فصلنامه حفاظت منابع آب و خاک
سال دوم شماره 2 (پیاپی 6، زمستان 1391)

This study was performed to investigate the effect of Polyacrylamide (PAM) on pattern of variation of runoff components consist of the amount of runoff during rainfall, cumulative runoff, the runoff commencement and cessation time and runoff amount at different time steps. The experiments were taken place in Soil Erosion and Rainfall Simulation Laboratory. In this study, three small cubic plots with dimensions of 0.5 m, total volume of 0.125 m3 and having 20% slope were used. The conducted experimental treatments were consisted of 0 (control), 0.4, 0.6, 1, 2, 3, 4 and 6 g PAM/m2. The results indicated that the PAM-treated plots had no significant reducing influence on runoff amounts (P=0.49). The reduction of runoff amount at different levels of PAM had also no specific trends. In addition, the maximum reduction in total runoff occurred in treatments 2, 6 and 1 g PAM/m2, respectively. The runoff commencement time was increased by increasing the amount of PAM to 2 g/m2 and runoff cessation time was decreased due to increasing amount of PAM level to 1 g m-2, respectively. The assessment of runoff amount in common time steps of different treatments also revealed that the different amount of PAMs had no significant effect (P > 0.12) on runoff control in all steps except the first and third time steps.

Reclamation of oil-contaminated soils is essential for optimal conservation of soil and water resources. Any decontamination of such soils from hydrocarbons contamination requires quantitative evaluation of soil hydraulic properties at presence of such contaminants. The objective of this study was to investigate the soil retention in NAPL-water-air three-phase systems. Consequently, soil retention curves were obtained using hanging column method with three primary NAPL-water ratios 25-75, 50-50 and 75-25. The parameters of soil retention curves were then obtained based on van Genuchten, Brooks-Corey and Campbell models. The model performance was also evaluated based on ME, RMSE, EF, CD and CRM. The results indicated that by decreasing the amount of NAPLs, the pore size distribution parameters of the hydraulic models (n, λ and 1/b) and their bubbling pressure parameters were both reduced. Therefore, bubbling pressure and slope of soil retention curves were increased. The results also showed that in a given amount of soil liquid phase, more suction is needed to drain out fluids in three-phase (NAPL-water-air) systems compares to two-phase (water-air) system. Thus, in a given quantity of NAPL, the porous media provide more retention for three-phase systems. Also, the calculated statistics indicated that van Genuchten model provides more reasonable predictions for NAPLs retention in three-fluid phase systems for monotonic drainage paths.

Soil contamination with heavy metals is one of the most important challenges in soil and water conservation area. Remediation of Cd as one of the most important environmental contaminants from contaminated soils due to its high mobility in soil-plant-human chain and adverse effects on human and animals, is very important. Phytoextraction is one of the biological remediation methods in which hyperaccumulator plants are used to take up pollutants from contaminated soils. The objective of this study was to investigate the capability of Land Cress (Lepidium sativum) for phytoremediation of cadmium from Cd-contaminated soils. For this purpose, a randomized block experimental design with six treatments of 0, 3, 5, 10, 25 and 50 mg Cd/ kg soil and four replicates was established in the greenhouse. When plants were fully developed, plants were harvested and cadmium concentrations in the soil, roots and shoots were measured. The results indicated that by increasing Cd concentration in soil, its accumulation in plant tissues was also increased. By increasing cadmium concentration in soil, its concentration within the roots and shoots was increased to 19.3 and 34 times, respectively. This indicates the high capability of both roots and shoots for cadmium uptake from contaminated soils. Total average cadmium concentration in roots and shoots was 65.18 and 60.86 mg/kg, respectively. With increasing cadmium concentration, the time needed for phytoextraction was also increased. The minimum time needed for phytoextraction was belonged to the 3 mg/kg Cd treatment. Since Land Cress has short growing period and high biomass, it can be used as hyperaccumulator plant to remediate cadmium from Cd-contaminated soils.

Crop simulation models are used for understanding plants response to the change of surrounding environment and to evaluate crop physiological and morphological characteristics to enhance crop production and to contribute to the efficient use of water and soil resources. Yet, the evaluation of these models is a prerequisite for their use in assessing different management strategies. In this study, CERES-Barley from DSSAT software package (version 4) was calibrated by using inverse modeling method and PEST model. This study was conducted with 11 experimental treatments each with three replicates in the form of complete randomized block design. The irrigated treatments were consisted of 100 (T100), 90 (T90), 80 (T80), 70 (T70), 60 (T60), 50 (T50), 40 (T40), 30 (T30), 20 (T20), and 10 (T10) percent of crop water requirement. The rainfed treatment was consisted of one irrigation at planting (November 1st) and the other at first spring (April 8th) before introducing water stress. The results indicated that the model could reasonably well simulate these amounts up to T50 with acceptable accuracy. The calculated SRMSE statistics between T50 and T100 treatments for the simulated grain yield, straw yield, and total crop yield was 5.5, 10.9, and 3.6 percent, respectively. The corresponding R2 values were obtained to be 95, 69, and 93 percent, respectively.

Soil conservation against flood erosion is very important for optimal use of soil and water resources. Stepped floodway channels are one of the essential structural approaches for soil protection against flood flows in high slope lands at urban areas. In these channels flows are characterized by intense turbulence and strong flow aeration, but most studies did not investigate the turbulence characteristics. In this study, highly turbulent airwater flows skimming down a large-size stepped chute were systematically investigated. An experimental study of detailed air-water flow properties measurements were introduced in different types of flow regimes on a stepped channel (θ = 21.8º, h=0.04m, l=0.10m) model to investigate the location and the flow depth at inception point of air entrainment and velocity profiles distributions. Detailed velocity and turbulence intensity measurements in flow direction were performed by use of a phase detection conductivity probe which was designed, developed and calibrated by writers. The results showed that the turbulence characteristics vary in different regions. The study showed further that the turbulence intensity increases rapidly close to the step bottom at the viscous sub layer and maximized for 0.4≤ y/dc ≤ 0.5 at intermediate region then decreases gradually in the upper region. It is hypothesized that the high turbulence levels in the intermediate region were caused by the continuous deformations and modification of the air-water interfacial structure.

Reclamation of saline soils is an important practice from soil and water resources conservation point of view. In saline soils, crop production is adversely affected by soluble salts within the root zone as well as by shallow saline water table. The first step for reclamation of such soils is reducing the soil salinity to optimum level by capital leaching. Reclamation of saline soils depends on quantity and quality of applied water, as well as soil drainage conditions. The objective of this study was to develop a model to estimate water requirement for reclamation of saline soils based on some obtainable soil physical characteristics. Consequently, a large area of 3,216 ha with S4A3 salinity/sodicity class in Khuzestan, Iran, was selected to obtain the required data. This experiment was conducted with two treatments and two replicates. In the first treatment, the experiment was conducted by applying just 100 cm water depth in four-25 cm intervals. In the second treatment, 5,000 kg/ha Sulfuric Acid was applied prior to salt leaching together with leaching water. The intermittent ponding method was conducted with double rings in a circular array. Soil samples were taken from 0-25, 25-50, 50-75, 75-100, 100-125 and 125-150 cm soil depths before, during and after each leaching water application interval. The required physical and chemical analyses were performed on the collected data. Several mathematical models were applied to the obtained data to verify their performances. The results indicated that the logarithmic model can estimate the capital leaching requirement much than other models. This empirical model with minimum weighted mean of capital leaching water (38 cm) represents the best performance from water saving point of view compares to other models.

Water scarcity is a widespread problem in arid and semi arid regions. In this condition, evaluating crop response to water stress and estimation of ET production function (ETPF) is essential. The objective of this study was to investigate the dynamic interrelations of yield, evapotranspiration and water use efficiency of potato (Solanum Tuberosom L.) under trickle irrigation condition. This study was conducted in Dehgolan region of Kurdistan province in spring season of 1388. The experiment was arranged based on completely randomized block with 3 replication of water supply (60%, 80%, 100%, 120% of crop water requierment). In this study, evapotranspiration values and total yield of treatments were measured. To reveal the interrelations of yield, evapotranspiration and water use efficiency, two types of water production function including: Linear and Quadratic were used. The results showed that when the ETPF is linear, the EI will be numerically equal to the yield response factor (Ky), when ET reaches maximum ET (ETm). When ETPF was quadratic, the ET needed to maximize WUE is less than the ET for maximum yield (Ym). The results were also revealed that maximum yield was achieved at 345 mm of evapotranspiration and maximum water use efficiency (26.6 kg/m3) was achieved at 222 mm of evapotranspiration where 55.4 percent was less than the maximum evapotranspiration (ETm). However, the maximum yield was only 27.7 percent more than the yield in maximum water use efficiency. The interrelation of Y, ET and WUE are demonstrated that if water supply is limiting, seeking maximum water use efficiency may be desirable.