JWSS - Journal of Water and Soil Science

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To determine the effects of field slope, emitter discharge, irrigation water volume and soil texture on soil moisture profile and soil surface wetted shape from a point source, field data were collected on three different soil types, three emitter discharges (4, 8, and 12 lph), four slopes (0, 2, 5, and 10%), and five irrigation water volumes (10, 20, 30, 40, and 50 liters) with three replications. The results showed that the surface-wetted area increases as the emitter discharge increases. The surface-wetted area decreased with a corresponding increase in emitter discharge in experimental fields with light-textured soils. In experimental fields with heavy textured soils and slopes greater than 5%, the changes in surface-wetted area due to the emitter discharge increases, were higher compared to slopes of less than 5%. Since, a higher emitter discharge would result in higher surface-wetted area, the results showed that for an equal volume of irrigation water, the soil moisture profile was deeper for lower emitter discharge. In general, the volume of wetted zone was higher for greater emitter discharges. It was found that as the volume of irrigation water increased, the volume of wetted zone would increase correspondingly. This effect is more prominent than that of emitter discharge. In general, the depth of wetting front was lower and the wetted surface area was greater for heavy textured soils as compared to the light textured soils. The wetted-surface area and the shape of wetting front in the direction of slope were affected by the soil infiltration, emitter discharge and volume of irrigation water where these effects were more critical in higher sloping lands.

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In this research, the presence of metalaxyl residues was studied in field-grown cucumber. Two different formulations of metalaxyl were used in the experiments. In the first experiment, cucumber plants were sprayed once and repeatedly by Ridomil-MZ 72 WP at 2.5 g/litre. In the second experiment, single and double applications of metalaxyl granule 5G were carried out at 5 g/m². Leaves and fruits were sampled at different times after each treatment and analyzed for metalaxyl residues by HPLC.

In leaf samples from single sprayed plots, metalaxyl residues declined rapidly following the treatment and more than 50% of the residues disappeared in the first two days, whereas in the leaf from single granule-applied plants, the residues increased during the first three weeks and then declined. Metalaxyl residues in cucumber sampled from single sprayed-plots were at a high level during the first three days after the spray and declined below the MRL (0.5 mg/kg) on the 7th day. In granule-applied plots, the residues increased during the first 7 days and the level below the limit was recorded 20 days after application. Residual values for plants sprayed with suspension showed a faster dissipation rate than granulated treatment. Metalaxyl recovered after three times of spraying and two times of granular application did not show any toxic accumulation of residues in fruit.

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Aggregation is an important temporal property of soil structure that is affected by intrinsic soil properties and also soil use and management. Aggregate stability has a strong influence on many processes in soil such as infiltration, aeration, strength, erosion, and soil’s ability to transmit liquids, solutes, gases, and heat. In this study, undisturbed soil specimens from 0-10 and 10-20 cm depths were sampled during summer 1999 from some regions in Iran including Golestan, Kermanshah, West Azerbaijan, and Mazendaran. After drying the samples in lab, the different sizes of aggregates were separated and the wet aggregate stability (WAS) and dispersible clay (DC) were determined on 2-2.8 mm aggregates according to Pojasok & Kay procedure (1990). The variance analysis of data showed significant differences among soils in all regions. The averages were compared by Duncan test to find the following order: Mazendaran > Golestan > Kermanshah > West Azerbaijan. Regression analysis of data of whole regions showed that the variability of aggregate stability was mainly explained by organic carbon content (R²=0.723 in P > 0.0001). The clay content had the greatest effect on aggregate stability in samples from Golestan while sand content had the greatest effect in samples from West Azerbaijan. The resulting equations from stepwise regression can be used to estimate aggregate stability from other soil variables in the study regions.

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The influence of the Sea Surface Temperatures (SSTs) on the seasonal precipitation over northern and southwestern parts of Iran was investigated. The warm, cold and base phases of the SSTs were defined and the median of precipitation during each of these phases (R_w, R_c and R_b, respectively) was determined. The magnitude of R_w/R_b, R_c/R_b and R_c/R_w were used as criteria for the assessment of the effects of the alternation of SST phases on seasonal precipitation. The results indicate that in association with cold SST phase, winter rainfall is above median over western and central parts of the coastal region, central and southern parts of Fars Province and all the stations studied in Khozestan Province. On the other hand, the prevalence of warm SST phase has caused about 20% decrease in winter precipitation over the Caspian Sea coastal area and northern parts of both Fars and Khozestan provinces. In association with warm SST phase in winter, precipitation during the following spring was found to be above normal for all the stations studied in the coastal region of the Caspian Sea. The highest sensitivity levels were found in Bandar- Anzali and Astara for which spring precipitation has increased by 80% due to the dominance of warm winter phase. However, the occurrence of boreal cold SST events causes shortage of precipitation in the eastern parts of the coastal areas along the Caspian Sea. A Possible Physical mechanisem justifying the influence of the Caspian Sea SST on the Precipitation variability was introduced. According to this mechanisem, temporal and spatial variability of the Siberian High is forced by the fluctuations in these SSTs.

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  This research was carried out to study the impacts of geomorphologic characteristics of claypan on land use and land degradation. Databank of the study area was constructed and digital terrain model of claypan was prepared. By using GIS techniques spatial distributions of the subsurface drainage network, sediment transportation index and wetness index were calculated. The results indicate that the depth to the claypan is between 0 (where the pan is exposed at the surface) to 605 cm. There are several depressions in the claypan which are filled by new sediments. Each depression has a catchment which is charged by the drainage water of its attributed lands. While a depression drains naturally or synthetically, the attributed soils over the depression are in non saline or moderate salinity condition otherwise, a marshland, a waterlogging area or a salt crust zone develops over there. The results also indicated that soil surface salinity is a function of depth to claypan and drainage condition of area. The trends of salinity extension are different for closed and open catchments and the depth to the claypan could be estimated using electrical conductivity. The results also show that analysis of microtopography of soil surface and soil stratification should be considered for designing irrigation and drainage networks.

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For an appropriate drip irrigation system design, a prediction of soil wetting pattern is needed for a given soil texture. The wetting pattern geometry is a key factor for emitter distance determination as well as crop type. The geometry of the wetting bulb is dependent on the parameters such as soil hydraulic properties, emitter discharge and the irrigation time. This study has been conducted in Albaji region in km 25 on the Ahvaz-Andimeshk road, in order to estimate the geometry of the wetting pattern under the point source trickle emitters in sandy soil with different discharge. The emitters were calibrated to provide 5, 10, 20, 30 and 40 liter per hour discharges. The maximum wetted soil surface and depth was measured by digging the irrigated soil. Two models were developed to predict wetted soil surface diameter and depth under a point source based on Buckingham's π theorem. The equations were calibrated by using the measured data. Then resulted scientific-empirical equations have been evaluated. Considering the maximum relative error of 14.3% and root mean square error of 3.8cm in estimation of the wetted soil surface diameter and depth, the models are recommended to estimate the geometry of the wetting bulbs with a high degree of accuracy, and can be used in designing and appropriate drip irrigation system management

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Soil physical and chemical properties, and test conditions might affect soil structural stability. In this study, the effects of test conditions as well as intrinsic soil properties on structural stability were investigated for selected soils from Hamedan Province. Mean weight diameter (MWD) and tensile strength (Y) of aggregates were determined by wet sieving method and indirect Brazilian test, respectively. The soil samples were pre-wetted slowly to matric suction of 200 kPa before the wet sieving. The pre-wetted samples were wet-sieved for 5, 10 and 15 min in order to simulate different hydro-mechanical stresses imposed on soil structure. Tensile strength of soil aggregates were also measured at air-dry and 500 kPa matric suction conditions. Short duration shaking (i.e. 5 min) could effectively discriminate the Hamedan soils in terms of structural stability due to their fairly low aggregate stabilities. The soil organic matter content had the highest impact on MWD followed by both clay and CaCO₃ content. The same was true for the Y values i.e. OM played the highest role in mechanical strength of soil aggregates. The highest coefficient of determination (R²) was obtained between Y and the intrinsic soil properties for matric suction of 500 kPa. The organic matter content had an important role in water and mechanically stable soil aggregates. The results indicated that short-duration wet sieving (i.e. 5 min) and measurements of tensile strength at matric suction of 500 kPa could be recommended for aggregate stability assessment in Hamedan soils

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Although soil organic matter (SOM) constitutes a small portion of soil bulk weight, it has a tremendous effect on physico-chemical and biological properties of soils. It is also one of the most important indicators of soil quality and its production. Soil organic matter determination is required for soil fertility management and soil pollution purposes. Wet oxidation procedure of Walkley-Black is a routine, relatively accurate and popular method for the determination of soil organic matter, but it involves the use of chromate and high cost of analysis. Therefore, loss-on-ignition (LOI) procedure as a simple and cheap method of SOM estimation which also avoids chromic acid waste has got more attention. The aims of this study were (i) to establish the relationships between LOI method and SOM as determined by Walkley-Black method for four major plains of Chaharmahal-va-Bakhtiari province and (ii) to determine the optimal temperature of the LOI. To do this, 205 soil surface samples were randomly collected from 0-25 cm depth of Shahrekord, Farsan, Kohrang and Lordegan plains to determine soil organic matter by Walkley-Black method and LOI procedure at 300, 360, 400, 500 and 550 oC for two hours. To determine the optimum temperature for ignition, 40 soil samples were selected to compare the SOM and CCE before and after ignition for each temperature. Results showed a positive, linear significant relationship existed between LOI and wet oxidation in each plain. Coefficient of determination (R2) of the equations was higher for individual plain than the overall equation. Coefficient of determination and line slope decreased and error (RMSE) increased with increasing ignition temperature. At higher contents of calcium carbonate, the rate of line slope decrease with increasing ignition temperature was more noticeable. This may be due to the destruction of carbonates at higher temperature. A temperature of around 360 oC was identified as optimum as it burned most organic carbon, destroyed less inorganic carbon, caused less clay structural water loss and used less electrical energy.

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The Madden Julian oscillation (MJO) is known as the primary mode of large-scale inter-seasonal variability in tropical regions, affectimg equatorial and sub-tropical climates. This study investigated the effects of the MJO on the occurrence of wet and dry spells in Fars province, central southern part of Iran, during November-April. Monthly precipitation data of nine stations spread over various parts of the province was analyzed during 1979-2005. Using two well-known MJO indices: MK and WH, the positive and negative phases of the MJO phases (enhanced and suppressed convective activity over the equatorial Indonesian region, respectively) were identified for monthly and seasonal scales. Precipitation-MJO composites were then constructed for the opposite phases. It was shown that for all the considered stations, seasonal precipitation during negative MJO phase was significantly greater (from about 2.5 to 6.0 folds) than the corresponding values during the positive phase. Moreover, the applied statistical tests proved that the frequency of wet or dry events was related to the prevalence of negative or positive MJO phase, respectively. As the positive MJO phase was engulfed, the probability of dry events varied from 60% to 84%. On the other hand, the probability of wet events was found to vary from 60% to 76% during the MJO negative phase.

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Expansive soils swell and shrink periodically when subjected to seasonal water content changes. As a result, they are a constant source of problem in the design and construction of foundations. In this study, the behaviour of an expansive soil was studied through a number of experiments involving cycles of wetting and drying using three different water qualities. Laboratory tests were performed on statically-compacted samples of an expansive soil in a modified Oedometer under constant surcharge pressure of 10 kPa. Vertical deformation of the soil sample was recorded continuously, and during the test, void ratio and water content of the sample were determined at different stages. The results indicated that the equilibrium condition was reached after about six wetting-drying cycles. It is shown that the swelling potential changes with changes in water quality the saline water reduced the swelling potential of the soil compared to the distilled water during wetting and drying cycles. Furthermore, the results showed that the variations of water content-void ratio paths during wetting-drying were the same (no hysteresis) when the equilibrium condition was achieved

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To study the effects of irrigation durations and land slopes on wetting pattern dimensions, some experiments were performed using an emitter with constant discharge of 4 liters per hour by 2, 4, and 6 hours irrigation durations. Experiments were conducted on lands with the slopes of 0, 5, 15 an 25 percent, with silty loam soil texture in 3 replications in Fathali region, Mogan plain, Iran. Results showed that increasing the land slope caused an increment in wetting pattern dimensions and bulk, in constant irrigation durations. When slope increased, the depth of infiltrated water along the emitter had a little decrease which wasn’t significant. The upstream and downstream components of wetting pattern were symmetrical on 0 percent slope but not on steep lands. So, optimizing the water use, which is saved in the soil, depends on the land slope and the crop should be planted 10 to 25 centimeters away from the dripper. The investigation of soil moisture distribution on wetting pattern in slope lands showed that contrary to the flat lands the main part of the moisture is accumulated in lower part of the emitter, and wetting pattern in these sloping lands was larger than in flat lands.

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Extensive tillage leads to the degradation of soil structure and aggregate stability. The effects of three different tillage implements including (combination tillage, chisel packer and disk), three levels of soil water content including (0.5, 0.7 and 0.9 plastic limit), three working speeds including (6, 8 and 10 km/hr) and two soil textures including (loam and silty clay loam soils) were studied. The study was carried out in Khuzestan Ramin Agriculture and Natural Resources University, in 2011. Soil aggregate mean weight diameter (MWD), geometric mean diameter (GMD) as determined by wet sieving method and soil surface roughness (SSR) were measured. Results showed that chisel packer with 0.744 mm MWD produced largest soil aggregates in both soils because of using narrow blade and shanks and small rake angles compared to other tillage treatments. Soil aggregate size was shown larger than other tillage treatments where chisel packer was employed but it was not suitable because of deep furrow shapes. Combination tillage was able to make a better soil condition to be used for seeding where the experiment was conducted.

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Evaluation of hydrologic behaviour and soil erosion as an environmental crisis is important in order to maintain watershed ecological safety at optimum level. The aim of this study is to evaluate the performance of the distributed hydrological WetSpa model in simulating erosion and sediment transport and also sedigraph in Taleghan watershed, Iran. Base digital maps and daily meteorological time series data for 9 years are the major model inputs. The calibration of global parameters was done for the first 5 years and the model validation was carried out for 4 years considering three month warm-up period at the beginning of both calibration and validation periods. The Nash-Sutcliffe criterion for the calibration and validation periods pointed out the efficiency of model simulation (82.7% and 79%, respectively). The next phase, the erosion module was calibrated for erosion and sediment transport simulation. The results showed the Nash-Sutcliffe efficiency criterion (60% and 64% for suspended sediment concentration and transport, respectively). Overall, the evaluation results reveal the good ability of WetSpa model in simulation of the hydrological processes e.g., runoff, raindrop detachment, runoff detachment, net soil loss, etc., in a given time and space

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Flood irrigation after planting induces wetting and drying cycles in arable soils. For this reason, the effect of this process on load-bearing capacity (pre-compaction stress pc) of a fine textured soil (silty clay) was studied. In this research, large air-dry disturbed soil specimens were prepared and some of them were exposed to five wetting and drying cycles. Next, the large soil specimens with/without wetting and drying cycles were compressed under three preloads (0, 100 or 200 kPa) and then the centre section of the preloaded soil specimen was firstly submitted to a plate sinkage test (PST). Then immediately one cylindrical sample was cored for confined compression test (CCT). The results showed that for reconstructed soil samples without wetting-drying cycles, the predicted pc using PST didn't significantly differ from the applied preload. Therefore, the PST can be used to determine the load-support capacity of the tilled soils. In PST, with an increase in soil water content from 0.9PL to 1.1PL, the amount of over-prediction in pc decreased. However, wetting-drying process significantly increased over-prediction in pc at the same water content. Hence, soil compressibility does not simply depend on the actual soil water content but also on the previous history of water content changes (i.e., wetting-drying cycles).

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The objectives of this study were to investigate the effect of dripper discharge and irrigation time on the wetted width in the sandy loam soil with high percentage of gravel and to evaluate previously developed models of estimation of the wetted width in the previous researches. The treatments included three irrigation times (T) of 4, 8 and 12 h and three dripper discharge rates (q) of 2, 4 and 8 l/h, with three replications. The wetted width of each dripper was measured 24 hours after irrigation application. The maximum and minimum wetted widths were 159.8 and 63.5 cm for T12q8 and T4q2, respectively. A linear model was developed as a function of two variables of irrigation time and dripper discharge rate was developed to predict the wetted width in sandy loam soil with high percentage of gravel. The evaluation of recommended models of wetted width for the studied soil showed that only one of six models was accurate enough to estimate wetted width. It can be concluded that the presence of gravels in the soil has a complex effect on width and depth of wetted zone. Thus, it is necessary to measure the wetted width and wetted depth in the field.

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Rainfall- runoff modeling and river discharge forecasting are an important step toward flood management and control, design of hydraulic structures in basins and drought management. The purpose of this study was simulating the daily flows in the Navrud watershed using WetSpa model. WetSpa is a hydrological- physical model that can predict flood on the watershed scale with different time steps. This model uses topography, land use and soil texture layers and also, the daily meteorological data to predict the flow hydrograph. In this study, the data of 4 stations (Khlyan, Khrjgyl, Gavkhs, Nav) during the water years 2006-2011 were used. 36 months from September 2006 and 36 months from September 2009 to September 2011 were selected for calibration and test of model, respectively. Simulation results of WetSpa model showed that this model simulates river Daily flow using collective measures of 0.63 and 0.61 in calibration and test periods, respectively. According to this result, it can be stated that the model estimates peak discharge and flow volume in both periods very well. Also, this model could simulate well the water balance of Navrud Basin.

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Surface runoff is one of the main causes of erosion and loss of soil fertility, sedimentation in reservoirs and reduction of river water quality. Therefore, the accurate prediction of basin response to precipitation events is very important. Hydrological models are simplified views of the actual watershed systems that can help study watershed functions in response to various inputs, and understand hydrological processes better. Due to the variety of Rainfall - Runoff models, choosing a suitable model for the basin is important for water resource planning and management. Thus, the abilities and limitations of basin hydrological models are important to consider in the selection of model. In this study, the performance of IHACRES model in daily runoff simulation of Navroud basin was investigated using evaluation criteria of Nash – Sutcliffe Index (NSH) and the mean total error and the data of Khlyan and Khrjgyl stations during the Water years 2006 - 2011. 36 months from September 2006 and 36 months from September 2009 to September 2011 were selected for calibration and test of model, respectively. Finally, results showed that Nash – Sutcliffe Index and Bias in calibration stage were 0.57 and 8/53, respectively and in verification stage, they were 0.48 and 14/9, respectively. So, the used model has an acceptable accuracy in simulating the studied basin flow.

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Petroleum pollution is an important environmental issue in most of the countries especially those have an oil industry. This study was conducted to investigate the effect of petroleum pollution on soil water repellency and its relation to soil structural stability in Bakhtiardasht area, Isfahan. Polluted and adjacent non-polluted locations were selected to be representative in the green space around the Isfahan Oil Refinery. Soil water repellency was assessed using water drop penetration time (WDPT) in the polluted locations. Soil sample with least aggregates disturbance were collected and selected soil physical and chemical properties were measured. Soil structural stability was evaluated using the wet-sieving method and mechanically dispersible clay (MDC) structural stability indices of mean weight diameter (MWD) and geometric weight diameter (GMD) of aggregates and MDC were then calculated. Results showed that the positive effect of petroleum pollution on the MWD and GMD become significant. Negative impact of petroleum pollution on MDC was also significant. Increment of total petroleum hydrocarbons (TPHs) increased the soil water repellency. A positive correlation was observed between soil water repellency and GMD. However, TPHs concentrations greater than 6.4% decreased the MWD and GMD presumably due to anionic repulsion between clay particles and hydrocarbon functional groups. Although greater water repellency increased soil structural stability in the polluted locations when compared to control locations, however, diminished water retention of polluted soil has created an unfavorable condition for the green space in the area.

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Rainfall-runoff modeling and prediction of river discharge is one important parameter in flood control and management, hydraulic structure design, and drought management. The goal of this study is simulating the daily discharge in Kasilian watershed by using WetSpa model and adaptive neuro-fuzzy inference system (ANFIS). The WetSpa model is a distributed hydrological and physically based model, which is able to predict flood on the watershed scale with various time intervals. The ANFIS is a black box model which has attracted the attention of many researchers. The digital maps of topography, land use, and soil type are 3 base maps used in the model for the prediction of daily discharge while intelligent models use available hydrometric and meteorological stations' data. The results of WetSpa model showed that this model can simulate the river base flow with Nash- Sutcliff criteria of 64 percent in the validation period, but shows less accuracy with flooding discharges. The reason for this result can be the small and short Travel time noted. This model can simulate the water balance in Kasilian watershed as well. The sensitivity analysis showed that groundwater flow recession and rainfall degree-day parameters have the highest and lowest effect on the results, respectively. Also, ANFIS with the inputs of rainfall 1-day lag and evaporation 1-day lag, with Nash-Sutcliff criteria of 80, was superior to WetSpa model with Nash-Sutcliff criteria of 24 percent in the validation period.

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Accurate design of drip irrigation systems requires sufficient understanding of horizontally and vertically distribution of water flow in soil and modeling the wetting pattern dimensions created under the drip source. Field and laboratory activities are not suitable for this purpose considering their time and financial constraints and it is necessary to apply accurate software for determination of several equations in different situations. This research aimed to present simple models for calculation of wetting pattern dimensions in different discharges and structures in drip irrigation system. For this purpose, HYDRUS-2D model was implemented for four discharges in the same soil texture and different soil textures in the same discharge. The values obtained from running the software such as depth and maximum diameter of wetting pattern have been fitted with time values and corresponding equations were obtained. The results of statistical indices for all obtained equations (R>0.96, RMSE<2.12 and MAD<1.38) represent suitable accuracy of corresponding equations in determination of pattern dimensions under the drip source. The results also showed that Loamy Sand and Silt textures, respectively, have maximum and minimum depth and wetting pattern diameter.