مجله مدیریت خاک
سال دوم شماره 1 (پیاپی 2، بهار و تابستان 1392)

Metallic minerals often contain high levels of arsenic and selenium، and thus metal ore mining activities cause the entry of these elements to environment. The study of soil contamination around mines and melting factories has been considered highly in the recent years. Considering mineral enrichment and mines development in Iran، the study of environmental issues is an urgent need. In this study، 120 soil samples were collected around Sarcheshmeh copper mine towards Rafsanjan plain in order to study arsenic and selenium concentrations. Two criterions include enrichment factor and geoaccumulation index were calculated to identify contaminated area and iso-concentration maps were drawn to for the distribution of heavy metals in the area. Results showed that these elements had a higher concentration in the area closed to the mine and they reduced dramatically in the further distance from the mine. The result of enrichment factor reveals that the mean concentration of arsenic was higher than the background value at the some sampling points due to abnormal enrichment in the studied area. Moreover، the results of geoaccumulation index calculation showed that selenium level was below critical value in three paths of while arsenic concentration ranged from low to hirh level in the polluted area.

Carbonates are the main component of the most soils of arid and semi-arid regions in the world. Most soil characteristics are greatly influenced by carbonates. Therefore، determination of soil carbonates by a relatively precise، rapid and economic method has a great importance. The acid-titration technique used in most laboratories is a relatively time-consuming and costly method. In this study، 30 soil samples (with a calcium carbonate equivalent of 13-91% in different land uses) with three replications were used to compare acid-titration method with acetic acid (pH)، pressure and، weight-loss methods. No significant differences were observed in measured carbonate levels using different methods. However، dot plots indicate that pressure method is the most precise among the four compared methods. One-way ANOVA results exhibited that pressure and acid-titration methods have minimum and maximum values of coefficient of variations، respectively. Overall، the pressure and weight- loss methods are recommended for soil carbonate measurement in the studied soils.

In the current study، the effects of both hysteresis and soil compaction on the calibration curve of a gypsum block were investigated. For this، block calibration curve for a heavy soil (silty clay) with three bulk densities (normal as in the field and plus or minus 10%) during two cycles of wetting and drying conditions were obtained. The results showed that block calibration curves varied between wetting and drying cycles under different soil compactions. By reducing soil compaction، hysteresis and its effect on the shape of block calibration curve was increased، probably because of a reduction in soil fine pores and more non-uniformity of pore distribution. The effect of soil compaction on block calibration curve was different with drying and wetting conditions، where at specific soil moisture، the block electric resistance increased with drying cycle but reduced with wetting cycle when soil compaction increased. During drying and wetting events، increasing soil compaction resulted in 16% increase and 3% decrease in soil field capacity، respectively. Thus، it is recommended that the soil compaction level of the specified location for block installation should be equal to that of the surrounding soil when using gypsum block.

The cation exchange capacity (CEC) is one of the most important soil chemical properties that influences other soil properties and is a suitable index of soil quality and use. Direct measurement of the CEC is difficult، costly and time-consuming. Therefore، the objective of this study was to predict the CEC by pedotransfer functions (PTFs) using readily available soil properties as predictors. The data were supplied from two provinces of Iran: 129 soil samples were collected from dominant soil series of Hamadan and Guilan provinces. The soil particle size distribution (PSD)، organic matter، CEC and pH have been measured in the laboratory. In this research in addition to conventional predictors of soil CEC such as soil textural fractions، pH and organic matter، fractal parameters of four PSD models including Bird، Perrier-Bird، Kravchenko-Zhang and Yang et al. have been used to predict CEC. In order to evaluate the predictability of CEC from fractal parameters of PSD، regression and artificial neural networks (ANNs) techniques have been used. The results showed that entering fractal parameters of PSD especially the parameters of Bird and Perrier-Bird to the models improved the statistical criteria of the models. In addition، ANN models performed better than regression models. Using new predictors in the PTFs improved the prediction of CEC.

Agricultural soils are continuously under wetting and drying cycles during flood irrigation. Large air-dry disturbed soil specimens with dry bulk density (BD) of 1. 2 g cm-3 were prepared and the effect of wetting and drying cycles on compactibility of fine and coarse textured soils was studied. The large soil specimens with/without wetting and drying cycles were compressed under three preloads (0، 100 or 200 kPa) and then the small soil samples for water content and bulk density measurements were removed. The results showed that the wetting and drying process resulted in increase in an BD for both soils without applying any compacting load. This process resulted in soil susceptibility to compaction for coarse textured soils، whereas it increased the resistance to soil compaction for fine textured soils. Therefore، in fields with coarse-textured soils and under flood irrigation، are more sensitive to soil compaction at harvest traffic at both soil conditions as compared with the fine-textured soils. Therefore، with reducing contact pressure and axal loads the soil compaction could be prevented.

چكيده (انگليسي): A large area of Iran is characterized with arid and semi-arid climate. These areas have been faced with the problems of soil salinity and degradation، due to inappropriate agricultural activities and natural resources mismanagement. Soil and water resources management is basically necessary to prevent soil degradation. This study was conducted to investigate changes in soil physical properties and cations in farmlands، unmodified rangelands and modified rangelands planted with Atriplex and Haloxylon in Mirzabailo plain، Golestan province. For this purpose، soil samples from different land uses including soils planted with grains as farmlands، rangelands planted with Haloxylon and Atriplex as well as natural rangelands were obtained for the determination of soil bulky density، aggregate stability، porosity، water infiltration، concentrations of some cations and cation exchange capacity (CEC). ANOVA procedure and LSD test were used to compare soil data among the land uses. Soil cation concentrations in modified rangelands were more than those in other land uses. Water infiltration in farmland soils was lower than that in the other soils. Natural rangeland soils had more aggregate stability (0. 71 mm) and soil porosity (59%) than those in the other land uses. The concentrations of Ca، K and Mg، and CEC in Haloxylon-planted soils were greater than those in the other soils. However، Na concentration was higher in farmland soils (58. 8 ppm) than the other soils. The overall results indicate that rangeland manipulation program and artifical restoration can result in a decline in soil characteristics and rangeland conversion to farmalands could accelerate this effect.