وجیهه درستکار

Topographical conditions of any given area are among the main factors which influence the variations of soil attributes, especially in small spatial scales. The current study was carried out aimed at investigating the influence of slope aspect and position on soil quality considering the local situations via comparing the amounts of soil pH, organic matter (OM), available phosphorus (P), mean geometric diameter of soil aggregates (MGD), and water-dispersible clay (WDC) in the soils located in south-facing and north-facing slopes in five different slope position, including summit, shoulder, backslope, footslope, and toeslope in the forests of Kalpoosh area, Northeast Shahrood. Surface soil samples (0 – 20 cm) were taken up from three different points which were two meters far from each other in every slope position, and after being passed from a 2-mm sieve, their mentioned properties were measured using standard methods. The data were statistically analyzed by applying Duncan test, one-way ANOVA. The results indicated the combined effects of slope aspect and position were significant on most of the selected soil properties (P < 0.01). In contrary to the most of the previous researches, the amounts of OM (2.64 %), P (10.13 mg/kg), MGD (1.30 mm), and WDC (2.23 %), in south-facing slopes were relatively more favorable compared to their corresponding values in north-facing slopes (2.13 %, 8.74 mg/kg, 0.95 mm, and 3.90 %, respectively). Considering that the area under investigation undergoes early coldness in fall as well as heavy snows, low soil temperature in north-facing slopes seemingly hinders plant growth and soil evolution. On the other hand, receiving more radiation, soils located on south-facing slopes can modify the impacts of early coldness so that they provide the appropriate temperature for plant growth and enhancement of soil conditions.

Increasing population and water consumption in agriculture and industry sectors enhanced the entry of various pollutants into the environment and water resources. In this study, the removal of lead from water by three adsorbents, sepiolite clay, corn biochar, and corn biochar-clay complex were investigated. For this purpose, the adsorption isotherms and kinetics were performed by the three studied adsorbents. By increasing the concentration in lead from 50 to 1500 mg L-1, the absorption capacity of the adsorbents increased, but the absorption percentage decreased. The results showed that the lead highest absorption capacity is related to the corn biochar adsorbent, while the clay-biochar complex had a higher absorption capacity than the clay adsorbent. To study the absorption process, Langmuir and Freundlich's isotherms were checked for each adsorbent and it was found that the absorption of lead follows both models, but the Langmuir model with the highest coefficient of explanation (R2) and the lowest sum of squared standard error (SSE) has the best fit. The effect of contact time with the adsorbent on the absorption rate was investigated and it was found that the absorption efficiency increased with increasing contact time. The pseudo-first-order, pseudo-second-order, Elovich and intraparticle diffusion kinetic models were fitted for lead at concentrations of 600, 1000 and 1500 mg L-1 in 30 to 1440 min. The Elovich model at the concentration of 500 mg/L and the pseudo-second order model at the concentrations of 1000 and 1500 mg/L showed the best fit with the laboratory data. At low concentrations, the clay-biochar complex showed better absorption performance, but biochar was a better absorber with increasing lead concentration than the other two adsorbents.

This research was carried out in a factorial split plot experiment based on a randomized complete block design with four replications in Semnan Agriculture Research Center, Bastam, central Iran, in 2019. Experimental treatments included irrigation as the main factor at three levels of 100, 75 and 50% of water requirement and sub-factors including cultivar at three levels (Titicaca, Q26 and Q29) and priming at two levels (no priming and hydropriming) as sub-factors. The percentage of water requirement of the plant was calculated using the CROPWAT program and applied from the 6-leaf stage of the plant. The results showed that drought stress reduced leaf area index, 1000-seed weight and grain yield in all three cultivars. Percentage of protein, malondialdehyde, proline, activity of antioxidant enzymes including catalase and ascorbate peroxidase increased in plants under drought stress. Hydropriming increased leaf area index and grain yield. Among the three cultivars tested, hydroprimed plants of Q26 genotype had the highest leaf area index, 1000-seed weight and grain yield compared to the other cultivars. Cultivar Q26 had the highest grain yield when supplied with 75 and 100% of water requirement and Titicaca cultivar had the highest grain yield (1067 kg/ha) in the presence of severe drought stress (i.e. 50% water requirement). In conclusion, Titicaca cultivar was more resistant to drought than other cultivars and cultivation of this cultivar is recommended in Bastam region. In the scope of the research, the application of hydropriming can be suggested to improve the physiological traits of quinoa under drought stress.

The cultivation of quinoa (Chenopodium quinoa Willd), an annual plant with high nutritional and economic significance, is expanding throughout the world. Quinoa is a traditional Andean seed crop highly tolerant to abiotic stresses. Since most seed crop cultivars are sensitive to drought stress, quinoa is regarded as a valuable candidate for the plant's exposure to harsh environmental conditions. Due to the importance of quinoa in arid regions, the effects of seed priming on yield and certain morphological and physiological traits were investigated in this study.

A factorial split-plot experiment based on a randomized complete block was designed with four replications was conducted in 2019 at Damghan Research Farm Station. The experimental treatments included drought stress based on the plant's water requirement at three levels (100% (control), 75%, and 50%) as the main factor, and sub-factors included three cultivars (Titicaca, Q26, and Q29) as well as priming at two levels (no priming and hydropriming) as a factorial experiment into sub-levels. To perform water requirement (WR) treatment, WR were calculated using the CROPWAT program and then applied to the 6-leaf stage plants.

The results demonstrated that drought stress (50% WR) reduced  relative leaf water content (13.1%), leaf membrane stability index (21.2%), chlorophyll content (38.7%), 1000-seed weight (18.2%), number of panicles per plant (27.5%), number of seeds per panicle (7.71%), and seed yield (40.4%). The use of hydropriming increased the membrane stability index, leaf chlorophyll content, 1000-seed weight, and the number of panicles per plant. Under 50% WR, the activity of antioxidant enzymes such as catalase and leaf ascorbate peroxidase increased by 139.58 and 42.55 percent, respectively, compared to the control. Additionally, drought stress increased quinoa seed protein content and decreased seed yield.. The percentage of seed yield reduction in drought stress was 50% and 75% of WR and was lower in Titicaca than the other two cultivars.  The comparison of the mean of irrigation interactions in the cultivars revealed that 100% WR produced the maximum quantities of Chl a, Chl b, and carotenoids in all three cultivars. Additionally, seed priming boosted the Chl a, and Chl b concentrations in Titicaca and Q26. Furthermore, the highest biological yield in the Damghan region was achieved in Q26 with 100% WR. Under normal irrigation conditions, Q26 cultivar had the highest seed yield, whereas under drought stress conditions, the seed yield of all cultivars decreased significantly. Nevertheless, this decline in the Titicaca cultivar was 12% less than in Q26 and Q29. The findings of the mean comparison revealed that priming improved seed yield in all three cultivars, with the Q29 cultivar producing the maximum seed yield at 1,452.03 kg/ha.

In general, Titicaca cultivar was more resistant to drought stress than other cultivars, hence its cultivation is encouraged in the Damghan region. Within the scope of this study, the use of hydropriming to improve quinoa's physiological features in conditions of drought stress is suggested. In conclusion, the results demonstrated that seed priming significantly increased seed yield, biological yield, leaf area index, and chlorophyll content in drought-stressed quinoa cultivars. These results indicated that seed priming can play a significant role in enhancing quinoa's drought resistance under low irrigation conditions. This study could contribute to the understanding of seed priming effects, which could be applied as an effective strategy to mitigate the negative effects of drought stress on quinoa cultivars.

With increasing population and water consumption in agriculture and industry, the entry of various contaminants into the environment and soil and water resources has been increased. Cadmium heavy metal is known as one of the polluting elements. In addition to toxicity, it has adverse effects on the health of living organisms, too. In this study, the adsorption method was investigated by the three adsorbents of sepiolite clay, corn biochar, and clay and corn biochar complex on the removal of cadmium metal from water. For this purpose, experiments related to adsorption isotherms and adsorption kinetics were performed by the three adsorbents. Parameters affecting the adsorption process include type of adsorbent, change in initial concentration of cadmium solution, and changes in adsorbent contact time were investigated. The adsorption capacity of the adsorbents increased with increasing cadmium concentration from 150 to 800 mg/l, but the adsorption percentage decreased with increasing concentration. The results showed that the highest adsorption capacity in cadmium was related to corn biochar, while the clay-biochar adsorbent had more adsorption capacity than clay adsorbent. Langmuir and Freundlich isotherms for each element and adsorbent were investigated to study the adsorption process. It was found that the adsorption of cadmium by the adsorbents follows both models. Freundlich model with the highest coefficient of determination (R2) and the lowest sum of squares of standard error (SSE) showed the best fit with laboratory data. The effect of adsorbent contact time on the adsorption rate was investigated and found that the adsorption efficiency increased with increasing contact time. Fitting quasi-first-order, quasi-second-order, Elovitch, and intra-particle dispersion models for cadmium at concentrations of 150 and 600 mg/l was performed at 30 to 1440 min. The Elovich model at concentrations of 150 and 600 mg/l cadmium showed the best fit with laboratory data. At concentrations of 150, clay-biochar complexes showed better adsorption performance, but at other concentrations of cadmium, biochar was a better adsorbent than the other two adsorbents. Based on the results inferred from adsorption experiments, it can be stated that the corn biochar compared to clay and biochar and clay and biochar complex compared to clay has a high ability to remove heavy metals from contaminated water, which can be used as a cheap and practical material used to remove contaminants such as cadmium.

In countries with arid and semi-arid climates, conserving water resources is important. For this purpose, different models were presented to determine the vulnerability of areas. In this research, a vulnerability map of Sabzevar aquifer has been prepared using a drastic model. Sabzevar aquifer located in the northeast of Iran with an area of 5455.4 square kilometers has a dry and desert climate with hot and dry summers and cold winters. The drastic model is obtained through 7-layer overlap (groundwater depth, net nutrition, aquifer environment, soil type, topography, influence of unsaturated area and hydraulic conductivity of the aquifer) and shows a detailed map of the aquifer vulnerability. ArcGis10.5 software was used to draw the drastic model map. The numerical value of the drastic model in the study area is between 81 and 159 (from low vulnerability to high vulnerability). Drastic map showed that a very small area from the west of the study area has low vulnerability and the central areas of the plain have high vulnerability. Other parts of the region are moderately vulnerable. Shallow groundwater depth in the central areas of the plain and also low slope in the above area has the greatest impact on the vulnerability of the region. Due to the volume of agricultural activities in the central areas of the plain, measures should be taken to prevent possible contamination of the aquifer. Due to the fact that the concentration of nitrate in groundwater sources was not available in the study area, so electrical conductivity was used to validate the zoning of the drastic model. The overlap of electrical conductivity with the drastic map showed that the electrical conductivity was high in the center of the vulnerable plain. This can also confirm the accuracy of the drastic model.

This research was performed to determine the effect of inoculation of two species of arbuscular mycorrhizal fungi (AMF) on soil available water (SAW) and glomalin concentration under drought and salinity stresses according to a factorial based on completely randomized design with three replications. Treatments included two plant species Atriplex canescens and Haloxylon ammodendron with inoculation of two fungal species Glomus geosporum and Glomus mosseae plus two levels of salinity stress at 7 and 14 dS m-1, and two levels of drought stress including maximum allowable depletion (MAD) of 50 and 80%. After one year of treatments, plant available water (PAW), least limiting water range (LLWR), integral water capacity (IWC), total and easily extractable glomalin concentration and soil organic carbon (SOC) content were measured. Results indicated a significant increase in SOC, glomalin concentration, PAW, LLWR, and IWC by increasing the salinity level in treatments inoculated with G. mosseae and G. geosporum. The highest percentages of increase in PAW (147%), LLWR (140%) and IWC (85%) as compared with control were observed under combined salinity and low drought treatment (14 dS cm-1 + MAD of 50%) in A. canescens inoculated by G. geosporum. The highest concentrations of total glomalin and easily extractable glomalin were observed in both plant species under salinity of 14 dS m-1 and severe drought treatment (MAD of 80%) with the inoculation by G. geosporum and G. mosseae. Overall the results of this research indicated a reduction in negative consequences of drought and salinity stresses in the soil under cultivation of A. canescens and H. ammodendron, with application of mycorrhizal fungi.

Traditional organic manure can be potentially beneficial for soil physical, chemical and biological properties by improving organic matter of soils. Recently, biochar, a carbon rich product of biomass produced by thermochemical conversion under oxygen-limited conditions, has been studied for its effects as a soil amendment. The use of a modified form of manure as manure biochar for soil improvement reduces some environmental, food safety and disposal problems of manures. However, biochar application has been shown to have a positive and negative effect on soil fauna such as earthworm depending on the type of feedstock for its production. Since earthworm function affects physical properties and amount of organic carbon of soils and because of the different effect of biochar and its feedstock on earthworm activity, this study hypothesizes that earthworm may differently alter soil physical properties and aggregates associated carbon in the biochar and its feedstock amended soils. The purpose of this study was to investigate the effect of cow manure and its biochar in the presence and absence of earthworm on bulk density, total porosity, saturated hydraulic conductivity, aggregate stability and content of organic carbon in soil aggregates during 30 and 90 days incubation.

A completely randomized design with 2×4×2 factorial treatment combination was used in triplicates. Treatment variants examined in this study included the following: (i) 2 levels of amendment type (cow manure and its biochar), (ii) 4 levels of applied amendment rate (0, 1, 2 and 5%), (iii) 2 levels of earthworm (with and without earthworm). The biochar was produced from cow manure (passed through 2 mm mesh) by slow pyrolysis at 450 °C. For this experiment, the soil sample was passed through 4 mm mesh. Then, amended soil and the control were moistened up to 70% water holding capacity. Then 5 adult Eisenia fetida with fully-developed clitellum and similar weight were added to half of them. Treatments were then incubated at laboratory temperature and constant moisture for 30 and 90 days. Based on evaporation loss, the soil moisture was kept constant by regular weighing of each pot. At the end of each time (30 and 90 days), samples were taken from different treatments to determine bulk density, total porosity, saturated hydraulic conductivity. Also, soil aggregates were separated by wet sieving, then aggregate size distribution was determined and mean weight diameter (MWD) was calculated, also organic carbon content in each aggregate size fraction was determined.

The results showed that the application of both organic amendments was effective in decreasing soil bulk density, increasing total porosity, saturated hydraulic conductivity and aggregate stability, but the effects of organic amendments on these physical properties were more pronounced in cow manure- than biochar-amended soils. Further reduction in bulk density following manure application is attributed to a dilution effect, resulting from mixing of the lighter material of manure with denser mineral fractions of the soil. In addition, cow manure has more content of organic carbon than its biochar which can increase total porosity by promoting aggregation. The greater porosity and aggregation of soils as affected by the application of organic amendments are apparently responsible for the increased saturated hydraulic conductivity. The results showed that the effect of cow manure on the soil physical properties reduced with time more rapidly than its biochar. It might be attributed to lower stability of manure to degradation than biochar in soils because manure contains higher content of labile organic compounds compared to biochar. Our results also showed that application of organic amendments led to increase organic carbon in soil aggregates, especially in 4-2 mm aggregates, indicating that the large macro-aggregates can be considered as a susceptible indicator to organic carbon managements in soil. Also, the organic carbon content of 4-2, 2-0.25 and 0.25-0.05 mm aggregates was 42.8, 27.8 and 20.8% (in 30 days incubation) and 27.2, 28.6% and 20.6% (in 90 days of incubation) higher in cow manure- than biochar-amended soils. The results also showed that earthworm reduced soil bulk density, increased total porosity, saturated hydraulic conductivity and aggregate stability regardless of soil amendment but such effect on bulk density and total porosity was more pronounced in cow manure- than biochar-amended soils. It means that type of organic amendments can influence on earthworm activity, thereby altering some soil physical properties. Also, earthworm led to increase carbon content in soil aggregates, especially in smaller aggregates.

The results showed that although application of cow manure improved soil physical properties more than cow manure biochar at both incubation times, it seems that cow manure biochar has a more stable effect on the soil physical properties over time. Also, application of organic amendments can lead to increase soil organic carbon by further increasing C in larger aggregates. Other results indicated that the improving effect of earthworm on soil physical properties (except for bulk density and total porosity) did not depend on the type of applied organic amendment in soil. The effect of earthworm on bulk density and total porosity was more pronounced in soils amended with cow manure than its biochar. Also, it is thought that earthworm increases organic carbon in soil by physical stabilization of organic carbon in soil aggregates, especially in smaller aggregates.

Water infiltration into the soil is one of important hydrological parameters. This study was conducted for Phillip and Horton parameters and final water infiltration rate prediction using artificial neural network and support vector machine (SVM). The soil water infiltration was measured in 100 points of Abarkouh city landscape (Yazd province) with double ring method. The samples from 0-30 cm of soil surface were analyzed for bulk density, texture, organic matter, sodium adsorption ratio, porosity, geometric mean particle diameter and geometric standard deviation of soil particle. The multilayer perceptron neural network (MLP) with 4 different scenarios with 3, 5, 7 and 9 inputs and SVM with 9 inputs were analyzed for infiltration parameters and final water infiltration rate prediction. The results showed that the network with 9 inputs had the greatest R2 and the lowest error in Phillip and Horton parameters prediction. The study of prediction ability of ANN for Horton and Phillip parameters showed that the greatest capability was related to final infiltration rate to net design as 9-5-1 with R2 equal to 0.84. The sensitivity analysis showed that the designed nets had greater sensitivity to soil sodium adsorption ratio and the organic matter than other 7 parameters. The SVM model had good ability to water infiltration rate prediction based on basic soil properties. SVM model had better ability in soil water infiltration rate prediction compared to ANN model.

Roughness estimation is one of error sources in flood simulation. In this study the flood was simulated in Atrak Olya, Chaylogh, Gelian and a part of Atrak river with different roughness coefficient using HEC-RAS ،GIS and HEC-GEO RAS and the effect of roughness coefficient on flood area, flood depth and velocity in different return period were studied. Results showed that for 100-year flood, the flood area and depth increased 1.1% and the flood velocity decreased around 4% for each 10 % increment of roughness coefficient. In addition, for each 10% decline in roughness coefficient, the depth variation was not considerable but the flood area decreased 1.1% and the flood velocity increased about 8.3%. The flood velocity to roughness variation was more sensitive than flood depth and area. Depth flood had the less dependence to roughness and it changes very low with more than 10% change in roughness coefficient. This trend is almost similar for all return periods

Drip irrigation benefits enhanced the worldwide use of this irrigation system. drip irrigation reduces significantly the wetted soil surface that lead to reduction of evaporative losses. claimed that wetting pattern is a major parameter in optimizing lateral placement and emitter spacing as well as in selecting emitter’s discharge. In other word, to achieve proper drip irrigation design, dimensions of the wetted zone (depth and width) should be accurately determined. Therefore, present study was conducted under clay loam soil to investigate the accuracy of numerical (HYDRUS-2D) and empirical (multivariate nonlinear regression) models in estimating wetting pattern for surface drip irrigation. The predicted values of soil moisture, wetted depth and width were compared with those obtained from laboratory experiments. Experimentations included determination of soil moisture, depths and widths of wetted zone after 1, 2, 3, 4, 5, and 6 hour of water application with three different discharge rates (2, 4 and 8 L/h). Statistical parameters revealed that there was no significant difference between models results and observed values. So that The normalized root mean squared error (NRMSE) varied from 5.8 to 8.2% and 7 to 7.7% for numerical and empirical models, respectively. The results also showed that The proposed empirical model predicts the wetting pattern with acceptable accuracy.

Subsurface drip irrigation has been widely applied in arid area as a water-saving irrigation technology. But, a comprehensive knowledge of wetting pattern in drip Irrigation is essential for designing and managing such system. Simulation models have been proved to be useful method for this purpose. Therefore, this research was carried out to investigate the dimensions of wetting pattern in subsurface drip irrigation in a clay loam soil using invers modeling method with Hydrus 2D and based on experimental results and empirical models. The results were categorized into four sections: 1. Laboratory results showed that only for emitters with 8 liters per hour and installed at 15 cm depth, the wetted dimension below the emitter is more than the one above the emitter. 2. Sensitivity analysis on soil hydraulic parameters showed that the most sensitive parameter is θs, but the soil porosity continuity (l) and the remaining moisture content (θr) are not effective parameters. 3. Wetting front in emitters with discharge rate more than 2 liters per hour and installed at 15 cm depth in the clay loam soil is reached to the soil surface, while it does not reach to the soil surface in the emitters installed at 30 cm depth, even with discharge rate up to 8 liters per hour. Therefore, the evaporation rate from the soil surface is minimized. 4. Statistical indices showed that there is no significant differences among the empirical, numerical and the observation data, so that the normalized RMSE for the numerical and empirical models varied from 4.4 to 6.2 and 3.4 to 8 percent, respectively. Consequently, the results of this study showed that the proposed empirical model and Hydrus model can be used for estimation of wetting pattern in the soil.

A significant amount of the oil meal is produced annually in the oil industry. Oil meal addition into the soil can improve the soil organic matter and micronutrients concentration. This study was conducted to investigate the effect of olive, sesame and black cumin meal (0, 2 and 5 g 100g-1 soil) on the soil Cu, Zn and Fe concentration in saline and non-saline soils by a greenhouse experiment. The soil basal respiration, organic carbon, carbohydrate and DTPA extractable Cu, Zn and Fe concentration were measured after 60 days of incubation. The results showed that the greatest organic carbon and carbohydrate content were observed in olive and black cumin treatments and the lowest was observed in the sesame treatment. Using oil meal in the soil improved the micronutrient concentration, as compared to the control treatment. Sesame meal had the greatest effect on the DTPA extractable Cu and Zn concentration increment. The DTPA extractable Fe concentration was the highest in the sesame treatment and the lowest in the black cumin one. In addition, salinity decreased the DTPA extractable Fe and Zn concentration, as compared to the non-saline soil. As the conclusion, oil meal incorporation in to the soil improved the soil organic carbon and micronutrient concentration. However, their effect depends on the meal quality and soil salinity.

Introduction Conservation and improvement the soil structural stability play a key role in soil management in agro ecosystems especially in arid and semiarid region with high erosion potential. Soil structure is an important soil physical property and has many effects on other soil physical, chemical and biological behaviors such as retention and movement of water, nutrients and pollutions, soil hydraulic and mechanical properties, soil aeration and erosivity. Wetting and drying cycles are one of important environmental factor affecting soil structural stability. Previous studies showed inconsistent results about the positive or negative effects of wetting and drying cycles on soil stability. This study was conducted to investigate the effect of wetting and drying cycles on the soil structural stability in the presence of safflower residues. Materials and Methods The agricultural soil was collected from the soil surface layer (0–20 cm) of Shahrood in Semnan province and passed through a 4 mm sieve. An experiment was conducted including two treatments i.e. number of wetting and drying cycles (0, 1, 2, 4, 8 and 10 cycle) and amount of safflower residues (0, 1 and 2 g 100 g-1 soil ). Plant residues were collected from safflower fields and after drying, milled and passed through a 1 mm sieve. Then crop residues were mixed into soil. The wet and dry cycles were applied during 2 month. In wetting periods the soil was kept in filed capacity and in dry periods the soil was kept in electrical oven in 40°C. The soil organic carbon and soil diluted acid carbohydrate concentration were measured at the end of the experiment. The soil structural stability was measured using high energy moisture curve. The soil drainable pores, soil suction at inflection point, stability index, stability ratio and Dexter's S index were calculated. Results and Discussion The greatest soil organic carbon was observed in control treatment (0 wet and dry cycle) and then it was decreased by increment of cycles in all crop residues levels. These cycles improve the microbial activity during the rewetting process and increase decomposition of crop residues. The soil organic carbon and diluted acid carbohydrate were highest in treatments including 2 g residues 100g-1 in all studied wet and dry cycles. The greatest soil drainable pore volume and the lowest soil suction at inflection point were found in treatment including 4 wet and dry cycles. The results showed that 2 and 4 cycles increased the soil drainable pore volume by 58 and 106 % compared to the control treatment (no applied cycle). More increment of wet and dry cycles decreased the soil drainable pore volume and this factor was declined by 40 % in 10 cycles treatment compared to 4 cycles. It means that wet and dry cycles can improved the soil structure because of rearrangement of soil particles and improvement of soil particle contact points. However, the high number of wet and dry cycles destructed the aggregate and decreased their stability. In addition, the physical protection of soil aggregates from soil organic matters declined through aggregate breakdown. This phenomenon provided fresh organic matter for decomposers and consequently the aggregate stability decreased. Appling only one wet and dry cycle could not significantly improve the stability ratio. This ratio improved considerably when 2 and 4 cycles were used. Following the aggregate breakdown in treatments including more than 4 cycles, the stability ratio decreased in all crop residue levels. Our results showed that the greatest and the lowest volume of coarse and medium pore were observed in 4 and 10 wet and dry cycles treatments but the greatest and the lowest volume of fine pores were observed in 10 and 4 wet and dry cycles treatments. It means that the structural stability improvement during 0-4 cycle changed the pore distribution and made larger pores but the aggregate breakdown with more than 4 cycles changed the pore volume again and increased the portion of finer pores. Conclusion Our results showed that the low number of these cycles can improve the soil aggregation and aggregate stability but the high number of these cycles has negative effect on aggregate stability. However, the presence of organic matter in soil can decreased the negative effect of wet and dry cycles. These results confirmed the importance of incorporating crop residues in to the soils after crop harvest.

Soil improvement with plant residues incorporation influences many soil properties. This study was conducted to investigate the effect of apricot and winter olive leaves (0, 1 and 3 g residue 100g-1 soil) on the soil structural stability using high energy moisture curve (HEMC) method in different soil salinity levels (1, 5 and 10 dS m-1). Apricot residues increased the soil organic carbon content and diluted acid carbohydrates and decreased the soil basal respiration more than the winter olive leaves. Increasing residues and salinity levels have also increased the soil organic carbon and the carbohydrates concentration in the soil. Also, the soil basal respiration has been reduced by increasing salinity. There were no significant differences between the apricot and winter olive residues in terms of their effectiveness on the soil drainable porosity (VDP), the soil suction in inflection point (τd) and the stability index (SI) in slow wetting method. However, the apricot leaves increased the soil drainable porosity and the stability index more than the winter olive in fast wetting method. This finding shows the different response and the structural instability of the soil for the two proposed organic matters. Plant residues increment by improving soil carbon and carbohydrates concentration, and salinity increment by improving divalent cation concentration have enhanced the soil stability ratio and the soil VDP ratio in both; fast and slow wetting methods. The results of this study showed that the application of native crop residues in the soils with low organic matter could improve the soil physical characteristics and these changes probably recover the soil physical fertility in the long term application.

Introduction Crop production in arid and semi arid regions especially in saline soils always has many problems. Soil low organic matter content is one of the limiting factors in arid condition. Incorporation of plant residues is a good strategy for increasing the soil organic carbon and consequently for improving soil physical quality (34). However, some studies have shown that addition of organic matter in to the soil can increase soil water repellency (17, 18). This study was conducted to investigate the effect of grape leaves and pomegranate peels on the soil structural stability and soil water repellency in different salinity levels.
Materials and Methods The arable soil was collected from the soil surface layer (0–20 cm) of Bastam Agricultural Research field in Semnan province and passed through a 4 mm sieve. A greenhouse experiment was conducted with three treatments including plant residues type (Grape leaves and pomegranate peels), amount of plant residues (0, 2 and 5 g 100 g-1 soil ) and salinity (1.5, 7 and 15 dS m-1). Plant residues were collected from grape and pomegranate gardens and after drying, milled and passed through a 1 mm sieve. Plant residues were mixed with soil and salinity treatment was applied with calcium chloride salt. Pots were filled with mixture of saline soil and plant residues and incubated in the greenhouse for 50 days. The soil organic carbon, soil hot water and diluted acid carbohydrate, soil microbial basal respiration, water dispersible clay and soil water repellency were measured at the end of the experiment.
Results and Discussion Pomegranate peels increased the soil organic carbon content and hot water and diluted acid carbohydrates more than the grape leaves (Table 5) due to greater C:N ratio and lower microbial decomposability (37). Soil microbial basal respiration was 15.5% lower in pomegranate peel treatments than grape leaves and (Table 5). Water dispersible clay decreased by increasing the amount of plant residues (Table 8). Soil organic carbon increased by the amount of plant residues. Soil organic carbon is an important factor in stability of soil aggregate and consequently decreases the soil water dispersible clay (7). Strong negative correlation between soil organic carbon and soil water dispersible clay can confirm these results. In addition, the soil carbohydrates are known as an important factor in stability of aggregate especially for macroaggregates (40).
Salinity increment from 1.5 to 15 dS m-1 caused a reduction in water dispersible clay from 45.1 to 31.2 g kg-1 soil (Table 9). Calcium as a divalent cation is an important factor in soil structural stability and probably decreased the soil water dispersible clay (7).
Soil repellency index was greater than 1.95 in all treatments and ranged from 2.3 and 5.9 in different treatments. These results indicated subcritical soil water repellency in soil. Soil water repellency index increased 38 and 67 percent in treatments with 2 and 5 g residues 100g-1 soil compared to control treatment (no residue) (Figure 3). In addition, soil hydrophobicity was 10% higher in the pomegranate peels treatments than in grape leaves treatments (Figure 4). Soil organic carbon and soil hot water and diluted acid extractable carbohydrates concentration increased by the plant residues addition. The soil organic components have a hydrophobic and a hydrophilic parts and the orientation of hydrophobic parts on the soil particle surface can make a repellent soil surface (6).
Soil calcium (Ca) concentration increased by salinity. This divalent cation in the soil solution could act as a bridge between the soil particles and functional groups of dissolved organic matters. This bridge could facilitate covering of soil particles by hydrophobic compounds and make a more stable soil structure by flocculating soil particle at high salinity levels (7). The hydrophobic coatings on the soil surfaces increased the solid–liquid interfacial free energy (γsl) and decreased the solid surface free energy (γsg) as indirect effects of salinity on repellency. In addition, water entering into the soil immediately dissolved the soluble salts which had precipitated in the initially dry soil. There is some evidence showing that surface tension of water (γlg) increases with salts. Decrease of γsg and the increase of γsl and γlg might cause the repellency increment (43).
Calcium bridge between soil particles could improve the soil structure with salinity increment. Increasing the SE by salinity in this study confirms this hypothesis. The soil SW depends on pore geometry and hydrophobic coating on soil particles, but the soil SE only depends on pore geometry. Thus, increasing the SE might be an indicator for better pores connection and stable structure (15).
Conclusion Many grape leaves and pomegranate peels are produced in Iran every year. These plant residues are potentially a good source for increasing the soil organic carbon. Our results showed that incorporation of these plant residues in to the soil could increase the soil organic carbon and carbohydrate concentration and improve the soil aggregates stability. However incorporation of residues into the soil increased the soil water repellency. In addition salinity increment induced soil hydrophobicity. More detailed studies are needed to understand the positive or negative effects of this subcritical hydrophobicity development in saline soils.

Arbuscular mycorrhizal fungi (AMF) are widespread endosymbionts in terrestrial ecosystems and their exudates have important effects on soil properties. A greenhouse experiment was conducted with six AMF treatments including four exotic species inoculums (Funneliformis mosseae، Claroideoglomus claroideum and Rhizophagus irregularis and a mixed isolate of three species)، one mixed native AMF species treatment and a sterilized soil (control) with four salinity levels (1، 5، 10 and 15 dS m-1). AMF increased the soil (EEG) and total (TG) extractable glomalin، and also the hot water (HWC) and diluted acid (DAC) extractable carbohydrates compared to control treatment in all salinity levels. The native AMF species had the greatest effects on EEG، TG، HWC and DAC at 10 and 15 dS m-1. Soil EEG and TG concentrations were higher in the mixed exotic AMF treatment than in each AMF species. The greatest glomalin concentration was related to F. mosseae at 1، 5 and 15 dS m-1 but at 10 dS m-1 the greatest glomalin concentration was related to C. claroideum. The greatest carbohydrate concentration was related to F. mosseae at 1 and 5 dS m-1 but at 15 dS m-1 significant differences were observed among the three AMF species. Our results showed that there is an interaction between salinity and different AMF species، and a combination of them determines the function of AMF.

Phytoremediation is one of the best methods for cleaning heavy metal contaminated soils. In this method, tolerant plants with high absorption potential are used to clean up the pollutant. The purpose of this greenhouse study was to find the most suitable plants with the highest Zn translocation factor and shoot concentration. Soil samples were collected from zinc and lead Bama mine in Isfahan province, Iran. To compare the hytoextraction power, Heliantus annus.L., Thlaspi caerulescens, Trifolium pretense L. and Amaranthus retroflexus were planted in 8 kilogeram pots. The experiment was conducted in completely randomized design with three replications. After seventy days, plants root and shoot were harvested and Zn concentration was measured. The result showed that Thlaspi caerulescens had significantly higher root and shoot Zn concentration (3125 and 4041 mg kg-1, respectively). The highest bioaccumulation factor and translocation factor was observed in Thlaspi caerulescens. Based on this research, Thlaspi caerulescens was one of the suitable Zn hyper accumulators for cleaning up the Zn pollution.

Limited information is available about the effect of preceding crop residues on bioavailability of zinc (Zn) in calcareous soil and its accumulation in wheat grain. In this experiment, residues of five crops including safflower (Carthamus tinctorius L.), sunflower (Helianthus annuus L.), bean (Phaseolus vulgaris L.), clover (Trifolium pretense L.) and sorghum (Sorghum bicolor L.) were incorporated into a calcareous Zn-deficient (0.5 mg kg-1) soil. A treatment without crop residue was also used in the experiment. This experiment was conducted in research greenhouse of Isfahan university of technology in 2010. Two wheat cultivars (Triticum aestivum cvs. Backcross and Kavir) differing in Zn-efficiency were studied in the experiment. Incorporating crop residues into the soil resulted in an increase of grain Zn concentration in both wheat cultivars although this increase was dependent on the preceding crop type. The greatest increase of grain Zn concentration occurred in the sorghum residues treatments. Although application of crop residues significantly decreased grain phytic acid to Zn molar ratio (as Zn bioavailability criteria for consumers), this ratio was still higher than 15, the critical Zn bioavailability level for consumers in foods. According to the results, despite the increase in the total Zn content, the bioavailability of Zn in wheat grain was not affected by crop residue treatments.

Presence of petroleum contaminants in soil may be toxic to human and organisms and act as a source of ground water contamination; hence, remediation of these compounds from environment is vital. In this study, first the feasibility of remediation of two petroleum-contaminated soil samples around Tehran Oil Refinery (oil refinery landfill and agricultural soils) was assessed using landfarming technique during a four month experimental period. The elimination of total petroleum hydrocarbons (TPHs) from soils treated through landfarming technique was then investigated in the rhizosphere of agropyron and fescue. The results showed that microbial respiration increased due to landfarming processes in both soils. Urease activity in the landfarming treatment for agricultural soil was 21, 45, 26, and 23% higher than the control at the end of first to the 4th months of experiment, respectively. However, no significant differences were observed between the landfarming and control treatments for landfill soil at the end of experiment. Furthermore, about 50 and 57% reduction in TPH-concentration was observed in the landfarming treatment for landfill and agricultural soils at the end of experiment, respectively. In the phytoremediation study, presence of TPHs in both landfarming and control treatments reduced dry matter yield of the studied plants. Urease activity in the rhizosphere of fescue and agropyron was higher than in the unplanted soil. Degradation of petroleum-compounds in the landfill soil under landfarming treatment was more than 20 and 40% in the presence of fescue and agropyron, respectively. The influence of agropyron on TPH-removal from agricultural soil under the landfarming treatment was also higher than fescue.