Saturated Moisture Content Research Articles

Geotechnical-Electrical Evaluation of Soil Compaction Parameters, South of Baqubah City

Soil compaction is fundamental for improving the geotechnical properties of a wide range of engineering structures. Evaluation of compaction parameters is crucial for maintaining the long-term performance of these structures. In this study, geotechnical-electrical relationships were adopted to evaluate the compaction parameters of soil south of Baqubah City. Forty-seven soil specimens, collected from eight locations, were prepared and compacted at various conditions that can be found in the geotechnical practice. First, laboratory tests such as sieve analysis, liquid limit, and plastic limit were carried out to characterize and classify the soil based on USCS classification. Second, the specimens were prepared in the lab using different moisture content, dry density, and compaction efforts. Electrical resistivity measurements were then conducted on compacted specimens using Kangda KD2571B2 instrument. All laboratory tests were performed based on ASTM standards. The results revealed that the soil at the site is fine-grained type CL of medium plasticity clay with sand. Optimum Moisture Content OMC and Maximum Dry Density MDD were, respectively, 14.72% and 1.83 g/cm3 for the Standard Proctor compaction test; and 11.08% and 1.90 g/cm3 for the Modified Proctor compaction test. Geotechnical-electrical relationships achieved showed that soil resistivity is strongly influenced by the main compaction parameters; moisture content, dry density, and compaction energy, particularly at low moisture content. A high correlation coefficient (R2 > 0.98) was achieved for the resistivity-degree of saturation and resistivity-volumetric moisture content relationships. These correlations were validated with R2 (0.896-0.934) between the measured and predicted data, which indicates the advantages of adopting the resistivity method as a complementary tool for the preliminary site investigation.

Multivariate roles of litter traits on moisture and flammability of temperate northeastern North American tree species

BackgroundTree litter is the primary fuel affecting surface fire behavior in most fire-prone forest and woodland ecosystems in northeastern North America. Fire exclusion and land use changes have dramatically altered fire regimes in many of these ecosystems, shifting toward species that reinforce the continued diminution of fire. Comparative litter flammability studies provide a useful approach to identify the corresponding leaf and litter bed traits that drive the positive feedback termed “mesophication” in these ecosystems.ResultsIn this study, we measured laboratory flammability and moisture characteristics of leaf litter from 17 common tree species in temperate forests of northeastern North America. Principal components analysis of flammability and moisture data resulted in species separating along a pyrophyte-to-mesophyte gradient. Pyrophytic Quercus litter was the most flammable of all species, and Pinus litter dried the most rapidly and flamed for the longest duration. The remaining mesophytic species grouped into either a high moisture retention-poor burning cluster (Acer rubrum, Betula alleghaniensis, Nyssa sylvatica, Carya glabra, C. tomentosa) or an intermediate flammability cluster (Acer saccharum, C. ovata, Tilia americana). Several litter traits were associated with multivariate factors. Leaf length, density, curling, surface area-to-volume, and litter bed bulk density were associated with the factor comprising saturation moisture content, flaming time, and consumption. Specific leaf area was related to moisture time-lag and flame height. Litter bed packing ratio was most related to smoldering duration.ConclusionsInterspecific variability in leaf and litter bed traits explained substantial differences in moisture dynamics and flammability among the species examined. These findings extend our understanding of litter traits’ influence on the combustion environment and affirm the potential effects of pyrophytic and mesophytic tree species on contemporary fire regimes in northeastern North American forests.

Rapid testing and prediction of soil–water characteristic curve of subgrade soils considering stress state and degree of compaction

The subgrade soil is generally in saturated or unsaturated condition. To analyze complex thermo-hydro-mechanical-chemical (THMC) behaviors of subgrade, it is essential to determine the soil–water characteristic curve (SWCC) that represents the relationship between matric suction and moisture content. In this study, a full-automatic rapid stress-dependent SWCC pressure-plate extractor was developed. Then, the influences of overburden stress and degree of compaction on the SWCC of subgrade soil such as high liquid limit silt (MH) and low liquid limit clay (CL) were analyzed. Accordingly, a new model taking into account the influences of overburden stress and degree of compaction based on the well-known Van Genuchten (VG) SWCC fitting model was presented and validated. The results show that with the increase of the degree of compaction and overburden stress, the saturated moisture content of subgrade soil decreases, while the air-entry value increases and the transition section curve becomes flat. The influences of the degree of compaction and overburden stress on the SWCC of MH is greater than that of CL. Meanwhile, there was a satisfactory agreement between the prediction and measurement, indicating a good performance of the new model for predicting the SWCC.

Study on the Mechanical Performance of Soft Sandy Soil Solidified by Epoxy Composites

In this work, we propose the stabilization of soft sea sand by an epoxy composite solidifier, which can be extremely beneficial in the fields of national defense, rescue engineering, and traffic emergency support under complex conditions. The effects of material ratio, curing time, curing temperature, and moisture content on the mechanical performance (compressive strength, bending strength, and splitting tensile strength) of solidified sea sand are investigated by indoor tests. The results indicate that the epoxy composite solidifier can rapidly enhance the mechanical performance of sea sand, thereby improving the beach trafficability and facilitating traffic emergency support. The strength of solidified sandy soil increases with the increase in curing time and temperature or with the decrease in moisture content. Furthermore, the epoxy composite solidifier exhibits good solidification capability under low temperatures and saturated moisture content. Keywords: epoxy resin; solidifier; sea sand; mechanical test

Evaluation and Development of Pedotransfer Functions and Artificial Neural Networks to Saturation Moisture Content Estimation

Modeling of irrigation and agricultural drainage requires knowledge of the soil hydraulic properties. However, uncertainty in the direct measurement of the saturation moisture content (θs) has been generated in several methodologies for its estimation, such as Pedotransfer Functions (PTFs) and Artificial Neuronal Networks (ANNs). In this work, eight different PTFs were developed for the (θs) estimation, which relate to the proportion of sand and clay, bulk density (BD) as well as the saturated hydraulic conductivity (Ks). In addition, ANNs were developed with different combinations of input and hidden layers for the estimation of θs. The results showed R2 values from 0.9046≤R2≤0.9877 for the eight different PTFs, while with the ANNs, values of R2>0.9891 were obtained. Finally, the root-mean-square error (RMSE) was obtained for each ANN configuration, with results ranging from 0.0245≤RMSE≤0.0262. It was found that with particular soil characteristic parameters (% Clay, % Silt, % Sand, BD and Ks), accurate estimate of θs is obtained. With the development of these models (PTFs and ANNs), high R2 values were obtained for 10 of the 12 textural classes.

Effects of void content on the moisture uptake and mechanical strength of a glass/epoxy composite

The effect of voids on the moisture uptake and transverse modulus and strength of a unidirectional glass/epoxy composite has been examined. To create voids, a foaming agent was mixed with the liquid epoxy resin prior to infusion. Micrographs of polished cross-sections indicate that voids are close to spherical in shape appearing in the matrix and at the fiber/matrix interface. The fiber, matrix, and void contents were analyzed by micrograph, burn-off, and density (Archimedes) methods. The void contents in the void-free and void-containing composites were respectively close to zero and 21%. Specimens were immersed in distilled water at 40°C until saturation. The weight gain was monitored periodically. For the void-free specimens, saturation moisture contents of about 0.60%. The void-containing specimens absorbed much more water, about 5%. The Fickian diffusion model provided good fits to experimental data although the transport mechanism for the void-containing composite appeared non-Fickian. Young’s modulus of the void-free composite was slightly affected by water absorption, although, the transverse tensile strength dropped significantly. Voids were found to substantially reduce transverse modulus and strength about 70%, for both dry and water saturated specimens. Moisture content analysis was in good agreement with experiments for the void-free composite but over-predicted the moisture content for the voidcontaining composite. Micromechanics predictions of the transverse modulus were within 21% of the experimental results for void-free and void containing composites at dry and water saturated conditions.

Modeling the drying process of Masson pine needle fuel beds under different packing ratios based on two-phase models in the laboratory.

When the moisture content of a fuel bed is higher than the fiber saturation moisture content (0.35 gg-1), the drying process is controlled by evaporation (>0.35 gg-1) and diffusion (>0.35 gg-1). Packing ratio has a significant effect on the drying process. Ignoring the impacts of packing ratio or the separate phases of the drying process is one main reason for inaccurate moisture content predictions. This study simulated the drying process in five Masson pine (Pinus massoniana Lamb.) needle beds with different packing ratios. Using the fiber saturation moisture content as the cut-off point, we divided the drying process into two phases. The drying mechanism of each phase was different and had its own drying equation. Using a model that does not distinguish the two phases of the drying process as a comparison, the prediction effect of the two-phase model was analyzed. The influence of the fuel bed packing ratio on the drying process was also analyzed. We found that, regardless of any changes in packing ratio, the two-phase model could better simulate the drying process, with a mean absolute error (MAE) and mean relative error (MRE) of the two-phase model 18.4% and 25.6% less than the one-phase model, respectively. The time-lag prediction model was established with the packing ratio, and the errors were all within the allowable range, but the prediction effect of the time-lag prediction model based on the two-phase model was larger. It was further demonstrated that considering the packing ratio of the fuel bed and distinguishing the two separate phases of the drying process could both effectively improve the prediction accuracy of the moisture content of fuel beds based on the semi-physical method.

Effect of hygrothermal aging on moisture diffusion and tensile behavior of CFRP composite laminates

Carbon Fiber Reinforced Polymer (CFRP) composites are widely used in aircraft structures, because of their superior mechanical and lightweight properties. CFRP composites are often exposed to hygrothermal environments in service. Temperature and moisture can affect the material properties of composites. In order to make clear the moisture diffusion behavior and the properties degradation of composites, the TG800/E207 composite laminates with four stacking sequences [0]16, [90]16, [±45]4s, and [(+45/0/0/–45)s]s are designed and manufactured. Moisture absorption tests are carried out at 80 ℃, 90 %RH. It is shown that the moisture absorption curves of composite laminates present a three-stage. A modified Fickian model was proposed to capture the diffusion behavior of TG800/E207 composite laminates. The relationships among the non-Fickian parameters, the environmental parameters and the stacking sequences of CFRP were correlated and compared. Results showed that the modified Fickian curve is sensitive to the diffusivity of Stage I and Stage II. Compared with unaged specimens, the maximum tensile stress for [0]16, [90]16, [±45]4s, and [(+45/0/0/–45)s]s decreased by 14.94 %, 28.15 %, 11.96 %, and 26.36 %, respectively. The strains at failure for [0]16, [90]16, [±45]4s, and [(+45/0/0/–45)s]s decreased by 55.38 %, 62.65 %, 46.41 %, and 31.71 %, respectively. The elastic modulus for [0]16, [90]16, [±45]4s, and [(+45/0/0/–45)s]s increased by 90.93 %, 94.57 %, 49.22 %, and 8.22 %, respectively. [90]16 sample has the minimum saturated moisture content and the maximum strength degeneration.

Experimental Study on the Evolution Law of Coal Mine Underground Reservoir Water Storage Space under the Disturbance and Water—Rock Interaction Effect

The void of the cracked rock mass of the goaf is the main water storage space of underground reservoirs, which is in a time-space dynamic evolution process. Before the formation of the underground reservoir, the water storage space was primarily affected by disturbances. After the safe operation of the coal mine underground reservoir, the water level of the mine rises and falls repeatedly and the water storage space is affected by the water-rock interaction. To study the void evolution law of a cracked rock mass under mining disturbance and the compaction and void deformation characteristics of caving gangue under the effect of the water-rock interaction, a simulation test of a coal mine underground reservoir is conducted. Furthermore, the rupture motion law and movement deformation characteristics of the overburden during coal mining are analyzed. The digital image method and fractal theory are introduced to describe the fractal characteristics of the rock mass void of the caving zone, fracture zone, and entire goaf during the mining process. Five prototype gangue samples with different immersion times are prepared with the same grain size grading as the similar model caving gangue. The influence of the immersion times on the compaction characteristics and evolution law of the void rate of the gangue are also studied. Based on the parameter fitting method, the stress–strain relationship equation of the gangue sample and void rate-stress relationship equation of the cylindrical gangue sample, considering the influence of the immersion times, are constructed. The results show that the overburden of the model is of a “two zone” structure and the entire structure moves and sinks asymmetrically in a “∩” shape. As the advancing distance of the working face increased, the fractal dimensions of the rock mass void of the caving zone and entire goaf increased logarithmically, and the fractal dimension of the rock mass void of the fracture zone first increased rapidly (60–80 cm) and then decreased linearly (80–200 cm). As the immersion time increased, the saturated moisture content and density of the gangue samples increased logarithmically and exponentially, respectively. Under the same stress, the strain of the gangue sample increased gradually, and the void rate decreased gradually (except for the initial loading).

Adaptabilities of Water Production Function Models for Rice in Cold and Black Soil Region of China

Crop water production function models (WPFMs) are required methods to study the relationships between yield and water consumption under regulated deficit irrigation (RDI). In this study, a pot experiment was established to study the effect of water deficit during both individual growth stages and across two consecutive growth stages of rice on yield, water consumption, and water use efficiency (WUE) in 2017 and 2018. Light, medium, and severe water deficits were set as 80~90%, 70~80%, and 60~70% of saturated soil moisture content, respectively. The accuracies of five WPFMs were tested based on the experimental results. The results showed that yields and WUE of a light water deficit were higher than those of medium and severe water deficits at each growth stage. The yields and WUE of light drought stress treatments in the flowering and milky stages were higher than the saturated soil moisture control by 4~7.4% and 5.3~20.6%, respectively. Water consumption decreased with increasing water deficit across two consecutive growth stages. The Minhas model had the highest simulation accuracy of the five WPFMs, with relatively lower AE, RMSE, Cv, CRM, and higher R2, which were 0.0002, 0.0634, 6.9965, 0.0002, and 0.9951 in 2017 and 0.0110, 0.0760, 8.9882, 0.0131, and 0.9923 in 2018, respectively. The sensitivity indices for the Minhas model more accurately reflected the sensitivity of rice yield to water deficit at different growth stages in 2017 and 2018, compared with the Jensen model, Stewart model, Blank model, and Singh model. Rice yield was most sensitive to water deficit at the jointing and booting stage. The results indicate that the Minhas model is the most suitable WPFM for guiding rice irrigation practices in cold and black soil regions of China.

Typical site seismic response analysis with reinforcement under earthquake and rainfall in the mountainous areas of China

Multi-tilted layered soil is widespread in the mountainous areas of China, and pile systems are widely applied to foundation support and repair. In order to investigate the seismic response of pile systems in multi-tilted layered soils under earthquake and rainfall, two models were built and tested through a large 1-g shaking table. The interlayer was tilted and highly weathered, and it was saturated during rainfall. The piles were embedded in the bedrock with different lengths. The results showed that: 1) The acceleration response was weakened in the interlayer, and it diminished as the earthquake amplitude increased. The structures showed the maximum acceleration response. 2) The existence of water in the tilted interlayer led to a greater response of the superstructure. The bending moment of piles varied under different containers, which was mainly due to the inertial force of the container and the potential sliding force of the covering layer. The water in the interlayer from rainfall promoted the bending moment caused by the potential sliding force, increasing the potential risk of instability of the system. 3) The motion mode of the container under rainfall was translation. The rotation angle of the container with saturated moisture content was significant and it increased with the increase of the earthquake amplitude.

Comparison of Infiltration Rates of Soils for Run-Off Management and Irrigation Planning in Makurdi Benue State, Nigeria

Understanding of initial infiltration rates and steady state infiltration rates of soil is very important for runoff management and irrigation scheduling. Therefore, a field experiment was conducted at the Teaching and Research Farm of Joseph Sarwuan Tarka University, Makurdi in 2018 to evaluate the initial and steady state infiltration rates of soils in Makurdi, Nigeria. Infiltration test was carried out using double ring infiltrometer at eighteen points. Initial and steady state infiltration rates and the cumulative infiltration were then calculated. Soil samples were collected from the adjacent area of the marked points at 0-15 cm and 15-30 cm depths for routine analysis. Undisturbed soil samples were also collected for the measurement of saturated hydraulic conductivity, bulk density, total porosity and moisture content determination. Simple descriptive statistic of mean, variance and standard deviation was used to analyze the data. The soils were predominantly sandy loan texture, with percentage sand, silt and clay as 710.7, 118.9, and 170.4 g kg-1 respectively. Soil bulk density and saturated hydraulic conductivity were 1.40 g cm-3 and 10.27 cm hr-1 at 0 – 15 cm depth, while soil organic carbon and CEC were 0.67 % and 6.62 cmol/kg respectively. The initial infiltration rate ranged from 7.40 - 87.46 mm hr-1 with a mean of 44.09 mm hr-1, meanwhile, the steady state infiltration rate ranged between 4.99 – 22 mm hr-1, with a mean value of 15.42 mm hr-1. High soil bulk density caused moderate to low infiltration capacity. The mean values for the steady state infiltration rate suggest that the soils of the study area have moderate infiltration capacity, therefore, water application for irrigation should be less or equal to the infiltration capacity of the soils to minimize water loss by surface runoff and erosion.

Effects of Drought Stress on Peramine and Lolitrem B in Epichloë-Endophyte-Infected Perennial Ryegrass.

Perennial ryegrass (Lolium perenne) infected by Epichloë endophytes contains alkaloids that are responsible for toxicosis in many countries. Drought may greatly affect the alkaloids contents of symbionts. The E+ perennial ryegrass was grown in pots with different soil moisture conditions (15%, 30%, 45% and 60% relative saturation moisture content, RSMC) for four months in a greenhouse of Lanzhou University, and then, the aboveground tissues were collected. The levels of peramine and lolitrem B in all plant samples were determined. The results showed that the drought stress significantly (p < 0.05) increased the peramine concentrations of perennial ryegrass but did not affect the lolitrem B concentrations. In addition, the drought stress significantly (p < 0.05) reduced the plant height and dry matter of perennial ryegrass. In conclusion, drought stress affects the peramine concentration in the perennial ryegrass–endophyte symbiont but may not affect the lolitrem B concentration.

The soil-water cost of heavy machinery traffic on a Queensland Vertisol, Australia

The development of larger, more powerful agricultural machinery to increase field efficiency has occurred in broad-acre agricultural systems, at the risk of significant soil compaction. The effect of heavy machinery on the increase in soil bulk density is often recorded as an indication of this compaction, but the soil-water effects are rarely directly measured. It is therefore important to understand the impact of soil compaction on the soil water characteristic under such machinery, which was the objective of this work. Using the John Deere 7760 (JD7760) cotton picker as a case study, a Vertisol from Jimbour, Queensland, Australia was investigated for changes in soil water potential after traffic from a conventionally and a controlled traffic farming (CTF) configured JD7760 to determine the magnitude of impact non-CTF systems have on Australian cotton production systems. Bulk density, saturated moisture content, and cracking pattern were also determined. The saturated hydraulic conductivity decreased significantly in response to traffic with the greatest relative reduction occurring in the lower depths. Bulk density increased significantly in response to traffic, with the greatest relative increase occurring nearer the surface. The cracking pattern and area of void represented by soil cracks was shown to be related to change in soil bulk density due to traffic. Plant available water was demonstrably reduced, and this significant decrease was inferred from cracking pattern analysis. Basic economics for the traffic systems are presented to provide an economic and environmental imperative to traffic system management.

Electromagnetic sensing and infiltration measurements to evaluate turfgrass salinity and reclamation

Scarce freshwater resources in arid and semiarid regions means that recreational landscapes should use recycled or low-quality waters for irrigation, increasing the risk of salinity and infiltration problems. We map salinity distribution within turf fields using electromagnetic sensing, evaluate need for leaching and evaluate post leaching results for subsequent management decisions. Electromagnetic measurements were made with two EM38 instruments positioned vertically and horizontally in order to determine salinity distribution. Sensor readings were coupled to GPS data to create spatial salinity maps. Next, optimal calibration point coordinates were determined via Electrical Conductivity Sampling Assessment and Prediction (ESAP) software. Soil samples from 0–15 and 15–30 cm depths were used for each calibration point. Laboratory soil saturation percentage, moisture content, electrical conductivity (ECe) and pHe of saturation extracts were determined for calibration to convert resistivity measurements to ECe. Next, ECe maps were created using ESAP software. Leaching for reclamation was performed by means of sprinkling. Treated municipal wastewater was utilized both for irrigation and for reclamation leaching. Low water content and high spatial variability of soil texture adversely affected the accuracy of the readings. Pre and post leaching surveys indicate that in one fairway there was only a 43% and 58% decrease in soil salinity at 0–15 and 15–30 cm depths, respectively which is very low relative to expected results considering the amount of water applied. This relatively low reduction in salinity and the lack of runoff during irrigation combined with infiltration measurements suggests that aeration techniques for healthier grasses led to water bypassing small pores thus limiting leaching efficiency. In this instance practices to improve infiltration lead paradoxically to less salinity reclamation than expected.

Dissolved organic carbon, an indicator of soil bacterial succession in restored wetland under freeze-thaw cycle

The moisture availability is of great significance to the physical, chemical and biological processes of soil, however, information regarding how freeze-thaw cycles (FTCs) affect the bacterial community of soil with different moisture contents is limited. In this work, we studied the relationship between FTCs and soil bacterial community under different moisture content (field capacity, FC and saturated moisture content, SMC). The results showed that FTCs decreased the richness and diversity of the soil bacterial community. Bacteria diversity were significantly decreased after the second FTC (FTC2). Thereafter, bacterial diversity with a saturated moisture content returned to the pre-freeze-thaw level, but the recovery of bacterial diversity in soil with the field capacity was lower than that of the saturated moisture content. Frequent FTCs accelerate the turnover of dissolved organic carbon DOC by affecting the carbon metabolism of microbial communities. Adjusting moisture to SMC can increase the stability of carbon. Our results provided reference to for the management of restored wetland.

Effect of hygrothermal environment on tensile properties of carbon fiber epoxy resin composites

[0]16, [90]16, [±45]4s and [+45/0/0/-45/-45/0/0/+45]s were fabricated to study the influence of the different ply lay-up on the moisture absorption and tensile properties of TG800/E207 carbon fiber epoxy resin composite laminates at a hygrothermal environment of 80℃ and 90%RH. Moisture absorption curves, damage morphology after moisture absorption, fracture morphology, load-displacement curves and strength degradation were analyzed. The results show that the moisture absorption curves of TG800/E207 composite laminates present multi-stage phenomenon. The moisture adsorption reached equilibrium at a moisture absorption time of 1 608 hours. The equilibrium moisture content of [90]16 is the lowest and its saturated moisture content is only 0.806%; the equilibrium moisture content of [+45/0/0/-45/-45/0/0/+45]s is the highest and its saturated moisture absorption rate is 0.876%. The failure load of [0]16, [90]16, [±45]4s and [+45/0/0/-45/-45/0/0/+45]s samples decreased by 13.8%, 27.36%, 10.7% and 25.6%, respectively. The saturated moisture absorption of [90]16 is the lowest, but its tensile strength degradation is the most serious.

Regionalization of hydrological model parameters using gradient boosting machine

Abstract. The regionalization of hydrological model parameters is key to hydrological predictions in ungauged basins. The commonly used multiple linear regression (MLR) method may not be applicable in complex and nonlinear relationships between model parameters and watershed properties. Moreover, most regionalization methods assume lumped parameters for each catchment without considering within-catchment heterogeneity. Here we incorporated the Penman–Monteith–Leuning (PML) equation into the Distributed Time Variant Gain Model (DTVGM) to improve the mechanistic representation of the evapotranspiration (ET) process. We calibrated six key model parameters, grid by grid across China, using a multivariable calibration strategy which incorporates spatiotemporal runoff and ET datasets (0.25∘; monthly) as reference. In addition, we used the gradient boosting machine (GBM), a machine learning technique, to portray the dependence of model parameters on soil and terrain attributes in four distinct climatic zones across China. We show that the modified DTVGM could reasonably estimate the runoff and ET over China using the calibrated parameters but performed better in humid rather than arid regions for the validation period. The regionalized parameters by the GBM method exhibited better spatial coherence relative to the calibrated grid-by-grid parameters. In addition, GBM outperformed the stepwise MLR method in both parameter regionalization and gridded runoff simulations at a national scale, though the improvement pertaining to watershed streamflow validation is not significant due to most of the watersheds being located in humid regions. We also revealed that the slope, saturated soil moisture content, and elevation are the most important explanatory variables to inform model parameters based on the GBM approach. The machine-learning-based regionalization approach provides an effective alternative to deriving hydrological model parameters from watershed properties, particularly in ungauged regions.

An experimental and finite element simulation study of moisture absorption in an ordered PVAF-reinforced thermoplastic starch composite film

A two-dimensional (2D) model was established by the finite element method to study the transient hygroscopic process and moisture-induced stress to better understand the moisture absorption microscopic process of ordered polyvinyl alcohol fiber (PVAF)-reinforced thermoplastic starch (TPS) composite films and the corresponding moisture-induced stress. The Mises stress contour of moisture distribution at five time points (36, 68, 100, 176, and 348 h) under four relative humidities (RH=57%, 75%, 84%, 98%) is demonstrated. The variation in moisture content along the two paths of width (AB) and thickness (CD) in the 2D model and the moisture-induced stress were also studied in detail. The results show that when the time t is 348 h, the saturated moisture contents along CD are 5.27, 17.22, 30.58, and 59.14%, and along AB are 5.27, 17.19, 30.57, and 59.07%. In addition, the change in moisture content, regardless of whether the path was AB or CD, mainly occurred before 176 h. The simulation results of moisture absorption are in good agreement with the experimental results. The ultimate moisture-induced stress is the largest in the fiber surroundings, which are 0.398, 1.30, 2.31, and 4.48 MPa at four RHs, respectively, and the internal moisture stress of 4.48 MPa was within the tensile strength (2–6 MPa) of PVAF/TPS (PVAF &lt;0.89 vt%), which resulted in composite film failure. This paper provides a new way to understand the moisture absorption mechanism and explore possible methods for improving the water-resistance of TPS films.

Effects of the buried straw layer on soil water and nitrogen distribution under different irrigation limits

At present, water and fertilizer use efficiency is low in many cultivation areas in southern China. Studies show that the buried straw layer can effectively conserve water and fertilizer. To investigate the optimal irrigation upper limit above the straw barrier and its effect on soil moisture and nitrogen distribution, an indoor soil column experiment was conducted. Six treatments were designed consisting of two levels of straw layer i.e., (with and without buried straw layer at 25 cm depth), and three irrigation water upper limits i.e., (saturated moisture content (s), field water holding capacity (f), and 80% of field water holding capacity (0.8f) as the upper limit of irrigation). The result revealed that the buried straw layer can inhibit water infiltration and significantly increase the water storage capacity and water storage efficiency of 0-25 cm soil depth. Under the condition of no evaporation, when the upper limit of irrigation water does not exceed the field water holding capacity, the storage efficiency of 0-25 cm soil water reaches 89%-91% after 6 d. Moreover, a buried straw layer can inhibit the deep percolation of nitrate nitrogen and increase the amount of nitrate-nitrogen in 0-25 cm soil. The 80% field water holding capacity irrigation upper limit combined with straw interlayer treatment had a higher nitrate-nitrogen content in the 0-25 cm soil layer than other treatments. Therefore, 80% of field water holding capacity as the upper limit of irrigation combined with buried straw layer is the optimal strategy to conserve soil water and nitrogen in the upper soil profile. Keywords: distribution of water and nitrogen, irrigation water levels, infiltration, water storage efficiency DOI: 10.25165/j.ijabe.20221505.6160 Citation: Rasool G, Zhang S X, Wu F, Guo X P. Effects of the buried straw layer on soil water and nitrogen distribution under different irrigation limits. Int J Agric & Biol Eng, 2022; 15(5): 141–145.