WATER AND SOIL SCIENCE (AGRICULTURAL SCIENCE)
Year:2015 | Volume:25 | Issue:2|Papers Count:19

Saturated hydraulic conductivity of soil, as one of the most important soil physical properties, has special importance in identifying, investigating and modeling of water, solute and pollutants transport in porous media. Despite numerous researches, measuring saturated hydraulic conductivity by direct methods is still costly, time consuming and professional. Therefore, estimating saturated hydraulic conductivity using rapid and low cost methods such as pedo-transfer functions with acceptable accuracy is essential. The purpose of this research was to compare and evaluate 12 pedo-transfer functions which were presented by many researchers to estimate the saturated hydraulic conductivity of the soils. The region studied in this research was a part of the Urmia plain in West Azerbaijan consisting soils of Nazlu, Khodaverdikhan and Golmankhaneh villages. 40 measuring locations were selected randomly. In each selected location, a 30 cm hole was excavated and soil saturated hydraulic conductivity was measured by Guelph permeameter. The excavated soils were used in the lab to determine their easily accessible parameters. The results showed that among the studied models, the Aimrun model had the best estimation for soil saturated hydraulic conductivity. For the mentioned model, the Akaike’s information criterion (AIC) and root mean square error (RMSE) parameters were -130.99 and 0.174 m/day, respectively. The results of the present research, emphasize on the importance of effective porosity application as an effective accessible parameter to increase the pedo-transfer functions accuracy.

Knowledge of drought phenomenon occurrence is useful in water resources management. Drought study is done based on some measured parameters. On the other hand, regional analysis is recommended where there is uncertain data (or data lacking) at some stations. In this research, the mentioned theory and the linear moment method were used for the Central basin of Iran. The precipitation data of 47 stations of the region were used. In order to determine homogeneous areas, we used some effective parameters of stations such as elevation, average annual precipitation, maximum 24 hours precipitation, seasonal drought index and standardized precipitation index. The study area was divided into homogeneous regions by using R software according to the mentioned parameters. Then, discordant stations were detected using the discordancy measure. The homogeneity of stations was tested using the H statistic. The best probability distribution was determined in each homogeneous area, and by using the selected distribution, drought severity maps representing 40%, 60% and 80% of mean annual precipitation were drawn. The results show that northern and western parts of the central catchment of Iran are more likely to be at risk of moderate and severe droughts.

One of the important parts of the urban and agriculture water conveyance systems are channel junctions. In this research, the effects of different factors such as inlet discharge ratio, bed elevation of lateral channels and height of weirs at the end of outlet channels on characteristics of the subcritical flow in 90 degrees four-branch open channel junctions with two inlets and two outlets were investigated experimentally. The results showed that as the inlet discharge ratio, bed elevation of lateral channels and height of weirs at the end of outlet channels increased, the outlet discharge in the main channel also increased. Increasing the inlet discharge ratio and decreasing the height of weirs at the end of outlet channels caused more fluctuation in the water surface profile at the junction, but variation of the bed elevation of lateral channels had no effect on fluctuations of the water surface profile. Furthermore, conjunction of the two inlet flows caused changing the velocity profiles in the inlet channels.

Solar net radiation (Rn) is one of the most important factors influencing soil heat flux and evapotranspiration rate process. This parameter is derived from the difference between downward and upward radiation fluxes reaching the earth’s surface. Field measurements of Rn are cost effective and difficult to maintain. Therefore, in the most cases, Rn is estimated by empirical, semiempirical and physical-based models. Recent studies show that the artificial neural network (ANN) is a reliable tool for estimating daily Rn with reasonable performance for the area where lack or shortage of field Rn exists. Using Irmak model and ANN approach, we tried to estimate daily Rn for one of the cold semi-arid sites located in Hamedan. For model evaluations, Rn data were measured in hourly base during December 2011 to December 2012 at Bu-Ali Sina University weather site. In this study, we used 11 daily meteorological parameters as the inputs of ANN to generate the Rn estimates (70% of the data set for training data and 30% for model validation). The results showed that the best model performance of ANN was obtained from a 11-2-1 architecture and the sigmoid function based on the back- propagation training algorithm. The least ANN error was observed by employing 10000 iterations for the training step and two neurons in the hidden layers. The results indicated that the daily net radiation from ANN was more accurate (R2>0.95) than the previously recommended Irmak model.

The shortage of water resources with high quality is becoming an important issue in the arid and semi-arid regions. For this reason the availability of marginal quality resources such as drainage water, saline water and treated wastewater has become an important consideration. Irrigation methods with high efficiency such as drip irrigation are suitable solutions for the optimal use of these resources. This study was carried out to investigate the effects of drip irrigation management strategies with saline water on maize yield and irrigation water productivity. The experiment was performed at split plots based on randomized complete block design. The effects of three irrigation management options; mixing, one-alternate and half-alternate of three levels of saline water (4, 5 and 6 ds/m) with Karoun river on maize yield, biomass and irrigation water productivity were investigated. These parameters were measured at the end of the growing season. The results showed that the effects of management and salinity on all indices were significant in level of one percent. Investigation on interaction effects of salinity and irrigation management showed that in halfalternate yield and irrigation water productivity were not significant even in water salinity of 6 ds/m, whereas in one-alternate strategy this decrease by application of water with salinity of 5 and 6 ds/m was significant. The yield reductions per unit increase of irrigation water salinity in mixing, one-alternate and half-alternate management strategies were calculated 3.6, 7.2 and 1.7 percent, respectively.

Aggregate stability is one of the most important soil physical properties which can affect the soil disruption by raindrops. This research was conducted to study the aggregates breakdown under raindrops impact and its relationship with aggregate stability in some semi-arid region soils of Zanjan province, Iran. Thirty soils samples with three replications were taken from thirty dryfarming lands at North West of Zanjan in 2011. Aggregate samples with diameters of 6-8 mm were taken from each farm soil and put in a flat box with dimensions of 24 cm × 30 cm and 6-cm depth. The soil boxes were separately affected by four simulated rainfall events with intensity of 60 mm h-1 for 30-min duration. The amount of aggregate breakdown in each soil box under each rainfall event was then determined by comparing of the mean weight diameter (MWD) of soil aggregates before and after each rainfall event. Aggregates stability was determined using two methods: wetsieving and water-drop test. Results indicated that the amount of aggregate breakdown on the basis of MWD values significantly varied among 30 soil samples (p£ 0.001), due to rainfall impact. Aggregate breakdown had no significant correlation with the aggregate stability determined using the wet-sieving method, whereas it was negatively correlated to the aggregate stability obtained based on the water-drop test method (R2=0.29, p£ 0.05). Aggregate breakdown in the soils was significantly related to geometric mean diameter of mineral particles, gravel and organic matter (R2=0.65, p£ 0.001).

Climate change via variations in temperature pattern, precipitation and other climate variables patterns affects all the hydrologic processes. One of the main consequences of the climate change is its impacts on agricultural water use, which can cause serious challenges for water resources management. The purpose of this research was to investigate the global warming impacts on reference evapotranspiration, precipitation deficit (PD) and vapor pressure deficit (VPD) in Urmia synoptic station. To achieve this goal, using the HadCM3 global circulation model and LARS-WG5 weather generator, the minimum and maximum temperature and precipitation values for 2011-2030, 2046-2065 and 2080-2099 periods based on A1B, A2 and B1 scenarios were simulated. Then, using the forecasted parameters, the reference evapotranspiration, PD and VPD were calculated and compared with the corresponding base data (1971-2010). The results show that in each of the three periods the precipitation in the spring will be decreased but the autumn precipitation will be increased in comparison with the base period. Meanwhile, the maximum event of the precipitation will be shifted from the spring season in the base period to the autumn season in 2090. Moreover, similar to air temperature, the reference evapotranspiration, PD and VPD will be increased in 2090 and such increment will be more in the warm months than the cold months. The amounts of these parameters’ increments in the A2 scenario are more than those in the A1B scenario and also in the A1B scenario are more than those in the B1 scenario.

Protecting the outer banks of rivers bend which are usually under severe toe erosion and reducing the area of Sedimentation in inner bank are among the major goals of rivers restoration. Such goals are achieved by many techniques that have been developed over the past decades. In this study in relation with sediment management an attempt has been made to experimentally investigate in a 90 degree mild bend the use of a new measure, namely trapezoidal vane shape (TVS) attached to the bank and compare the results with the common measure results, rectangular vane shape(RVS). Both TVS and RVS were attached to the outer bank where considerable toe scour was expected (at the angle of 70o from the beginning of the bend). Vanes were installed at angles of 23, 30, 40, 60 and 70 relative to Upstream external bank. The results showed that the scour hole was formed only around the nose of TVS when the vane installation angle relative to Upstream external bank was less than 40 degrees. The scour was extended up to the outer bank for the vane installation angles (relative to Upstream external bank) more than 40 degrees. For the RVS, the scour dimensions were extended up to the outer bank for all vane angles. The maximum scour hole for the RVS was more than, up to 65%, than for the TVS in all tests. Sediment which moved from the score hole was usually deposited downstream of the vane and created a point bar. This developed point bar for TVS was closer to the outer bank than RVS.

Using permeable spur dikes is one of the controlling methods of rivers’ bank erosion. In this study, the influence of Bandal- like spur dike on the longitudinal velocity profile is investigated in nonsubmerged situation. Bandal-like is a new type of spur dike that is made of combination of permeable and impermeable spur dike. Due to its combinatorial construction, this structure has important effect on the velocity controlling and decreasing. In this study, longitudinal velocity profiles around series of Bandal-like spur dikes in 3 permeability rates of 30%, 45% and 64%, were investigated. The results indicated that this structure played an important role in controlling and decreasing the velocity in the banks due to the permeable zone. Also by increasing permeability percentage from 30% to 64%, the value of max u increased about 6% in velocity profiles.

By passing water flow through obstacles (trees in rivers, piers of bridge and any hydraulic structure), vortex flows emerge at the downstream of them and by overlapping of these emerged vortexes, shallow waves with propagation direction perpendicular to the water flow direction are formed. In this study the impact of obstacles on the formation of transverse waves has been studied. For this purpose, cylindrical and triangular obstacles were used. For the triangular obstacle, two states of collision in corner and side of it were considered. Discharges of 5, 15 and 25 L s-1 and placement of barriers in parallel position with the arrangement of 60×60, 60×120, 120×120, 180×180 (mm×mm), were considered. Totally, 36 series of experiments were carried out. The results showed that the barrier had much impact on the formation of transverse waves. The maximum amount of relative amplitude (A/H) (A: The maximum wave amplitude, H: depth of flow) for the cylindrical obstacles with 60×120 (mm×mm) arrangement in the flow rate of 5 L s-1 and the minimum amount of it for the triangular obstacles with flow hitting its corner and the flow rate of 15 L s-1 at the arrangement of 60×120 (mm×mm) were achieved with the values of 61.1% and 3.46% , respectively. Also, in order to estimate the Strouhal number as a function of P/D, T/D and N (P: distance between obstacles, D: diameter of obstacles and N: number of obstacles in each row) for desired shape, some relationships were developed using SPSS software.

In this study, a comparison between the artificial neural network (ANN) and linear regression models for estimating the dry weight of corn and its P uptake, based on the extracted P from soil by different extractants was done. For this purpose, 25 surface soil composite samples (0-30 cm) were collected from different points of East Azerbaijan province, and then corn plants (single cross 704) were cultivated in these soils under the greenhouse condition with three replications. After 60 days, the plants were harvested and the shoot dry weight and its P concentration were measured. The results showed that the coefficient of determination (r2) values between the extracted soil P, obtained by Colwel and Olsen's tests and corn shoot dry weight were 0.49 and 0.44, respectivly. The results of ANN showed that the Olsen's test for estimating the corn shoot dry weight and distiled water for estimating the shoot P concentration were supreoir. For prediction of the important indices of the corn shoot dry weigh and P uptake, based on P concentration measured using different extractions, higher values for coefficient of determination were obtained by applying some conventional methods of ANN with respect to those obtained by applying linear regression methods, so it was concluded that ANN could be used in soil P testing.

Large woody debris is transported and accumulated in front of piers by floods which increases the scour around the bridge piers and it may cause the bridge failure. In this study, the effect of woody debris accumulation on the scour around a circular pier installed on the pile cap was experimentally investigated. The experiments were performed under clear water condition with two discharges of 30 and 40 L s-1 with and without debris accumulation in front of the pier for different sizes of the woody debris. The results showed that in the case of no debris accumulation, the scour around the circular pier with pile cap was 80% less than that around the pier without pile cap. The existence of the debris in front of a pier with pile cap significantly increased the depth, width and length of the scour hole. The accumulation of this debris could increase the scour depth 12-14 times as compared with the case of no debris. In addition, a new equation was presented using dimensional analysis for prediction of the maximum scour depth in the existence of debris accumulation in front of a circular pier.

For Trapezoidal weirs most of the proposed discharge coefficient relationships have been obtained experimentally. Also, some theoretical relationships have been proposed based on ignoring the streamline curvature and considering the hydrostatic pressure distribution. In this paper, a numerical model was developed for recently proposed Boussinesq type equations which incorporated the streamline curvature with considering the non-hydrostatic pressure distribution for unsteady flow conditions. The model was employed to determine the discharge coefficient of trapezoidal broad crested weir, the results of which were compared with the compiled experimental data and with available relations. The results showed that the discharge coefficient computed by Level 4 equation, had presented higher accuracy in comparison with the experimental relation for the tested crest weirs. Also modeling these equations was easier compared to the three-dimensional models. These equations could be incorporated with the available one-dimensional of models to produce rating curves and to design water measurement structures for a continuous flume invert.

In this research, SWAP model was evaluated to estimate soybean grain yield, biological yield, leaf area index, water productivity, and available soil water content in soil profile. The sensitivity of SWAP model was analyzed based on the field results obtained from soybean planting with four furrow irrigation treatments including full irrigation, conventional deficit irrigation at 75% and 50% soil moisture deficit compensation, and partial root zone drying at 50% soil moisture deficit compensation in 2008 agronomical year. Then it was calibrated, validated and evaluated based on the field results of the agronomical year 2009. The results of this study indicated that this model simulated grain yield better than biological yield. The best and the worst simulations of soybean water productivity were obtained at partial root zone drying and conventional deficit irrigation treatments at 50% soil moisture deficit compensation, respectively. Based on calculated statistical indices in this research, the best simulations of the model that had the best fitting with the measured data, were at grain yield, water productivity, leaf area index, biological yield, and volumetric soil water content (the least RMSE and ME and the highest R2), respectively. Also the results of the model sensitivity analysis showed that SWAP model was sensitive to soil input data, i.e. residual moisture and saturated hydraulic conductivity, and with any little change in these input data, output results (the amounts of simulated parameters) varied greatly.

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.

Vehicles are of the sources of heavy metals such as lead and cadmium in the roadsides. The present study was carried out in order to investigate, changes of lead and cadmium levels in the soil and Canola caused by vehicle traffic at Saveh-Hamadan road on the basis of factorial design with complete randomized blocks. Soil and plant samples were collected at the distances of 5, 10, 20, 40, 80 and 160 meters from the road edge. The amounts of cadmium and lead were measured in root, shoot and seed of the plant and soil. The results showed that the amount of the lead decreased with increasing the distance from the road in both of the soil and plant. So that, the highest amounts of the total and absorbable lead belonged to the soil samples with the closest distance (5m) from the road, that were 38.86 and 3.79 mg kg-1, which showed an increase of 3.68% and 8.59% compared to those at the distance of 160 meters respectively. The maximum amount of soil total cadmium was 3.62 mg/ kg-1 observed at a distance of 40 meters. Also the levels of accumulation of lead and cadmium in the shoot were more than those in the root and seed sections. While the roadside soil was contaminated with cadmium, the plants were contaminated with both lead and cadmium. Therefore, livestock feeding from these plants threatens their animals and finally human health. The results of this study may be used in planning land use along the road, transportation management and urban traffic control.

The adjacency of Kashan aquifer to the saltwater front of the Salt Lake has caused a hydraulic gradient, resulting in the advancement of saltwater into the aquifer. Owing to the current situation, qualitative simulation of groundwater of Kashan plain has been implemented with Artificial Neural Network and Multi Variable Regression models in this study. For this purpose, prior to the model implementation, first we attempted to determine the dominant type of water. Results showed that the sodium chloride was the dominant type of water. Therefore, in addition to the water table fluctuations and precipitation amount, the chloride concentration in the previous year was considered as the model's input, while the output was the chloride concentration in this year. The results indicated that the MLP produced more accurate results than the RBF and MLR models, so that, the corresponding adjusted R2 values for these models were 0.97, 0.89 and 0.34, respectively. The outcomes revealed that the linear hyperbolic tangent activation function and Momentum algorithm produced better results than the other applied algorithms and functions. The resulted outcome of sensitivity analysis showed that concentration of chloride in the previous year and water table fluctuations had the most effect on the chloride concentration simulation.

Groundwater qualitative changes trend of Miandoab Plain (in the wet and dry periods) in the period of 1992-2012 was analyzed using the non-parametric modified Mann-Kendall test for lag-1 autocorrelation cofficient. The results showed that among the 25 sampling stations for 14 water qualitative variables, about 58% of the series had significant (P≤5%) increasing trend. Also 32% of them showed significant decreasing trends. The remaining 10% of the series exhibited no trend at the 5% significant level. In the case of the wet period 23.7% of the series exhibited upward significant trend and 6.3% of the series had significant decreasing trend at the 5% level. About 70% of the series showed no trend (at 10% significant level). In the dry period, 22% of the series had significant increasing trend (at 10% level), 10% with decreasing trends and 68% of them had no significant trends. The results showed that in the wet period, the steepest increasing trends of groundwater qualitative variables were observed in the west and southern part of the Miandoab Plain. The declination of groundwater level led to increasing trends for water qualitative parameters in the eastern part of the plain. The results of Sen’s slope estimator showed that, the EC and SAR had increasing trends for the both dry and wet periods. For example, the trend line slope of the groundwater EC for the wet period was equal to 20 μS cm-1 year-1.

In this study the effect of the shore green belt on reduction of wave height and energy of the attacking waves has been studied. Experiments were conducted for two patterns of rectangular and triangular arrangements with spacings of 5×5 and 10×10 (cm×cm), 3 ratios of the diameter to width; 2.10, 2.30 and 2.40, 5 shore slopes of 0, 3, 5, 7 and 10% and 5 ratios of diameter to wave heights 4.3, 2.3, 2.4, 2.6 and 2.8. The dynamic pressure was measured at several points of the shore model by a pressures transducer. The absorbed wave force by the green belt was measured directly by a system of load cell. Results showed a considerable effect of green belt on reduction of the wave height and energy. For all of the shore slopes, the maximum values of momentum absorption and wave height reduction were obtained in the 5×5 (cm×cm) triangular pattern with ratio of the diameter to width equal to 2.40. The force absorptions for the two rectangular and triangular patterns with spacing of 5×5 (cm×cm) were more than those for the patterns with spacing of 10×10 (cm×cm). The average of the force absorption ratio, between the two spacings of 5×5 and 10×10 (cm×cm), at the rectangular pattern was 1.4 and for the triangular pattern was 1.3.