نشریه پژوهشهای خاک (علوم خاک و آب)
سال بیست و هفتم شماره 1 (بهار 1392)

Iran is now faced with salinity problems in about 34% of its area in addition to harsh conditions of climate in about half of the country. To develop correlations between soil salinity and climatic factors, 1:1000000 soil salinity map of Iran and long term meteorological data were used in this study. Mean soil salinity shows fair correlations with different climatic variables developed as simple and multiple linear regression models (R2 of 0.56 to 0.72). Since predictors of these regression-based models consisted of different climatic variables, the General Circulation Model (GCM) - derived data were found suitable to link to the models for projection of salinity in upcoming decades. Data of HadCM3 model obtained from IPCC-SRES scenarios of A2 and B2 were used for projection of monthly Tmin, Tmax, annual precipitation and evapotranspiration for the next nine decades. Predicted variables were inserted in the developed regressions to project future status of soil salinity. At country wide scale, results showed that for the upcoming 90 years, mean soil salinity may increase from 1.5 to 4.7 dS/m, based on different scenarios and time intervals. This paper also describes importance of climatic factors in generation of Iran’s main playas in addition to special hydrologic, geologic, and topographic attributes of these regions. Results of this study revealed that playa’s climate will shift to harsher conditions, as a result of climate change. This fact was confirmed via simulation of the well-known aridity indices (including De Martonne and UNEP indices) for the next nine decades. This also signals that global climate change is likely to increase salinity of the main lakes, wetlands, lagoons and playas of the country. Therefore, strategies to mitigate climate change consequences should be planned and executed, especially in agricultural lands of arid and semi-arid regions of the country.

In order to evaluate the effects of phosphorus solubilizing microorganisms, to study the biological phosphate fertilizers effectiveness, and to compare them with chemical phosphorus fertilizers in corn cultivation in Iran, a 3-year field experiment was conducted in corn fields of Fars province, Khozestan (Dezful area), Varamin, and Karaj. In each site, an experiment was performed in the form of randomized complete block design with 4 treatments and three replications. The treatments were: a) control (without phosphorus application), b) application of phosphorous as microbial phosphate source, c) application of phosphorus as Golden Bio-phosphate source, and d) application of phosphorus as triple super phosphate. Fertilizers rates were based on soil test. Since there was some organic matter, sulfur, and zinc in the organic fertilizers, equivalent amounts of these compounds were also applied to the other treatments. Results showed that, there was a positive and significant effect of P application on grain yield. In all study sites, triple super phosphate was more effective than the other sources. Microbial phosphate effects were the same as triple super phosphate and were in the second place. Although Golden bio-phosphate fertilizer had a positive and significant effect on grain yield in Varamin and Dezful, but in overall, there was no significant difference between the control and Golden bio-phosphate source. In general, application of microbial phosphate can be recommended instead of triple super phosphate, but additional research is needed before recommendations can be made regarding use of Golden bio-phosphate for corn.

Interrill erosion has been known as one of the common erosion forms in agricultural lands. This study was carried out to evaluate WEPP process-based model in predicting interrill erosion rate using rainfall simulator. For this purpose, different rain intensities of 25, 50 and 75 mm/h were simulated on three soil samples with different particle size distributions on four slopes of 2.5, 5, 7.5, and 10%. The model was evaluated with and without calibration, each at shear stresses less than the critical value (τ<τ0) and all shear stresses (τ >0), as well. The results of model evaluation without calibration for τ<τ0 showed that WEPP tended to over-estimate interrill erosion rates. For τ >0 due to the flow-driven processes, the differences between predicted and measured values decreased. In consequence of model calibration, the values of baseline interrill erodibility (Kib) for τ<τ0 and τ >0 were 6.44-11.05 and 3.57-9.56 times less than the model-predicted ones. Also, it was found that the efficiency of the model depended on soil type. The results of model calibration indicated that WEPP tends to over-estimate very small erosion rates and to under-estimate high values. Also, considering τ<τ0 compared to τ >0, the efficiency of the model was enhanced. For τ<τ0, as a result of model calibration using the averaging and optimizing methods, the coefficients of determination (R2) of 0.76 and 0.66 and also the model efficiency values of 0.68 and 0.58 were obtained, respectively. For τ >0, these values were 0.67 and 0.60 for R2 and 0.55 and 0.60 for model efficiency, respectively. The findings of this study reveal the need for a standard approach for measuring interrill erodibility and recognizing the dominant erosion based on critical shear stress.

In this study, the effects of various fertilizers were evaluated on quantitative and qualitative characteristics of vegetative organs in saffron (Crocus sativus L.). Field study was conducted at the Experimental Farm of the Shahed University using a factorial randomized complete block design. The treatments consisted of three levels of chemical fertilizers (0, 50% and 100% of the recommended amount of fertilizer) and four levels of non-chemical fertilizers (control, vermicompost, bio fertilizer containing Pseudomonas and Bacillus, and integrated application of bio fertilizer and vermicompost). In order to determine the best type of fertilizer in saffron cultivation, characteristics such as physiological attributes, photosynthetic pigments, and leaf chemical elements were measured. The results showed that sole application of bacteria had the greatest effects on morphological characteristics. Application of bacteria along with vermicompost increased the amounts of pigments significantly. Also, integrated application of bacteria, vermicompost, and 100 percent fertilizer was the most effective treatment on leaf chemical elements. Application of plant growth promoting bacteria (PGPR) showed positive effects on most of the studied characteristics: Compared to the control (no fertilizer), it increased leaf length, fresh and dry weight, chlorophyll b, total chlorophyll, carotenoids, zinc, and phosphorus concentrations by, respectively, 61.64%, 79.71%, 82.05%, 4.01%, 4.90%, 4.23%, 20.18% and 20.23%. Because of the environmental and economic importance of inputs in agriculture, it is recommended to use the two types of growth promoting bacteria to achieve the highest quantitative and qualitative vegetative growth in saffron.

Quantitative knowledge of soil hydraulic properties such as the soil moisture characteristics curve (SMC) and the hydraulic conductivity curve is crucial for flow and transport modeling in hydrologic and agricultural engineering. However, many laboratory and field methods are currently available for direct measurement of the soil hydraulic properties, but, most or all of direct methods are too time consuming and costly. Chin et al. have developed a one-parameter method for estimation of Fredlund and Xing SMC model using regression analysis. This study was carried out for evaluation of this method for estimation of SMC and available water (AW). Forty five soils from UNSODA database and forty two soils from Iranian soils with a wide range of hydraulic properties were selected. Smallest root mean square error (RMSE) was obtained when the basic point of SMC was set at the matric suction of 33 kPa. Large coefficient of determination (R2=0.96) and small RMSE (0.026) between estimated and measured soil moisture confirmed that the studied approach was a suitable method for estimation of SMC in quite divers soils. Small RMSE and positive and significant correlation between measured and estimated available water showed that the approach properly estimates the AW as well. Comparison of the results demonstrated that one-parameter method is more accurate than the several previously developed pedotransfer functions for the Iranian soils.

Preferential flow pathways cause leaching of significant amount of nutrient elements from the root zone. The objectives of this study were to evaluate the influence of petrochemical sludge on preferential flow and transport parameters of bromide in convection-dispersion equation (CDE) and mobile-immobile models in a calcareous loam soil. The soil was taken from the research farm of University of Mohaghegh Ardabili. The sludge was prepared from the Tabriz Petrochemical Company. The used rates of fresh sludge were: 0, 25, 50, 75, and 100 t ha-1. After air drying, the sludge was mixed with the air-dried soil and filled in PVC tube (25 cm height and 15 cm diameter) and kept in greenhouse at the temperature of 22 ± 4 ˚C and moisture of 70 to 80 percent of field capacity for 6 months. The experiment was conducted as completely randomized blocks design with 5 sludge rates at 3 replications. Saturated hydraulic conductivity (Ks) and bromide breakthrough curves (BTCs) were measured in soil columns at the end of the sixth month. Dispersivity (λ) at the CDE and MIM models, immobile water (θim) and solute exchange coefficient (α) at the MIM model were estimated by fitting measured BTCs data (time and relative concentration of bromide) to these models using HYDRUS-1D software. All sludge rates significantly decreased Ks by 55% to 67% and increased bromide breakthrough time by 60.29% to 63.19% compared to the control. Dispersivity at both CDE and MIM models significantly increased only for the 50 t ha-1 of sludge compared with the control. The sludge did not significantly affect θim and α parameters. The results showed that petrochemical sludge controlled preferential flow of bromide in the studied soil from semiarid region.

Wind and water erosion are among the main causes of damage to the soil and environment. In previous studies, a great emphasis has been placed on the role of aggregates stability in erosion control and prevention of particles movement and displacement. For this purpose, the use of polymeric materials to control wind erosion has been considered, but the amount and duration of their effects on aggregate stability in different soils must be determined. This study aimed to investigate the impact of a Polyvinyl Acetate-based polymeric emulsion on dry aggregate stability, time-variation of dry Mean Weight Diameter (MWD), and optimum amount of polymer in different soils. To do this, three different soils were selected with light, medium, and heavy texture and soil characteristics such as determination of initial water content, particle size analysis, hydrometer tests and Atterberg Limits were determined. Later, 12 treatments were applied using four levels of 0, 25, 40, and 50 g/m2 of polymeric material with concentrations of 0, 25, 40 and 25 gr/lit and with three different soils. Then, in one day, one month, three, and six months intervals after preparation, the MWD of treatments were measured in three replications. Statistical analysis showed that, in many time intervals, application of polymeric material had significantly increased the MWD compared to water treated (control) samples, and both the amount of polymeric material and the volume of added emulsion affected aggregate stability. Compared to the water treated samples, the effect of all polymeric treatments on dry aggregate stability of sandy soil were considerable even after 6 months. MWD values of all polymeric treatments of the silty loam soil were higher than the control samples till 3 months but, after six months, only the MWD of polymeric treatment of 50 gr/m2 was still greater than the control. Also, in polymeric silty caly loam soil, only the MWD of the 50 gr/m2 treatment was still greater than the control samples after six months. Finally, polymeric treatment with 25 gr/m2 application was chosen as effective treatment because of having the lowest applied polymeric material and lowest polymeric emulsion volume.

Cobalt has not been categorized as an essential plant nutrient, although it has been shown to be useful to some crops. On the other hand, cobalt is discharged on soils as part of some wastes and effluents. The effect of cobalt on the growth of pinto bean has not been studied yet. To evaluate the effect of cobalt on pinto bean, a pot experiment was carried out in 2010 in the Shahrekord University greenhouse with 5 soil cobalt levels (0, 20, 70, 150 and 220 mg Co/kg dry soil) in a completely randomized design. After physiological maturity, leaf area, stem length, root length, stem and root dry weights were measured. Strong linear relationships were observed between soil cobalt concentration and cobalt concentration in root, stem, and leaf and, therefore, the whole plant (p<0.01). Most of the absorbed cobalt was retained in the root. At 20 mg Co/kg soil, all growth indices, including allometric coefficient, improved (p<0.01). All growth indices were negatively affected in a linear manner with increasing soil cobalt concentration. Relative growth inhibition initially decreased but increased afterwards with higher soil cobalt concentrations. Overall, a tolerance threshold of 70 mg Co/kg of dry soil (or 350 mg Co/kg dry weight of aerial parts) was estimated for pinto bean.

Drought and salinity are the most important stresses which reduce crop production in arid and semiarid areas. Therefore, effect of halophilic exopolysaccharide-producing bacteria was investigated on decreasing drought and saline stresses. In the first step, the best isolates of halophilic exopolysaccharide-producing bacteria were selected from a saline soil in Eshtehard, Iran. Determination of 16S rRNA gene sequences of the isolates showed that TP7 and TP5 isolates were most closely related to Bacillus subtlis susp. Inaquosorum) T) (98.5% sequence similarity) and Marinobacter lipolyticus SM19(T) (97.7 % sequence similarity), respectively. Then, a study was carried out in factorial arrangement with completely randomized design on wheat. The factors included four bacteria treatments: without inoculation of bacteria (B1), isolated bacteria TP7 (B2), isolated bacteria TP5 (B3), and both isolates of bacteria (B4). Besides, four levels of soil salinity (2, 4, 8, and 16 dS m-1) and two soil moisture levels (75% and 25% of available water) were also part of the study. The results showed that the inoculated treatments had higher dry and fresh root and shoot weights, germination rate, and germination percent compared to non-inoculated treatment. This increase was remarkable in the treatments inoculated with both bacteria (B4) under the two moisture levels and at salinity levels of 8 and 16 dS m-1.

This research was carried out to evaluate the possibility of using native plant growth-promoting Rhizobacteria (PGPR) for improvement of nutrition and growth of pistachio seedling under drought stress condition. Hence, a greenhouse experiment was performed as factorial arrangement on the basis of completely randomized design (CRD) including seven bacterial treatments and three drought stress levels with four replications. Bacterial treatments included control (T1), inoculation with two IAA producing isolates (T2), one ACC-deaminase producing isolate (T3), two isolates with high phosphate solubilizing potential (T4), four isolates with high siderophore producing potential (T5), mixture of Acc-deaminase and IAA producing isolates (T6) and mixture of all isolates (T7). Drought stress levels included D0, D1, and D2 by using 80%, 50%, and 20 % of available water, respectively. The mean of shoot and root dry matter, total leaf area and number, plant height and root volume significantly decreased by drought stress. Considering the results of means comparison, the maximum shoot weight, plant height, total leaf area and number was obtained in plant inoculated with ACC deaminase producing bacteria (T3), while the minimum was observed in plants with no inoculation (T1). The mixture of ACC deaminase and IAA producing bacteria (T6) had statically similar effects to ACC deaminase producing bacteria in severe drought stress. T3 treatment had the most significant effect on all root parameters under severe drought level. Drought stress resulted in significant increase in concentration and significant decrease in uptake of P, Fe, and Zn by plant. The highest concentration and phosphorus uptake by plants were, respectively, related to T6 and T3 and the minimum belonged to the control (T1). These results suggested that plant inoculation with IAA (T2) and/or ACC deaminase producing bacteria and the mixture of these bacteria could improve certain growth indices in drought stress conditions.

Using rhizobial inoculants in legumes cropping including chickpeas has attracted attentions because of economic advantages, decreasing chemical fertilizers utilization, and environmental health issues. Iran has 10 years of experience on production and utilization of these inoculants. For production of any rhizobial inoculant, it is vital to have a collection from effective and well-known strains of rhizobia. The aim of the current study was to characterize the isolates of chickpea rhizobia (collected by Soil and Water Research Institute from different parts of Iran) and to evaluate their genetic diversity. Bacterial isolates were purified on YMA plates and were subjected to microscopic, morphological, and plant infection analyses. Out of 120 isolates, 82 were able to nodulate the host plants and were considered as nod+ isolates. Identification of the isolates was carried out using biochemical test including utilization of carbohydrates, amino acids, and ability for growth in different cultural conditions. Results of the biochemical tests were used for clustering of isolates. Results showed that, the isolates could be divided into six groups, of which the majority belonged to M. ciceri. Six representatives were selected from each cluster and their 16 rRNA sequence was determined. Results of the study revealed that isolates C-22, C-35, C-35A, C-97 and C-105 belong to M. ciceri and the isolate SWRI-9 was M. mediterraneum.