Showing 45 results for Distribution
E. Sahebjalal, F. Dehghany, M. S. Tabatabaeezade,
Volume 17, Issue 65 (12-2013)
Abstract
Groundwater is the most important source of water supply for agricultural purposes in arid and semi-arid areas. In many areas, excessive use of high quality water resources leads to reducing the available water resources and turning to the use of low quality water resources. Thus, knowing the temporal and spatial variation of groundwater quality is a necessary factor for implementation of sound water resource management and establishment of the suitability between water quality and its usage. In order to investigate water quality changes, this study was divided into two phases. In the first phase, for evaluation of the quality of groundwater for irrigation 76 wells were sampled in Bahadoran plain, in the year 2006. The SAR, EC, ions B3+ and Cl- were analyzed as the evaluation indexes. Then, using geostatistical methods the maps of each parameter were prepared. Finally, considering FAO criteria, these maps were overlaid and separate water quality maps were derived. The EC map indicated that in 48 and 52 percent of the groundwater lies in severe and slight to moderate restriction class for irrigation purposes. Moreover, the thematic map of infiltration restrictions indicates that the groundwater has no restriction in 66 percent of the area while 11% of groundwater causes low to moderate and 23 percent causes severe limitation. In the next phase, to examine changes in groundwater salinity during a 5-year period, 38 wells were sampled and the groundwater salinity map for the year 2011 was prepared. Finally, using subtraction of the salinity maps of given years, the salinity changes map was derived. The results of thematic map showed that groundwater salinity increased in 26.47 percent of the study area. In contrast, there was a decrease of about 31.14 percent in groundwater salinity over the 5-year period while 42.39 percent of the region’s groundwater remained unchanged. Since the study area is under cultivation of pistachios and salt threshold of this tree is 8 ds/m so the area of about 8 percent of the area was added to the previous limited areas. Therefore, irrigation management and planting development plan in Eastern and Southeastern areas should be revised.
M. Najafi-Ghiri, H. R. Owliaie,
Volume 18, Issue 69 (12-2014)
Abstract
Although addition of amendment materials to soil is not for changing of soil K status, secondary effects of these materials can be important in K distribution among soluble, exchangeable and non-exchangeable forms. In this research, effect of addition of 2% zeolite, 2% vermicompost and 1% zeolite+ 1% vermicompost on 10 calcareous soils of Fars province belonging to five orders was investigated. The experiments were done as a randomized complete block with three replicates. Samples were incubated at 22±2 °C and 50% of saturated moisture content for 90 days. Then different forms of K were determined in the samples. Zeolite application induced 279 mg kg-1 increase in exchangeable K and 24 mg kg-1 decrease in non-exchangeable K, but it had not a significant effect on soluble K. Although vermicompost application increased soluble and exchangeable K, its effect was more sensible for soluble K (139 mg kg-1). Zeolite+vermicompost application increased all forms of K. Increase in soluble K with vermicompost application may increase risk of K leaching but zeolite application can preserve K in exchangeable phase and inhibit K leaching and fixation.
F. Jafari, H. Khademi,
Volume 18, Issue 70 (3-2015)
Abstract
Dust deposition occurs extensively in arid and semiarid regions of the world. Since dust particles are fine-sized, they have a high adsorption capacity and also high contamination potential. The objective of this study was to evaluate the temporal and spatial distribution of the rate of atmospheric dust deposition in different locations in Kerman urban area. Dust samples were collected monthly using glass traps installed on the roof of 35 one-story buildings in Kerman for 7 months from April 20 to Nov. 20, 2012 (a total of 245 samples). After each monthly sampling, traps were washed and dust samples transferred to the laboratory and weighed. The mean dust deposition rate of 7 months was mapped using the inverse distance weighting (IDW) approach. The wind rose of Kerman was drawn by WRPLOT 7.0.0. The results showed that the average rate of dust deposition decreased during the 7 months studied from 17.4 to 5 g/m2. month, which could be attributed to the decrease in wind velocity. The spatial distribution of the samples also showed that the dust deposition rate varied from 4.84 in the southern parts to 14.84 g/m2.month, mostly in the northern locations of the city. The wind rose based on the average wind speed of the 7 months of sampling indicated the prevailing wind blows from north, northeast and northwest and the dust spatial distribution well follows the wind direction. In general, the rate of dust deposition in Kerman city is high and therefore, the source of dust has to be well detected and proper management practices are necessary.
H. Beigi. Harchegani, G Banitalebi,
Volume 18, Issue 70 (3-2015)
Abstract
Texture fractal dimension is a physical index to describe soil particle size distribution having a variety of applications. Fractal dimension may be calculated from three relations of mass-time, mass-diameter and modified mass-diameter (Kravchenko-Zhang) with two linear and nonlinear options for fittings. The aim of the present study was to compare methods and select an appropriate one and fitting option for determining the fractal dimension using hydrometer data. Sixty soil samples were collected from four fields of Taqanak, near Shahrekord. After removal of organic matter and other initial treatments, hydrometer readings were obtained at 0.67, 1, 2, 5, 15, 30, 60, 120, 180, 1440 and 2880 minutes and were converted to mass-time or mass-diameter data. Nonlinear fitting of the Kravchenko-Zhang mass-diameter relation was selected as the most appropriate method of calculating the fractal dimension of solid particles, due to its highest coefficient of determination and smallest mean square error and lowest Akaike Information Criteria. Error analysis also confirmed this conclusion. There was a significant, though not very strong, relationship between the fractal dimension obtained by linear and nonlinear fitting of mass- diameter and Kravchenko-Zhang mass-diameter methods. These relationships can be used to correct the fractal dimension determined by other methods and fitting options.
S. Norouzi, H. Khademi,
Volume 19, Issue 72 (8-2015)
Abstract
Spatial and temporal distribution of dust deposition rate (DDR) in Isfahan city and the influencing climatic parameters were studied. Dust samples were collected using glass trays placed on the roof of one-story buildings from 20 sites in Isfahan city for 12 months. Climatic data were obtained from Meteorological Organization and analyzed. The highest and the lowest amount of DDR in agreement with the direction of prevailing wind were observed for dry months with eastern and northeastern wind directions and wet periods with western and southwestern wind directions, respectively. This can indicate dust emission from the desert located in eastern part of Isfahan city. Statistically significant inverse correlation between DDR and precipitation and relative humidity, and significant and positive correlation of DDR with Min and Max temperatures in all the studied months and also with Max and average wind speed for dry sampling months may well justify the temporal distribution of DDR in the city. In dry months, finer particles from eastern desert can be transported a longer distance and deposited in the western part of the city, far from the source area. In wet seasons, however, soil aggregates become coarser as a result of particle adhesion. This, in turn, results in the deposition of dust near the source area as the transporting power of dust reduces.
V. Rahmatabadi , M. Behzad, S. Borumandnasab , H. Sakhaei Rad,
Volume 19, Issue 73 (11-2015)
Abstract
In order to increase the distribution uniformity of sprinkler irrigation systems, some influential parameters such as wind speed, arrangement, space and type of sprinklers must be studied and controlled. In this study, a set of experiments were conducted based on ISO 7749/2(1990) standard to evaluate the ADF 250 and Nelson, F80APV sprinklers. To study the effects of wind velocity, operating pressure, various sprinkler layouts and spacing on water distribution uniformity, the experiments were conducted based on a single sprinkler method. Four operating pressures in the range of one recommended by the manufacturer for each sprinkler were applied and three sprinklers’ spaces on lateral pipelines (22, 26, and 30 m) were simulated for square and rectangular layouts to estimate the water distribution uniformity. Results showed that the distribution uniformity of Nelson sprinkler in existing wind velocities and operating pressures had smaller changes than ADF sprinkler. The 4.5 bar pressure for ADF sprinkler was better than other pressures, and operating pressures for Nelson sprinkler did not have any significant effect on distribution uniformity. With the decrease of sprinkler spacing to the wetting diameter in the simulated space, uniformity coefficient was increased. The recommended sprinkler spacing to the wetting diameter for these sprinklers ranged from 0.4 to 0.5 for square and rectangular layouts.
A. Khosravi-Dehkordi, M. Afyuni, A. Soffianian,
Volume 20, Issue 77 (11-2016)
Abstract
Pollutants are considered the disturbing factors of environment, and among them the heavy metals are more important considering their non-degradability and physiological effects on organisms in low concentrations. The goal of this research was to investigate the effect of industrial landuse on Cd and Pb concentrations in surface soils of the southwest Isfahan. According to satellite images and topographic maps (1:50000) of the study area, soil samples (depth: 0–20 cm) were collected using random sampling. A total of 38 surface soil samples were obtained from industrial areas (lowest distance = 1480 m) in the area of 73481 ha. Total concentrations of Cd and Pb in the digested solution were measured by Atomic Absorption Spectrophotometry (AAS). Using Arc GIS, the spatial distribution patterns and Cd and Pb variography of samples were analysed and finally the best models of spatial distribution of heavy metals were achieved. The primary results showed that the mean concentrations of Cd, and Pb of surface soil samples in industrial areas were 1.8 to 31.5 mg Kg-1 higher than the world’s mean values, respectively. Although the mean concentrations of Cd and Pb were respectively 8 to 700 mg Kg-1 lower than the standard of Iranian Department of Environment for industrial landuse.
H. Saghi,
Volume 21, Issue 1 (6-2017)
Abstract
The water supply networks have always been of significance to researchers as a hydraulic system of transferring and distributing water. The pressure gradient is the main reason of water transfer in networks, and in case of non-standard pressure increase, the undesirable phenomenon of leakage occurs in the network. Leakage in urban water distribution networks causes water waste and enormous financial losses. Therefore, there exists the need to manage and minimize the amount of leakage. In this study, a water distribution network is modeled using the potentialities of hydraulic analysis model, the EPANET 2.0, and, by presenting a new model, the leakage location is recognized. In order to do this, we, firstly, entered all the network parameters into the software. Then, the network was analyzed supposing the non-occurrence of leakage and the amounts of nodal pressures were measured. Moreover, the nodal pressures were estimated by creating a hypothetical leakage in one of the network nodes and analyzing the network. Finally, the position of leakage was determined by defining the leakage index and comparing it in various nodes. The results show that the suggested method is efficiently capable of predicting the leakage position in the network so it can safely replace other methods, especially destructive methods used in recognizing the leakage position in the network.
A. R. Vaezi, Z. Bayat, M. Foroumadi,
Volume 22, Issue 2 (9-2018)
Abstract
Soil erosion by surface runoff introduced as surface erosion is one of the main mechanisms of land degradation in the hill slopes. Slope characteristics including aspect and gradient can control the differences of soil properties along the hillslope. This study was conducted to investigate the effect of slope aspect and gradient on variations of some soil properties in the short slopes. Five hills including both north and south aspects with different gradients (9-10%,
13-16%, 17-22%, 29-31% and 33-37%) were considered in a semi-arid region with 30 ha in area, in the west of Zanjan, northwest of Iran. The hills were weakly covered with pasture vegetation covers. Soil samples were collected along the slopes from two depths (0-5 cm and 5-15 cm) in four positions with 2 m distance along each slope with two replications. A total of 160 soil samples were analyzed for particle size distribution (sand, silt and clay), gravel and bulk density. Surface erosion was determined based on the variation of grain size distribution and bulk density. Differences of the grain size distribution and surface erosion between the two slope aspects and among the slope gradients were analyzed using the Tukey test. No significant difference was found between slope aspects in surface soil erosion. Nevertheless, surface soil erosion was affected by slope gradient in each slope aspect (R2= 0.78, p< 0.05). Surface erosion in the north slopes was more dependent on the slope gradient, as compared to the corresponding south slopes. In the south slopes, surface erosion was affected by the movement of silt particles from soil surface, while in the north slopes, it was significantly affected by the loss of clay particles.
M. A. Geranmehr, M. R. Chamani, K. Asghari,
Volume 22, Issue 3 (11-2018)
Abstract
A water distribution network (WDN) may not be able to satisfy all required demands when it’s in the pressure deficit mode or under over-loaded demand conditions. Analysis of the network in this mode requires pressure dependent analysis (PDA). Unlike demand driven analysis (DDA), PDA needs an extra equation for every node to relate the nodal demand and the nodal pressure; so it should be solved with the other network’s equations simultaneously. In this paper, based on the Particle Swarm Optimization (PSO) algorithm, a decision support system has been developed by using MATLAB and EPANET for PDA simulation in WDNs. A four-loop network selected from the literature was analyzed using different scenarios and different pressure dependent functions presented by the previous investigations. The results showed that the proposed model (PSO-PDA) was as accurate as the previous ones and provided better convergence. The results of the nodes’ pressure and discharge also indicated minor differences obtained by different PDA functions. However, the differences between the results of PDA and DDA were considerable.
A. Cheraghi Tabar, E. Adhami, H. R. Owliaie,
Volume 22, Issue 4 (3-2019)
Abstract
The present study was conducted to evaluate zinc availability and forms, as well as their relationships with soil properties in some soil samples of Kermanshah and Ilam provinces. Sequential extraction included Mg(NO3)2 (soluble + exchangeable), NaOAc pH = 5 (carbonatic fraction), Na-hypochlorite at pH = 8.5 (organic fraction), hydroxylamine hydrochloride at pH 2 (Mn oxides associated Zn), hydroxylamine hydrochloride (amorphous Fe oxides associated Zn), ammonium oxalate (crystalline Fe oxides associated Zn), and HNO3 (the residual Zn). DTPA-Zn was in the range of 0.34-3.7 mg/kg. The results showed that soluble+ exchangeable, Mn oxides and crystalline Fe oxides associated Zn were not detectable by atomic absorption. Distribution of Zn fractions was in the order of Organic-Zn < Car-Zn < amorphous Fe oxides-Zn < Res-Zn. Organic matter bound Zn and amorphous Fe oxides associated Zn and the residual fractions showed a significant negative correlation with the calcium carbonate equivalent. It seemed s that calcium carbonates were the major factor in controlling the Zn content in the studied soils.
N. Sadeghian, A. Vaezi,
Volume 23, Issue 2 (9-2019)
Abstract
Sediment selectivity during transport may provide basic information for evaluating on-site and off-site impacts of the soil erosion. Limited information is, however, available on the selectivity of sediments in rill erosion, particularly in the rainfed furrows. Toward this, the sediment selectivity was investigated in three soil textures (loam, loamy sand sand clay loam) under 10% slope using 90 mm.h-1 rainfall intensity for 40 min. Soil samples were passed from a 10 mm sieve and packed in to the erosion flume with 0.4m × 4 m in dimensions. Particles size distribution (PSD) was determined in the sediments (PSDs) and compared with the original soil PSD (PSDo). The proportion of PSDs and PSDo was stated as PSDs/PSDo to show the selectivity of soil particles by rill erosion. Based on the results, all three soils appeared as the coarse particles (coarse sand and very coarse sand) in sediments with the PSDs/PSDo>1, indicating the higher selectivity of these particles by rill erosion. Loamy sand was the most susceptible soil to rill erosion among the studied soils, which generated a higher runoff (0.0035 m2.s-1) and sediment load (0.1 kg.m-1.s-1) during rainfall. The PSDs of this soil were similar to those of the original soil PSD. This study revealed that the stability of aggregates could be regarded as the major soil factor controlling rill erosion rate and the sediment selectivity in the semi-arid soils. With an increase in the water-stable aggregates, soil infiltration rate and as a consequence, shear stress of flow could be decreased in the rills.
Z. Amiri, M. Gheysari, M. R. Mosaddeghi, M. S. Tabatabaei, M. Moradiannezhad,
Volume 23, Issue 2 (9-2019)
Abstract
Location of soil moisture sampling in irrigation management is of special importance due to the spatial variability of soil hydraulic characteristics and the development of root system. The objective of this study was determination of the suitable location for soil moisture sampling in drip-tape irrigation management, which is representative of the average moisture in the soil profile (θavg) as well. For this purpose, soil moisture distribution (θij) at the tassel stage of maize and one irrigation interval (68-73 day after plant) were measured at the end of season. The results showed more than 70% length of the root of plant was located in 30 cm of the soil depth. By accepting ±10% error in relation to the averaged soil moisture, some region of soil profile was determined which was in the acceptable error range and also near the averaged soil moisture (0.9θavg<θRec<1.1θavg). By overlapping θRec in one irrigation interval, the appropriate location for soil moisture sampling was the horizontal distance from drip-tape line to 20 cm and the depth of 10-20 cm from the soil surface. To determine the appropriate place for soil moisture sampling, the development of root system and the maximum concentrated root length density in the soil profile extracting the maximal soil moisture should be taken in to account, parallel with the averaged soil moisture.
S. Z. Kiani Harcheghani, A. R. Hosseinpur, H. R. Motaghian,
Volume 23, Issue 2 (9-2019)
Abstract
Adsorption is one of the most important processes controlling the concentration of zinc (Zn) in the soil solution. The presence of nutrient anions in the solution can affect Zn2+ adsorption. In this study, the effect of orthophosphate, nitrate and chloride anions on the Zn2+ adsorption in five calcareous soil samples of Chaharmahal-va-Bakhtiari province was investigated. In order to study the Zn adsorption isotherms, solutions containing 25, 50, 75, 100, 150 and 200 mg/L Zn of ZnSO4 source were used in KH2PO4, KNO3 and KCl electrolytes (electrolytes concentration equal to 50 mM). The Freundlich, Langmuir, and linear equations were used to investigate the ability to describe the Zn adsorption. Based on the results, the Freundlich and Langmuir equations could describe the Zn adsorption. The results of this study showed that Zn in the presence of orthophosphate anion had the maximum adsorption capacity and an adsorption intensity higher than that of chloride and nitrate anions; meanwhile, in comparison with nitrate and orthophosphate anions, adsorption energy (k), maximum buffering capacity (MBC), and distribution coefficient (kf) in the presence of chloride anion were higher (p< 0.05). The results of this study, therefore, showed that in the presence of anion orthophosphate, Zn adsorbed more intensity and strongly, while adsorption energy was less than the presence of the other two anions. Therefore, it could be concluded that Zn and phosphate fertilizers should not be applied together in the soil.
S. Barkhordari, M. Hashemy Shahdany, A. Bagherzadeh Khalkhali,
Volume 23, Issue 3 (12-2019)
Abstract
Seepage losses and poor operational activities are the two main source of water losses throughout the agricultural water conveyance and distribution systems in irrigation districts. This study aims to investigate the performances of two strategies of “canal lining” and employing the “Canal Automation” in order to reduce the losses mentioned above. The investigation was carried out on a couple of main canal reaches of Moghan Irrigation Districts. Two numerical models were simulated by Seep/w software to compare the seepage rate between the canal with and without concrete lining. The results reveal that the ability of concrete lining to reduce seepage losses along the canal is about 10%. Performance assessment of the “Canal Automation” strategy to minimize operational losses within the main canal was carried out employing Model Predictive Control (MPC). The results of the latter strategy indicate that employing the MPC not only reduces the operational losses along the canal by 15% but also improves the operation of the main canal so that the minimum efficiency and adequacy performance indicator was obtained 100% and 83% respectively. Therefore; due to Executive considerations and financial constraints in the same cases, the potential of each of the two strategies can be considered to reduce the conveyance and distribution losses and ultimately choose the most suitable option.
Y. Dinpashoh, E. S. Alavi,
Volume 23, Issue 4 (12-2019)
Abstract
Identifying the rainfall characteristics and understanding the rainfall-related processes is one of the key factors in the scientific management of water resources. Selection of the design storm is the first step in the estimation of the design flood. Determining temporal rainfall patterns is very important as one of the design rainfall properties in flood estimation and the design of drainage systems. This study was concerned with the pattern of rainfall depth during its occurrence at the Dez dam station. In order to plot Huff curves in the Dez dam station, the recorded data of the rain gauge was used. For this purpose, all 280 storms from 1972 to 2016 in different seasons were classified into the five distinct classes including i) 0-2 hours, ii) 2-6 hours, iii) 6-12 hours, iv) 12-24 hours, and v) more than 24 hours. Furthermore, for each class and in each of the seasons, the Huff curves were plotted using all storms information single class. Moreover, for the considered station, all recorded events were considered in a single class and the general Huff curve was plotted using the probability of 50%. In general, the highest number of storms in the Dez dam (about 32.9%) was grouped in the second quartile. However, it was about 55, 48.5 and 50.4 percent in the case of short storms (0-2 hours) for spring, autumn and winter, respectively. In contrast, low percentages were obtained for the rainfalls having long durations. The Logistic equation was extracted for all Huff curves. These curves would be useful in efficient water resources management. The value of the correlation coefficient between the amounts obtained from the Logistic model and the corresponding values extracted from the curves was more than 0.99, which was significant in 1 percent.
A. Kaghazchi, S. M. Hashemy Shahdany, A. Roozbahany, M. E. Banihabib,
Volume 24, Issue 3 (11-2020)
Abstract
The main purpose of the study is the operational simulation of main irrigation canal and evaluation of water delivery and distribution locally, regionally and overall using adequacy, efficiency, and equity indicators and “Desirability of water delivery and distribution” indicator. To achieve this goal, the hydrodynamic model of Roodasht irrigation network’s main canal was developed. The results of the calibration and validation of the hydrodynamic model showed that the two processes were satisfactory. All available scenarios including normal, water shortages and fluctuations were considered for water delivery and distribution in different conditions. In the local assessment, the adequacy varied from 7 to 85%, and the efficiency in all scenarios was 100%. The adequacy, efficiency, and equity indicators in the regional evaluation varied from 6 to 89, 91 to 100, and 13 to 46%, respectively. The overall evaluation of the canal showed that the most desirable situation is related to a harsh fluctuation increasing with the adequacy, equity and efficiency indicators equal to 82, 23 and 91%, respectively. Calculation of the “Desirability of water delivery and distribution” indicator showed poor performance in all operational scenarios except harsh fluctuation scenario with 82% of which, the canal performance was estimated in fair level.
N. Shahabinejad, M. Mahmoodabadi, A. Jalalian, E. Chavoshi,
Volume 24, Issue 3 (11-2020)
Abstract
Wind erosion is known as one of the most important land degradation aspects, particularly in arid and semi-arid regions. Soil properties, by affecting soil erodibility, can control the wind erosion rate. The aim of this study was to attribute the soil physical and chemical properties to the wind erosion rate for the purpose of determining the most important property. To this aim, wind erosion rates were measured in-situ at 60 points of Kerman province using a portable wind tunnel facility. The results indicated that wind erosion rates varied from 0.03 g m-2 min-1 to 3.41 g m-2 min-1. Threshold wind velocity decreased wind erosion rate following a power function (R2=0.81, P<0.001). Clay and silt particles, shear strength, mean weight diameter (MWD), surface gravel, dry stable aggregates (DSA<0.25mm), soil organic carbon (SOC), calcium carbonate equivalent (CCE) and the concentrations of the soluble Ca2+, K+ and Mg2+ were inversely proportional to the wind erosion rates following nonlinear functions. On the other hand, Wind erosion was significantly enhanced with increasing the sand fraction, soluble Na+, electrical conductivity (EC) and sodium adsorption ratio (SAR). According to the final results, among the studied soil properties, SAR and MWD were s the most effective properties controlling wind erosion in the soils of Kerman province. Therefore, it is recommended to consider suitable conservation practices in order to prevent the sodification and degradation of arid soils.
E. Moradi, D. Namdar Khojasteh,
Volume 24, Issue 4 (2-2021)
Abstract
Wind erosion is one of the environmental problems worldwide, particularly in arid and semi-arid areas of Iran. Different methods and models have been proposed to measure and monitor wind erosion in the recent years. One of the accurate models for measuring f wind erosion is the USEPA model. The purpose of this study was to evaluate the quantification of wind erosion with the USEPA model and the comparison of different interpolation methods for drowsing high-precision soil erosion mapping. For this purpose, 50 samples from 0-30 depth were taken from the study area. Based on the analysis of the physical properties of the soil, including the distribution of the primary and secondary particle sizes, climatic parameters such as evaporation and transpiration, rainfall, wind speed and also, the vegetation and topography characteristics of the area, the erosion rates of Q, Q30 and Q50 were measured. Interpolation methods including general kriging, IDW, LPI and RBF were compared. The results showed that the highest erosion emission rate of Q50 was 39 ton ha-1. The highest and lowest erosion rates for the Q30 index were 0.060 and 2.694 ton ha-1, respectively; for the Q index, the highest and lowest erosion rates were 0.009 and 0.055 ton ha-1, respectively. The results also showed that the IDW method for the Q50 index with the minimum error rate (RMSE) values of 3.94 and the mean absolute error (MAE) with the valueof 1.89 had the best performance among the studied models. The LPI model Q had the best performance with the lowest error (0.0086) and absolute absolute error (0.0021).
Z. Savari, S. Hojati, R. Taghizadeh Mehrjerdi,
Volume 25, Issue 3 (12-2021)
Abstract
Soil salinity and its development are the main problems that should be prevented by correct management methods. Recognition of saline districts and the preparation of salinity maps are the first steps in this way. Nowadays, the application of auxiliary data in digital soil mapping is increasing due to the current associated problems in the preparation of traditional maps. The objectives of this study were to map soil salinity by the Regression Kriging (RK) method, to identify areas with high salinity, and to investigate the relationship between soil salinity and soil-forming factors in Khuzestan Province. For this purpose, 291 surface soil samples (0-10 cm) were randomly collected in April 2014. Auxiliary variables or soil-forming factors were included in the land parameters such as slope, watershed and wetness index, OLI and TIRS images of Landsat 8, and the category maps (soil, land use, and geological maps). Also, kriging approaches were used to compare the precision of different mapping methods. The results indicated that the Regression Kriging method has a higher precision compared with other methods so that the coefficient of determination, Mean Absolute Error (MAE), and Root Mean Square Error (RMSE) were estimated as 0.84, 0.41, and 6.21, respectively. The Decision Tree Regression method could also create a good relationship between soil salinity and auxiliary variables. The results showed that some auxiliary variables were more effective on the prediction of soil salinity including 2, 4, 5, and 7 bands of Landsat 8, Brightness Index, Wetness Index, Multiresolution index of Valley Bottom Flatness (MrVBF), Channel Network Base Level (CNBL), NDVI, SAVI and soil map. A Digital map of soil salinity was prepared by the obtained rules, and then it was assimilated with the map of error of variance to prepare the final soil salinity map. Accordingly, soil salinity was found to have an increasing trend from north to south in Khuzestan Province which indicates a salinity problem in the south of the Province. The main reasons for the high salinity in the south and southwestern parts of the area could be attributed to the high water table levels, differences in topography, capillary movement of salt to the soil surface, the difference in the type of land uses, and also groundwater quality and irrigation water which is altered by the frequent application of wastewaters and animal manures.
