the highest ash content (32.5 %), CS biochar has the highest content of volatile solid (25.36 %) and WS biochar has the highest content of fixed carbon (55.38 %). Biochar can effectively improve the water retention capacity of soil. The final water contents of the WS, CS and RS biochar soil samples are 132.3 %, 101.0 %, and 20.7 % respectively higher than that of the soil without biochar. Moreover, biochar can effectively reduce the degree of soil cracking. The addition of WS, CS and RS biochar can reduce soil cracking by 9.21 %, 16.57 %, and 7.46 %, respectively. WS contains more total cellulose than CS and RS, so WS biochar is the best choice to improve soil water retention ability. Therefore, biochar technology helps to optimize soil water retention while avoiding environmental pollution from straw burning.

Reduction of nitrogen loss in runoff from sloping farmland by a ridged biochar permeable reactive barrier with vegetated filter strips

IntroductionEutrophication due to nitrogen (N) loss from sloping farmland has a high risk in the Three Gorges Reservoir. Biochar and vegetated filter strips (VFS) are used to control nutrient runoff and increase soil water-holding capacity, soil nutrient retention, and crop yield. However, surface biochar application has limited ability to control N loss, especially from sloping farmland.MethodsIn this study, different widths of ridged biochar permeable reactive barrier (RB-PRB) with VFS were employed to intercept N loss in runoff from sloping farmland. Adsorption characteristics of biochar for nitrate and ammonium N were evaluated using isothermal and kinetic adsorption models before field experiments. N index values for ammonium (NH4+), nitrate (NO3−), dissolved N (DTN), particulate N (PN), and total N (TN) lost through runoff were monitored from April 2019 to January 2020.ResultsNO3− and NH4+ sorption on biochar was predominantly physical adsorption with a maximum capacity of 4.51 and 4.12 mg g-1, respectively. During the research period, the dominant transportation pathway of N loss involved dissolved total N movement through subsurface flow, which accounted for 65.55% of the total loss. TN loss for CK was 1954 g·hm-2, while RB-PRB and VFS decreased N loss from sloping farmland by 36.7%. The interception efficiency of RB-PRB was highest at 0.3 m width. VFS successfully intercepted particulate N and reduced it by 32.75%. In terms of soil nutrients, the RB-PRB and VFS interventions led to a substantial 41.69% increase in the TN content of the soil at a 0.4 m width.DiscussionThe findings suggest that biochar has a favorable adsorption effect on NH4+ and NO3−, an appropriate width of RB-PRB with VFS could effectively reduce nitrogen loss from sloping farmland. Simultaneously, it enhances the water and fertilizer retention capacity of sloping cropland soil; however, the long-term implications necessitate further validation.

Expansive soil improvement using industrial bagasse and low-alkali ecological cement

Cement is the primary material used for mitigating expansive soil hazards due to its easy availability and relatively low cost. However, the most commonly used ordinary Portland cement renders the soil strongly alkaline after treatment, and the development of cracks in the soil is not effectively controlled under the influence of wet-dry cycles following cement stabilization. These two drawbacks significantly impact both the ecological environment and the strength of the cement-stabilized expansive soil. This study innovatively proposes an improvement to the method of cement stabilization of expansive soil by incorporating low-alkali ecological cement and industrial sugarcane bagasse (a byproduct of sugar production). After assessing the basic physical properties of the expansive soil, it was improved by mixing with industrial bagasse and low-alkali ecological cement. Through experiments on dry-wet cycles, soil-water characteristic curve tests, direct shear tests, and electron microscopy scans, we explored the enhancement of the expansive soil. Our focus was on the development of cracks, soil moisture migration patterns, changes in shear strength, and microstructural alterations. The following conclusions were drawn from the experiments: i. Compared to the method of ordinary Portland cement stabilization, the pH of expansive soil improved by low-alkali ecological cement combined with industrial sugarcane bagasse is more suitable for plant growth. ii. The unique tubular structure of industrial sugarcane bagasse provides elastic space for soil deformation, inhibiting the development of soil cracks. iii. The water retention capacity of expansive soil significantly increases after improvement with low-alkali ecological cement and industrial sugarcane bagasse. Within the range of matrix suction for plant growth, soil moisture changes more slowly, providing a more stable water supply for plants. iv. The combination of 1.2% industrial sugarcane bagasse and 7% low-alkali ecological cement exhibits the highest shear resistance, maintaining strength exceeding that of untreated expansive soil after five wet-dry cycles. v. SEM analysis confirms the effectiveness of industrial sugarcane bagasse and low-alkali ecological cement in improving expansive soil. This study improved the widely used cement stabilization method for expansive soil in practical engineering applications. Additionally, it introduced an additional utilization pathway for industrial bagasse residue waste. This research provides a new direction and reference for the combination of waste utilization and natural disaster management in the treatment of expansive soil hazards.

Study on the Impact of Vegetation Restoration on Groundwater Resources in Tianshan Mountain and Yili Valley in Xinjiang, China

China has implemented a series of ecological protection and restoration projects in Tianshan Mountain and Yili Valley in Xinjiang, which have significantly improved regional vegetation coverage. Vegetation improves soil structure through roots, especially increasing non-capillary porosity, which enhances the precipitation infiltration performance, thus reducing surface runoff, increasing the interception and infiltration of groundwater resources, and enhancing regional water retention capacity of soil. In order to quantitatively study the impact of ecological conservation and restoration (represented by fraction of natural vegetation coverage, FVC) on groundwater storage (GWS), we investigated GWS changes in this region, identified the main factors, and quantified their relative impacts. Here, we combined data from the Gravity Recovery and Climate Experiment (GRACE) satellite, GRACE Follow-On (GRACE-FO), and Global Land Data Assimilation System (GLDAS) hydrological model from January 2003 to December 2020 and evaluated GWS changes. We used the variable importance in projection and partial least squares regression methods to determine the main influencing factors. We found that (1) before and after 2012, GWS decreased at a rate of 0.80 cm/yr and 0.75 cm/yr (with statistical significance p &lt; 0.01), respectively. (2) Before 2012, the main factors affecting the decrease in GWS were agricultural planting areas, and after 2012, they were temperature, evaporation, and FVC, with relative contributions of 54.72%, 34.59%, and 10.69%, respectively. FVC has a positive regulating effect on the increase in regional GWS.

Effects of soil heterogeneity and preferential flow on the water flow and isotope transport in an experimental hillslope

Soil water movement plays vital roles in hillslope runoff generation and groundwater and surface water interaction. However, there are still knowledge gaps about the impacts of soil heterogeneity and preferential flow on the internal water flow and transport process. In this study, the vertical soil heterogeneity focused on the variations in soil retention capacity, and the consideration of lateral preferential flow emphasized the higher hydraulic conductivity. We combined isotopic tracing and numerical modeling in an artificial hillslope, focusing on monitored processes of the artificial rainfall and isotopic tracing experiment. The results showed that the soil moisture quickly accumulated at the bottom of the hillslope during rainfall events, while the 2H enrichment occurred in the topsoil derived from enriched isotope injection in the second artificial rainfall. The evaporation process slowed down the mixing of new water in the topsoil and old water in the lower layer. We found that the vertical soil heterogeneity had significant influences on the internal water and isotope transport paths within the hillslope. The lateral preferential flow played an important role in the water flux and transport time to the seepage face. The coupling of isotopic tracing, which reflects the water transport and mixing with the hillslope, effectively improved the model simulation and mechanism analysis of hillslope water flow. Our findings provide new insights into the mechanisms governing soil water flow and transport dynamics in hillslopes, taking into account vertical soil heterogeneity and lateral preferential flow.

Potential of Irrigated Agricultural Production of Corn (Zea mays L.) in Semi-Arid Region using Geoprocessing

This work aimed to evaluate and map the potential of irrigated agricultural production for corn for the watershed of the region of the middle course of the Paraíba River. Using SPRING, a map of soil irrigation potential and soil retention capacity was prepared and a partial map was generated through matrix crossing. Using average annual rainfall data, the climate condition map was prepared. After using LEGAL, the agricultural production potential map was generated through the matrix crossing between the partial map and the climate scenario. For maize, a Full climatic condition (C1) was identified in 2.02% of the basin's total; the full climatic condition with prolonged rainy season (C2) and the climatic condition moderated by excess water (C3) were not identified; the climatic condition Moderate by water deficiency (C4) in 0.86%; the unfit condition due to severe water deficit (C5) in 97.12% of the basin. The potential of irrigated agricultural production for maize did not show Very High (MA), High (A), Medium (M) and Low (B) potential, only the Very Low (MB) potential in 100% of the basin.

Efeito da aplicação do biochar na mobilidade do corante têxtil vermelho drimaren em uma camada de solo aluvionar

ABSTRACT The region of Alto Capibaribe, in the Brazilian semiarid, faces an environmental issue due to contamination from textile activities. Inadequate release of dyes and other toxic substances threatens human health and water resources, such as alluvial reserves. Thus, biochar, a low-cost adsorbent produced by biomass pyrolysis, helps mitigate these problems by increasing soil retention capacity. This study analyzed the effect of applying biochar, produced from coffee husks, a biomass already established in biochar production, at temperature of 530 °C with a pyrolysis time of 10 to 12 hours, in a homemade metallic furnace, resulting in a product with 67.11% carbon. This biochar was applied to evaluate the mobility of the textile dye Red Drimaren, at a concentration of 25 mg.L-1, used for garment dyeing in local industries, in a subsurface layer of an alluvial deposit located in the dry bed of the Capibaribe River. Fourier Transform Infrared Spectroscopy (FTIR) showed that the highest spectral vibrations are in the range of 1400-1800 cm-1, indicating the presence of amine and amide functional groups, favoring the biosorption process. The pH in water is higher than in KCl for all situations, with biochar being basic and the alluvial soil being acidic. The zero charge point values are equal to 6.96 and 7.96 for the proportions Soil+0.25%BC and Soil+1.00%BC, respectively. Layers with 0.25%BC and 1.00%BC added had an increase in adsorptive capacity of 31.68% and 8.62%, respectively, compared to the natural soil sorption capacity. Kinetic data best fit the pseudo-second-order model, and intra-particle diffusion was not the determining mass transfer process nor the occurrence of the adsorption process. Linear and Freundlich isotherm models consistently described the process under varying concentrations, and the Langmuir model did not show a valid physical significance.

Nitrogen retention capacity of paddy soil improved under long-term garlic-rice rotation

ABSTRACT Although significant differences in soil nitrogen levels exist under different paddy-upland rotations, the main reason for this is unclear. The nitrogen retention capacity and loss of ammonia volatilisation, leaching, etc. of paddy soil with large differences in nitrogen levels from two long-term rotations, garlic-rice and wheat-rice, were measured using the soil column simulation method. The results showed that the loss rate of leaching was only 5.4%, whereas that of ammonia volatilisation was up to 22.8%, which was the main nitrogen loss way of paddy soil under the two rotations. The average ammonia volatilisation rates under wheat-rice rotation with high and low nitrogen application rates were 12.1% and 40.2% higher than that under garlic-rice rotation, leading to a decrease in the total nitrogen loss amount and rate through ammonia volatilisation by 29.8% and 8.8%, respectively. As a result, nitrogen retention in the soil under garlic-rice rotation increased by 12.7%. In conclusion, the long-term garlic-rice rotation could significantly inhibit ammonia volatilisation, thus improving the soil nitrogen retention capacity. The straw return may increase soil organic matter content, reduce ammonia volatilisation loss, and enhance soil nitrogen retention capacity and productivity.

An eco-friendly versatile superabsorbent hydrogel based on sodium alginate and urea for soil improvement with a synchronous chemical loading strategy

In this paper, an eco-friendly versatile superabsorbent material was designed for soil improvement, and a synchronous chemical loading strategy was proposed. In this strategy, urea not only acted as fertilizer but also acted as a crosslinker to construct an alginate network. The microstructure, chemical structure, thermal stability and composition of the obtained SA/urea hydrogel were characterized in detail. Adsorption behavior and application performance in agriculture were evaluated. The results demonstrated that urea had two different conformations in the network. The SA/urea hydrogel had abundant pore structures with excellent water absorption performance. It could not only improve the water retention capacity of soil but also release nitrogen, phosphorus and potassium elements with degradation for as long as 9 weeks. Moreover, the hydrogel could promote plant growth, increase the nutritional composition of plants and inhibit the accumulation of harmful nitrate in plants. With advantages, including biodegradability, high water absorption, controllable degradation, excellent water retention, sustained NPK release and improved plant nutrition value, the SA/urea hydrogel has great potential for soil improvement in agriculture as an eco-friendly versatile water retention agent and can be expected to extend to more fields as a novel superabsorbent material.

Nitrogen retention capacity of paddy soil improved under long-term garlic-rice rotation

Nitrogen retention capacity of paddy soil improved under long-term garlic-rice rotation

Characterizing water transfer in compacted soils in the context of energy storage, contribution of magnetic resonance imaging (MRI)

The concept of energy geostructures consists in enhancing existing civil engineering structures from an energy point of view thanks to the insertion of heat exchanger tubes. In order to consider the use of compacted soil embankments for heat storage [1], a good knowledge of water movement is required. Indeed, the increase in temperature of the exchangers leads to a migration of liquid/vapour water to the surface layers [2]. A loss of moisture may alter the thermal capacity of the soil [1] and therefore the system energy efficiency. To determine unsaturated hydraulic properties, the Instantaneous Profile Method (IPM) consists in inducing transient flow in a long cylindrical sample of soil and then measuring the resulting water content and/or pore water pressure profiles at various time intervals [3]. The unsaturated hydraulic conductivity (ku) is then computed using Darcy’s law.&#x0D; The direct evaporation technique allows the measurement of the suction profile in a soil column submitted to drying [4] using filter papers whose water retention curve is known. This method is quite reliable but requires long equilibrium time. Thus, the tests need several weeks and do not give accurate results at the early stages of drying, as the soil state is close to saturation. The analysis of the results when the soil retention capacity is low is therefore complicated, especially when the flow is coupled with temperature variations.&#x0D; In this study, this classical method was compared to a faster alternate method using nuclear magnetic resonance imaging (MRI) that allows for non-intrusive, continuous and small-scale monitoring of the effect of thermo-hydraulic solicitations on water transfer within the sample. The use of MRI for monitoring the drying/wetting front progression appeared in 1970 [5]. Simpson et al. [6] presented the successive studies that have made it possible to develop a method for monitoring the movement of water within a sample. These measurements can be 1D, 2D and 3D.&#x0D; The tests were performed on a sandy lean clay sampled in the Paris region in France. The soil was dried, pulverized, and sieved through a 2 mm sieve before experiments. The compaction state was selected to optimize the heat storage capacity [4] with a water content of 16.3% and a dry density of 1.79 Mg.m-3. Ten cylindrical samples of 70 mm in diameter and 20 mm in height were compacted and superimposed with introducing filter paper disks between them. The regular weighting of each sample and each filter paper during three months allowed the derivation of the ku curve by the IPM method.&#x0D; For the MRI method, 9 samples of 36 mm in diameter and 10 mm in height were compacted at the initial state then brought to different degrees of saturation. The measurement of the water proton relaxation time using a Bruker Biospec 24/40 superconducting magnet (100 MHz), allowed the definition of a calibration curve which connects MRI signal to the water content of the samples (Figure 1b). A Single Point Imaging pulse sequence [7] was used to obtain the signal intensity (encoding time 75 µs &lt; t &lt; 200 µs). In an image acquired with the SPI method, the intensity of each voxel (S) is :&#x0D; (1) Whereis the magnetization in a pixel and is the transverse relaxation time.&#x0D; The calibration curve is shown in Figure 1b. Then, a larger sample of 30mm in height was compacted and exposed to an air flow at 20°C and 30% relative humidity through using a remote humid air generation system. 27 measurements points were monitored with an interval of 1.1 mm along the sample. Four examples of the recorded profiles are shown in Figure 1c. The evolution of the water content inside the sample is then calculated using the calibration curve to interpret the water migration in the samples submitted to humidity- and temperature-controlled air (Figure 1a). The pre-established retention curve of the soil will be used to calculate its matric suction. At each depth, the flow velocity and the hydraulic gradient will be calculated from the water content profiles and suction profiles respectively in order to determine the unsaturated hydraulic conductivity. &#x0D; These experimental developments allow the non-intrusive and continuous quantification of water movement in unsaturated soils during the application of coupled thermo-hydraulic solicitations. The understanding of these fundamental parameters is a key step for studying thermo-hydromechanical behavior of compacted soils considered for heat storage. The results provide insight into the feasibility of these structures in terms of their long-term energy efficiency and stability.

Effect of soil hydrophobicity on soil-water retention curve of a silt loam soil

Soil wettability is an important property that affects the behaviour of fine-grained soils. Previous studies have shown that hydrophobicity induced by organic or silane additives may affect the soil-water retention curve (SWRC). However, current findings regarding the effect of hydrophobicity on the SWRC are controversial. Previously, organic or silane additives were assumed to change only the soil wettability. Nevertheless, this study shows that polyvinyl alcohol (PVA) can change the hydrophobicity, pore size distribution (PSD), and specific surface area (SSA) of soil, thus affecting the SWRC. PVA-treated soil is hydrophobic when cured at 20 ℃, but hydrophilic when cured at 100 ℃. No thermal degradation is indicated in the PVA at 100 ℃ based on thermogravimetric analysis and a comparison of mass loss, and the sole difference between the PVA-treated soils cured at 20 and 100 ℃ is their wettability. This study managed to make the hydrophobicity caused by PVA to become an independent variable separated from the PSD and SSA by controlling the ambient temperature. The wetting and drying curves are measured under isopiestic humidity control in the high-suction domain (2.7–298.7 MPa), whereas pressure plates are used for the drying curves in the low-suction domain (0–800 kPa). The results obtained indicate that soil hydrophobicity significantly accelerates drainage when the matric suction is between 100 and 400 kPa, and an increase in PVA content increases the water retention capacity of soil. When the matric suction exceeds 2.7 MPa, the effect of soil hydrophobicity on the SWRC of the soil weakens. At this time, the SWRC is dominated by the van der Waals force, and the SSA contributes significantly to the process. Additionally, this study enables some controversial findings from previous studies to be explained, which is of great significance in soil and agriculture sciences.

Density and salinity effects on the water retention capacity of unsaturated clayey dispersive soil

Density and salinity effects on the water retention capacity of unsaturated clayey dispersive soil

Effect of Bamboo biochar on strength and water retention properties of low plastic clay and silty sand

Biochar is a carbon-rich stable product derived from the thermochemical decomposition of biomass. The properties of biochar vary with types of feedstock, heating rate, pyrolysis temperature, etc. Consequently, the mechanical and hydrological properties of biochar amended soil (BAS) also differ with types of biochar and soils. However, the effect of bamboo biochar (BB) amendment on soil strength and water retention properties is missing in the previous literature. Bamboo biomass was pyrolysed at 600 °C to produce biochar. BB and soils (low plastic clay (CL) and silty sand (SM)) were mixed to prepare BAS. The samples were prepared by mixing BB in five ratios, i.e., 0%, 1%, 2%, 3.5% and 5% of dry soil weight. The biochar application has increased optimum moisture content, alkalinity (pH) and Atterberg limits, whereas, reduced maximum dry density and specific gravity of both the soils (CL and SM). The unconfined compressive strength (UCS) of CL soil was noted to increase by 10.5% with 2% biochar content and decreased after that, whereas the UCS of SM soil was found to decrease continuously with the biochar content increment. Therefore, the unconfined compressive strength (UCS) result showed that biochar application has contrary effects on both soils. The measured gravimetric water content (GWC) of BAS was increased with biochar increment in both soils. However, GWC increased more in CL than in SM soil at the same biochar content. The microstructural analysis showed that the biochar amendment filled the pore space of the soil matrix, resulting in an increase in UCS and GWC values. The increased water retention capacity and strength (UCS) of biochar amended CL soil provides evidence that it could be used as a landfill cover material.

Superabsorbent polymer used for saline-alkali soil water retention

BackgroundEnhancing the water retention capacity of soil is an effective measure to curb soil salinization. Superabsorbent polymer (SAP) with a strong absorbing water ability is particularly suitable as a water-retaining agent in agriculture. However, their limited salt tolerance restricts their applicability in saline-alkali soil. Hence, this research aimed to develop a salt-tolerant superabsorbent polymer (ST-SAP) that can be utilized in saline-alkali soil. MethodsST-SAP, prepared by using 2-acrylamide-2-methylpropanesulfonic acid (AMPS), acrylic acid (AA) and acrylamide (AM), was evaluated by swelling and reswelling experiments. The salt-tolerant mechanism of ST-SAP was studied by XPS, FT-IR and CT. The water retention capacity of saline-alkali soil, collected from Lop Nur of Xinjiang and containing 18.13 wt% total dissolved salt, was determined to validate the effectiveness of ST-SAP in high-salt soil. Significant FindingsThe ST-SAP synthesized in this study exhibited excellent swelling capacity (69.04 g/g) under high salt condition. Notably, ST-SAP presented exceptional stability under high salt condition, due to the complexation reaction between Ca2+and its three hydrophilic groups (R-SO3H, R-COOH, R-CONH2). Moreover, when 2 wt% ST-SAP was added to the saline-alkali soil, the water retention time was extended to 28 days, confirming the efficacy of ST-SAP in saline-alkali soil.

Fabrication of stalk fiber/geopolymers-based slow-release fertilizer with agricultural waste and loess for promoting plant growth

The reutilization of agricultural waste is an important strategy to ensure the sustainable development of modern society. In this work, corn stalk fiber (CoS), a typical discarded biomass from agricultural production, was composited with loess-based geopolymer (LoGP), along with loading urea and in-situ grafting polymer of acrylic acid, which afforded a novel slow-release fertilizer of corn stalk fiber/geopolymer (N @ CoSP/LoGP). Its composition, microstructure and morphology were characterized by SEM, FT-IR, XRD, TG and BET. Its water absorption, water retention capacity, swelling behavior, and N sustained-release performance were also measured. And the sustained-release mechanism was discussed by using a kinetic model of dissolution and release. It was found that the prepared composited fertilizer could enhance the water retention capacity of soil, and the maximum swelling rate of N @ CoSP/LoGP in water and 0.9 wt. % NaCl solution were 263.2 g/g and 62.5 g/g, respectively. Its swelling rate kept to 80 % than that of the initial value after 6 cycles, the water holding capacity of soil, containing 2 wt. % of N @ CoSP/LoGP, reached more than 25 days. Furthermore, the promoting plant growth action of N @ CoSP/LoGP was tested through pot experiments of corn. It indicated that the prepared composited fertilizer could effectively promote the germination and growth of corn crop as it released 60.6 % of nutrients within 45 days. In summary, a strategy for reutilization of agricultural waste and low-cost loess was explored, and the obtained composited fertilizer has great potential application in agricultural production.