جستجوی مقالات مرتبط با کلیدواژه « sodic soils » در نشریات گروه « آب و خاک »

Over the last few years, due to the depletion of Lake Urmia located in the northwest of Iran, the proportion of surrounding saline agricultural lands increased at a fast pace. Digital mapping of regional soils affected by salt is essential when monitoring the dynamics of soil salts and planning land development and reclamation schemes. The soil hydraulic and mechanical parameters are very important factors that affect water and chemical transport in soil pores. In the salt-affected soils, saturated hydraulic conductivity (Ks) is very low due to the high contents of sodium and weak aggregate stability. Penetration resistance (PR) indicates soil mechanical strength to penetration of a cone or flat penetrometer; it is important in seedling, root growth and tillage operations. Generally, PR values exceed 2.5 MPa, while root elongation is significantly restricted. The analysis of spatial variability of Ks and PR is essential to implement a site-specific soil management especially in the salt-affected lands. The objective of this study was to evaluate the influence of two different bare and agricultural land uses on the spatial variability of Ks and PR in the salt-affected soils around Lake Urmia.   This study was conducted in the agricultural and bare lands of Shend Abad region located at the 15 km of Shabestar city, northwest of Iran (45° 36ʹ 34ʺ to 45° 36ʹ 38ʺ E and 38° 6ʹ 37ʺ to 38° 7ʹ 42ʺ N). Totally, 100 geo-referenced samples were taken from 0-10 cm soil depth with 100×100 m intervals (80 ha) in agricultural (n=49) and bare (n=51) land uses. Sand, silt, clay, organic carbon (OC), mean weight diameter of aggregates (MWD), sodium adsorption ratio (SAR) and electrical conductivity (EC), were measured in the collected soil samples. The EC and SAR were measured in 1:2.5 (soil: distilled water) extract. Ks was measured using constant or falling head method. Bulk density (BD) and field water content (FWC) were measured in the undisturbed soil samples taken by steal cylinders with 5 cm diameter and height. Total porosity calculated from BD and particle density (PD). PR was directly measured at the field using a cone penetrometer. The best fit semivariograms model (Gaussian, spherical and exponential) was chosen by considering the minimum residual sum of square (RSS) and maximum coefficient of determination (R2). Ordinary Kriging (OK) and inverse distance weighting (IDW) interpolation methods were used to analyze the spatial variability of Ks and PR. Spatial distribution maps of soil variables were provided by Arc GIS software. The accuracy of OK and IDW methods in estimating Ks and PR was evaluated by mean error (ME), mean absolute error (MAE), root mean square error (RMSE) and concordance correlation coefficient (CCC) criteria.The CCC indicates the degree to which pairs of the measured and estimated parameter value fall on the 45° line through the origin.     According to coefficient of variation (CV) from the study area, the most variable soil indicator was Ks (CV=155.6%), whereas the least variable was PD (CV= 3.05%) both in bare land use. The Lognormal distribution was found for Ks data in the studied region. The Pearson correlation coefficients (r values) indicated that there are significant correlations between Ks and OC (r=0.36), sand (r=0.60), SAR (r=-0.35), EC (r=-0.22), BD (r=-0.52), TP (r= 0.31), silt (r=-0.60), and clay (r=-0.43). Also, significant correlations were obtained between PR and FWC (r=-0.32), BD (r=0.21), and TP (r=-0.21). The spatial dependency classes of soil variables were determined according to the ratio of nugget variance to sill expressed in percentages: If the ratio was >25% and <75%, the variable was considered moderately spatially dependent; if the ratio was >75%, variable was considered weakly spatially dependent; and if the ratio was <25%, the variable was considered strongly spatially dependent. The strong spatial dependences with the effective ranges of 2443m were found for Ks. The PR and PD variables had the least (335 m) and the highest (2844 m) effective range, respectively. The range of influence indicates the limit distance at which a sample point has influence over another points, that is, the maximum distance for correlation between two sampling point. The models of fitted semivariograms were spherical for Ks and exponential for PR. According to RMSE and CCC criteria, there was not found significant difference between Ks estimates by OK and IDW interpolation methods. The high CCC and low RMSE values for OK compared with IDW indicated the more precision and accuracy of OK in estimating PR in the studied area. Generally, the spatial maps showed that from agricultural to bare land use by nearing to Lake Urmia, the BD and PR increased and consequently TP and Ks decreased. The results showed that Ks negatively related to the SAR, EC, BD, silt and clay and positively related to the OC, sand, MWD and TP in the study area. Also, PR negatively related to the FWC and TP and positively related to the BD and silt. The spatial dependency was found strong for Ks. The PR revealed the smallest effective range (335 m) among the studied variables. As a suggestion, for subsequent study, soil sampling distance could be taken as 335 m instead of 100 m in order to save time and minimize cost.

Seepage reduction in earth canals is a practical way for maintaining available water resources. The use of proper and inexpensive materials is a practical way for decreasing seepage losses in canals. Experiments showed that seepage in small channels and field canals is usually more than conveyance canals. One of the most important factors for determining seepage rate is permeability of constituent materials of bed and sidewall of canal, which depends on porosity size. Smaller porosity size results in less permeability, which is proportion to squared diameter of the porosity USBR (1963).
Garg and Chawla (1970) showed the seepage rate is high in unlined canals.
Aylward and Newton (2006) determined water losses rate to be 25% in an earth canal with 82 km length and found water losses volume to be 11.9 million cubic meter along a period of 210 days of irrigation season. The results showed that water losses decreased by 30% through 45% by controlling seepage and also water losses in the canal are directly proportional to permeability.
The purpose of this research is to introduce an economic lining in order to reduce seepage losses of four-degree irrigation canals and increase their water conveyance efficiency. Hence, it is recommended to use sodium carbonate and sugarcane and sugar beet factory waste instead of use of heavy machinery for compacting of soil

Salinity and sodicity are the most important land degradation problems particularly in arid and semi-arid regions. Due to the depletion of Urmia Lake located in the northwest of Iran during recent years, the proportion of surrounding saline agricultural lands increased at a past pace. In the salt-affected soils, aggregate stability is weak due to the high contents of sodium. The analysis of spatial variability of mean weight diameter of aggregates (MWD) and sodium adsorption ratio (SAR) is necessary to implement a site-specific soil management especially in the salt-affected soils. The main object of this study was evaluating the effects of different land uses (bare and agriculture) on the spatial variability of MWD and SAR in the salt-affected soils around Urmia Lake. This study was conducted in the agricultural and bare lands of Shend Abad region located at the 15 km of Shabestar city, northwest of Iran (45° 36ʹ 34ʺ E and 38° 6ʹ 37ʺ N). Totally, 100 georeferenced
samples were taken from 0-10 cm soil depth with 100×100 m intervals (80 ha) in agricultural (n=49) and bare (n=51) land uses. Sand, silt, clay, organic carbon (OC), CaCO3, pHe, MWD, SAR and electrical
conductivity (EC), were measured in the collected soil samples. Thewet sieving method was used to determine MWD of wet aggregates. The sieves were: 2, 1, 0.5, 0.25 and 0.106mm. The EC and SAR were measured in 1:2.5 (soil: distilled water) extra. The SAR was calculated from concentrations of Na+ and Ca+ + Mg+. The best fitsemivariogram model (Gaussian, spherical and exponential) was chosen by considering the minimum residual sum of square (RSS) and maximum determination coefficient (R2). Ordinary kriging (OK) and inverse distance weighting (IDW) interpolation methods were used to analyze spatial variability of MWD and SAR. Spatial distribution maps of soil variables were provided by Arc GIS software. The accuracy of OK and IDW methods in estimating MWD and SAR was evaluated by mean error (ME), mean absolute error (MAE), root mean square error (RMSE) and concordance correlation coefficient (CCC) criteria.The CCC indicates the degree to which pairs of the measured and estimated parameter value fall on the 45° line through the origin. According to the results of coefficient of variation (CV) from the study area, the most variable (CV=113.05%) soil indicator was SAR (bare land use), whereas the least variable (CV= 3.52%)
was pHe (agricultural land use). The Pearson correlation coefficients (r value) indicated that there are significant (P <0.01) correlations between MWD with OC (r=0.58), sand (r=0.60), SAR (r=-0.57), EC (r=-0.56), CaCO3 (r=-0.38) and clay (r=-0.48). Also, negative correlations (P <0.01) were observed between SAR with sand (r=- 0.61), OC (r=-0.38) but positive correlations (P <0.01) were found between SAR with EC (r=0.61), pHe (r=0.56), CaCO3 (r=0.40) and Clay (r=0.62). The spatial dependency classes of soil variables were determined according to the ratio of nugget variance to sill expressed in percentages: If the ratio was >25% and <75%, the variable was considered moderately spatially dependent; if the ratio was >75%, variable was considered weakly spatially dependent; and if the ratio was <25%, the variable was considered strongly spatially dependent. The strong and moderate spatial dependences with the effective ranges of 1903 and 1614m were found for SAR and MWD,
respectively. The OC and EC variables had the least (660m) and the highest (1987m) effective range, respectively. The range of influence indicates the limit distance at which a sample point has influence over another points, that is, the maximum distance for correlation between two sampling point. The models of fitted semivariograms were Gaussian for both MWD and SAR. The best prediction according to CCC criterion was obtained by OK for SAR (0.382) and IDW (^2) for MWD (0.325). The spatial maps showed that from agricultural to bare land use by nearing to Urmia Lake, the MWD decreased by decreasing OC and increasing EC and SAR. Results showed that MWD negatively related to the SAR and EC and positively related to the OC and sand in the study area. The SAR correlated positively with EC and Clay and negatively with sand andOC. The spatial dependency was found strong for SAR and the moderate for MWD. The soil OC showed the smallest effective range (660m) among the studied variables. As a suggestion, for subsequent study, soil sampling distance could be taken as 660m in order to save time and minimize cost.

Soil micromorphology is a branch of soil science which studies undisturbed soil samples using microscopic methods and the image analysis technique can promote speed, accuracy and ability of micromorphic studies. Soil pores due to their effect on the most of processes and properties of soils and also on interaction between soil, water and plant, have spacial importance. In this study, soil pores type and total porosity of saline-sodic soils were studied using micromorphic and Image Analysis techniques in a transect composed of eight soil profiles in the west of Urmia Lake. According to microscopic observations, pore types in these soils were vughs, channels and planar voids but Voids size and frequency in different horizons of each profile and all eight profiles were different. Average values of vughs, channels and planar voids in each thin section were about 45- 50%, 35-45% and 5-25%, respectively. Comparison between thin section description and Image Analysis showed that frequency and the range of size of pores in Image Analysis technique was greater than that of thin section description. The differences of measured total porosity between Image Analysis and thin section description in profiles 1 to 4 were 10.7, 7.83, 6.7 and 9 percent respectively. The reason of this difference is that, in thin section description technique, some of voids are too small, so they cannot be seen and are not measurable, whereas, in Image Analysis technique the measurement of size and frequency of voids were based on the number of pixels and this leads to greater values in Image analysis technique.

In order to comparision of the micromorphic properties of saline-sodic and nonsaline-nonsodic soils in the west of Urmia Lake, four soil profiles (2profile in saline-sodic soils and 2profiles in nonsaline-nonsodic soils) were investigated. These profiles were described and sampled using standard methods. soil samples were used for physico chemical analysis and undisturbed and oriented samples were used for thin section preparation. Thin sections were studied using polarizing microscope in PPL and XPL lights. Thin sections studies showed that saline-sodic soils are structure less (apedal), and their voids are mostly vughs and channel and as a result, their, nonsaline-nonsodic soils are pedal with compound packing voids, vughs and planar voids and as a result, The b.fabric in these to group of soils is crystallitic. In saline sodic soils pedofeatures are illuvial clay coatings, salt accumulations including coatings and infillings of halite in channel and vughs. These pedofeatures were not seen in nonsaline-nonsodic soils. Organic coatings were seen as black colored films on peds and in some cases mixed with groundmass of saline-sodic soils.Calcium carbonate accumulations as nodules and coatings and nodules and coatings of iron and Mn oxides were seen in both saline-sodic and nonsaline-nonsodic soils.

Micromorphology is the branch of soil science that is concerned with the description, interpretation and, to an increasing extent, the measurement of components, features and fabrics in soils at microscopic level. The advantage of micromorphology is that, in micromorphological studies the soils are studied in their natural and undisturbed form and so, one can follow the processes that take place in a low rate. In this research, in order to study the micromorphic properties of saline-sodic soils in the west of Urmia Lake, four soil profiles were studied. The profiles were described and classified using standard methods. Disturbed soil samples were used for physic-chemical analysis and thin sections were prepared from undisturbed and oriented samples and were studied using polarizing microscope. According to the results, the most of studied soils were apedal and their voids were mainly vughs and channels. These soils were vughy, channel and massive microstructure and their b-fabric were mainly crystallitic. The micromorphic pedofeatures in these soils were illuvial clay coatings, accumulations salts as discontinues coatings of cubic and suhedral halite crystals on voids and aggregates, continues halite coatings and halite infillings in vughs and channels, calcium carbonate accumulations as typic nodules, infillings and coatings, redoximorphic accumulations as nodules in the groundmass and coatings on voids and skeletal grains, and finally, organic coatings as black films on peds and in some cases mixed with groundmass of the soil.

Proper management of saline and sodic soils is essential for optimal conservation of soil and water resources. Accumulation of soluble salts within the root zone is one of the major problems in arid and semi-arid regions. To overcome this problem، leaching of accumulated salts from such soils is necessary. The most important task in leaching practices is assessment of water quantity required for leaching of saline and saline-sodic soils. Therefore، reliable estimation of the required leaching water quantity is vital for reducing soil salinity to a desirable level. The objectives of this study were to introduce an empirical model to account for reclamation water and to compare the obtained results with some available models. Consequently، a large scale field experiment was conducted in jofeir region at south part of west Khuzestan plains، covering an area of 21285 ha with S3A2 salinity-sodicity classes. The intermittent pounding experiment was conducted with six double ring infiltrometers in a circular array. All experiments were accomplished by applying 100 cm of water in four-25 cm intervals. The leaching water was supplied from Karun rive. Four mathematical models were applied to the collected experimental data to derive a suitable empirical model. The results indicated that the proposed power model with maximum correlation coefficient of 0. 83 and minimum standard error of 0. 44 can provide reasonable estimates for leaching process compares to the previously proposed models. The results indicated that the empirical relations given by Rajabzadeh (2009)، Hoffman (1980) and Laffelar and Sharma (1977) can not resemble the field conditions. However، the empirical relationships introduced by Pazira and Kawachi (1981) and Revee (1957) overestimate the depth of reclamation water. The empirical models of Pazira and Keshavarz (1989)، Asadi et al.، (2013) and Dieleman (1963) underestimated the depth of required reclamation water compares to the newly proposed model.

Salinity and sodicity are of major problems of arid and semi-arid regions soils and account for lowering soil quality. In order to improve the physical and chemical qualities of these soils، a composite sample of a saline-sodic clay soil (ECe= 11. 5 dS/m، SAR= 13. 23) from Bilverdi agricultural research center of Islamic Azad University of Tabriz branch was collected. The experiment carried out in a greenhouse، was factorial with complete randomized design with 3 replications. The experimental factores (treatments) were a)polyacrylamide (PAM) (0، 0. 25 and 0. 5 g/kg soil)، b) pumice (0، 50 and 100 ton/ha) and c) municipal waste compost (0، 30 and 60 ton/ha). After complete mixing of these amendments with pre-wieghed amount of soils in plastic pots، the pots were kept in the greenhouse under 18-25 ◦c. The soil moisture varied in the range of 0. 5 FC to FC. Ten wetting and drying cycles were imposed to the pots using tap water with EC=0. 387 dS/m and SAR= 1. 014. After incubating of the pots for 100 days under the described conditions pH، saturated electrical conductivity (ECe)، sodium adsorbtion rate (SAR) and organic carbon (OC) were determinded in the disturbed samples taken from the pots. Saturated hydraulic conductivity (Ks) and slope of soil moisture curve at the inflection point (Si) were also determinded in undisturbed samples taken from the surface layers of the pots. Analysis of variance and mean comparisons between the treatments showed that pumice and compost reduced pHsignificantlyby 0. 37 unit in comparision to the control. Pumice and PAM also reduced ECe from 34. 9 to 43. 97 percent relative to the control. while compost raised ECe by 186. 69 percent relative to the control. The result clearly showed a positive effect of pumice and compost on reducing SAR by 58. 97 percent and positive effect of PAM and compost on increasing OC by 26. 67 percent in comparision to the control significantly. Due to strong adhesive effect of PAM for the soil particles، and thus its aggregation effect، this amendment led to more larger pores and as a result significantly raised Ks up to 3 cm/hr (638. 3%) and Si to 0. 074 unit (160. 87%) as compared with the control. Generally، it seems that using PAM at the beginning of saline-sodic soils reclamation may considerably facilitate the practice because it greatly improves hydraulic conductivity. Taking the benefits of pumice or compost will be the next step

Soil salinity and sodicity are considered as the important factors limiting the plants growth. This study was conducted to assess the influence of the sample size on the accuracy of estimation of soil salinity and sodicity status, made by ordinary kriging, inverse distance weighting and spline estimators in Eslamieh area, Rafsanjan city. First, electrical conductivity (EC) and sodium adsorption ratio (SAR) were measured for 100 observation points, collected from three depths using a regular grid sampling pattern with an interval of 500 meter. These properties were mapped using aforesaid estimators. Then, random omission of 20, 40 and 60 samples from the total primary dataset (100 samples), was done and in each new situation, EC and SAR were mapped again. At the end of all 10 stages used to omit the samples, the index of standardized root mean square error (RMSE%) was measured for each estimator. Finally, the obtained contents of RMSE% were statistically compared using Friedman and Wilcoxon tests. The results showed using relatively high number of samples (all 100 observation points), three analyzed estimators have no significant difference (95% confidence level). In the cases of lower sample sizes, Friedman test revealed a significant difference among the estimators; whereas using Wilcoxon test, as a supplementary procedure, no significant difference was observed between the results obtained from ordinary kriging and inverse distance weighting. Hence, thanks to the relatively good precision, ease of processing and lower required sampling points, the inverse distance weighting estimator is recommended for future studies in the studied area.

Soil salinization is a process in which the accumulation of soluble salts in soil profile can affect soil physical and chemical properties، such as osmotic pressure، permeability and hydraulic conductivity. These، in turn، can seriously impair or completely stop the growth of plants. In this study، four theoretical models for predicting soil leaching contains including Series of Reservoirs Model (SRM)، Theoretical Plate–Thickness Model (TPTM)، Convection – Dispersion Model (CDM) and Numerical Model (NM) were studied in order to select and introduce the best model for predicting ultimate soil salinization. The results of these models were compared with real data obtained from field experiments. To do this، 15 basin plots (each has one square meter) were firstly built. Then، five leaching depths of 20، 40، 60، 80 and 100 cm were applied to basins in three rows. Results revealed that the investigated models showed different performance for the different depths of leaching. Overall، Series of Reservoirs Model (SRM) was able to estimate the ultimate salinity more accurately.

Management of natural resources such as water and soil is one of the important subjects in suppling food requirements of increasing population of the world. Soil salinization and sodification caused by salt accumulation are the common phenomena that manifest in irrigated agriculture in arid and semiarid regions. The aim of this research was study of desodification of saline and sodic soils at central region of Khuzestan province-IRAN. For this purpose, two experimental areas (Sl, S2) were selected and four treatments with three replications by series of double rings were applied. The treatments included 25, 50, 75 and 100 cm water application. It was concluded that 39 and 55% of initial exchangeable sodium percentage in Pilot S1 and S2 was reduced by 100 cm water leaching at one meter layer of Soil respectively.

Salt-affected soils cover up to 20 million hectares of our country. The objective of this study was to derive PTFs of some salt-affected soils to predict the parameters of van Genuchten equation and water retention at a pre-defined potential from readily/easily obtainable soil characteristics. For this purpose، 68 soil samples were chosen from south part of Tehran (saline and saline-sodic soils). Moisture retention curve for these samples were determined at matric potential of 0، -10، -33، -100، -300، -500، -1000 and -1500 kPa. Particle size distribution، calcium carbonate، bulk density، organic carbon، EC and SAR were measured and RETC program was used to obtain the Van Genuchten equation parameters. As to the EC and SAR effect on pore size distribution of soil، these parameters were used in pedotransfer functions as predictor parameters. Also، performance of derived functions in estimation of moisture retention curve was compared with a number of functions (13 functions) that previously were provided by different researchers. Generally، the result of this study showed: 1- Water retention at a pre-defined potential and parameters of van Genuchten equation can be estimated by pedotransfer functions with reasonable accuracy (point transfer functions: 0. 844 ≤ R2Adj ≤ 0. 577 and 0. 0296 ≤ RMSE(cm3/cm3) ≤ 0. 0121)، 2- Sensitivity analysis results showed that the sensitivity of most point functions to changes in bulk density was more than the rest of the parameters and clay-silt ratio، EC، and sand were at the next levels، 3- Considering the coefficient of EC in the equations، partial coefficients of correlation، and results of sensitivity analysis، higher amounts of EC could somewhat affect pore size distribution and، consequently، the shape of moisture retention curve of the soils. This change، which is caused by swelling and shrinkage، to some extent can be predicted via introduction of EC and SAR parameters in developing the equations،4- Comparison of previous functions with those obtained in this study show that derived functions in this research are the best functions for estimation of soil moisture retention curve.

To determine the appropriate depth of leaching water requirement for Saline-Sodic soil reclamation, some field experiments are recommended. Having the results of such field experiments, the so-called leaching curves will be obtained. These empirical curves will enhance determining the amount of leaching water to reduce the soil salinity and sodicity to desirable levels. The objectives of this study were to conduct such experiments in order to obtain soil Desalinization & Desodification curves and to compare the obtained results with some empirical models. Furthermore, it was supposed to determine a new empirical model for the saline-sodic soils in central part of Khuzestan province. In this study, the field experimental results of a heavy texture, Saline-Sodic soils, which was carried out by cylinder infilterometer are presented. In this regards three different sites were selected in the most saline-sodic parts of the study area for which 1.0 meter depth of leaching water were applied intermittently. The field salt leaching data and calculated valves were used to verify a newly proposed empirical model obtained by curve estimation technique. The results indicated that the empirical relationships proposed by Revee, Dielman and Verma and Gupta can not resemble to the field conditions. However, the empirical relationships introduced by Laffelar and Sharma, Hoffman, Pazira and Kawachi and Pazira and Keshavarez could estimate the depth of required reclamation water 1.5 times more than the newly proposed empirical model. The theoretically calculated values with the proposed exponential model, could well simulate the real experimental data.