The effect of water quality on soil water retention, structure, and hydraulic conductivity in two soil textures was studied. Undisturbed soil samples were treated in 5 wetting and drying periods with 6 different types of water quality consisting of 2 levels of EC (0. 2 and 10 dS m-1) and three levels of SAR (1, 5 and 12). Undisturbed soil samples were equilibrated on sand box apparatus to soil matric suctions of 0, 10, 20, 40 and 60 cm and on pressure plate apparatus to soil matric suctions of 100, 300, 1000, 2000, 4000 and 15000 cm. The van Genuchten-Mualem model was fitted to simulate the measured soil water characteristic curve. Soil physical quality index (S) and the inflection point of water retention curve (θ INFL) were evaluated using fitted parameters. Also, the macro-porosity, meso-porosity, micro-porosity, available water content (AWC100 and AWC300), and saturated hydraulic conductivity were measured. The study was conducted in a completely randomized design with three replications. Results showed that increasing EC caused soil particles flocculation, by developing some new pores and, consequently, increasing water retention capacity. Although increase in SAR dispersed soil particles, alteration of some macro-pores and meso-pores to micro-pores enhanced water retention, especially at high matric suctions. But, the available water content did not change significantly. Also, increase in water EC enhanced water retention at all matric suctions and the highest moisture content at inflection point was seen at EC of 10 dSm-1. The increase in SAR and decrease in EC were directly related to decrease in saturated hydraulic conductivity. Soil physical quality index (S) decreased by sodium increment, which indicated the reduced soil physical quality.

Soil water infiltration and its characteristics are important in water management both in agriculture and hydrology. Water repellency of soil, a phenomenon that often occurs in forest soils, reduces infiltration greatly and enhances soil degradation by various ways. In this study two clay loam and sandy loam soils were sampled from Kaleybar forest area, East Azarbaijan province. They were artificially hydrophobized into five different degrees of water repellency by using stearic acid. Water drop penetration time test (WDPT) was applied to assess the severity of the repellency. Effects of the repellency were investigated on cumulative infiltration and infiltration coefficients of the Kostiakov and Philip models. Results indicated that in the both soils, cumulative and average infiltration rate (average of triplicate infiltration measurement data) at the beginning of the experiment and the average steady state infiltration rate decreased with increasing of repellency from degree 1 to 5. The average value of the initial infiltration rate decreased from 1.37 to 0.31 in sandy loam soil, and from 1.50 to 0.23 in clay loam soil with increasing the severity of the repellency from degree one to five. Steady state infiltration rate was greatly reduced from 0.037 to 0.0001 in sandy loam soil, and from 0.02 to 0.008 in clay loam soil. Water repellency significantly affected Kostiakov c and Philip sorptivity S. The Kostiakov model in comparison to the Philip model was more appropriate for estimating cumulative infiltration in different degrees of water repellency.

Background and Objectives: There are rare and contrary reports about the effects of microbial biofilms formation on the physical, chemical and biological properties of soil. There is no possibility of direct study of microbial biofilms in the soil due to limited scientific techniques; therefore, other similar materials are used as analogue for biofilm. Arabic gum is one of the analogues of biofilm, which is also discussed in some case studies. However, so far no report on its effect on different soil texture classes has been presented. Therefore, in order to evaluate the effects of Arabic gum on several soil characteristics of two different soil texture classes, the present study was designed and conducted. Materials and Methods: To do this study, two different soil types including clay loam and loam texture classes and different amounts of Arabic gum (0, 5 and 10 g per kg of soil) with three replications were investigated in a factorial experiment in a completely randomized design (CRD). Arabic gum was mixed with soil and after one-month incubation time, the disturbed and undisturbed samples were taken from the soils and different soil characteristics including bulk density (Db), soil moisture content (θ s), saturated hydraulic conductivity (Ks), saturated water content, soil aggregate stability (WAS), mean weight diameter of aggregate (MWD), mass fractal (Dm) of aggregates, soil acidity (pH), organic carbon (OC) content, cation exchange capacity (CEC) and microbial respiration (Rs) were measured. Results: The results showed that the effect of applied amounts of Arabic gum on θ s, soil Db, Ks and Rs in loam soil was lower than that of clay loam, whereas the application of 10 g Arabic gum per kg soil in clay loam soil caused an increase by approximately 12, 18 and 317 percent, respectively, in the volumetric and gravimetric θ s and the Ks; while these effects were not seen in loam soils. Usage of 10 g Arabic gum per kg soil also reduced the Db of clay loam soil up to 5%, while no changes were found in the Db of loam soils. Also, in treated soils, both applied amounts of Arabic gum (5 and 10 g per kg soil) showed positive changes in soil OC and the WAS, MWD and Dm of aggregates, being independent from soil type. According to the results, the amount of 5 g Arabic gum per kg soil can be recommended to improve the characteristics of the clay loam soils. Conclusion: The use of Arabic gum can improve the physical, chemical and biological properties of soil. In fine-textures soils with higher contents of clay, much less amount of it is needed, while in coarse-textured soils, more amount of this polymer are needed; in the other words, the effect of microbial biofilm formation is more pronounced in fine-textured soils.

Background and Objectives: Soil and groundwater contamination by petroleum hydrocarbons might cause negative environmental impacts. It may adversely affect soil physical conditions and quality such as hydraulic properties via raising soil water repellency. Soil structure is an important physical characteristic depending on pore size distribution and continuity, and it can affect several soil physical and chemical processes. Soil structure might be affected by physical weathering processes such as wetting/drying and freezing/thawing cycles. It is possible to reproduce the natural soil structure in the laboratory by imposing wetting/drying and freezing/thawing cycles on the repacked soil samples. This would minimize the possible changes in soil structure during core sampling from the field. Few studies have been conducted about the interactive effect of oil contamination, soil texture and structure on soil water repellency and hydraulic properties. The present study aims to investigate the interaction effects of crude oil application, soil texture and weathering-induced structure on soil water repellency and hydraulic properties.Methodology: In this study, the effect of crude oil application and physical weathering on water repellency and hydraulic properties of two soils (sandy loam and clay loam) was studied in a factorial experiment of completely randomized design with three replicates. Soil samples were collected from 025 cm layer of agricultural lands in Chaharmahal-va-Bakhtiari province, central Iran (sandy loam and clay loam soils were located in 32° 43' N 51° 59' E and 32° 29' N 50° 42' E, respectively). The soil was ground and sieved through a 4-mm mesh to exclude the gravel particles and plant residues. Crude oil was solved in the n-hexane and added to soil with the concentrations of 0.5 and 1 %w/w of total petroleum hydrocarbons (TPHs). Besides, a control without crude oil addition was included in the experiment. The treated soils were then poured into stainless cylinders (height and diameter of 5 cm) and packed to natural bulk density of 1.45 and 1.43 g cm-3 for sandy loam and clay loam soils, respectively. Half of the prepared soil samples were tested immediately and named “repacked” treatment and the rest wetted and dried for five months under normal conditions in the greenhouse and was named “physical weathering” treatment. Thus, a total of 36 soil samples were prepared (2 soil types × 3 levels of water repellency × 2 weathering treatments × 3 replicates). Then, water repellency was determined by water drop pentetration time (WDPT) on the treated soil cores. Soil water characteristic curve and saturated hydraulic conductivity (Ks) were measured on the soil cores and modeled by van Genuchten equation. Soil physical quality indicators including field capacity (FC), permanent wilting point (PWP), available water colntent (AWC), macroporosity (Macro-P), mesoporosity (Meso-P), microporosity (Micro-P), and Dexter’s index for soil physical quality (SDexter) were calculated as well.Findings: The results showed that soil hydraulic properties were significantly affected by the experimental treatments. Water retention was greater in the clay loam soil compared to the sandy loam soil. Oil contamination reduced soil water retention at all matric suctions (0 to 15000 cm) due to oil-induced water repellency and soil resistance against wetting (as observed by an increment in WDPT). The effect of oil contamination on water retention was greated in the sandy loam soil than in the clay loam soil due to lower specific surface area of coarse-textured soils. The Ks, saturated water content (s) and residual water content (r) decreased, and scaling () and shape (n) parameters increased significantly due to oil-induced water repellency. The Ks of 1% TPHs-treated samples (i.e., 5.64 cm h-1) was significantly lower than that of control (i.e., 7.98 cm h-1). The s and r significantly decreased by 1% oil contamination (i.e., 0.457 and 0.112 cm3 cm-3) compared to the control (i.e., 0.547 and 0.122 cm3 cm-3), respectively. However, the parameters  and n were significantly greater in the 1% TPHs-treated samples (i.e., 0.240 cm-1 and 1.56) compared to the control (i.e., 0.130 cm-1 and 1.36), respectively. Physical weathering significantly increased s. The The Ks and Macro-P were significantly greater in the sandy loam soil whereas the Meso-P and Micro-P were significantly greater in the clay loam soil. The FC, PWP and AWC were significantly greater in the clay loam soil than in the sandy loam soil. The FC, PWP, Meso-P and Micro-P decreased but the Macro-P and SDexter increased in the oil-contaminated soil samples. The AWC significantly decreased from 0.084 (control) to 0.049 cm3 cm-3 due to 1% oil contamination. Physical weathering intensified the oil-induced water repellency (i.e., an incement in WDPT from 23.9 in repacked soil to 30.2 s in weathered soil), and reduced water retention in the sandy loam soil more than in the clay loam soil. The Ks, Macro-P and Micro-P were significantly greater in the weathered soil samples than in the repacked ones.Conclusion: As coarse-textured soils with low specific surface area are more prone to water repellency compared to fine-textured soils, they became water-repellent quicker upon physical weathering. It seems that physical weathering stimulated soil structure formation and intensified the oil-induced water repellency. The findings of this study are important for the management of oil contamination in different soil (texture and structure) conditions.

Introduction: Water for agriculture is one of the most important factors in arid and semi-arid areas and municipal wastewater treatment is an important resource for this purpose. Wastewaters even after treatment may contain many types of microorganisms that are pathogenic to humans and dangerous for the environment. Therefore, potential of transfer contaminations is a serious problem regarding use of treated wastewater for agriculture. Due to the risk of transfer contaminations through the use of wastewater, the study of transfer microbes in soil in recent decades has been of interest to researchers. Thereafter various irrigation techniques can be used associated with treated wastewater for agriculture. Accordingly, the present study was conducted on Fecal Coliform in the wastewater treatment in laboratory columns.Materials and Methods: The present study was conducted in Agriculture Faculty of TarbiatModares University for 62 days in 2013. This study was conducted on Fecal Coliform in the wastewater treatment in laboratory columns, having 30 cm diameter and 60 cm height. They were irrigated using surface drip irrigation system (DI). Samples of the effluent and soil solutions were collected from the experimental columns after each irrigation events. Soil texture was clay-loam that was collected from south of Tehran wastewater treatment plant. Three models of one site sorbtion's model, attachment/ detachment two kinetic site and attachment/ detachment one kinetic site, were used for simulation of Fecal Coliform transport by inverse solution option of the HYDRUS-ID model. For calibration of the model and estimating the model input parameters, soil hydraulic and transport parameters were inversely estimated. Results represented that the HYDRUS-1D with reasonably accurately simulated the outlet flow. To simulate the transfer of the bacteria in the soil, one site sorption model, two kinetic sites model (particle transport using attachment/detachment) and one kinetic site model were used.

Engineering properties of soils besides the chemical and biological properties can be a tool for justifying the behavior of soil. In this study bulk density, hydraulic conductivity, soil penetration resistance and Shear strength were measured. Different levels of depth and puddling intensity and their interactions on the properties in randomized complete design with three replications in a factorial experiment was investigated. Results indicated puddling intensity decreased the soil hydraulic conductivity, bulk density, penetration resistance, shear strength and with increasing depth, bulk density, penetration resistance and shear strength increased. The changes in bulk density were 0. 68-1. 32. The highest and lowest hydraulic conductivity were reported 0. 3 and 8. 5 in treatment P0 depth 10 cm and treatment P2 depth 30 cm respectively. It can be said that puddling treatment P1 is more suitable than treatment P2 to keep moisture, reduce physical and mechanical damage, energy required to prepare the paddy fields.

Introduction: Mulch tillage system is an intermediate system which covers some of disadvantages of no tillage and conventional tillage systems. In farms in which tillage is done with a chisel plow, runoff and soil erosion have a less important relation to moldboard and disk plow and naturally absorption of rainfall will be developed. Thus, the mulch tillage system is an appropriate alternative to conventional tillage and no tillage (Backingham and Pauli, 1993). The unwanted vibration in machinery and industry mainly processes most harmful factors, for example: bearing wear ,cracking and loosening joints. ...

Soil compaction is one of the effective factors in reducing soil physical quality, which due to tillage operations can affect the relationship between water, soil and crop yield. The aim of this study was to investigate the effect of some tillage treatments on the compaction behavior of a silty clay loam soil. Core sampling was carried out during three years of tillage after barley harvest. The experiments were conducted as a randomized complete block design with three treatments i.e. conventional tillage, reduced tillage and no-tillage in 6 replications. Soil compaction characteristics including pre-compression stress, compression index and swelling index were determined based on confined compression test )CCT) at 100 hPa matric suction. The results showed that the tillage treatment had a significant effect on pre- compression stress, bulk density and soil moisture at the confidence level of% 5. The lowest amount of pre-compression stress with a value of 19.95kPa is related to conventional tillage treatments and the highest value with a value of 31.62 kPa is related to non-tillage treatment. The compression index was showed the highest value in conventional tillage compared to other treatments. The results of cyclic loading-unloading at a constant stress level (i.e. 50% of pre-compression stress) showed that the studied soil was less sensitive to repeated loading for no-tillage than reduced and conventional tillage treatments which can be attributed to weaker structure for the later. As the conclusion, the no-tillage treatment can be described as a treatment being less susceptible to compaction. However, consecutive implementation of this tillage treatment might require subsoiling operations every few years to disturbed the deep subsoil hard pans.

Groundwater aquifers are one of the main sources of drinking water and agricultural water supply. However, increasing the use of nitrogen fertilizers is a serious threat to underground water and human health due to the high dynamics of nitrate in the soil. Therefore, in this study, the effect of 0%, 1%, and 2% by weight of cocopeat, biocharcocopeat, and vermicompost modifiers on nitrate transport in sandy loam and clay loam soils was investigated. The soils were obtained from the agricultural research center of Hamadan province. After that, the experiments were carried out in the form of a completely randomized design in three replications, in the irrigation and drainage laboratory of the Faculty of Agriculture of Bu-Ali Sina University of Hamedan. Then the soil columns with a length of 70 cm and a diameter of 6 cm were filled with soil up to a height of 50 cm. Pure potassium nitrate salt solution was used as an artificial pollutant with a concentration of 150 mg/lit. During the experiment, a constant water head load of 5 cm of the pollutant solution was continuously maintained on the soil columns, and sampling of the columns' drainage was done at different times. The results showed that the use of modifiers affected the physical and chemical properties of the soil. These changes included an increase in organic carbon, organic matter, electrical conductivity and porosity, and a decrease in apparent density compared to the control soil.

Considering that biochar is highly regarded as a soil conditioner, it is necessary to investigate its environmental effects and effects on soil properties, including clay dispersion. Dispersion of clay in arid and semi-arid regions, in addition to destroying soil resources, causes environmental pollution and increases soil erosion. For this reason, there is a need to overcome this problem with existing solutions. This study aimed to investigate the effect of the application of different levels (0, 1.5, and 3% wt) of cow manure biochar on the amount of spontaneously and mechanically dispersible clay and the mean weight diameter of aggregates (MWD) in two calcareous soils with different textures (clay loam and sandy loam) in periods of 40, 80, and 120 days after application. The results showed that the application of 3% biochar increased the spontaneously dispersible clay by 4.2%, as well as the levels of 1.5% and 3% of biochar increased mechanically dispersible clay compared to that of the control by 4.3% and 30.8%, respectively. The amount of mechanically and spontaneously dispersible clay increased over time. While the effect of soil texture on spontaneously dispersible clay was insignificant, the amount of mechanically dispersible clay in the clay loam soil was 61.2% more than that of the sandy loam soil. Results also indicated that addition of 1.5% and 3% of biochar decreased the MWD of aggregates by 24.2 and 20.6% in the sandy loam and 16.5 and 13.6% in the clay loam soils, respectively. The mentioned decrease in MWD caused an increase in dispersible clay. The results of this research can provide the necessary information regarding the effect of biochar on the amount of clay dispersion to recommend using biochar as a soil conditioner.