نشریه پژوهشهای خاک (علوم خاک و آب)
سال بیست و هشتم شماره 3 (پاییز 1393)

Rhizosphere has different chemical and biological properties from the bulk soil. Information about phosphorus (P) availability in the rhizosphere soils treated with municipal sewage sludge (MSS) is limited. Therefore، the objectives of this research were to evaluate the rhizospheric effects of wheat (Triticum aestivum L.) on phosphorus availability and biological properties in 10 calcareous soils treated with MSS under rhizobox conditions. Dissolved organic carbon (DOC)، microbial biomass carbon (MBC)، microbial biomass phosphorus (MBP)، metabolic quotient (qCO2) and available phosphorus (by 4 chemical extractants including Olsen، MehlichІ، BrayІІ and calcium chloride methods with different extraction mechanism)، were determined in the rhizosphere and bulk soils. The results showed that DOC، MBC and MBP strongly increased and qCO2 strongly decreased in the rhizosphere soil compared with the bulk soil. Also، the amount of P extracted with different tests in the rhizosphere was lower compared to the bulk soils. The correlation studies showed that dry yield of wheat had positive relationship with MehlichІ and Olsen-P in the rhizosphere and the bulk soil، respectively. The results of this research showed that MehlichІ and Olsenextractants could be used to estimate plant-available P in the rhizosphere and bulk soils، respectively.

For controlling iron deficiency of kiwi trees، a completely randomized block design experiment was conducted during 2012 and 2013 in Mazandaran، north of Iran. The experiment contained three types of soil injection: 1- iron sulfate (Fe0=0، Fe1=1 and Fe2=2 kg per tree)، 2- sulfuric acid (AS0=0، AS1=1 and AS2=2 L per tree)، and 3- organic matter (OM0=0، OM1=2 and OM2=4 kg per tree). These treatments were carried out early in 2012 and compared with fertigation of iron chelate (100 gr of Fe-EDDHA each year per tree). Biennial results showed that Fe2AS1OM2 caused the highest fruit yield and the largest leaf area. The highest leaf chlorophyll index (SPAD reading) was observed in Fe2AS2OM2. Single fruit weight and size were highest in Fe1AS2OM2. Soil injection of ferrous sulfate and sulfuric acid increased iron concentration in leaves، but organic matter had no such effect. Applying sulfuric acid also decreased phosphorus concentration in leaves. In conclusion، results of this two-year experiment confirmed superior benefits of soil injection of 2 kg of iron sulfate، 0. 5 L of sulfuric acid، and 4 kg of organic matter per tree، compared to iron chelate application، in kiwi orchards.

Under arid and semi-arid conditions, water deficiency may limit the use of nitrogen by plant and lead to a decline in crop production and water use efficiency. Therefore, in order to study the effect of drought stress and various fertilizers on different aspects of water use efficiency and biomass of isabgol, a factorial experiment was conducted in a randomized complete blocks design with four replications under microcosm conditions. Treatments included two levels of drought stress (non-stress and with stress) as the first factor, two levels of mycorrhizae (inoculated with G. intraradices and non-inoculated) as the second factor and three fertilizer types (separate application of Azotobacter chrococcum, application of 40 kg N/ha as urea fertilizer, and combined application of azotobacter plus 20 kg N/ha as urea) as the third factor. The results indicated that drought stress reduced the root and shoot biomass on average by 31% and 28%, respectively. But, mycorrhizae caused the increase of root and shoot biomass on average by 65% and 24.7 %, respectively. Water use efficiency increased for the aboveground biomass and total biomass production in drought stress plus mycorrhizae and 40 kg N/ha as urea. However, water use efficiency for seed and mucilage production was only affected by drought stress and mycorrhizae. In conclusion, results showed that water use efficiency for seed production was only increased by mycorrhizal inoculation under drought stress. However, water use efficiency for mucilage production not only increased in drought stress conditions, but also it increased more in mycorrhizal inoculation treatment under drought stress conditions.

Soil is a heterogeneous environment whose properties have spatial and temporal changes. Soil and vegetation have reciprocal relationship and influence each other. Thus، investigation of spatial variability of soil properties with other environmental change is essential. In order to analyze spatial variability of soil properties in Dareh Viseh rangelands، 78 soil samples from 0-30 cm soil depth were taken and transferred to laboratory. Soil properties including clay، silt، sand، and organic matter were measured in laboratory. After normalizing the data، the semi-variograms were obtained and evaluated. Then، kriging، inverse distant weighting، and radial basis function methods were evaluated for the obtained data. To compare these methods، the cross validation was used by statistical parameters of Mean Absolute Error (MAE) and Mean Bias Error (MBE). The results showed that the kriging method provided a reasonable prediction for silt، sand، and organic matter of soil، while the radial basis function provided better estimation for prediction of clay in the study area.

Soil contamination by heavy metals around big cities and intensive vegetable cropping in these soils may be a threat to human health. A factorial greenhouse-experiment was conducted to evaluate the effects of different levels of cadmium (Cd) (0، 5، 10، 20 and 40 mg/kg) and soil calcium carbonate (13. 5، 44. 5 and 67. 5 percent) on some growth indices of two common vegetables، namely، radish (Raphanus sativus) and spinach (Spinacea oleracea)). Leaf area and wet weight of spinach and radish and wet weight of radish root were used to assess their marketing properties. Cd concentration in both plants was increased by soil Cd levels and it had a dramatically decreasing effect on plant growth indices and marketing properties of both vegetables، especially those of spinach، but soil calcium carbonate had no significant effect in this regard. All measured plant growth factors i. e. wet weight، dry weight، chlorophyll A and B were dramatically changed and depressed by Cd toxicity. Applied Cd at 40 mg kg-1 decreased leaf area and wet weight of spinach by 77% and 86 percent، respectively. In radish، these figures were about 36% and 32 percent. Radish root wet weight was decreased to 49 percent when compared to no-Cd treatment. Spinach showed a lower marketing value than radish despite the fact that Cd concentration in radish leaf was higher than that of spinach. Soil Cd concentration had less effect on radish marketing property (root wet weight). Radish root marketing properties were less affected despite having higher Cd concentration. This means that، in comparison with spinach، there is more risk to human health of a high Cd radish entering into human food chain.

Soil organic matter could be effective on mobility of heavy metals and underground water pollution. This study was conducted in order to evaluate the effect of different levels of vermicompost on the mobility of Pb and Cd in the soil columns. Three levels of vermicompost comprising 0% as the control (V1)، 2% (V2)، and 4 wt% (V3) were mixed with soil in Polyethylene columns filled with a clay loam soil and irrigated with Cd- and Pb-enriched (20 and 40 mg L-1، respectively) waste water during 8 periods of 10 days. Drainage waters were collected at the end of each period and characteristics such as pH، electrical conductivity (EC)، oxidizable organic carbon، Pb، and Cd concentration were measured. At the end of the 8th period، soil samples of the depths of 0-20 and 40-60 cm were collected and analyzed. The results showed that the maximum concentration of Pb and Cd، OC، and EC of the drainage water was in the first study period and this trend was reduced in the subsequent periods. The reverse trend was observed for the pH. The highest concentration of Pb and Cd was measured at a depth of 0-20 cm in soil column due to the low mobility of these elements in the soil profile. In both depths (surface and deep)، more concentrations of Pb and Cd were adsorbed by soil particles in the control treatment، suggesting the positive role of vermicompost in enhancement of the mobility of these elements and more removal from soil columns. Higher ratio of Pb concentration in surface to deep layers showed lower mobility of this element compared with Cd. Therefore، higher organic matter contents in soils enhance heavy metals mobility، particularly Cd، toward lower soil layers.

Soil temperature is one of the key parameters affecting most hydrologic and agricultural processes. Therefore، its measurement and prediction is very crucial. Since soil temperature is measured only in the synoptic meteorological stations، lack or shortage of data is the major challenge in many agricultural studies. In this study، soil temperature data were predicted at three different depths of 5، 10 and 30 cm by an Artificial Neural Networks using meteorological parameters recorded at Shiraz synoptic stations during the period 2000-2008. Due to the large number of variables used in this study to predict soil temperature، identifying the more effective variables could improve the results. Therefore، using a multivariate statistical technique of principal component analysis (PCA)، which effectively reduces the number of variables and inputs the effective variables to the network، the soil temperature was predicted by (PCA-ANN). At first، PCA was used to reduce the input variables and 8 meteorological variables were altered to 8 main components. The first four principal components accounted for over 99% of the total variance. In order to evaluate ANN and PCA-ANN models، correlation coefficient (r)، Root Mean Square Error (RMSE) and Mean Bias Error (MBE) were used. Results showed that the statistical parameter values (verification period) with 0. 98، 1. 61 and 0. 2 for r، RMSE، MBE، respectively، had the best results on soil temperature at 5 cm depth for PCA-ANN model. The results indicated the importance of preprocessing the variables by PCA. The PCA-ANN model in comparison with the ANN model had an easier structure، the ability of faster training، and more accurate results.

Assessment and mapping of desertification potential has been considered as a planning tool in management of desert areas. Based on the importance of these maps، despite the development of techniques and quantitative methods in recent years، experts try to provide methods with fewer errors and more reliability. In this regards، studying desertification hazard zonation models revealed that in evaluation of indices، only the absolute value of each index in each work unit has been considered and their priorities in critical condition has been neglected، thereby leading to unrealistic results. Therefore this study aimed to present a model to classify desertification severity based on indices priority and the importance of each indicator in each work unit. In this regard، Shannon entropy model was used. This model، derived from information theory، evaluates potential risk of desertification by analytic hierarchy process in work units and finally presents the result as evaluation maps. The results showed that 0. 43% and 8. 92% of the study area faced severe and relatively severe desertification، while the greatest proportion of desertification belonged to medium (57. 18%) and relatively medium (33. 48%) class of desertification، respectively. However، quantitative value of desertification severity for the total area was 0. 065، corresponding to medium class (V) of desertification.

Oil contamination is one of the most common and usual kinds of pollution in aquatic and terrestrial ecosystems. One of the economical and effective methods for decreasing or eliminating oil contamination is using plants and microorganisms. Soils contain a wide variety of oil decomposing microorganisms، of which pseudomonad، Rhodocoous and Nocardia are the most important. To evaluate the effect of oil decomposing bacteria on bioremediation of oil contaminated soils with and without plant (the role of rhizosphere)، this research was conducted in greenhouse condition. Fifteen soil samples form depth of 0-30 cm were collected from around an oil refinery، where soils were exposed to oil contamination for a long time. Oil decomposing bacteria were isolated and purified from the collected soil samples، then their bioremediation efficiency was determined. A greenhouse experiment was conducted as completely randomized design using bacteria (4 levels)، plant (2 levels) and pollutant (4 levels) as variable factors. Sixty days after beginning of the pot experiment، wheat plants were cut and fresh and dry weight of their root and shoot and also the concentration of pollutants in soil were determined. The results indicated significant effects of bacteria، pollution، and their interactive effect on shoot fresh weight، as well as the effects of pollution and interaction of bacteria with pollution on shoot dry weight، with similar effects of pollution on fresh and dry weight of root. Pollution decreased the fresh and dry weight of root and shoot، while inoculation of bacteria improved root and shoot weight، due to elimination of pollutant. The effects of all treatments on pollutant concentration were significant. Planting and bacteria inoculation decreased pollutant concentration in soil significantly. Bacteria were more efficient than the plant in decreasing soil pollutant، and plant did not increase bacterial efficiency significantly. Thus، the difference between plant and plant+bacteria treatments was not significant.

Heavy metals in high concentrations in soils are potential health risk for humans، animals، and plants. Soil samples were collected in five replicates from 20 points with four land use including: roads، refineries، residential area (Sadra town)، and farmland. Heavy metals were determined using flame atomic absorption (Analyticjena)، while DTPA was chosen as trace elements extractor. In this study، soil surface concentrations of lead، cadmium، zinc، chromium، and nickel were measured to evaluate the potential risk of pollution. The results of soil pollution evaluation showed that the soils pollution levels were low and non-contaminating. ANOVA (Duncan''s test) result showed that all the elements were significantly different in various land uses. The findings revealed that Ni of soil refinery was significantly different than the others. Soil Pb showed significant differences between urban and road land uses، but there was no significant difference between agriculture and refinery. According to the results، soil Cr of refinery was different than that of road and urban areas but was similar to the agricultural land. Cd of soil surface in urban areas had significant difference with refinery and road but was similar to agricultural soil. Also، soil Zn in refinery area was significantly different compared with the others.

Plants uptake boron (B) from the soil solution، in which boron concentration is controlled by adsorption and desorption reactions on soil organic and inorganic colloids. Considering the importance of aluminosilicate minerals in ion adsorption and desorption reactions in soil، in this research، B adsorption behavior on kaolinite was studied as a function of equilibrium concentration، pH، kaolinite concentration، and ionic strength. Adsorption isotherms on kaolinite at pH 5 and 8، and at concentration range of 0 to 1319 μmol/L، indicated that B adsorption increased with increase in its equilibrium concentration and its maximum adsorption at pH 8 reached 20 μmol/L. Adsorption edges also indicated that B adsorption proportionally increased with pH until pH 9، where it reached a maximum level. It was then reversed by further increase in pH. Experimental data at constant B concentration exhibited an adverse effect of kaolinite concentration on B adsorption. Boron adsorption at three levels of ionic strength showed a negative effect between salt concentration and B adsorption. This adverse effect is likely due to the effect of ionic strength on kaolinite charging behavior، and on the boron solution speciation، and the competitive adsorption of nitrate ion with B. Due to the high amount of boron adsorption on kaolinite and similarity in anion adsorption by different aluminosilicate clay minerals، it can be concluded that these minerals play an important role in boron adsorption in soil and controlling its availability for plants.