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.

Soil saturated hydraulic conductivity (Ks) is one of the main parameters in water and solute transport studies in soil and irrigation and drainage projects designs. So, knowledge about the Ks spatial distribution pattern has great importance. The aim of present study was to predict spatial distribution pattern of Ks in the experimental field of Sistan Dam, Zabol University, using different interpolation methods. For this purpose, a set of 113 single ring Beerkan infiltration experiments were carried out over the study area in a grid of average distance about 80 m. The Ks was obtained through Beerkan calculating algorithms, BESTslope, BESTintercept and BESTsteady. The relative fitting errors were 5. 19% and 9. 39% for BESTslope and BESTintercept algorithms, respectively, that are satisfactory. The interpolation methods were compared using evaluation criteria such as the weighted determination coefficient (ω r2) and standard error (SE). Based on the results, the spatial correlation of Ks was moderate and it had the exponential structure. The results showed that Log Kriging (LOK) achieved the highest ω r2 and lowest SE values for estimating Ks over the study area with a dominant soil textures of loam and sandy loam. However, the difference between LOK and the other interpolation approaches was not significant. Moreover, among the interpolation methods, BESTsteady algorithm, which had the simplest calculating procedure, had the highest precision in estimation. So, according to the results, LOK with an exponential semivarigram model is suggested as the best interpolation method for predicting the spatial distribution of Ks, based on values obtained from the simple and applicable algorithm, i. e. BESTsteady, in loam and sandy loam soils.

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.

One of the most important problems in the soil erosion research is the dependency of measurements and estimates on the scale. Recently, studies in the field of soil erosion scaling have resulted in development of some different models. This research aimed to investigate the scaling of rill erosion in field conditions. Artifitial rills with length of 1 to 8 meters and width of 5 cm were created in a plot with a slope of 5% in an agricultural soil with sandy loam texture and weak aggregate stability. The experiments were caried out under two target flow rates of 0. 11 and 0. 24 liters per second. Sediment concentration was measured during the event for 30 minutes, and its time changes were investigated along different rills. To scale rill erosion, the changes with rill length of the mean sediment concentration and particle detachment rate, both at three initial unsteady, final steady and total event conditions, were evaluated and modeled. The temporal changes of sediment concentration exhipited an exponentially decreasing trends almost in all cases. The average sediment concentration increased linearly with rill length (spatial changes) at lower flow rates, and exponentially (reaching a certain limit) under the higher flow rates in all three conditions. Also, the particle detachment rate decreased exponentially with rill length under both flow rates in all three cases of unsteady, steady and total event averages. The results generally confirmed the models and theories of the exponential decrease in the particle detachment rate with increasing rill length.

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.

The fertility of agricultural land is a function of the amount of organic material available in the soil. Due to the low amount of this material in the agriculture soil, use of organic materials is important. Biochar is a kind of organic materials which has high stable properties, in recent years attracts the attention of researchers. The goal of this research was to study the effect of sugarcane bagasse biochar on some chemical properties of a sandy loam soil. For this purpose, from prepared biochar in different temperatures of 200-600°C, biochar products in temperature of 300 °C which had the highest stable organic matter yield index (7.2%) was selected as the optimum biochar. Then the effect of this organic matter, after mixing it with a sandy loam soil at 4 levels (0, 2, 5 and 10 g per kg soil), on chemical characteristics of this soil, such as organic carbon, total nitrogen, available phosphorus, cation and anion exchange capacity were determined. The results showed that the addition of sugarcane bagasse biochar in all levels caused increasing significant of organic carbon, total nitrogen, available phosphorus, anion exchange capacity, EC, cation Exchange capacity and decreased pH of the soil. Sugarcane bagasse biochar with treatment of 10 g per kg soil showed greatest impact on anion exchange capacity of the soil (7.4 times compared to the control) and the lowest impact on the reduction of soil pH (0.01 times compared to the control).

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.

Uranium is a radioactive heavy metal. Development of nuclear industries and application of phosphate fertilizers contain uranium impurity resulted in soil contamination with uranium. A Pot experiment had been conducted under controlled condition. The experiment carried out in completely randomized design with two factors, including two plants (soybean and sunflower) and six levels of uranium (0, 50, 100, 250, 500 and 1000 mg/kg). Plants harvested after 40 days of experiment and before the generative stages. Soil samples were extracted by DTPA and AAAcEDTA. Uranium concentration in plant tissue increased by increasing the uranium in soil. The ratio of uranium in root: shoot was between 20-100 in sunflower and soy bean. Extraction efficiency of DTPA and AAAcEDTA increased by increasing of uranium in soil. The results of the experiment showed that AAAcEDTA extracts more uranium in all applied uranium concentrations. Both extractants had a good correlation with uranium in plants; however, extraction efficiency of AAAcEDTA was well correlated by uranium concentration in plant tissues. The results of the experiment suggest that AAAcEDTA is suitable extractant for uranium as phytoavailability indicator.

Background and Objectives: Rhizosphere processes have an important role in zinc (Zn) fractions in soils. Plant roots have the ability to transform metal fractions for easy uptake by root exudation in the rhizosphere. In the peresent study, the effects of EDTA, citric acid and poultry manure extract (PME) on fractionation of Zn in the rhizosphere of corn (hybrid (KSC. 704)) were investigated in two contaminated soils with different texture. Materials and Methods: This research was conducted as factoriel in a completely randomized pattern with three replicates in greenhouse condition and citric acid and EDTA were used at concentrations of 0, 0. 5 and 1 mmol kg-1 soil and poultry manure extract at concentrations of 0, 0. 5 and 1 g kg-1 soil. Three seeds of corn were planted in the rhizobox. After 10 weeks, the plants were harvested and rhizosphere and bulk soils were separated. Dissolved organic carbon (DOC), microbial biomass carbon (MBC) and Zn fractions were determined in the rhizosphere and bulk soils. Results: The results showed that there is a difference between rhizosphere soils properties and bulk soils. In both soils, DOC and MBC in the rhizosphere were significantly (P≤ 0. 05) increased, while, pH in the rhizosphere was significantly (P≤ 0. 05) decreased comared with bulk soils. In sandy loam and clay loam soils, the average of exchangeable Zn and Zn associated with organic matter in the rhizosphere were significantly (P≤ 0. 05) lower than those in the bulk soils, while, the average of Zn associated with iron-manganese oxides, Zn associated with carbonate and residual Zn in the rhizosphere were significantly (P≤ 0. 05) higher than those in the bulk soils. In the rhizosphere and bulk soils of both soils, the maximum amounts of Zn fractions in different fractions were respectively, in the order of associated with iron-manganese oxides, residuals, associated with organic matter, associated with carbonates and exchangeable fractions. A significant correlation was found between Zn uptake by shoots with Zn associated with iron-manganese oxides in both soils (r = 0. 71, P<0. 05). In sandy loam soil, the highest Zn uptake by shoots was observed in the 1 g kg-1 PME treatment. In clay loam soil, the highest Zn uptake by shoots was observed in the 0. 5 g kg-1 PME treatment. In sandy loam soil, 1 mmol kg-1 EDTA and in clay loam soil 1 mmol kg-1 citric acid treatments resulted in the release of the highest Zn concentrations in the iron-manganese oxides fraction. The results of average comparison showed that the average of the exchangeable Zn and Zn associated with iron-manganese oxides in the sandy loam soil were significantly (P≤ 0. 05) higher than those in clay loam soil, while the average of the Zn associated with organic matter and residual Zn in clay loam soil were significantly (P≤ 0. 05) higher than those in sandy loam soil, which can be attributed to different soil characteristics. Conclusion: The results of the present study showed that soil physical, chemical and biological changes due to the corn roots caused not only Zn depletion in mobile soil Zn fractions, but also lead to change soil’ s stable Zn fractions. Since the excessive use of chelators can lead to increase more availability of soil’ s zinc without increasing the plant’ s absorption, so administration of higher concentration levels is not recommended.