WATER AND SOIL SCIENCE (AGRICULTURAL SCIENCE)
Year:2015 | Volume:25 | Issue:4/1|Papers Count:22

In this research, the dam break problem has been presented from the viewpoints of importance, mechanism, spatial and temporal analyses as well as governing mathematical equations. For this purpose, the output hydrographs of the Vanyar dam site have been computed by breach model under a fictitious dam break scenario (overtopping) as the first step. In the next step, the output hydrographs have been routed through the downstream river by using HEC-RAS model. Then water levels and wave front arrival times have been computed at all cross sections. Finally the obtained results have been imposed to Geographic Information Systems in order to obtain the presentation of the results to develop floodplain maps. Considering the obtained results, the output hydrograph’s shapes have moderate slope, because gradually breach mechanism occurs in the dam in this scenario. Furthermore, the power of the flood is considerably decreased without any significant financial damages under the geomorphological and topographical downstream conditions of the river close to the dam site. However, the study shows that some villages and installations in the downstream may be prone with some minor damages. Also the maximum flood plain and wave front arrival time at the downstream have been calculated.

Water repellent soil is a soil that is not immediately wetted when a drop of water is placed on its surface. Soil water repellency is formed by complex waxy organic compounds. During the decomposition of the organic matters, these waxy compounds cover soil particles and the soil becomes water repellent. Due to the influence of the size and arrangement of the pores on soil water retention curve, the slope of the retention curve at its inflection point that has been defined as soil physical quality index (S), reflects different aspects of soil physical quality such as penetration of water, air and roots and bulk density. In this study, two clay loam and sandy loam soils from the forest and grassland (converted to dryland farming) around the Kaleybar city, East-Azarbaijan province (Iran), were sampled and artificially hydrophobized by stearic acid at different concentrations to obtain five different degrees of water repellency. The purpose was to investigate the effects of water repellency on soil water retention curve, van Genuchten model coefficients and soil physical quality or S index. To achieve these objectives, laboratory-scale studies were conducted in disturbed soil columns (in triplicate). Results indicated that with increasing water repellency (from degree 1 to 5) in both soils, soil water retention curve and van Genuchten coefficients were affected significantly (p<5%). The S index decreased from 0.0592 to 0.0254 in sandy loam soil and from 0.0681 to 0.0537 in clay loam soil with increasing water repellency from degree 1 to 5. Statistical comparison indicated significant difference (p<0.05) in the values of the parameters n and m of van Genuchten model, saturation, field capacity, residual and inflection point moisture between various degrees of water repellency. The value of the a in van Genuchten model varied significantly (p<0.05) among all of water repellency degrees in sandy loam, but in the clay loam only the second degree of water repellency significantly affected the value of a in van Genuchten model.

Soil water and nutrients are important factors controlling plants growth. Legumes inoculation with nitrogen fixing bacteria and phosphorus (P) fertilization can improve plants growth in drought stress conditions. The effects of Sinorhizobium meliloti inoculation, soil water and P levels on leaf chlorophyll index, nitrogen (N) and P concentrations in alfalfa (Medicago sativa cv. Ghareyonjeh) shoot and root were studied by conducting an experiment under greenhouse conditions in a clay loam soil. The study was performed as a factorial experiment based on a randomized complete blocks design including soil water conditions at three levels (0.5FC-0.6FC, 0.7FC-0.8FC and 0.9FC-FC), P at three levels (0, 30 and 60 mg P kg-1 soil equal to 0, 60 and 120 kg P ha-1 as Ca (H2PO4)2.H2O, respectively) and bacterium inoculation at two levels (with and without S. meliloti inoculation), with three replications. The leaf chlorophyll index was measured during the growth period. After harvesting, concentrations of N and P in the alfalfa shoot and root were measured. The results indicated that the leaf chlorophyll index and shoot N concentration were significantly increased by decreasing soil moisture content from 0.9FC-FC to 0.5FC-0.6FC (water deficit stress) and shoot and root P concentrations were significantly decreased (p<0.01), while the root N concentration was not change significantly. The P fertilization caused increment of the leaf chlorophyll index, shoot and root N and P concentrations (p<0.01). The leaf chlorophyll index, shoot and root N and shoot P concentrations were increased by S. meliloti inoculation but the root P concentration was not change significantly. Application of P and S. meliloti inoculation improved the drought stress tolerance of alfalfa. In general, in order to improve nutrition and growth of alfalfa and its drought stress tolerance, application of 30 or 60 mg P kg-1 soil and S. meliloti inoculation can be recommended under with and without drought stress conditions.

Side weirs are flow diversion and protection devices that are widely used in irrigation, land drainage and urban sewage systems. This study investigates the discharge coefficient of rectangular and triangular sharp crested side weirs and identifies the effective factors on this parameter by using dimensional analysis and statistical approaches. In addition to calculating the discharge coefficient, equations with 5 percent error for rectangular and 3 percent error for triangular shape have been proposed. For checking the effect of factors on this parameter sensitivity analysis is performed. The results demonstrate that the most important effective factors on discharge coefficient of the rectangular and triangular weirs are Froude number and dimensionless ratio of the main channel wide to the depth of flow in the upstream of the weir, respectively. Error of discharge coefficient (Cd) can be increased up to 7 percent for rectangular weir and 4 percent for triangular side weir with ignoring these factors. Also accurate estimation of discharge coefficient, merely with considering the upstream hydraulic condition, is not correct. The geometry of the cross section should be considered as an effective factor for determination of discharge coefficient, and this approach, decreases error of the calculation up to 3 percent.

Nowadays, application of remote sensing data in water resources, particularly in irrigation management has been widely acknowledged by researchers. In this research feasibility of the use of energy balance model for estimation of evapotranspiration and assessment of agricultural water productivity in a large irrigated area of the Qazvin plain irrigation network was studied, using satellite data. The SEBAL Energy balance algorithm was used to calculate evapotranspiration. SEBAL uses the reflectance capability of solar radiation that is received by satellite sensors and estimates the evapotranspiration from the residue of energy balance equation. In this study, moderate-spatial resolution of Landsat 7 ETM+ images for the semi-arid climate of the study area of Qazvin Plain were considered and the resulted evapotranspiration values were modified and adapted using the FAO-56 methodology for 2001. The results showed a good agreement between FAO Penman- Monteith data and the resulted actual ET values from Landsat 7 ETM+ images in 2010. Values of total daily evapotranspiration varied from 3.8 to 6.7 mm per day. Also, agricultural water productivity for dry biomass was estimated to be about 0.92 and 1.22 kg m-3 based on ground data and the resulted data from Landsat 7 ETM+ images, respectively.

Small portion of soil phosphorous (P) is usable by plants. To investigate the effects of alfalfa green manure (2% w/w) and roots of corn and canola in single and intercropping systems on available P concentration in soil, a greenhouse experiment was conducted using rhizobox system. The experiment was arranged as a split factorial design with 3 replications, two levels of green manure (0 and 2%), 4 zones with distance from root (rhizosphere, near rhizosphere, near bulk soil and bulk soil) and 4 culture systems (corn, canola, mixed culture and control (not cultivated)) based on completely randomized design. Canola and corn were cultivated at the middle part of rhizobox in mixed or separate forms. The plants were harvested 85 days after sowing and the soil samples were taken from different parts of the rhizobox. The results showed that the green manure reduced the soil pH more than 0.19 and enhanced the dissolved organic carbon concentration (DOC) and soil available P by 25 mg L-1 and 9.47 mg kg-1, respectively. The soil pH and available-P were increased while the DOC was decreased from rhizosphere toward the bulk soil. The bulk soil (over 16 mm distance from root) was not apparently affected by the root activity. Also the results showed that the green manure addition increased the dry weight in corn and canola and also increased the P concentration and uptake in canola while it decreased the P concentration and uptake in corn. Dry weight of intercropping system was more than that of single culture of corn and canola.

To select a statistical distribution to describe a set of data, there are several criteria that can be used. Rather than the selection of a criterion according to traditional methods, the combination of two or more criteria may be used to achieve the best choice. But when more than two criteria are applied to find out the best model, selection becomes more difficult. In these cases, the use of multi-criteria decision making (MCDM) is essential. This study compares eleven commonly used distributions in hydrology based on five selection criteria. These selection criteria are: The Kolmogorov-Smirnov test, the errors in skewness and kurtosis, the errors in cumulative distribution function, the errors in probability distribution function and the root mean square error. Three MCDM methods, namely, simple additive weighting, weighted product method and fuzzy majority approach, are employed. In the present study, we examine the sensitivity of the results of MCDM by changing the weights and number of criteria. The methods are applied to a case study of Mahabad River, a major river flowing into Lake Urmia in northwestern of Iran. Results of this study have shown that three-parameter Weibull, three-parameter Weibull and generalized extreme value distributions have the best fit for peak flow, volume and duration of Mahabad River flood data, respectively. The result of this study can be used to improve the flood frequency analysis.

In this research the effect of roughness for different bed slopes on the control of sedimentary density current in subcritical conditions was investigated. The results showed that for each bed slope increasing the roughness height had considerable effect on reducing the load discharge of density current front (from 40% to 70% for concentration of 10 g L-1 and 35% to 55% for concentration of 20 g L-1). Also the amount of water entrainment rate reduced with increasing the roughness height (from 50% to 60% for concentration of 10 g L-1 and 48% to 60% for concentration of 20 g L-1). Finally, an equation for predicting water entrainment as a function of Richardson Number and relative roughness was presented. Sensitivity analysis of the proposed equation in this research showed that the effect of Richardson number on estimation of the water entrainment is much more than the effect of relative roughness on it.

Accurate prediction of river flow discharge is very important for optimization and management of surface water resources. One of the applicable ways for simulating and predicting hydrological data such as river flow is using time series models. But one of the major problems for prediction of hydrological data by time series models is assignment of the generation approach of the random and stochastic series. In this study, it is attempted to define a systematic framework for generating random component of a time series model. In this case, after initial tests on the Siminehrood river peak flow discharge time series during 1967-2011, the ARMA models were evaluated and the ARMA (1,0) model was selected as the best model. Then residual series of the selected ARMA model was extracted and fitted by ARCH and PARCH nonlinear models approaches to obtain the ARMA-PARCH and ARMA-ARCH models. Results showed that using combined ARMA-PARCH and ARMA-ARCH models reduced the error of models up to 92.22 and 92.16 percent, respectively. It was observed that between the two combined models, the ARMAPARCH model had more accuracy and less error than the ARMA-ARCH model. Also with the selected combined model, the maximum and minimum points of the peak flow discharges were modeled well for the studied station.

Burning of crop residues has adverse impacts on soil and environment. Limited information is available about the effects of crop residue burning on different forms of soil carbon. A factorial experiment with a complete randomized design was conducted to evaluate the effects of burning of sugarcane, and maize residues and different sampling depths as experimental factors on different forms of organic carbon including microbial biomass (MBC), permanganate-oxidizable (POX), total organic carbon (TOC), fine particulate organic carbon (FPOM) and coarse particulate organic carbon (CPOM) in some soils of Khuzestan Province. Composite soil samples with three replications were taken from 0-5, 5-15, and 15-30 cm depths in 5 points of the selected two sugarcane and two maize farms before and after burning of the plant residues. According to the results, the amounts of TOC (from 7.2 to 9.0 g kg-1 in maize and 13.2 to 14.2 g kg-1 in sugarcane farms), CPOM (from 1.4 to 1.6 g kg-1 in maize and 2.7 to 2.85 g kg-1 in sugarcane farms) and FPOM (from 2.3 to 3.1 in maize and 3.8 to 4.5 in sugarcane farms) were significantly increased in the soil 0-15 cm depth, due to the burning of both crops residues. The results also indicated that the burning of residues decreased the amounts of MBC (from 155 to 123 mg kg-1 in maize and 112 to 65 mg kg-1 in sugarcane farms) and POX (from 240 to 209 mg kg-1 in maize and 362 to 315 mg kg-1 in sugarcane farms) in the soil 0-5 cm depth. Also, the MBC and POX values in 5-15 and 15-30 cm depths were lower than those in 0-5 cm depth of the soil. However, burning of the sugarcane and maize residues had no influence on the amounts of MBC and POX parameters. The results also implied that the amounts of TOC, MBC, POX, FPOM and CPOM were affected by the type of residues. Accordingly, the TOC, POX, FPOM and CPOM values were higher in sugarcane farms, but maize farms showed higher amounts of MBC (128.7 mg kg-1 vs. 60.8 mg kg-1).

To investigate the spatial distribution and vertical changes of heavy metals in the alluvial sediments of Sungun copper mine, sampling was performed in two stages. In the first stage twelve samples of alluvial sediments and mine tailings from depth of 0-5 cm and in the second stage 9 sediment samples from three depths of 0-50, 50-100 and 100-150 cm were collected. The samples were washed out using 0.1 N chloridric acids to prepare the extract which then was analyzed for Cu, Zn and Mn and also for Cu, Zn, Mn Cd and Al in the first and second stages, respectively. The tailing samples were digested by Aqua Regia to get the extract. Evaluation of the pollution indices showed that Cu in 80% of the samples was the main cause of pollution and the most polluted sample was the one collected from the end of Pakhir valley. The highest concentration of Zn was also detected in the same sample. Analyzing the tailing samples showed the highest Mn concentration which represented the tailing impact on the accumulation of heavy metals in the downstream sediments with concentration of 26.5 mg/kg. The results also represented the highest concentration of the metal in 0-50 cm depth. The maximum decrease of concentration was for Cu and the minimum of it was for Mn which was due to decrease of concentration of the materials in water during vertical movements through the sediment. Also heavy metals didn’t accumulate in coarse texture sediments and leached to the lower horizons and reached the finer grain sediments.

Soil is a suitable place for vegetation and plant growth, and if this valuable wealth is not preserved, shortage of food, erosion and damage of natural resources will be occured. In this paper effects of different grazing intensities in reference area, key area (moderate grazing) and critical area (heavy grazing) on soil characteristics were investigated at mountainous rangelands of Nesho in Mazandaran province. Sampling was performed by a random-systematic strategy and sampling unit was linear transect. In each region, 3 transects of 50 m were settled at a distance of 50 m on the downstream slope. Five repeats of patches were randomly selected and for determination of three functional attributes including stability, infiltration and nutrient cycling, 11 soil surface indicators were scored according to the Landscape function analysis (LFA) method instructions. Along each transect at intervals of 10 m, a square 1×1 m2 plot was placed for measuring the canopy cover and soil sampling. The results of LFA method showed that the reference area had the highest stability, infiltration and nutrient cycling and also significant differences with moderate grazing and heavy grazing (p≤0.05). Results of the statistical analysis of the soil characteristics showed that the different grazing intensities had significant effects on the organic matter percentage, available potassium and soil surface resistance to penetration. By comparing the results obtained from the LFA method and analysis of the soil samples taken from the area, it was found that both methods were almost led to similar results, regarding the effect of grazing intensity on soil characteristics.

In measurements of crop evapotranspiration by lysimeter, climate of cultivated field may be different from lysimeter point, also a lysimeter cannot be utilized for measurements of several crops during a limited time. For measurements of the standard maize evapotranspiration by the water balance method, soil water content was measured in a field experiment under furrow irrigation system during 2003 and 2004. Maize root depth was varied in respect to time and for reducing the error of measured soil moisture and calculating the stored water in soil profile, soil water content was only measured in the root zone until the root reached to its maximum length (1.8 m). In this study, the measured standard evapotranspiration of maize via water balance equation in the field, was compared with the estimated values using the methods of Penman-Monteith, Hargreaves- Samani and MSM2 model (Maize Simulation Model). The results showed that applying the water balance method for measuring maize standard evapotranspiration was simple and favorable in field conditions. The investigations confirmed that by use of MSM2 model, modified Hargreaves and Penman-Monteith’s equations, the standard maize evapotranspiration values could be estimated, with the errors of -2%, 5% and -25%, respectively. The results showed that with limited data condition, if only, the minimum and maximum air temperature were available, the maize standard evapotranspiration value could be estimated favorably, using the modified Hargreaves-Samani’s equation and crop coefficient.

Groynes are constructed in arch or straight streams in order to protect river banks and reduce their erosion. Local scour at the nose of groynes is one of the most important issues in designing groynes that is created due to the contraction of the flow section and presence of strong vortexes. In this study, experiments were carried out on series of straight groynes located in a laboratory channel bend with different flow discharges and different angles under clear water scour condition. The maximum scour depths and sedimentation (deposition) area between them were measured and compared with each other. In order to assess the flow pattern, velocity measurement around the groynes was done with an Electromagnetic velocitymeter. Results showed that the maximum scour depth was around the normal groyne and for the three normal, repelling and attracting arrangements, the first groyne had the maximum scour depth while this depth was minimum at the last one. Also for the normal and repelling groynes, for a given ratio of velocity to the critical velocity, the sedimentation area between the first and second groynes was greater than that between the second and third groynes and for the attracting groynes, the inverse trend was confirmed. For various angles of groynes, while increasing the ratio of velocity to the critical velocity, the deposition between the groynes was reduced.

Agrohydrological models that simulate soil moisture and salinity profile are useful tools for improving irrigation management and increasing irrigation efficiency and crop yield. In this study soil moisture and salinity profile were simulated by AquaCrop software, and compared with field measured soil moisture and salinity data. This study was carried out as split plot design (factorial form). Treatments consisted of three levels of irrigation water salinity (S1, S2, S3 corresponding to 1.4, 4.5, 9.6 dS/m) as main plot, two wheat varieties (Ghods and Roshan) and four levels of irrigation water amount (I1, I2, I3, I4 corresponding to 125, 100, 75, 50% of crop water requirement) as sub plot. Based on the results, soil moisture and salinity profiles were moderately sensitive to volumetric water content at the field capacity (θFC), and soil water content at the saturation (θSat) levels, respectively. Overally, the model accuracy in estimation of the moisture was higher than that in estimation of soil salinity at the soil profile. For Roshan cultivar, the average values of NRMSE, NME, d, CRM and R2 for the simulated soil water contents were 11.72%, 26.81%, 0.79, 0.045, and 0.62, while for the simulated soil salinity they were 24.2%, 52.81%, 0.72, 0.187, and 0.58, respectively. For Ghods cultivar, the average values of these parameters for simulated soil water contents were 11.8%, 26.87%, 0.79, 0.055, and 0.61, while for the simulated soil salinity they were 24.6%, 52.97%, 0.72, 0.193, and 0.57, respectively. The model estimated soil moisture at the deeper soil layers and salinity at the surface soil layers more accurate than those in the surface and deeper soil layers, respectively. According to the statistical indices, the AquaCrop model’s accuracy in estimation of the soil moisture at different depths and times was higher than that in estimation of salinity.

Trees have noticeable effects on soil resources distribution and its biochemical processes in arid and semiarid regions. Organic materials are naturally much more in the understory soil than that in the open areas soil. This study tries to reveal and compare the effects of Acacia nilotica and Prosopis juliflora trees on the physical and chemical properties of the soil. To achieve the goals, the understory soil of A. nilotica, P. juliflora and the control soil at three depths of 0-20, 20-40 and 40-60 cm with three replications, were sampled and analyzed based on the complete randomized block experiment with three replications. The studied parameters including; mineral nitrogen, dissolved organic nitrogen, nitrogen mineralization potential, total nitrogen, organic carbon percentage, lime, EC, pH and soil texture were measured. Likewise, analysis of the criterion plant (Lepidium sativum) was performed to determine the efficiency of Acacia nilotica and Prosopis juliflora trees on the amount of nitrogen absorption. Nearly, in all the studied parameters the two mentioned trees had a significantly different effect on the soil with respect to the control soil. Hence the result confirmed the high potential and positive effects of these nitrogen-fixing trees (NFTs) on the soil quality as compared to the site without these trees. The results of this study also indicated that the both of these trees had increased the amount of soluble organic nitrogen, nitrogen mineralization potential, soil organic carbon content and total nitrogen in the studied plants compared to the control. Meanwhile, in the superficial soil, A. nilotica and P. juliflora remarkably increased the mineral nitrogen and total nitrogen, respectively.

In order to offer a way to save Lake Urmia, first the present climatic conditions and the factors that affect its drying should be identified. Then its rehabilitation may be undertaken by managing these factors. Factors like increasing water uses (surface and groundwater) from the Lake Urmia basin, climate changes, dam construction on the rivers feeding the Lake Urmia and the Causeway Bridge play role in Lake Urmia drying. Each of the mentioned factors leads to natural feedback that its role should also be considered in a systemic approach. In this study, different hydrological time series variables such as river discharge, water level of the Lake Urmia, air temperature, precipitation, quantitative and qualitative parameters of the surface and groundwater, evaporation from the Lake Urmia basin as well as the procedures of modeling and forecasting, trend analysis, hydrological drought, meteorological drought and zoning have been investigated. According to the results a decreasing trend was detected for the river discharges, precipitation, evaporation and the Lake Urmia water level series while an increasing trend was observed in the qualitative parameters of ground and surface waters and river deficiency volume series. Results obtained from the modeling of the Lake Urmia water level showed a climatological opportunity in restoration of the Lake Urmia. Finally, by studying the quantitative, qualitative, hydrometric and synoptic parameters, some solutions were presented for the Lake Urmia restoration.

Mahabad reservoir dam plays an important role in supplying agricultural and drinking water for Mahabad city. Therefore, the water quality of this reservoir because of its strategic situation is important, and has been investigated as the goal of this research. In this regard, Novotny index and Vollenweider graph were used. At the first step, water qualitative data in three stations of SW4, SW7 and SW8, that are indicators of water quality conditions in Koter, Beytas branches and main reservoir, were collected in the period time of January 2010 to December 2011 respectively. At the next step, the Eutrophication condition was studied, using the selected indices, in each station. The results showed that the Total Phosphor, Total Nitrogen, Chlorophyll a and saturation percentage of Hypo-limnetic Oxygen concentration were in the high Eutrophic level in sub layer of the reservior. Among the mentioned parameters, the concentration of Phosphor was more than 0.02 mgL-1 and according to the universal standards it was an important agent in creation of the Eutrophication. The presented indices showed that an intensive and dangerous eutrophication was governed in Mahabad dam reservoir. The concentrations of qualitative indices were beyond the universal standards so that this situation was creating an undesirable condition.

During the past two decades, bendway weirs have been used as erosion conrol structures in river bends. These structures are constructed for erosion control at the outer bank with suitable upstream angle. This research investigates the effect of the angle and length ratio of weirs on the resistance coeficients of the flow (f, n) in a sinusoidal channel and in different hydraulic conditions. Three angles (60o, 75o and 90o), three length ratios (0.2, 0.3 and 0.4) and three submergence ratios (2.6, 2.8 and 3) were used as variables. All experiments were performed in alive bed condition with a continuous sediment injection. The results showed that the Darcy-Weisbach’s f and Manning’s n coefficients decreased with increasing of the angle and length ratio. Flow resistance coefficients “f” and “n” increased 90% and 20%, respectively and “C” coefficient decreased 27% due to weirs construction.

This work investigates the relationship between the seasonal streamflows and the dominant modes of climate variability. For this work, monthly and seasonal data from 33 hydrometeric stations located in the Northwest of Iran were used during the period of 1971-2009. Continuous wavelet transform was implemented on the mean seasonal streamflows for all sites. Cross-wavelet analysis was also applied to the seasonal streamflows and three selected teleconnection indices [North Atlantic Oscillation (NAO), Pacific-North America (PNA) and Southern Oscillation Index (SOI)]. The wavelet cross-spectra of all seasons revealed strong climate-streamflow covariance within (2–6)-years time interval just after 1991. Correlation analysis within (2-6)-years time interval between the seasonal streamflow and the selected teleconnection indices showed the largest positive correlations with the NAO, for spring and winter seasons after the change point (1991). In contrast, PNA and SOI showed statistically significant correlations for all seasons before 1991. The cross-wavelet spectra and the correlation analysis within (2–6)-years interval also confirmed the occurrence of a change point around 1991 in seasonal streamflows.

The analysis of the urban pathway inundation via modeling is an effective step towards the enhanced management of urban transportation and the reduction of the hazards caused by the infrastructure damages. Given the complexity associated with data and the information related to the pathway inundation (such as topography, hydrology, buildings and so on) the rational, SCS and SWMM models can be utilized as reliable and efficient estimation methods in small urban areas with relatively small basins. The present paper is adhering to the Digital Elevation Model (DEM) and employing data such as elevation spots, the intensity-duration curves of precipitation, segmented plans, urban usage, and with execution of the mentioned models determines the surface outlet runoff as well as the dimensions of each drainage canal. In this regard, our research aims at re-evaluating the proper dimensions and flow of each drainage canal through the comparison of the obtained results with the current status of the drainage. The results obtained from the implementation and execution of the models demonstrated 7 percent reduction in the dimension of the drainage canals according to the current status of the region.

Biosorption is one of the effectively used methods for gathering heavy metals from aquatic solutions. The objective of this study was to assess the effects of wheat straw humification and sterilization on the release of the Pb adsorbed on fresh and humified wheat in aqueous solutions. Wheat straw (< 2mm) was incubated in 70% moisture content and lab temperature for 60 days. After 1, 20 and 60 days, two sterile and unsterile subsamples were prepared and a high concentration of Pb (800 mg kg-1) was applied to the subsamples in NaNO3 solution (0.001 N) at pH 6. The percentages of the Pb adsorbed on humified wheat straw were significantly higher in unsterile condition (60.96%) compared to the sterile fresh wheat straw (26.96%). The release of the Pb adsorbed on the fresh and humified wheat straw was characterized by an initialy rapid step followed by a slow step. The release of the Pb adsorbed on the sterile and unsterile fresh wheat straw was high and fast, and reached to a zero amount in 4 h. But the release of the Pb adsorbed on the more humified wheat straw (incubated for 60 days) was not stopped. These result show that more Pb can be retained and immobilized on the humified plant residues compared to the raw plant residues. Comparing R2 and SE of the tested kinetic models showed that the first order model was suitable for applying to the releasing data of Pb from the unsterile-unfermented plant residues (sampled in first and 20th days) and from the sterile -unfermentedplant residues (sampled in first, 20th and 60th days). In contrast, Elovich function model was suitable for the releasing data of Pb from the un-sterile -humified (sampled in 60th day) wheat straw. Results showed that there were different controlling mechanisms in release of Pb from the fresh and humified plant residues. The overall differences in the releasing parameters of Pb between the sterile and un-sterile wheat straw showed the function and ability of the microorganisms in Pb adsorption, retention and immobilization in aqueous solutions.