Soil Water Movement Research Articles

A Thermodynamic Formulation of Water Potential in Soil

AbstractIn the mid‐20th century, harnessing of thermodynamics in describing water movement in soil, viz the concept of water potential, marks the emergence of modern soil physics, unsaturated soil mechanics, and vadose zone hydrology. Yet to date, a seamless linkage between thermodynamics and water potential is still missing, leading to several long‐lasting dilemmas regarding soil properties, for example, abnormal soil water density, peculiar film water viscosity and relative permittivity, pore water pressure, and water freezing temperature depression. Here, a thermodynamic framework is established by synthesizing recent advancements in soil‐water interaction. The classical thermodynamic concepts are revisited, highlighting the difference between macroscopic systems commonly treated in conventional theories and the intermolecular scale system subject to external fields. Soil water is conceived as an intermolecular scale open thermodynamic system subject to external fields of gravity, osmosis, and adsorption. The formulated thermodynamic framework is verified by reducing to the conventional definition of matric potential and a recently proposed unitary definition. The accuracy of the framework is further justified in terms of mechanical equilibrium criteria. The framework predicts the existence of spatially varied pore water pressure in soil pores and can serve as the theoretical basis for reconciling the physical origin of abnormal soil behavior such as water density, film water viscosity, relative permittivity, and negative or positive pore water pressure.

Changes in Soil Moisture, Temperature, and Salt in Rainfed Haloxylon ammodendron Forests of Different Ages across a Typical Desert–Oasis Ecotone

Soil water and salt movement during the freeze–thaw period facilitate soil and water conservation and agroecological environment maintenance in the desert–oases transition zone of the Hexi Corridor; however, our understanding of soil salinization and the shifting water, heat, and salt states in soil ecosystems of Haloxylon ammodendron forests at different ages is poor. We analyzed the soil moisture, temperature, and salinity characteristics of Haloxylon ammodendron forests of different ages in the Hexi Corridor of Northwest China and determined their coupling. Our results indicated that shallow (0–120 cm) soil temperatures significantly correlated with air temperatures. With increased forest age, the soil freezing period shortened and the permafrost layer shallowed. Changes in soil temperature lagged those in air temperature, and this lag time increased with forest age and soil depth. With increases in forest age and planting years, the water in the shallow soil layer gradually declined, and the surface aggregation of salt increased. In deep soils (120–200 cm), both soil moisture and salinity increased with the number of planting years. Accordingly, the clay layer and deep root system of Haloxylonammodendron greatly influenced the transport of soil water and salt; and temperature is a key driving force for their transport. Thus, water, temperature, and salt content dynamics were synergetic.

Simulation of water and nitrogen movement mechanism in cold regions during freeze-thaw period based on a distributed nonpoint source pollution model closely coupled water, heat, and nitrogen processes at the watershed scale.

The nitrogen cycle in cold regions during the freeze-thaw period is complex. Although previous studies have investigated the phenomenon of nitrogen transport and transformation, the underlying mechanisms are vague. Existing models have limitations in terms of loose coupling or weak physical mechanisms. Therefore, a new distributed nonpoint source pollution model, the water and energy transfer processes and nitrogen cycle processes model in cold regions, was developed in this study, with closely coupled water, heat, and nitrogen processes at the watershed scale. The model considered the driving effects of pressure, gravity, solute, and temperature potentials on water and nitrogen movement in soil and the transformation relationship among nitrogen forms. Physical evaluation and simulations were conducted for the Heidingzi River Watershed during two freeze-thaw periods: 2017-2018 and 2018-2019. The soil temperature absolute error was < 0.82℃. The relative errors in stratified liquid water, soil nitrogen content, river flow rate, and river nitrogen concentration were mostly < 10%. Nitrogen transport with water had an obvious "upward agglomeration effect" during the freezing period and a "concentrated release effect" during the thawing period, which was attributed to changes in soil water potential as the freezing front moved down. Disregarding the effects of solute potential and temperature potential will result in an underestimate of the outflow of pollutants during the thawing period. The model can be applied to reveal water quality deterioration in cold regions during thawing.

An improved pore-solid fractal model for predicting coastal saline soil hydraulic properties based on changepoints determined by genetic algorithm-support vector regression

Coastal soil is an important reserve land resource. The accurate prediction of soil hydraulic properties plays an important role in understanding the improvement of soil properties after reclamation in coastal areas. With the development of modern mathematical theory, the pore-solid fractal (PSF) model has become an important basis for simulating soil hydraulic properties. The accuracy of PSF model depends on the accurate acquisition of changepoints and fractal dimensions. Previous studies have found that micro-CT scanning combined with image processing could accurately obtain fractal dimensions. However, we still need soil water retention data to determine changepoints, which greatly limits the application of fractal models for estimating soil hydraulic properties. In this case, we determined the relationship between changepoints and soil physical and chemical properties and established a genetic algorithm-support vector regression (GA-SVR) model to predict changepoints. Then an improved PSF model was adopted to predict soil water retention curve in coastal areas of Jiangsu Province based on image processing. The results showed that soil physical and chemical properties changed the soil water movement and changepoints by affecting soil pore distribution. In coastal saline soil, four parameters (BD, silt, EC, SOM) were selected to predict changepoints. The mass fractal dimension (Dm) was mainly influenced by the porosity and the heterogeneity of pore space. The porosity, pore diameter and specific surface area were the determining factors of DS value. Reclamation activities in coastal reclamation area changed Dm value but had no clear effect on DS value. By combining predicted changepoints, measured water content at the suction of changepoints and fractal dimensions, the accuracy of the PSF model had been greatly improved.

Improved water and ions dynamics in a clayey soil amended with different types of agro-industrial waste biochar

Biochar is a beneficial amendment for fine-textured soils. In addition, the interaction of biochar particles with soil components influences the dynamics of water and ions, which is particularly important to remediate salt-affected soils. We investigated the effect of sugarcane bagasse (SB), orange bagasse (OB), and corncobs (CB) biochar on water movement and ion leaching in clayey soil. Non-amended soil (CT) column and soil amended with gypsum (CTG) served as controls. Water infiltration, water flow rate, cumulative leached cations, anions, and exchangeable cations (Ca2+, Mg2+, K+, and Na+) were determined. Biochar increased the water infiltration and water flow rate by 80% and 71%, respectively. The SB and CB treatments increased the ion removal from the soil by 48%, whereas the OB increased the removal by 19%. The OB´s lower surface area and water holding capacity likely influenced its performance. Biochar reduced the Ca2+ and Mg2+ concentration on the soil exchange complex by 44% and 76%, respectively, and increased K+ by 233%. However, the most exciting result was the reduction of exchangeable Na+, 90% in the SB and CB treatments and 50% in the OB treatment. Considering that a high concentration of Na+ on the exchange complex contributes to soil structural degradation, biochar application, especially SB and CB, can potentially improve soil quality and mitigate salt-affected soils.

An analytical approach to estimating electrostatic repulsion between soil particles

The electrostatic repulsion between soil particles has an important effect on the stability of soil aggregates and soil water movement. However, the electrostatic repulsive pressure is traditionally quantified through a complicated numerical method. In this study, the analytical expressions for calculating the midplane potential between soil particles in 1:1 and 2:1 electrolytes were derived respectively, consequently an analytical method for estimating the electrostatic repulsive pressure was obtained. The theoretical solutions of midplane potential between particles and electrostatic repulsive pressure are in good agreement with the numerical ones, and correctly predict the swelling pressure of montmorillonite. The surface potential, midplane potential and electrostatic repulsive pressure between soil particles calculated by the analytical method increase with increasing charge density, which depends on ionic polarization or/and polarization-induced covalent bond. For example, electrostatic repulsive pressure is the highest in non-polarized Li+, decreases in polarized Na+, and the lowest in K+ solution due to potassium’s relatively high polarization and polarization-induced covalent bond. The percentage of large soil pores (> 1 mm) and electrostatic repulsive pressure appear in a negative correlation, which is consistent with changes in the soil water infiltration rate, whereas the percentage of small soil pores (< 0.5 mm) has a positive relationship to electrostatic repulsive pressure. The ion polarization or/and polarization-induced covalent bond affect soil pore distribution and control soil water infiltration through significantly affecting the electrostatic repulsive pressure between soil particles. The analytical estimation of electrostatic repulsion is of great significance for understanding the physical/chemical processes in soils and quantifying the relations between mesoscopic processes and macroscopic phenomena.

Evaporation, infiltration and storage of soil water in different vegetation zones in the Qilian Mountains: a stable isotope perspective

Abstract. The processes of water storage have not been fully understood in different vegetation zones of mountainous areas, which is the main obstacle to further understanding hydrological processes and improving water resource assessments. To further understand the process of soil water movement in different vegetation zones (alpine meadow (AM), coniferous forest (CF), mountain grassland (MG) and deciduous forest (DF)) of mountainous areas, this study monitored the temporal and spatial dynamics of hydrogen- and oxygen-stable isotopes in the precipitation and soil water of the Xiying River basin. The results show that the order of soil water evaporation intensities in the four vegetation zones was MG (SWLslop: 3.4) &gt; DF (SWLslop: 4.1) &gt; CF (SWLslop: 4.7) &gt; AM (SWLslop: 6.4). The soil water in the AM and CF evaporated from only the topsoil, and the rainfall input was fully mixed with each layer of soil. The evaporation signals of the MG and DF could penetrate deep into the middle and lower layers of the soil as precipitation quickly flowed into the deep soil through the soil matrix. Each vegetation zone's water storage capacity of the 0–40 cm soil layer followed the order of AM (46.9 mm) &gt; DF (33.0 mm) &gt; CF (32.1 mm) &gt; MG (20.3 mm). In addition, the 0–10 cm soil layer has the smallest soil water storage capacity (AM: 43.0 mm; CF: 28.0 mm; MG: 17.5 mm; DF: 29.1 mm). This work will provide a new reference for understanding soil hydrology in arid headwater areas.

Short-term Tillage and Soil Nutrient Management on Soil Water Movement in a Lixisol in a Tropical Climate

Aims: The study was conducted to assess the effects of different soil tillage practices and soil amendments on soil hydraulic characteristics.&#x0D; Study Design: The study was a 3 × 4 split-plot experiment arranged in randomized complete block design (RCBD) with 3 replications.&#x0D; Methodology: The treatments comprised 12 main plots, namely no till (NT), plough-plant (PP) and plough-harrow-plant (PHP) and 36 sub-plots, namely no amendment (NA), NPK 60:40:40 (100% NPK), 4 tons/ha poultry manure (100% PM) and 2 tons/ha PM + NPK 30:20:20 [½(NPK + PM)]. Soil bulk density (BD), volumetric moisture content (VMC), total porosity (TP), aggregate stability (ASt), and infiltration parameters were measured under the different treatments.&#x0D; Results: Among the different tillage operations, the NT plot had the lowest BD, but highest TP, VMC and ASt. With regard to the soil amendments, TP was highest under the ½(NPK + PM) treatment. The cumulative infiltration amount (F) and infiltration capacity (K0) were highest in the NT plots. However, sorptivity (S\(\theta\)) was highest and lowest in the PP and NT plots, respectively. The infiltration parameters were highest in the ½(NPK + PM) plots. Further, the combined application of NT + ½(NPK + PM) resulted in the highest F, S\(\theta\) and K0.&#x0D; Conclusion: The, NT, ½(NPK + PM) and NT + ½(NPK + PM) improved the soil hydro-physical properties.

Influences of pedodiversity on ecosystem services in a mountainous area

Pedodiversity has an important influence on soil water movement, sediment transport, plant growth, biodiversity maintenance, and many other ecological processes related to ecosystem services. However, the influence of pedodiversity on ecosystem services is still unknown, especially in mountainous areas. In this study, the relationships between the pedodiversity and two essential ecosystem services, soil retention (SR) and water yield (WY) services, were analyzed, and the influences of pedodiversity on the temporal changes in the SR (DSR) and WY (DWY) during 2000 and 2015 were determined. The results showed that pedodiversity was generally positively correlated with the SR, but it was negatively correlated with the WY. This indicates that a higher pedodiversity is favorable to soil and water conservation. Both the SR and WY decreased during the study period. The Shannon index was significantly negatively correlated with the DSR, indicating that pedodiversity was conducive to maintaining the temporal stability of the SR. However, a positive correlation was found between pedodiversity and the DWY, indicating that the higher pedodiversity area exhibited a more significant decreasing trend in the WY. This in turn suggests that pedodiversity helps improve the water retention capacity. The influence of pedodiversity on ecosystem services is mainly a direct effect. However, the influences of the environmental factors had both direct and indirect effects. The results of this quantitative analysis of the influence of pedodiversity on ecosystem services provide evidence that protecting pedodiversity is necessary, and they also provide a new direction for pedodiversity research.

Water and salt transport characteristics in a soil column in the presence of a low-permeable body

Soil water infiltration is an important factor affecting surface runoff, soil erosion, and soil solute transmission. Increasing soil infiltration reduces runoff and erosion. The presence of low-permeable body in soil can enhance soil infiltration capacity. However, different depths of low-permeable body have unknown effects on water infiltration and salt transfer. In this work, we evaluated the effects of low-permeable body with varied depths (control (CK), 0, 0.5, 1, and 1.5 cm) on silty loam soil water and salt movement using 15 soil columns (23 cm internal diameter, 50 cm length). Experimental results showed that low-permeable body increased infiltration rate and wetting front migration rate. Infiltration rate and wetting front propulsion rate decreased with the increase of the burial depth. Compared with the CK, when the depth of wetting front reached 20 cm, the infiltration time of 0, 0.5, 1, and 1.5 cm burial depth treatment was shortened by 72.24%, 56.29%, 44.61%, and 31.01%, respectively. Simultaneously, the existence of low-permeable body led to the increase of soil water content and salt content in the same soil layer, which indicated that the low-permeable body enhanced the soil holding capacity and reduced the salt leakage to the deep soil. Furthermore, the Philip’s model and the algebraic model were used to describe the infiltration process. Fitting results showed that the sorptivity in the Philip’s model increased with burial depth, while the comprehensive shape coefficient in the algebraic model decreased. Therefore, this study provides a reference for the application of low-permeable body in the improving soil infiltration capacity and controlling salt transport.

Quantifying the impact of induced topsoil and historical subsoil compaction as well as the persistence of subsoiling

Mechanical soil compaction increasingly occurs in arable land but the state and effects of historical compaction from regular operations are still poorly documented. Therefore, a typical field was selected and the effects of both newly formed topsoil compaction and historical developed subsoil compaction (below 30 cm) on soil physical and hydraulic properties, soil water movement, soil mineral nitrogen leaching potential and crop parameters were evaluated on a Luvisol under a winter rye (Secale cereale L.) and summer maize (Zea mays L.) rotation system. Three subsoil compaction levels were included, i.e., a i) highly compacted headland zone, and a moderately compacted in-field zone ii) without and iii) with deep tillage by subsoiling in the winter of 2016. Topsoil compaction on the other hand was induced by one machine pass with a rotary cultivator in addition to the regular machine passes during field preparation for the summer maize season of 2017, and compared with a control without extra compaction. For subsoil compaction treatments, both visual evaluation and lab or field based measurements indicated that soil physical and hydraulic properties were deteriorated in the headland compared with in-field zones. As a result, both winter and summer crop above-ground biomass were decreased in the highly compacted headland zone because of the restricted root growth, which further increased the risk of soil mineral nitrogen leaching. The alleviation effect of deep tillage remained after ∼ 2 years, which significantly increased maize height in the extremely dry and hot summer of 2018. For topsoil compaction, one traffic pass with a rotary cultivator increased topsoil penetration resistance and water content but summer maize above-ground biomass was not affected. Overall, prevention and alleviation of subsoil compaction are essential in increasing the resistance and resilience to the continuing deteriorating climatic conditions.

Effect of biochar on soil properties and infiltration in a light salinized soil: Experiments and simulations

AbstractThe sustainable development of agriculture in Xinjiang Province, China has been threatened by soil salinization. Biochar can be an effective amendment to improve salt‐affected soils. An appropriate amount of biochar application and incorporation depth are key factors for amending performance. However, few studies have investigated the effects of differing biochar application amounts on saline soil properties, including soil water infiltration, using a combination of experiments and simulations. In this study, acidulated biochar was applied at rates of 0, 10, 25, 50 and 100 t ha−1 to a farmland topsoil to investigate the impacts of biochar on Xinjiang saline soil's physical and chemical properties and infiltration characteristics. The soil's physical and chemical properties that were investigated included soil pH, soil organic carbon content, soil salt content, saturated hydraulic conductivity (Ks), soil water retention curves, and infiltration characteristics including cumulative infiltration (CI) and wetting front (Zf). HYDRUS‐1D was applied to predict soil water movement under different biochar incorporation depths. Results showed that the rate of change of soil pH, soil organic carbon content, soil salt content and Ks were −0.009, 0.102 g kg−1, 0.045 g kg−1 and 0.035 cm day−1, respectively, per ton of biochar applied. Soil water retention curves showed that biochar enhanced soil water retention capacity and available soil water content (AWC) in the silt clay loam soil. The Philip model was a good (R2 &gt; 0.80) fit to soil water infiltration and indicated that biochar amendment promoted infiltration rates. The van Genuchten model was good for describing soil hydraulic parameters (R2 &gt; 0.99) and could be used for HYDRUS‐1D simulations (R2 &gt; 0.99, RRMSE &lt;6.8% and NSE &gt;0.98). The optimum biochar application amount for the light salinised soil in Xinjiang was recommended as 25 t ha−1 incorporated to 30 cm depth based on the AWC, soil salt content and incorporation depths. The study provides a reference for future field experiment design.Highlights Effects of biochar on salt‐affected soil studied using a combination of experiments and simulations. Acidulated biochar amendment of saline soils can reduce pH and increase SOC. Biochar incorporation depth was considered to affect soil water infiltration. The biochar application amount at 25 t ha−1 incorporated to 30 cm depth was recommended

Experimental Investigation of the Different Polyacrylamide Dosages on Soil Water Movement under Brackish Water Infiltration.

The use of soil conditioners in conjunction with brackish water irrigation is critical for the efficient development and use of brackish water as well as the enhancement of the structure of saline soil and stimulating crop growth. This study investigated the effects of different polyacrylamide (PAM) dosages (0, 0.02%, 0.04%, and 0.06%) on the water flow properties of sandy loam during brackish water infiltration using one-dimensional vertical and horizontal soil column infiltration experiments. The results showed that: (1) PAM could lower the soil infiltration rate and increase soil water retention performance under brackish water infiltration conditions. (2) PAM had a significant effect on the parameters of the Philip and Kostiakov infiltration models. The soil sorption rate S and the empirical coefficient λ were the smallest, and the empirical index β was the largest when the PAM dosage was 0.04%. (3) PAM dosage displayed a quadratic polynomial connection with the soil saturated water content and the saturated hydraulic conductivity. The soil saturated water content was highest when the PAM dosage was 0.04%, the intake suction hd of the Brooks-Corey model increased by 15.30%, and the soil water holding capacity was greatly improved. (4) Soil treated with PAM could absorb more water under the same soil water suction, whereas the soil unsaturated hydraulic conductivity and its growth rate decreased. The soil saturated diffusion rate Ds, as well as the soil water diffusion threshold, rose. Finally, the 0.04% PAM dosage could improve soil hydrodynamic characteristics under brackish water infiltration, which is beneficial for the efficient utilization of brackish water.

Analysis of mulched drip irrigation with brackish water in cotton fields using the HYDRUS-3D numerical model

This study combined continuous monitoring in the field using computer modeling to understand soil water movement and salt transport so as to design a suitable irrigation system for cotton using mulched drip irrigation with brackish water. A reasonable irrigation regime was determined and verified using thresholds of water and salinity stress in the various stages of cotton growth. In addition, some key factors, such as emitter discharge rate, emitter spacing, and initial water content, were screened for simulation, and irrigation uniformity and desalination rate were selected as the indicators for evaluation. The results showed that: ( i) The HYDRUS-3D model was a useful tool for designing suitable irrigation regimes, and the determined suitable irrigation quota was 5160 m3 hm−2 under mulched drip irrigation with brackish water during the growth period of cotton in 2019. ( ii) The irrigation uniformity and leaching rate decreased with an increase in the emitter discharge, and the linear relationship between uniformity, leaching rate, and emitter discharge could be identified. ( iii) The irrigation uniformity and leaching rate decreased with an increase in emitter spacing, and power functions might be used to calculate uniformity, leaching rate, and emitter spacing. ( iv) The irrigation uniformity and leaching rate increased with an increase in initial water content, and the relationship between the two indexes and initial water content was defined by a linear function and a power function, respectively. These results provided a valuable reference for the rational use of drip irrigation with brackish water.

Quantification of root water uptake and redistribution using neutron imaging: a review and future directions.

Quantifying root water uptake is essential to understanding plant water use and responses to different environmental conditions. However, non-destructive measurement of water transport and related hydraulics in the soil-root system remains a challenge. Neutron imaging, with its high sensitivity to hydrogen, has become an unparalleled tool to visualize and quantify root water uptake in vivo. In combination with isotopes (e.g., deuterated water) and a diffusion-convection model, root water uptake and hydraulic redistribution in root and soil can be quantified. Here, we review recent advances in utilizing neutron imaging to visualize and quantify root water uptake, hydraulic redistribution in roots and soil, and root hydraulic properties of different plant species. Under uniform soil moisture distributions, neutron radiographic studies have shown that water uptake was not uniform along the root and depended on both root type and age. For both tap (e.g., lupine [Lupinus albus L.]) and fibrous (e.g., maize [Zea mays L.]) root systems, water was mainly taken up through lateral roots. In mature maize, the location of water uptake shifted from seminal roots and their laterals to crown/nodal roots and their laterals. Under non-uniform soil moisture distributions, part of the water taken up during the daytime maintained the growth of crown/nodal roots in the upper, drier soil layers. Ultra-fast neutron tomography provides new insights into 3D water movement in soil and roots. We discuss the limitations of using neutron imaging and propose future directions to utilize neutron imaging to advance our understanding of root water uptake and soil-root interactions.

Numerical simulation of soil water movement by gravity subsurface hole irrigation

AbstractAridity and soil erosion are two bottlenecks restricting the sustainable development of the Loess Plateau and are also fundamental reasons for the ecological fragility of the region. A gravity subsurface hole irrigation system was proposed to regulate rainfall–runoff, achieve rainwater stylization, and reduce soil erosion. Based on HYDRUS-2D/3D, a mathematical model of soil water movement under gravity subsurface hole irrigation was created. Thirty-five scenarios were designed to analyze five cumulative infiltration volumes (I) and wetting front migration distance (W), and changes under different combinations of saturated hydraulic conductivity (Ks), infiltrating hole diameter (D), infiltrating pipe depth (B), matric potential (Ψm), and infiltration time (T). The results indicated that when Ks, D, B, and T increased, I also increased, while Ψm increased and I decreased. In addition, when I and Ψm increase, W increases. However, when D and B increase, W decreases. Ks promotes W in a vertical downward direction but inhibits W in the vertically upward and horizontal directions. The simulation results established the I estimation model and the W estimation model (power function continuous multiplication form). There was acceptable uniformity among the predicted and measured values, and its reliability was verified experimentally.

Spatial variability of one-parameter model of soil water characteristic curve at field scale in black soil region of northeast China

The soil water characteristic curve (SWCC) is an important parameter for simulating soil water movement and solute transport, and has obvious spatial variability. The models fitting the SWCC generally contain two or more parameters, which makes the spatial variability of the soil water characteristic curve difficult to express. This paper established a one-parameter model of the soil water characteristic curve based on the Gardner model and analyzed its spatial variability with multifractal and joint multifractal methods. Parameter B in the one-parameter model had moderate variation. The local information leading to spatial variability of parameter B in the top soil layer (0–15 cm) and deep soil layer (15–20 cm) was its low values and high values, respectively. At the single scale, spatial variability of parameter B was mainly caused by the bulk density and clay content in the 0–5 cm soil layer, and by the bulk density and sand content in the 5–10, 10–15, and 15–20 cm soil layers. At the multiscale, the most obvious two factors that led to spatial variability of parameter B were the bulk density and silt content in the 0–5 cm soil layer, bulk density and sand content in the 5–10 cm soil layer, and bulk density and clay content in the 10–15 and 15–20 cm soil layers, respectively. The relationships between parameter B and soil properties had scale dependence.

Evaluation of Different Models for Predicting Soil Water Retention from A Semiarid Region of Duhok

A study was carried out to examine the capability of bi and uni- models to explore water retention data for two different textured soils from a semiarid region Duhok-Iraqi Kurdistan. A soil hydraulic model, can be used to derive the parameters of soil hydraulic properties for describing soil water movement. The program "SWRC Fit," which performs nonlinear fitting of soil water retention curves for the two examined soils using six models, was employed for this purpose. The six models are the Brooks Corey, van Genuchten, Kosugi, Fredlund and Xing model as uni models and Durner and Seki as a bimodal model used for this purpose. The program can be carried out straightly from a web page at http://purl.org/net/swrc/; The program was used for determining Fifteen parameters of soil hydraulic for two different textured soils. As related to Berderash sandy loam soil the LN uni-model revealed better performance than the FX, BC and VG models and at same time the FX, BC and VG models exhibit similar fitting precision on average. Whereas bi-models is shown that the Durner’s bi- model (DB) revealed very well fitting performance than that of the bi-log-normal distribution model (BL) models, regarding to Zawita clay soil it revealed that the uni -models, of BC, VG, FX and LN revealed good fitting performance with similar fitting precision on average. Whereas in bi- models it was noticed that the log-normal distribution model (BL) gave very well-suitable performance than that of the Durner’s b- model (DB). After comparing between the uni-models and bi-models of the six mentioned soil hydraulic models from accuracy and coefficient determination (R2), for two different textured soils under the study it can be illustrated: firstly, for fine texture soil (clay soil) the most precision fitting performance was found by model (BL), whereas for light texture soil (sandy loam soil) the most very well-fitting performance was noticed by (DB) model, and secondly the bi-models hydraulic were better than uni-models in fitting performance.

The Variability of Stable Water Isotopes and the Young Water Fraction in a Mountainous Catchment

AbstractSoil water movement is an important component in water cycle, which is also closely correlated with the transport of nutrients and contaminants in the catchment. Although there have been many studies in quantifying the water residence in soil, the understanding of the controlling factors is limited and could be controversial. Here, stable isotopes of water to explore the water age distribution in a mountainous catchment in the southwest China are used. The results are consistent with the regional climate pattern that the water vapor of the study catchment is brought by monsoons from Pacific Ocean in summer and prevailing westerly winds in winter. The estimated young water fraction is found to be strongly correlated with topographic gradient but presents no significant correlation with drainage area or vegetation coverage. Comparison between the difference in young water fraction of two adjacent sub‐catchments suggests that soil water in the steeper sub‐catchment tends to favor deep vertical infiltration, resulting in longer flow path, longer mean residence time, and smaller young water fraction. This difference between the soil water movement and the hydrological response revealed in this study has impacts on the biogeochemical cycles in the catchment.

Role of earthworms in soil fertility and its impact on agriculture: A review

Soil fertility is defined as the capacity of a specific kind of soil to function, within natural or managed ecosystem boundaries to sustain plant and animal productivity, maintain or enhance water and air quality, and support human health and habitation. Perhaps no other living organism in the soil is as important as an earthworm in helping to increase soil health. Earthworms are the most commonly occur in the soil. The activities of burrowing and feeding by earthworms have many valuable effects generally on soil quality for crop production. Earthworms increase soil aeration, infiltration, structure, nutrient cycling, water movement, and plant growth. Earthworms are one of the major decomposers of organic matter. They get their nutrition from microorganisms that live on organic matter and in soil material. When they move through the soil eating, earthworms form tubular channels or burrows. These burrows can persist for a long time in the soil. Earthworm burrows increase soil porosity which increases the amount of air and water that get into the soil. Increased porosity also lowers bulk density and increases root development. Earthworm excrement or casts increase soil fertility because it contains nitrogen, phosphorus, potassium, and magnesium. Earthworm casts also contain microorganisms which increase in abundance as organic matter is digested in their intestines. The cycling of nutrients from organic matter and the increase in microorganisms facilitates plant growth. They cast along with binding agents released by earthworms also improve soil structure and increase aggregate stability. The soil biota benefits soil productivity and contributes to the sustainable function of all ecosystems. The cycling of nutrients is a critical function that is essential to life on earth. Earthworms (EWs) are a major component of soil fauna communities in most ecosystems and comprise a large proportion of macrofauna biomass. Their activity is beneficial because it can enhance soil nutrient cycling through the rapid incorporation of detritus into mineral soils. In addition to this mixing effect, mucus production associated with water excretion in earthworm guts also enhances the activity of other beneficial soil microorganisms. This is followed by the production of organic matter. So, in the short term, a more significant effect is the concentration of large quantities of nutrients (N, P, K, and Ca) that are easily assimilable by plants in fresh cast depositions. In addition, earthworms seem to accelerate the mineralization as well as the turnover of soil organic matter. Earthworms are known also to increase nitrogen mineralization, through direct and indirect effects on the microbial community. The increased transfer of organic C and N into soil aggregates indicates the potential for earthworms to facilitate soil organic matter stabilization and accumulation in agricultural systems, and that their influence depends greatly on differences in land management practices.