Research Article
R. Ghobadian; H. Shekari
Abstract
Introduction: The concentration changes of suspended load along the river reach and the contributing factors are of importance for hydraulic and environmental engineers. The first step to calculate the concentration of suspended sediment load is determining the flow hydraulic characteristics along a ...
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Introduction: The concentration changes of suspended load along the river reach and the contributing factors are of importance for hydraulic and environmental engineers. The first step to calculate the concentration of suspended sediment load is determining the flow hydraulic characteristics along a river reach. Although most of flow in nature are unsteady, the quasi-steady flow condition was considered to be simple in this study and the water surface profile along the river reach with irregular cross sections was calculated by standard step-by-step method. In order to calculate suspended sediment load under non-equilibrium condition, the advection-diffusion equation with source term was numerically solved. In the present sediment model, ten discretization methods, five relations for calculating capacity of suspended sediment load, eight relations for diffusion coefficients and eight relations to calculate particle fall velocity were used and their effects on suspended sediment distribution along 18480 m of Gharasoo river were investigated.
Results and Discussion: The HEC-RAS model output was used to calibrate the present hydraulic model. The models were run with the conditions as same as Manning roughness coefficient and river geometry conditions. The results showed that the calculated water surface profile along the river reach by two models are completely overlapped each other. In other words, the present model has a very good accuracy to predict the water surface profile in the river reach. As most commercial 1-D models (same as HEC-RAS) only consider the equilibrium condition for sediment transport and the bed or total load sediment, comparing the results of present sediment model with them seems not to be reasonable. Therefore, to validate the present suspended sediment model and finding the best method of discretization, an especial shape concentration hydrograph was introduced to the present model as input hydrograph and the model was run when the source term has been deleted deliberately. The volume below the input concentration hydrograph and calculated hydrographs in different cross sections was compared to each other. Comparing the hydrographs showed that the maximum error in calculating the volume of concentration hydrograph with the input hydrograph was 0.029% implying that the model satisfies the conservation laws as well as reliable programing. Among ten discretization methods, the best method for discretization of the advection-diffusion equation was Van Leer's method with the least error compared to other methods. After validating the model, effect of five relations for calculating capacity of suspended sediment load was investigated. The results showed that using the Wife equation estimated the amount of suspended sediment higher than other equations. The Toffaletti equation also estimated suspended sediment load lower than other equation. Among eight particle fall velocity formulas, Stokes relationship estimated the fall velocity larger than other equations. Hence, the Stokes equation application decreases the possibility of suspending the sediment particles. However, employing Van Rijn and Zanke relationships resulted in a greater suspended sediment load distribution along the river reach. Among eight relationships for diffusion coefficients, Elder and the Kashifipour - Falconer equations exhibited the lowest and the highest amount of diffusion in the concentration hydrograph, respectively. Furthermore, the calculated suspended sediment concentration under non-equilibrium conditions was 11.7 % higher than that under equilibrium conditions along the river reach.
Conclusion: Most 1-D numerical models only simulate the bed and total loads sediment transport under equilibrium condition while sediments are transported under non-equilibrium conditions in nature. Sediment transport under non- equilibrium conditions may be greater or lower than the equilibrium condition known as the capacity of sediment transport. In this research, a numerical model was developed to simulate the suspended sediment transport in a river reach under non-equilibrium conditions. The amount of suspended sediment concentration was calculated for each sediment grain size. The results showed that the distribution of suspended load along the river reach is not significantly sensitive to the fall velocity relations while the type of sediment transport equation affected the suspended sediment transport concentration. The concentration of suspended sediments for non-equilibrium conditions was also 11.7% higher than the concentration of sediments in equilibrium condition.
Research Article
M.R. Goodarzi; R. Piryaei; M.R. Moosavi
Abstract
Introduction: Due to climate change that is happening, the security of water and food in Iran has caused many worries, which include small towns like Boroujerd. A comprehensive assessment is necessary as well as the productivity of water resources, because it can provide information for government ...
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Introduction: Due to climate change that is happening, the security of water and food in Iran has caused many worries, which include small towns like Boroujerd. A comprehensive assessment is necessary as well as the productivity of water resources, because it can provide information for government agencies and the public to develop appropriate patterns. The aim of this study is the use and productivity of water resources in Borujerd city, the aim of this study to utilize appropriately the existing water resources in the city of Boroujerd and it is based on recycling and reusing water resources and reduced harvesting of ground water. So the potential of water saving and return to the cycle has been evaluated, and the results can be used as a potential solution for water shortage in Boroujerd in the future.
Materials and Methods: Water, energy, and food security globally are achieved through a communication approach, an approach that integrates governance and management into all over sectors and scales. A communication approach can support the transition to a green economy which aims instead, among other things, the use of resources and policy coherence. Given the increasing communication between sectors in space and time, reducing economic, social and adverse environmental concerns can increase overall resource efficiency, more benefits and provide human rights for water and food. Therefore in a relationship-based approach, common policy and decision making an approach which reduces the composition and creates collaboration among sectors is in need.
Currently, the most reliable tool to produce climate scenarios is the paired 3D Atmosphere-Oceans General Circulation Models which called AOGCM in this paper. AOGCM is based on the physical relationships that are presented by mathematical relations. In formulating its AR5 synthesis report, the IPCC has made use of new RCP scenarios of greenhouse gas (GHG) emissions. The IPCC society has used new scenarios as trajectory representatives of various concentrations of greenhouse gases. New scenarios have four key trajectories called RCP2.6, RCP4.5, RCP6.0 and RCP8.5 that are based on their radiative stimulus in 2100 and different specifications of the technology level, social and economic situation and future policies.
LARS-WG is a random weather generator that can be used to simulate atmospheric data at a station under current and future climate conditions. The first version developed in Budapest in 1990 as part of an agricultural risk assessment in Hungary, then reviewed and moderated by Semenov in 1998. This model produces a daily time series of minimum and maximum temperature, rainfall and solar radiation.
Results and Discussion: Concerning precipitation variations, it can be concluded that changes in winter months from January to March in RCP2.6 will decrease by 20%. Rainfall variations in the spring are the same and have equal status with the base time. In summer, two scenarios experience a 40% reduction, in fall, RCP2.6 shows a 20% increase in rainfall and the scenario RCP8.5 shows about 10% precipitation reduction. The two scenarios show at least 1.5 degrees Celsius increase and the highest increases are in fall, and in October, a rise of 2.5 degrees has seen. Maximum temperature changes which indicate the temperature increase to 2 degrees at least in both scenarios. In scenario RCP8.5, in winter and fall, the maximum temperature is increased to 2.5 and 3 degrees, respectively. Boroujerdʼs water and sewage company harvests 22 hm3 (MCM) water annually for its population of 240,654 people. If the necessary measures are taken for gray and black water purification, Boroujerdʼs daily city sewage that is 35416/6 m3 daily, can return to the water cycle. The city's total wastewater is 12,750,000 m3 per year and it is possible to prevent underground water harvesting with purification. Rainfall is another important resource never utilized in Boroujerd. The gable roof and those with more than 15 degrees gradient can be used to collect the rainwater in the high rainfall season. The total roofs are 136.13 ha and according to the average rainfall 0/454m, it can be the maximum use of this resource. The annual volume of precipitation for this city is 612612/45m3 which is significant. Supposedly, it could provide 3.6% of fresh water. Also, if the volume of sewage is considered for purification, the amount of available water source reaches 13362612/45m3 which can meet 60/74% of current water demand.
Conclusion: Rainwater is not used as a natural resource in Borujerd city and flows into seasonal rivers as runoff. It can be said that harvesting rainwater is an opportunity to reduce water shortage in the future. Rainwater system transferred through the water pipelines and sewage system. It is possible to store rainfall and water remained after snow melts for dry seasons and its surplus can be used to supply. Also due to climate changes and agriculture in Borujerd city, a plan should be provided to reduce the use of water in the summer which is expected to be implemented shortly.
Research Article
M. Nasiri; M. Hamidi; H. Kardan Moghaddam
Abstract
Introduction: The issue of seawater intrusion has become an environmental problem considering the increasing trend in groundwater extraction from coastal aquifers. Increased groundwater exploitation and lack of coastal aquifers management have caused seawater intrusion into coastal aquifer. The intrusion ...
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Introduction: The issue of seawater intrusion has become an environmental problem considering the increasing trend in groundwater extraction from coastal aquifers. Increased groundwater exploitation and lack of coastal aquifers management have caused seawater intrusion into coastal aquifer. The intrusion has led to the salinization of aquifers, causing many problems in the exploitation of water resources. This pumping has continually increased the risk of seawater intrusion and deterioration of freshwater quality in the sari-Neka aquifer. Seawater intrusion limits the usage of groundwater for agriculture, industry, and public water supply.
Materials and Methods: For the present study, Sari-Neka aquifer was selected. The study area is located in the southern shores of the Caspian Sea, in the northern part of Iran. The MODFLOW version 2000 is used to simulate a steady-state and transient groundwater flow system in Sari-Neka aquifer. To simulate solute transport, MT3DMS and SEAWAT are used. In MT3DMS, advection package, dispersion, and source/sink mixing packages are used. The numerical code MT3DMS does not consider the effect the density. Thus, SEAWAT-Variable Density Flow package was initialized. The necessary data for modeling of groundwater flow can be categorized into water resources data, meteorological data, hydrodynamic characterization, topography map, and geological information. To build the flow model, flow type (steady-state and transient state), initial conditions (groundwater level in September 2010 for the steady-state) and type of boundary conditions (general head boundary), flow package (LPF package), temporal discretization (48 monthly stress periods from September 2010 to August 2014 in transient condition) and monthly time steps were assigned to the model. To prepare the flow and transport model grid, the study area was discredited horizontally into 3694 active square cells (500×500 m). The MT3DMS model was used to simulate the qualitative changes on the aquifer surface and the SEAWAT model to simulate the depth of the aquifer. Therefore, the conceptual model of solute transport was prepared by making the necessary changes in the conceptual flow model. September 2010 groundwater level data and TDS and Cl data are taken as the initial conditions in the flow and transport model, respectively. The Caspian Sea bordering the study area in the north is represented by a constant TDS concentration of 35000 mg/l and constant CL282.2 meq/l. In this model, we entered the water heads of the observation wells, hydraulic conductivity, storage coefficient, effective porosity, aquifer discharge, and aquifer recharge, porosity, Coefficient of molecular water diffusion, Longitudinal dispersivity, Horizontal transverse dispersivity, vertical transverse dispersivity.
Results and Discussion: The calibration of the flow model was carried out for both steady and transient conditions using the trial and error approach. Monthly groundwater levels of data from 14 observation wells were used for calibration purposes. Steady-state calibration for the flow model was performed by comparing the observed groundwater levels and calculated values of groundwater levels in September 2010. During calibration, hydraulic conductivity values were adjusted, until groundwater level values calculated by MODFLOW were matched the observed values within an acceptable level of accuracy (±1m). After steady-state calibration, the transient model was simulated for the four year period between September 2010 and August 2014 that was divided into 48 stress periods with monthly time steps. At the end of flow model calibration, the resulting hydraulic conductivity ranged from 5.3 to 21. 6 m/day, while the resulting specific yield values were from %3.4 to % 5.9. The validation flow model was simulated for the period between September 2010 and August 2014 (12 stress periods). The values of the correlation coefficient in the steady-state model, transient model and validation model in the flow model were obtained 0.99, 0.98, and 0.97, respectively. The results illustrate a good agreement between the observed and calculated groundwater levels. The transport model was calibrated using TDS and CL concentration data from September 2010 to August 2014 (8 stress periods) by adjusting parameters affecting the dispersion process. To confirm the accuracy of the model, TDS and CL concentration data from August 2014 to September 2015 were used for validation purposes. By considering the TDS and Cl concentration in September 2010 as the initial condition, the transient model was run. Transport model calibration was achieved through a trial-and-error. The values of the correlation coefficient in the transport model for TDS are obtained 0.83 and 0.87 in the transient model and validation model, respectively. The values of the correlation coefficient in the transport model for CL were obtained 0.82 and 0.86 in the transient model and validation model, respectively.
Conclusion: After the validation of transport model and assuming all the hydrogeologic conditions remain, a predictive 6-year simulation run using SEAWAT model indicates that further seawater intrusion into the coastal aquifers can occur in the study area.
Research Article
N. Afshar Bakeshloo; K. Zarafshani; B. Farhadi Bansouleh
Abstract
Introduction: Kermanshah Province with one million hectares of arable land play an important role in food security and economy of Kermanshah province. For example, Kermanshah province holds third in wheat yield per hectare; second in chickpea production; third in maize production; third in sugar beet ...
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Introduction: Kermanshah Province with one million hectares of arable land play an important role in food security and economy of Kermanshah province. For example, Kermanshah province holds third in wheat yield per hectare; second in chickpea production; third in maize production; third in sugar beet yield per hectare; and seventh in tomato production. However, unsustainable behavior of farmers in one hand and overuse of water consumption have depleted water reserves which in turn has developed “prohibited plains” in the region. For example, several regions such as Mahidasht, Islamabad, and Kangavar are consider as forbidden areas and still extending in size. In addition, with the continued overuse of water resources we will soon experience huge sinkholes across the province. Therefore, there is a need to study the content and value of virtual water in order to zone cultivated areas based on virtual water. This could be an effective way to maintain water resources and prevent environmental crises.
Materials and Methods: This study used quantitative documentary research method. Using secondary data source, we collected data from various sources such as FAO data bank, Agricultural Jihad Organization data source, Meteorological organization, Agricultural Research Center, and Department of Soil and Water Management. This documentary research sought to investigate the content and value of virtual water used in irrigated and rainfed farming across wheat, barley, chickpea, maize, sugar beet, and tomatoes during 2014-2015 using CROPWAT, AGWAT, and EXCEL software. In addition, the share of green and blue virtual water was estimated in the study. Finally, 12 provinces were zoned from classes A to Z based on virtual water content and value of the products.
Results and Discussion: Results revealed that wheat with 1.96 to 3.68 m3/kg is the most consumable product that about 60 percent of the cultivated areas of wheat are located in areas of the province that are inappropriate in terms of content and value of virtual water. Also, tomato with the value of 0.09 to 0.38 m3/kg had the lowest virtual water content and average value of virtual water. According to the results, the sugar beet product is in desirable condition in terms of virtual water content and had moderate conditions in virtual water value. Finally, about 80% of maize produced in areas that are not in a desirable position in terms of virtual water content and value.
Results of green and blue virtual water showed that spring products such as sugar beet, tomatoes and maize received their water requirement from surface and groundwater resources. In addition, the largest blue component of wheat was related to Harsin city and the lowest was related to Javanrod city. For irrigated barley, the smallest and the largest share of blue virtual water were related to cities of Qasr Shirin and Sahne respectively.
Conclusion: Overall, the results of this study revealed that irrigated wheat and barley have a poor condition in terms of the content and the value of virtual water. However, since wheat and barley are considered as a strategic products policymaker should take appropriate measures in order to provide sustainable cultivation of wheat and barley. For example, improved farming, plant breeding, changing the growing season according to climatic conditions, developing cultivation in suitable areas, as well as applying appropriate pricing and support policies, including training of beneficiaries, and improving insurance policies could provide appropriate measures if Iran is to be self-sufficient in wheat and barley production.
Results of this study has practical significance for agricultural policymakers in Iran in general and Kermanshah province in particular. For example, zoning of crop cultivation based on the content and value of virtual water provided in this study can be an effective tool in modelling cropping pattern and sound water management policies. In addition, effective cropping pattern as well as sound water management resources would encourage farmers to engage in climate smart agriculture. Moreover, cultivation zoning based on content and value of virtual water is considered as a climate smart agriculture technique. This in turn would create resilient farming system in the study area. Through resilient farming system, farmers better adapt to climatic condition more effectively.
Research Article
M. Motallebian; H. Ahmadi; A. Rauf; N. Cartwright
Abstract
Introduction: Aquifers are the major source of freshwater in many parts of the world. Saltwater intrusion (SWI) is a serious environmental issue since 80% of the world’s population live along the coast and utilize local aquifers for their water supply. Globally, coastal aquifers are under threat from ...
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Introduction: Aquifers are the major source of freshwater in many parts of the world. Saltwater intrusion (SWI) is a serious environmental issue since 80% of the world’s population live along the coast and utilize local aquifers for their water supply. Globally, coastal aquifers are under threat from saltwater intrusion (SWI). SWI is caused by changes in coastal aquifer conditions resulting from ground water extraction, climate drivers, sea-level rise, oceanic over topping events, and land use change. Under natural conditions, these coastal aquifers are recharged by rainfall events, and the regional groundwater flow towards the ocean counters the intrusion of saltwater into the freshwater region. However, over-exploitation of coastal aquifers in some regions has resulted in a reduction in fresh groundwater levels (and hence reduced natural flow) and this has led to an increase in saltwater intrusion. Saltwater intrusion degrades the quality of coastal aquifer groundwater resource which can lead to a reduction in crop yield efficiency, limitation on the drinking water resource as well as soil fertility and salinity of operated wells. Such problems are more crucial where groundwater aquifers are shallow.
Materials and Methods: The aim of this study is to investigate the effect of Lake Urmia water-level fluctuations on groundwater table and rate of the intruding or receding of salt water to the coastal aquifer. In order to achieve this purpose, Rashakan coastal aquifer in the vicinity of Lake Urmia in the northwest of Iran was simulated. In this study, SEAWAT model was used to simulate the problem. SEAWAT was specifically designed for the simulation of SI, although it has many other applications as well, notably the combined simulation of groundwater flow and heat transfer. SEAWAT as a widely used, three-dimensional variable-density groundwater flow and transport model has been developed by the USGS based on MODFLOW and MT3DMS and includes two additional packages: Variable-Density Flow (VDF) and Viscosity (VSC). First, the model was calibrated and then the simulations were defined in four scenarios as follows: a) The rate of the intruding or receding of salt water to the coastal aquifer during recent years b) The effect of the drop-in lake water level on groundwater level changes trend regardless of changes in lake water density c) The effect of the drop-in lake water level on groundwater level changes trend in view of changes in lake water density d) The effect of the drop-in lake water level on the rate of the intruding or receding of salt water.
Results and Discussion: In this study, simulations were carried out under four scenarios in order to investigate the effect of Lake Urmia water-level fluctuations on groundwater table and rate of the intruding or receding of salt water to the coastal aquifer. In the first scenario, in order to assess the rate of the intruding or receding of salt water to the coastal aquifer in recent years, three profiles have been investigated in the north and the center and south of the study area, and the results showed that in recent years there has been no significant change in the displacement of the salt-water wedge and this change was less than 50 meters and only the upper part of wedge connected to the lake was more affected by dropping water level of lake, which was due to retreat of the boundary imposed by lake water recession. In the second scenario, the effect of the drop-in lake water level on groundwater level changes trend, regardless of changes in lake water density, was investigated. The findings of the study showed that if the concentration of lake water is considered constant, the increase and decrease in groundwater level across the aquifer would be almost equal to the increase and decrease the lake water level. In the third scenario, the effect of the drop-in lake water level on groundwater level changes trend in view of changes in lake water density was investigated and the findings was also made with the second scenario, where the results showed that when the effect of the density changes is neglected, the groundwater level is affected by the lake water level changes more than about 2 times that when the density changes are considered. However, increasing and decreasing concentrations, and consequently increasing and decreasing the density, may have a great effect on the reduction and increase of groundwater levels. In the fourth scenario, the effect of the drop-in lake water level on the rate of the intruding or receding of salt water was also investigated. It can be concluded that when concentration changes and as a result of variations in density are affected, by decreasing the level of the lake, saltwater wedge would be intruded and when the effect of the density changes is neglected, saltwater wedge would be receded.
Conclusion: The results of this study indicated that during recent years there has been no significant change in the location of the salt water wedge, and this change is less than 50 meters. The upper part of wedge connected to the lake is more affected by dropping water level of lake, which is due to retreat of the boundary imposed by lake water recession. Also, the findings of the study showed that if the concentration of lake water is considered constant, the increase and decrease in groundwater level across the aquifer will be almost equal to the increase and decrease of the lake water level. When the effect of the density changes is neglected, the groundwater level is affected by the lake water level changes more than by about 2 times that when the density changes are considered. Despite the decreasing of about 7 meters of lake Urmia water level, due to increase the density of water, the wedge has intruded. This research shows that in the event of an increase in the water level of Lake and consequently a decrease in water density, Saltwater wedge would be receded.
Research Article
H. Ghased; A. Roozbahani; M. Hashemy Shahedany
Abstract
Introduction: Inter-basin water transfer projects include essential, various, complex parameters where mostly have a qualitative inherent. Making an appropriate decision on these projects have not been convenient due to diverse impacts and effectiveness of the parameters as well as irregular and qualitative ...
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Introduction: Inter-basin water transfer projects include essential, various, complex parameters where mostly have a qualitative inherent. Making an appropriate decision on these projects have not been convenient due to diverse impacts and effectiveness of the parameters as well as irregular and qualitative intrinsic of the criteria. The main objective of this study is the evaluating and prioritizing of the practical inter-basin water transfer scenarios to Central Plateau of Iran employing three approaches of the analytic hierarchy process (AHP), DEMATEL and Shannon Entropy, and proposing this approach for decision making in water resources.
Materials and Methods: In this study to supply municipal water consumption deficit of 580 Million cubic meters for three provinces of Esfahan, Yazd, and Kerman, eight practical inter-basin water transfer scenarios were selected. The scenarios transfer water from the great Karun watersheds, including Behesht-Abad, Bazoft, Khersan, and Gukan basins, to the mentioned provinces located in the Central Plateau of Iran. Four criteria, considering the proposed UNESCO criteria for the qualitative and quantitative evaluation of these projects, were assigned including technical risks and performance difficulty (C1); political and social obstacles (C2); environmental difficulties (C3); and prime cost of a cubic meter of water (C4). Upon employing three approaches of the AHP, Shannon Entropy, and DEMATEL, the criteria weights for decision making were determined. Finally, the selected eight scenarios of the study were prioritized, considering the positive and negative measures within the multi-criteria decision making, by using the COPRAS technique.
Results and Discussion: Regarding the results of the AHP method, criteria with the highest and the lowest importance were obtained as the technical risks and performance difficulty and the environmental challenges respectively. In the following, results of the DEMATEL method, considering cause and effect graphs, as well as the impact and influence of the criteria, revealed that criteria of C1, C2, and C3, got the second, fourth, and the third ranks respectively, while the C4 criterion was placed in the first rank. Also, the results showed that the former criteria, C1 to C3, were considered as cause criteria, and the latter one, C4, was an effect criterion. In the following, the weight of the criteria was computed using the Shannon Entropy method. Accordingly, the C4 criterion, including the lowest weight (Wj ) and the highest Ej value, had a common impact on the scenarios. While, the C1, with the highest weight and the lowest Ej value, was selected as the most influential and essential criterion. Then, the COPRAS technique was employed to find out the best scenario. The obtained results revealed that the 8th scenario was selected as the best scenario and the most suitable one was based on the assigned criteria. Moreover, the results showed that, except the scenarios 5 to 8 and the second one, other scenarios had various weights by using the different weighting method.
Conclusion: In this study, eight inter-basin water transfer scenarios were evaluated upon four criteria, including technical risks and performance difficulty; political and social obstacles; environmental challenges; and prime cost of a cubic meter of water. In the following, weights of the mentioned criteria were determined to employ three approaches of the AHP, Shannon Entropy, and DEMATEL, and COPRAS technique was used to prioritizing of the criteria. The obtained results revealed that 8th scenario, including water transfer from the base flow of the Behesht-Abad basin to Esfahan province, through the pumping and short water conveyance tunnel, and from the Kheran-Kersan Dam 3 to Yazd and Kerman provinces was selected as the best scenario for water transfer to central plateau of Iran. Application of the approach is recommended in complex decision making in water resources management, mostly incorporated with conflicts and inhomogeneous qualitative and quantitative criteria, due to practical utilization of this method in the evaluation and prioritizing of scenarios. It is worth noting that the proposed method was conducted in forms of fuzzy and crisp configurations.
Research Article
M. Nazeri Tahroudi; Y. Ramezani; C. De Michele; R. Mirabbasi Najafabadi
Abstract
Introduction: The erosion, sediment transport, and estimation problems in the streamflow are the most complicated and essential subjects in the river engineering studies. It is important to model and predict these parameters correctly to determine the effective life of the hydraulic structures ...
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Introduction: The erosion, sediment transport, and estimation problems in the streamflow are the most complicated and essential subjects in the river engineering studies. It is important to model and predict these parameters correctly to determine the effective life of the hydraulic structures and drainage networks. On the other hand, river flow discharge is considered as one of the main components of water resources, which affects sediments. The increasing need of urban and rural communities for limited resources on the one hand, and issues related to climate change and atmospheric precipitation over the past few years, more and more attention is paid to the attitude of surface flows. The phenomena of erosion, sediment transport, and estimation of sediment load in the rivers due to its damages are one of the most critical and complex issues of river engineering. The primary goal of the frequency analysis is to relate extreme events to their frequency using probability distributions. In the frequency analysis of meteorological and hydrological events, the observed data would be analyzed for a long time at a basin. In these analysis, the assumption of independence and stationarity is considered. In fact, the basic assumption is that the studied data are spatially and temporally independent. The main issue is identifying actual distribution across different exiting distributions when using the frequency distribution to estimate the magnitude of the event. There is no appropriate general distribution for all types of rainfall regimes, river flows, etc. On the other hand, in order to analyze the frequency of a similar case, there is no agreement on the use of a particular distribution function. The experience gained so far in the field of statistical analysis of hydrological data shows that some data are more consistent with some specific statistical distributions.
Materials and Methods: In this study, the frequency analysis of total sediment load of the Zarinehrood basin was investigated in the south-east of Lake Urmia with consideration of the peak flow discharge at the Chalekhmaz hydrometric station during the statistical period of 1992-2016 using copula functions. At first, the correlation of these data was investigated using Kendall Tau correlation statistics, and the correlation coefficient was calculated as 0.75. In this study, Ali-Mikhail-Haq, Clayton, Frank, Galambos, Gumbel-Hougaard, Plackett, and Farlie-Gumbel-Morgenstern copula functions were used. In the conventional method of estimating the return period of extreme values, different statistical distributions are fitted on the studied data. After fitting the statistical distributions on the data series, the accuracy of each distribution is evaluated by one of the goodness of fit tests, such as the Kolmogorov-Smirnov test. After statistically controlling the goodness of fit test and determining the acceptable distributions, the root means square error (RMSE) and the Nash-Sutcliffe criterion are calculated to select the best fit model. Each of the fitting distributions that have the highest Nash-Sutcliffe (NS) criteria, and the lowest RMSE is chosen as an appropriate distribution.
Results and Discussion: With the fitting of 65 different distribution functions into the series, the Weibull distribution for total sediment load values and generalized Pareto distribution for peak flow discharge values were selected based on the evaluation criteria as appropriate marginal distributions. The results of the evaluation of the accuracy and efficiency of copula functions were studied by using root mean square error, Nash-Sutcliffe, BIAS, and AIC statistics. In this regard, the results were compared with the experimental copula functions. Finally, the Galambos copula was selected from the candidate copulas as superior copula function. The conditional and joint return period of the total sediment load based copula was proposed with a probability of 10 to 90 percent.
In univariate mode, the lowest probability of exceedance is 50%. In a bivariate mode, this possibility is presented more accurately. With a possibility of exceedance of 50%, it can be observed that the total sediment load at Chalekhmaz station during the studied period is about 400 tons per day. This is about 56% higher than its univariate mode, which is the average long-term of the total sediment load is closer to the Chalekhmaz station.
Conclusion: By comparing the bivariate analysis and its return period with univariate mode, the results indicated that more accurate calculation. Also the results showed the estimation of total sediment load is closer to the total sediment load of the Chalekhmaz station in bivariate analysis mode. Also, the results showed that in univariate mode, estimation of total sediment load at Chalekhmaz station was less than its actual value during the two-year return period. Regarding the results, the generated return curves can be used as the type curves for the management of water resources in the basin.
Research Article
B. Karimi; N. Karimi
Abstract
Introduction: Among irrigation methods, a drip irrigation system (surface and subsurface) is more acceptable in arid and semi-arid regions due to high water use efficiency and potential crop yield. Pulse drip irrigation (with suitable management practices) is one of the drip irrigation methods (includes ...
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Introduction: Among irrigation methods, a drip irrigation system (surface and subsurface) is more acceptable in arid and semi-arid regions due to high water use efficiency and potential crop yield. Pulse drip irrigation (with suitable management practices) is one of the drip irrigation methods (includes a set of cycles, each cycle consisting of the irrigation phase and a resting phase) that have high potential to improve the uniformity of soil moisture distribution. Suitable design and management of pulse or/and continuous drip irrigation systems substantially require a proper understanding of the moisture distribution pattern around the emitter. One of the critical parameters concerning the moisture distribution pattern, taking into account the wetted area of emitter. Important parameters of the wetted area include the down wetted area (Ad) for the surface and subsurface drip irrigation system as well as the up wetted area of an emitter (Aup) for the subsurface drip irrigation. Modeling the wetted area pattern and considering this parameter in design as one of the criteria for increasing water efficiency in surface and subsurface drip irrigation systems is critical and important.
Materials and Methods: In this research, experiments were carried out in a transparent rectangular cube with dimensions of (3 * 1 * 0.5 m) using three different soil textures (fine, heavy, and medium). The drippers were installed at three different soil depths (surface, 15cm, and 30cm). The emitter discharge was considered 2.4, 4, and 6 lit/hr. Also, these experiments were carried out for two continuous and pulse irrigation systems. In pulse irrigation, the pulse cycles were considered 30-30, 20-40, and 40-20 min. The first number refers to the irrigation time, and the second number refers to the resting time of the system in each cycle. In this research, using a nonlinear regression model, empirical models were developed to predict the wetted area of the moisture front. The input parameters of the suggested model include emitter discharge, saturated hydraulic conductivity, application time, soil bulk density, emitter installation depth, initial soil moisture content, pulse ratio (the ratio of irrigation time to complete period of each cycle) and the proportions of sand, silt and clay in the soil.
Results and Discussion: The results of this study show that the highest and the lowest down wetted area (for surface and subsurface drip irrigation systems) are related to sandy and clay soils, respectively. Also, the highest up wetted area in the subsurface irrigation system is related to loamy and clay soils. The results of the comparison between measured and simulated values of down and up wetted area indicated that these models have acceptable precision and accuracy in estimating the wetted area of the wetting front in surface and subsurface drip irrigation (with pulsed and continuous application). The comparison between the measured and simulated down wetted area of the emitter (for surface drip irrigation with pulsed application) showed that the R2, MAE and RMSE values varied between 0.98-0.99, 0.0027-0.0065 m2 and 0.0034-0.0082 m2, respectively. Concerning statistical values, it is evident that these models have excellent performance in estimation of down and up wetted area for subsurface drip irrigation. For subsurface drip irrigation with the pulsed application, the values of R2, MAE and RMSE for the down wetted area of emitter, ranged 0.91-0.99, 0.002-0.0077 and 0.0032-0.0098, respectively. These models also estimate up wetted areas with less error, and the values of R2, MAE, and RMSE for all treatments varied between 0.89-0.99, 0.0015-0.0067 m2, and 0.0019-0.0077 m2, respectively.
Conclusion: This paper was aimed at presenting relationships for estimating the up and down wetted area of emitter for surface and subsurface drip irrigation (with pulsed and continuous application). Regarding the importance and applicability of empirical models, in this research, nonlinear regression models (NLR, which are more widely used among researchers) were applied. For NLR method, different ten input variables (i.e., emitter discharge, saturated hydraulic conductivity, application time, soil bulk density, emitter installation depth, initial soil moisture content, pulse ratio (the ratio of irrigation time to complete period of each cycle) and the percentage of sand, silt and clay) were considered. The results of this study indicate that the NLR model can estimate the up and down wetted area, and the statistical indices values are within acceptable ranges. Considering these relations in designing surface and subsurface drip irrigation systems can improve the performance of these systems.
Research Article
S. Khalife; S.A. Esmaili; K. Esmaili; S.R. Khodashenas
Abstract
Introduction: Flood is a natural phenomenon that can cause numerous financial and life casualties in civil, industrial, and agricultural areas. Therefore, knowing its characteristics such as its peak during a period and in different places of the river is of the utmost importance. In general, forecasting ...
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Introduction: Flood is a natural phenomenon that can cause numerous financial and life casualties in civil, industrial, and agricultural areas. Therefore, knowing its characteristics such as its peak during a period and in different places of the river is of the utmost importance. In general, forecasting these characteristics and changes in depth and flow in the river could be done using the flood routing methods. Flood routing is one of the most important issues in water engineering projects. Hydrologic routing is common particularly in braided rivers and rivers with the lack of mid-basin data. To do that, there is a need to perform cross-sections and determine the river slope in every region. The Muskingum method is frequently used to route floods in the hydrology literature. The implementation of metaheuristic algorithm methods has shown satisfactory results in this regard. Therefore, in this study, we evaluated the efficiency of the Symbiotic Organisms Search (SOS) in estimating the optimal parameter estimation of the Non-linear Muskingum model.
Materials and Methods: This study evaluated the performance of Symbiotic Organisms Search (SOS) algorithm in estimating the optimum parameters of the Muskingum Non-linear model. To investigate the research’s findings desirability, the results of the Symbiotic Organisms Search (SOS) were compared to the results of otherMeta-Heuristic methods including the Genetic Algorithm (GA), the Particle Swarm Optimization (PSO), and the Imperialist Competitive Algorithm (ICA). Meta-heuristics sample is a set of solutions which are too large to be completely sampled. Meta-heuristics may make few assumptions about the optimization problem being solved, and they may, therefore, be usable for a variety of problems. SOS algorithm simulates the interactions between two species in a way that one species seeks to find the most suitable. SOS algorithm starts with an initial population called ecosystem. In the early stages of ecosystem, a group of organisms (decision variable) are randomly generated in the search space. Each organism is a candidate for a solution that corresponds to a certain degree of fit, representing the degree of conformity with the intended purpose (amount of objective function). This algorithm uses a new solution by mimicking the biological interaction between the two species in the ecosystem. Three distinct phases (cross-use), commensalism, and parasitic, similar to the biological interaction model in the real world, are introduced. Each interaction is defined based on the type of interaction. In this way, the two-way profit represents the cooperation phase, the one-way profit represents the commensalism phase, and the one-way profit and the other side losses represent the parasitic phase. In all phases, each is being interacted randomly with the other. This process continues until the process is completed (reaching the maximum number of iterations). In this research, the Kardeh River in Khorasan Razavi province was chosen as a real instance and Wilson River as a previous instance (1974), to investigate the performance of algorithms used in the non-linear Muskingum equation in the flood routing model. In this study, minimizing the sum of squares (SSQ) between the volume of real and routed outputs was considered as an objective function to evaluate the optimum parameters of K, X, and m in the non-linear Muskingum equation. The obtained optimum parameters from algorithms for both rivers showed that the SOS, PSO, and ICA algorithms could approximate the SSQ to optimal value and all meta-heuristic algorithms could route the output flood as well.
Results and Discussion: The SSQ algorithm results for the rivers showed the minimization of the sum of squares (SSQ) which MSE was equal to 5.85 and SSQ was equal to 128.78 for the Wilson River, and MSE was equal to 0.505 and SSQ was equal to 4.55 and had better functionality than the GA algorithms same as the PSO and ICA algorithms. The meta-Heuristic methods were from solutions which succeeded to estimate these parameters. In this study, the novel Symbiotic Organisms Search (SOS) was used to estimate the non-linear Muskingum model parameters. The observational data of two river studies of Kardeh and Wilson Rivers were employed. The results of SOS implementation were compared to other meta-heuristic algorithms such as GA, PSO, and ICA to investigate the SOS functionality. In this research, firstly, the experimental example used by the researchers was investigated to survey the optimum Non-linear Muskingum flood routing model parameters. The results showed the SOS precise estimation was comparable to the previous methods. According to the results, the SSQ was improved by using the objective functions as compared to the other reported algorithms at a rate of 7% in GA, and 0.004% in ICA. In the second experimental river, which is a real flood routing, estimated statistical parameters for the Kardeh River were 0.5059 for MSE and 4.5528 for SSQ in the SOS algorithm. This shows that the appropriate functionality of the Symbiotic Organisms Search algorithm in estimating the optimum Non-linear Muskingum flood routing model parameters. Finally, this research work highlights the SOS ability to optimize the Muskingum model parameters.
Conclusion: In the SSQ flood stream, SOS showed good performance, such as the PSO and ICA algorithms. In this regard, SOS was 13% better than the GA in the objective function SSQ and MSE, and improved the objective function SSQ and MSE by 0.002 and 4%, respectively, in respect to the PSO and ICA. This denotes the appropriate functionality of the Symbiotic Organisms Search algorithm in estimating the optimum non-linear Muskingum flood routing model parameters. The findings indicate the SOS ability to optimize the Muskingum model parameters. Therefore, using the SOS in flood routing with the Muskingum model is recommendable.
Research Article
M. Mosapour; A. Forghani; A. Sabouri
Abstract
Introduction: Potassium is the second essential nutrient for plants. Potassium has a high abundance in the soil, but only a small part of it can be used. The principal forms of potassium in the soil are solution potassium, exchangeable potassium, non-exchangeable potassium, and structural potassium. ...
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Introduction: Potassium is the second essential nutrient for plants. Potassium has a high abundance in the soil, but only a small part of it can be used. The principal forms of potassium in the soil are solution potassium, exchangeable potassium, non-exchangeable potassium, and structural potassium. To evaluate the state of potassium in the soil, three forms of soluble, exchangeable, and non-exchangeable are used. The Q/I curve is used to describe the availability of potassium, due to the competition between calcium, potassium, and magnesium ions by soil exchange sites. This curve represents the supply power of soil potassium. The objective of this study was to investigate soil potassium Q/I curve and relationships between its parameters and soil characteristics in some calcareous soils of Lorestan province.
Materials and Methods: In this study, 16 topsoil samples (0-30 cm) were obtained from the calcareous soils of Lorestan province. The experiment was carried out by a completely randomized design with three replications. To prepare the Q/I curve, six suspensions were prepared from each soil sample containing 1 g of soil and 10 ml of calcium chloride 0.01 M and 10 milliliters of potassium chloride with concentrations of 0.33, 0.66, 1, 1.33, 2 and 2.5 mmol. The solutions were shaken for one hour. They were then left for 20 hours to reach the balance. The samples were centrifuged and the soluble and solid phase were separated and then the soluble potassium solution was read using a potassium flame photometry. Calcium and magnesium concentrations were measured by titration with EDTA. Then, 20 ml of 1 M ammonium acetate (NH4OAC) was added to the solid phase of each sample. Then, the concentration of exchangeable potassium was measured using a flame photometer. Then the Q/I curve was plotted for each sample. In addition, the association analysis was performed using a stepwise multivariable regression method.
Results and Discussion: According to the Q/I curve, ARK0 (potassium activity ratio at equilibrium) ranged from 0.087-0.047 (mmol.L-1). The maximum amount of PBCK (potential buffering capacity) was observed in soil No.11 with value of 45.834 (mmol.kg-1)/(mmol.L-1)0.5 and the lowest value obtained for soil No.13 with value of 23.329 (mmol.kg-1)/(mmol.L-1)0.5. In fact, in soils with PBCK, the soluble potassium activity has a lower oscillation and is better buffered. The low amount of PBCK in soil No.13 indicates low soil power to supply potassium and the necessity of using potassium fertilizers. The lowest and most easily converted easy potassium (ΔK0) were observed for soil No.12 and 4 with a value of 1.269 and 23.243 (mmol.kg-1) respectively. There was a negative correlation between PBCK and ARK, suggesting those high-PBCK soils, lower ARK, are more stable than those with lower PBCK. The KL (available Potassium) with ΔK0 and Kx (Hardly exchangeable K) showed a significant and positive relationship (r=0.70, p<0.01). Therefore, it can be concluded that by increasing each of the two parameters ΔK0 and KX, the amount of potassium (KL) is increased. Also, a positive and significant correlation was found between potassium potential buffering capacity with clay content (r=0.79, p<0/01) and the cation exchange capacity (r=0.73, p<0.01). Therefore, the cation exchange capacity of soils can be used to estimate the buffering capacity of soils and therefore recommend potassium fertilizers. Available potassium (KL) showed a positive and significant correlation with soil organic matter because its organic material is a part of potassium. Also, organic matter can alter the amount of potassium by changing the pH value. Other Q/I curve parameters, such as ARK0, Kx, and ΔK0 did not show any significant correlation with any soil properties. According to regression analysis, it was determined among all soil characteristics the only amount of clay can be used as a proper attribute in order to estimate the potential of potassium in soil according to the following equation: PBCK=17.857+0.482 Clay R2 = 0.631. Also, the amount of organic carbon (O.C) was determined as the proper variable for estimating the KL value according to the following model: KL=14.468+9.017 O.C (R2 = 0.318).
Conclusion: Due to potential buffering capacity (PBCK) in these soils, it seems that soils can be able to provide the absorbable potassium relatively. Therefore, fertilizer recommendation can be performed by considering the amount of determined variables by the Q/I curve.
Research Article
K. Kiani Jam; M.R. Bihamta; D. Habibi; A. Asgharzadeh; A. Saremirad
Abstract
Introduction: Nowadays, increasing soil contamination by heavy metals is one of the most important issues around the world, and is the focus of attention. Lead as the most dangerous heavy metal and persistent chemical pollutant affects the environment, especially the metabolic and physiological activities ...
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Introduction: Nowadays, increasing soil contamination by heavy metals is one of the most important issues around the world, and is the focus of attention. Lead as the most dangerous heavy metal and persistent chemical pollutant affects the environment, especially the metabolic and physiological activities of organisms and ultimately cause serious damage to the environment and human health. The purpose of this study was to investigate the effect of mycorrhizal fungus (Rhizophagus irregularis) on some biochemical traits of 10 wheat genotypes in three different concentrations of lead heavy metal (0, 218 and 437 ppm) in soil.
Material and Methods: The present study was conducted as factorial experiment based on randomized complete block design with three replications. The factors included lead in three concentrations (0, 218 and 437 mg / kg), mycorrhizal inoculum (addition and no addition), and 10 wheat genotypes (Shiraz, Sepahan, Sirvan, Back Cross Roshan, Marvdasht, Sivand, Bahar, Pars, Roshan, and Pishtaz). Soil samples were prepared from a depth of 0-25 cm of the research farm of Islamic Azad University, Karaj Branch. Samples were taken randomly. After soil drying and passing through a 2 mm sieve, they were transferred to the soil science laboratory to determine some of the physical and chemical properties. According to the soil test results, the soil was sandy loam, a semi-light soil with 25% clay, 25% silt and 50% sand, with pH = 7.49 and salinity of 1.63 dS. m-1, and also free of heavy metals. The soil was sterilized for four hours by an autoclave at the temperature of 121 °C and a pressure of 1.5 atm. After soil preparation, the lead was added to the soil at three concentrations of 0, 218 and 437 ppm, and stored in a pre-embedded bag with 60% moisture content to achieve a two-week equilibrium. In order to inoculate the mycorrhizal fungus, after removal of 3-4 cm from the soil surface, Rhizophagus irregularis (35 g) was added to the soil surface, then 30 to 40 seeds were placed on the soil surface and covered with soil. In the control samples without mycorrhizal fungus, a certain amount of mycorrhizal fungus placed at 105 ºC to kill the fungus and then added to the pots.
Results and Discussion: Malondialdehyde concentration increased by increasing the concentration of lead. The highest concentrations of proline were belonged to the level 218 ppm of lead, in Pars cultivar in both treatments of with and without mycorrhiza fungus as well as Sirvan cultivar in the treatment of without fungi, respectively. The activity of Catalase was highest in the treatment of 218 ppm of lead without fungus. Roshan cultivar also showed high levels of ascorbate peroxidase activity in 218 ppm of lead. Similar to cultivar, BC Roshan and Pishtaz cultivars also showed high ascorbate peroxidase activity in this concentration of lead. The amount of hydrogen peroxide was reduced by changing the concentration of lead from 0 to 218 ppm, while its amount increased at 437 ppm concentration. With increasing lead concentration, the amount of chlorophyll a decreased while chlorophyll b increased. Using mycorrhizal fungus, the amount of malondialdehyde, proline and hydrogen peroxide and catalase content decreased compared with control. It seems that lead, due to its concentration in the environment, leads to the induction of oxidative stress and the formation of free radicals and thus change in the amount of biochemical traits of wheat such as malondialdehyde, proline, hydrogen peroxide and chlorophyll a and b and activity of catalase and ascorbate peroxidase. The genotype of the plant is very important factor in tolerating the toxicity of lead, and it deals with various protective mechanisms. Not only the plant genotype but also environmental factors such as the use of mycorrhizal fungus are effective in reducing the harmful effects of lead, and helps plants tolerate the stress caused by lead toxicity.
Conclusion: Lead in the soil causes changes in the biochemical content of wheat cultivars. The amount of change depends on the plant's genotype, lead concentration, and other factors in the soil, such as symbiotic fungi. As shown in the present study, mycorrhizal fungus was effective in eliminating the negative effects of lead during symbiotic with wheat. It is suggested further studies to determine the concentration of lead and even other heavy metals in wheat genotypes and to compare with Iranian national standards in order to overcome the concerns about the entry of these metals into the diet.
Research Article
J. Khallizadeh; E. Dordipour; M. Baranimotlgh; A. Gharanjiki
Abstract
Introduction: Iron deficiency is one of the most important nutritional disorders in plants, particularly in calcareous soils and deeply affects the yield and quality of the product. Due to the major role of iron in the synthesis of chlorophyll, chlorosis occurs in young leaves in deficiency conditions. ...
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Introduction: Iron deficiency is one of the most important nutritional disorders in plants, particularly in calcareous soils and deeply affects the yield and quality of the product. Due to the major role of iron in the synthesis of chlorophyll, chlorosis occurs in young leaves in deficiency conditions. In such condition, biochar can help to increase OM, soil fertility level, and iron use efficiency and, to reduce iron chlorosis. The aim of this study was to investigate the effect of iron- impregnated biochar on the availability of iron and the elimination of soybean iron chlorosis in a calcareous soil.
Materials and Methods: Calcareous soil with iron deficiency (0-30 cm) was collected from the east of Golestan province and prepared for cultivation. Two types of biochar were produced from wheat straw and particleboard through slow pyrolysis (increasing 5 °C/min) at 300 °C for 2 hours under restricted oxygen conditions in an electric furnace, and then impregnated with iron sulfate solution. FTIR spectra and SEM images of biochars surfaces were also provided. A pot experiment was conducted as a factorial based on a completely randomized design with four replications. Factors were biochars (wheat straw biochar (WB) and particleboard biochars (PB) each one with 2.5% w/w), iron impregnated biochars (Fe impregnated wheat straw biochar 2.5% w/w (Fe- IWB1) and 5% w/w (Fe-IWB2), 2.5% w/w (Fe-IPB1) and 5% w/w (Fe-IPB2) Fe impregnated particleboards, Fe- Sequestrene (S) and control without Fe and biochar (C), and two soybean cultivars (Williams and Saman). The sown pots were maintained near the field capacity for 12 weeks. Then, SPAD numbers, concentration and uptake of active iron in young and senile leaves and active iron content in soil were determined after harvest.
Results and Discussion: With increasing application of iron impregnated biochar, active iron content increased in the soil. SPAD numbers of the upper leaves of both soybean cultivars in Fe impregnated biochars were significantly higher than those of non-impregnated biochars and control treatments (P ≤ 0.05). Iron chlorosis symptoms in soybeans decreased following the increased application of Fe impregnated biochars, consequently, there were no iron chlorosis symptoms in 5% Fe impregnated biochar treatments. Also, the active iron concentration of the upper leaves and the amount of leaf active iron uptake significantly increased as a result of Fe impregnated biochars application in both soybean cultivars compared to control and non-impregnated biochars (P ≤ 0.05). The highest concentration of active iron in upper leaves was observed in 5% w/w Fe impregnated biochars treatments, but its value for cultivar Williams in Fe impregnated wheat biochar was higher than that in Fe impregnated particleboard biochar. The results of the SEM images indicated that wheat biochar had more quantity of and fine pores (also CEC) than that of the particleboard biochar, and the surface areas of both biochars were rough and dark after impregnation with iron, indicating the adsorption or accumulation of iron at their surfaces. Also, there was a significant positive correlation between the active iron concentration with SPAD numbers in the upper leaves (r = 0.88 **) and dry weight of soybean shoots (r = 0.87 **). Cultivars responses to Fe impregnated biochars showed that iron uptake and active iron concentration in the upper leaves of Williams variety were significantly less than those of Saman variety at both levels of Fe impregnated biochars (P ≤ 0.05), which indicates that cultivar Williams is more susceptible to the iron chlorosis. The results of this experiment and reports from other studies show that the application of impregnated biochars from nutrients besides increasing SOM, permeability and soil moisture, CEC and soil fertility level, also increases the acquisition and use efficiency of iron in the plant.
Conclusion: The results of this study showed that due to the strong adsorption of soil iron, non-impregnated biochar application in the level of 2.5% had no significant effect on the concentration and uptake of active iron and spad numbers of the plant. However, using Fe impregnated biochar and increasing their application in calcareous soils with iron chlorosis resulted in a significant increase of active soil iron content, concentration and uptake of active iron and SPAD numbers of the plant, and, conversely, a decrease of leaf chlorosis. Therefore, besides improving the physical, chemical and biological properties of the soil, the application of Fe impregnated biochar can also be a promising approach to eliminate iron chlorosis in sensitive plants, particularly soybeans in calcareous soils.
Research Article
S. Sangsefidi; A. Lakzian; A.R. Astaraei; M. Banayan; M. Mazhari
Abstract
Introduction: Nitrification inhibitors are compounds that slow biological oxidation of ammonium to nitrite by reducing the activity of Nitrosomonas bacteria, without affecting the subsequent oxidation of nitrite to nitrate, either by inhibiting or interfering with the metabolism of nitrifying bacteria. ...
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Introduction: Nitrification inhibitors are compounds that slow biological oxidation of ammonium to nitrite by reducing the activity of Nitrosomonas bacteria, without affecting the subsequent oxidation of nitrite to nitrate, either by inhibiting or interfering with the metabolism of nitrifying bacteria. The first step of nitrification is inhibited (i.e., the activity of Nitrosomonas bacteria) by the nitrification inhibitors, while the second step for oxidation of nitrite (NO2-) to nitrate (NO3-) is normally not influenced. In recent years, numerous compounds have been identified and used as nitrification inhibitors, particularly in agricultural soils. They are chemical compounds that slow the nitrification of ammonia, ammonium-containing, or urea-containing fertilizers, which are applied to soil as fertilizers, such as thiourea, carbon Sulfide, thioethers, ethylene, 3-amino-1,2,4-triazole, dicyandiamide (DCD), 2-amino-4-chloro-6-methyl pyrimidine, ammonium thiosulphate and 3,4-dimethylpyrazole phosphate (DMPP). These inhibitors reduce the losses of nitrogen in soil. Some nitrification inhibitors are very effective in the efficiency of the nitrogen fertilizers. Recently, a lot of attention has been paid to nitrification inhibitors from an environmental point of view. Some nitrification inhibitors are very expensive and not economically suitable for land application. Nonetheless, many farmers and researchers apply these compounds for many purposes in some specific places. On the other hand, there are many inexpensive natural nitrification inhibitors such as Artemisia powder, Karanj (Pongamia glabra), neem (Azadrachta indica) and tea (Camellia sinensis) waste which can compete with the artificial nitrification inhibitors such as 3, 4-dimethylpyrazole phosphate (DMPP), dicyandiamide (DCD) which are very common nitrification inhibitors. Applying 1.5 kg ha-1 of DMPP is sufficient to achieve optimal nitrification inhibition. 4-dimethylpyrazole phosphate (DMPP) can significantly shrink nitrate (NO3) leaching. 4-dimethylpyrazole phosphate (DMPP) may also decrease N2O emission and the use of DMPP-containing fertilizers can improve yield. The aim of this study was to compare the effect of 3, 4-dimethylpyrazole phosphate (DMPP), Dicyandiamide (DCD) and powder Artemisia (ART) at the presence of Urea, cow manure and Vermicompost.Material and Methods: Effects of three nitrification inhibitors, (3, 4-dimethylpyrazole phosphate (DMPP), Dicyandiamide (DCD) and powder Artemisia (ART)) at the presence of three nitrogen sources (Urea, cow manure and Vermicompost) were investigated in a calcareous soil under lettuce cultivation in a greenhouse condition. The changes in the soil mineral nitrogen (nitrate and ammonium), plant nitrogen, nitrate accumulation in leaves and some of growth characteristics such as lettuce chlorophyll content, leaf area index, leaf dry weight and root dry weight were determined. The experiment was carried out in a completely randomized factorial design with three replications. Soil ammonium and nitrate concentration were measured during the experiment. The growth characteristics of lettuce were also measured at the end of experiment. Nitrogen and nitrate contents were also determined in lettuce leaves. Results and Discussion: The results of the experiment showed that soil nitrate decreased at the presence of three nitrification inhibitors but the soil nitrogen ammonium increased significantly. Application of nitrification inhibitors also reduced the concentration of nitrate in the lettuce leaves during two harvesting times. Moreover, the nitrogen concentration in the plant increased at the presence of nitrification inhibitors. The application of nitrification inhibitors influenced the plant growth characteristics and changed the lettuce growth characteristics. Chlorophyll content increased significantly in lettuce leaves. Leaf area index, leaf and root dry weight of lettuce increased notably when 3, 4-dimethylpyrazole phosphate (DMPP) and powder Artemisia (ART) nitrification inhibitors were applied to the soil samples. These growth characteristics, however, reduced significantly when dicyandiamide nitrification inhibitors was applied to the soil samples. In addition, the symptoms of toxicity were observed in lettuce plant when dicyandiamide nitrification inhibitors were applied to the soil samples. In general, the highest efficiency of nitrification inhibitors was recorded at the presence of urea fertilizer source and the greatest efficiency was observed initially for powder Artemisia (ART) and then for 3, 4-dimethylpyrazole phosphate (DMPP) and dicyandiamide, respectively, when urea fertilizer was applied to the soil samples. There was a positive correlation between soil nitrogen content and plant nitrate in the first and second harvest. The correlation between soil ammonium and plant nitrate (in the first and second harvest) and soil nitrate was negative.
Research Article
J. Ghaderi; F. Nourgholipour
Abstract
Introduction: Due to the compatibility of canola with different conditions, economic value, its price and importance of rotation with cereals, it has the highest level of cultivation area among the oilseed crops in Iran. Phosphorus (P) deficiency is a widespread macronutrient deficiency and is one of ...
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Introduction: Due to the compatibility of canola with different conditions, economic value, its price and importance of rotation with cereals, it has the highest level of cultivation area among the oilseed crops in Iran. Phosphorus (P) deficiency is a widespread macronutrient deficiency and is one of the major limiting constraints for canola production. Despite its importance, it limits crop yield on more than 40% of the world’s arable land and 70.2% in Iran. Moreover, global P reserves are being depleted at a higher rate and according to some estimates, there will be no economic P reserve by the year 2050. This is a potential threat to sustainable canola production. Most of the P applied in the form of fertilizers may be adsorbed by the soil, and would not be available for plants lacking specific adaptations. It is widely accepted that the most realistic solution to the problem of P deficiency is to develop new plant cultivars that adapt to P-deficient soils. Phosphorus efficiency is a term that generally describes the ability of crop species/genotypes to give higher yield under P-limiting condition. Plant species as well as genotypes within the same species may differ in P efficiency. This study was conducted to determine the effect of phosphorus fertilization on the grain yield and phosphorus efficiency indices in different canola cultivars.
Materials and Methods: The present study was carried out at the research farm of the Mahidasht Agricultural Research Station located 20 km away from Kermanshah (with elevation of 1265 m). This experiment was conducted as factorial in a randomized complete block design with three replications with 2 factors including canola varieties and different amounts of phosphorus fertilizer. The first factor consisted of five triple superphosphate (TSP) levels (0, 16, 32, 49, and 61 kg per ha) and the second factor consisted of three cultivars (Okapi, Opera and Zarfam). This research was conducted on soil where the amount of available phosphorus was lower than the critical level required for canola (15 mg kg-1). Prior to sowing, all phosphorus treatments with 30 kg ha-1 of zinc sulfate fertilizer as well as one-third of nitrogen fertilizer (100 kg ha-1 urea) were applied during planting and mixed thoroughly with the soil. The remaining urea fertilizer was applied at two stages of stem growth (120 kg ha-1) and early flowering (100 kg ha-1). Each experimental plot had an area of 12 m2. Irrigation method was sprinkler. Grain and straw yield were determined after the harvest and seed samples (harvesting stage) were taken and rinsed with distilled water, oven dried at 70 °C, ground, digested and analyzed for determining the P concentration. Analysis of variance was performed using SAS software and mean comparisons performed by Duncan’s multiple range tests (P ≤ 0.05).
Results and Discussion: The results showed that the interaction effects of phosphorus fertilizer rate and canola cultivars on leaf P concentration, grain and straw yield, grain P concentration and uptake, and P efficiency indices were significant. In average of the two-years, the highest grain and straw yields (3203 and 4613 kg ha-1, respectively) were obtained from 300 kg ha-1 P fertilizer rate for Okapi cultivar. Under the P deficiency condition, no significant difference was observed between cultivars in terms of grain yield. Significant differences were observed among three cultivars in terms of P efficiency. Opera cultivar was efficient in absorption (0.84) and Zarfam cultivar was efficient in phosphorus utilization (152 kg grain / kg fertilizer), but Opera was phosphorus efficient. With application of phosphorus fertilizer, phosphorus use efficiency decreased and the highest amount was found for the control treatment which produced 169 kg seeds per kg of phosphorus. The lowest amount of this characteristic was obtained for 300 kg phosphorus fertilizer treatment. Considering the correlation between phosphorus stress factor and P uptake efficiency, it seems that P efficiency was dependent on P uptake (R2 = 0.477 **) rather than P utilization (R2 = 0.076 ns).
Conclusion: Phosphorus uptake efficiency can be used for selecting P efficient cultivars of canola under farm condition. Application of Opera and Okapi cultivars with 80 kg of fertilizer per ha in similar conditions of this experiment would be advisable and excess phosphorus fertilizer application would not significantly increase grain yield. Selecting suitable varieties could decrease application of chemical fertilizers in the soil.
Research Article
A. Sharifi; H. Shirani; A.A. Besalatpour; E. Esfandiarpour
Abstract
Introduction: Interrill erosion is one of the major types of erosion playing key role in the transport of fine particles of the soil, particularly in arid and semi-arid regions, which leads to the decrement of soil fertility and surface water pollution. Land-use change is one of the main ways which reflect ...
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Introduction: Interrill erosion is one of the major types of erosion playing key role in the transport of fine particles of the soil, particularly in arid and semi-arid regions, which leads to the decrement of soil fertility and surface water pollution. Land-use change is one of the main ways which reflect the interaction of human activities and the natural environment and can impact soil aggregation, aggregate stability, and erodibility. Hence, this research aimed to evaluate the susceptibility of soils under different land-use types (four types) to interrill erosion using both rainfall simulation test and soil aggregate stability indexes. The location of study area was around Jiroft city.
Materials and Methods: This study was conducted in four types of land use around Jiroft city in southern Iran, including disturbed pasture, undisturbed pasture, protected forests, and artificial forest. For each land use, 25 points were selected (A total of 100 points for all land uses). To measure soil physical and chemical properties, disturbed and undisturbed soil samples were collected from each point at a depth of 0–20 cm. The samples were transported to the laboratory where these samples were then air-dried. Some soil properties such as texture, organic carbon, electrical conductivity, soil acidity, calcium carbonate equivalent, and bulk density were measured, and available nitrogen, phosphorus, and potassium in the soil and sediment samples were also determined. Furthermore, some characteristics of soil particles, including the geometric mean diameter, geometric standard deviation, particulate organic matter, water-dispersible clay, tensile strength of soil aggregate, mean weight diameter and fractal dimension of aggregates were determined. To assess how susceptible are soils to interrill erosion, rainfall simulator was used to generate rainfall with an average intensity of 60 mm/h.
Results and Discussion: According to the results, the undisturbed pasture revealed the highest content of organic matter, particulate organic matter, clay, and tensile strength, while the minimum values of bulk density, sand percentage, and fractal dimension have been observed in this land use. For this reason, it is assumed that the aggregates of undisturbed pasture (intact rangeland) show more stability than other three land uses. The maximum and minimum values of bulk densities were observed in the protected forest (1.58 g cm-3) and undisturbed pasture (1.43 g cm-3), respectively. On the other hand, the highest value of aggregates fractal dimension, as well as minimum values for mean weight diameter and dispersible clay in the protected forest demonstrated that this land use had either no aggregate or its aggregates were very fine. As a matter of fact, lack of organic matter and insufficient clay content can be considered to be the reasons for poor aggregate stability in this land use. The highest and lowest values for tensile strength of soil aggregate were found in the undisturbed rangeland (64.82 kPa) and protected forest (34.38 kPa), respectively. The variations in the tensile strength of soil aggregate can be attributed to the changes in the contents of clay and organic matter in different land uses. Moreover, despite the maximum amount of total organic matter in the undisturbed pasture (or intact rangeland), the amount of sediment organic matter in this land use was lower than the other three land uses. It is because of the fact that most of the OM in this area was of a stable organic matter type, which was under the soil surface and was accordingly protected from surface erosion. The particle size distribution of sediment was smaller in the undisturbed pasture, whereas it was found to be larger in the protected forest. The reason can be attributed to the coarse-textured soil in the forest compared to the finer-textured soil in the undisturbed pasture (or intact rangeland). In addition, the highest sediment concentration and the highest rate of erosion were observed in the disturbed pasture. The artificial forest accounted for the minimum sediment concentration, while the artificial forest, as well as the protected forest, revealed the lowest erosion rate.
Conclusion: The results of the current research demonstrated the high rate of interrill erosion in all land uses so that the disturbed pasture and artificial forest accounted for the highest and the lowest rate of erosion (7 and 2 ton/ha) respectively. According the results, intrinsic soil characteristics such as soil texture played major role in some land uses, while for the others, the slope impact was more crucial. On the other hand, both erosion rate and sediment concentration revealed the same trend under four different land uses of the study area. Therefore, because of the fact that the highest and the lowest rate of erosion, as well as sediment concentration, were found to be in the disturbed pasture, and the artificial forest, respectively, therefore the sediment concentration can be considered to be an important index for soil erosion. Due to high rates of erosion occurring in the study areas, some measures have to be undertaken to prevent and control soil erosion in this area. To achieve this aim, preventing people from entering the vulnerable area, avoiding livestock grazing, protecting existing plants and restoration of native plants can be mentioned as efficient measures to improve conditions.
Research Article
B. Kamali; A. Mahdavi; A. Sotoodehnia
Abstract
Introduction: Over application of phosphorous-containing fertilizers is common among the farmers. Excess amounts of phosphorus can potentially cause more phosphorous losses through water flow on the soil surface or leaching into the soil profile. The ability of highly phosphorus-fertilized soils to maintain ...
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Introduction: Over application of phosphorous-containing fertilizers is common among the farmers. Excess amounts of phosphorus can potentially cause more phosphorous losses through water flow on the soil surface or leaching into the soil profile. The ability of highly phosphorus-fertilized soils to maintain excessive amounts of phosphorus and prevent losses largely depends on the phosphorus adsorption capacity of the soil. The purpose of this study was to investigate and compare phosphorous adsorption isotherms in soil samples of four agricultural areas located in Qazvin plain and determine the most appropriate equation to describe the equilibrium adsorption in the studied samples. Identification of the most accurate model of adsorption kinetics using the investigated kinetics equations in one of the soil samples was another objective of this study. The linear regression analysis and correlation between physical and chemical properties of different soils with adsorption coefficients of Langmuir equation was also investigated. Based on mentioned points, the results of this study can help to increase the availability of applied phosphorous for plants, reduce phosphorous losses and proper management of phosphate fertilizers consumption in the study areas.
Materials and Methods: In order to study the soil properties and phosphorous adsorption, soil samples of four villages included Zaaferan (A), Koochar (B), Mehdi Abad (C) and Kamal Abad (D) were taken from 0 to 30 cm depth and stored in plastic bags after air drying. Batch experiments using a standard method recommended by the SERA-IEG17 group were used to determine the amount of phosphorous adsorbed to soil particles. The steps to perform the equilibrium were as follows:
1- Dry soil samples were crushed and passed through a 2 mm sieve.
2- One gram of the soil sample was placed in a 60 ml container.
3- 0.01 M CaCl2 solution was prepared and different concentrations of phosphorous including 0, 5, 10, 15, 20, 30 and 80 mg/l were created by adding certain amounts of KH2PO4 to this solution. 25 ml of these solutions were added to each soli sample to give a 1:25 soil to solution ratio and three drops of chloroform were added to each container to prevent microbial activity.
4- The suspension samples were placed in a shaker machine (250 rpm) at 25°C for 24 hours.
5- Then, the samples were removed from the shaker and allowed to settle for one hour and then passes through a fine filter (Mesh 42).
6- Phosphorous concentration was measured by the molybdate-vanadate method followed by spectrophotometric determination at 470 nm.
7- The amount of phosphorous adsorbed in each soil sample was calculated from the difference of the initial and secondary concentration values.
The adsorption kinetics experiment was similarly performed, with the exception that one soil sample with average adsorption value (sample C) was selected and the phosphorous solution at a concentration of 20 mg/l added to the soil samples. Phosphorous contact times with soil were considered as 0.17, 0.5, 1, 2, 4, 8, 16, 24, 48 and 72 hours. In this study, using CurveExpert 1.4 software and by matching Pseudo-first-order, Pseudo-second-order, Intra-particle diffusion, Kuo and Lotse (1974), Barrow and Shaw (1975) and Panda et al. (1978), equations on the data obtained from kinetics adsorption experiments, and the coefficients were estimated in these equations (adsorption parameters). Furthermore, by calculating the coefficient of determination (R2) of these equations and the standard error of the estimate (s), the most appropriate and accurate model of phosphorous adsorption kinetics for the soil sample was determined. Similarly, from Langmuir, Freundlich, Linear and Van Huay equations, the most appropriate isotherm was determined for estimating phosphorous equilibrium adsorption in the studied areas. Also, correlation and linear regression analysis were performed to determine the relationship between the physical and chemical parameters of the soils and the coefficients of Langmuir isotherm using Minitab software.
Results and Discussion: According to the results, the highest coefficient of determination (R2) and the lowest standard error of the estimate (s) for all four samples were related to Langmuir, Freundlich, Van Huay and Linear equations, respectively. Therefore, in this study, Langmuir isotherm was the most accurate model for estimating equilibrium adsorption of the phosphorus to the soils of the study areas. However, the Freundlich and Van Huay equations also showed a good correlation with the laboratory data. Comparison of the results of various studies in these fields showed that the type of isotherm corresponds to phosphorous adsorption data in each experiment is related to the physical and chemical properties of soil and adsorption sites. The amounts of maximum phosphorous adsorption capacity (qm coefficient in Langmuir equation) for the soil samples A, B, C and D were 0.49, 0.31, 0.42 and 0.4 mg/g, respectively. In kinetic study, Although, Kuo and Lotse, Barrow and Shaw and Panda et al. equations had a coefficient of determination (R2) above 0.95 ; the highest accuracy was related to the Kuo and Lotse equation with R2 of 0.974. The coefficients of this model included k (reaction rate) and m (constant coefficient) were 0.007 l/gr.min and 13.2, respectively. Based on the results of this study and other adsorption studies, soil physical and chemical properties including EC, PH, soil calcium content, clay content and porosity were among the parameters affecting adsorption rate and the type of the most accurate equation of adsorption estimation. Considering the soil properties that were most correlated with adsorption coefficients, it can be concluded that the high percentage of clay and low levels of organic matter and soluble calcium are the main causes of the high phosphorous adsorption in soil. The correlation coefficients (r) of these three soil parameters with the maximum adsorption capacity (qm) were 0.61, -0.97 and -0.92, respectively.
Conclusion: According to the results of this study, Langmuir was the most accurate isotherm model and the soil sample of Zaaferan area has the most adsorption capacity with qm of 0.49 mg/g, which is related to low levels of soil organic matter. Therefore adding organic matter to the soils can be used as a solution to increase cultivated plants access to applied phosphorous and reduce phosphorous adsorption into the soil and thus reduce losses and leaching of excess phosphorous in the profile or soil surface.
Research Article
B. Bahmanabadi; A. Kaviani
Abstract
Introduction: The exact estimation of evapotranspiration has significant importance in the programming of irrigation development and other distribution systems and water usage. Since the main user of water in the country is the agriculture sector, therefore, the exact estimation of plants’ water demand ...
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Introduction: The exact estimation of evapotranspiration has significant importance in the programming of irrigation development and other distribution systems and water usage. Since the main user of water in the country is the agriculture sector, therefore, the exact estimation of plants’ water demand has been adverted extensively. The assessment methods of reference evapotranspiration are classified in two types of direct and indirect. The calculation of reference evapotranspiration in scientific and in vitro form and with high accuracy is possible by using lysimeter but in comparison to the indirect methods that are based on the climatic data of weather stations, the use of lysimeter is unfortunately inefficient. This is not just for the time consuming and high cost of lysimeter but it is for the limitation of weather stations and spottiness of the estimated values; in this way it is not possible to expand the obtained results to the large scale. Remote sensing is an authentic technique for the assessment of evapotranspiration in large scale which do not consume much time and money. The existence of different satellites by having different spatial and temporal resolution, redouble the importance and usability of this technique
Material and Methods: Actual evapotranspiration assessment in the region were done based on SEBAL, SSEB and TSEB algorithms on 46 imageries of MODIS, seven imageries of Landsat7 (ETM+) and seven imageries of Landsat5 (TM) in years of 2001-2003. Multiplicity of imageries of MODIS show the proper time resolution of this sensor and is a reason for less errors in the assessment of reference evapotranspiration. In the evaluation of the three algorithms of SEBAL, SSEB and TSEB in the three satellites.
Result and Discussion: In the evaluation of the three algorithms of SEBAL, SSEB and TSEB in the three satellites, MODIS shows the least errors (respectively, RMSE=0.856, 1.385 and 2.7 mm/day), then Landsat7 is placed in the second class by having higher spatial resolution (respectively, RMSE=1.042, 1.56 and 2.76 mm/day) and Landsat5 has the highest errors (respectively, RMSE = 1.14, 1.97 and 3.06 mm/day). NDVI was found at the lowest amount in the beginning of cultivation period because of germination and sparseness of vegetation, and increase respectively by increasing temperature and crop canopy. L factor has a significant importance in the assessment of SAVI which is related to the area crop coverage percentage. Amount of L has been estimated as L=0.6 that has the least errors in comparison to the others.
Conclusion: In this study, the proper amount for L factor in estimation of the SAVI amount was about 0.6 which was based on the investigations on soil correction factor, the results of statistical indexes and the type and dispersal of vegetation in the region. The accuracy estimation of evapotranspiration of two single-source algorithms of SEBAL and SSEB and one two-source algorithm of TSEB in Bushehr province were evaluated. SEBAL algorithm presented more exact results based on statistical indexes among two single-source algorithms and the obtained results in 95% level of this algorithm showed significant differences with lysimetric measurements. This algorithm was chosen as the premier algorithm in the region. Two-source algorithm of TSEB showed the highest amount of errors. Satellite imageries by having higher spatial resolution estimated evapotranspiration with higher accuracy, the reason of which is proper choosing of cold and hot pixels. Although, because of having proper time resolution and variation of image numbers and also presenting of more time series in comparison to ETM+ and TM, MODIS was more adverted. ETM+ which is located on Landsat satellite was lied in the second place because of its resolution and having higher spatial resolution.
Research Article
Nooshin Ahmadibaseri; A.A. Sabziparvar; M. Khodamoradpour; L. Alados Arboledas
Abstract
Introduction: Surface Solar Radiation (SSR) as the largest source of land-surface energy is an important parameter in meteorological and climatological studies. Limitations in ground-based measurements have encouraged the users to approach low cost and reliable methods to estimate radiation components, ...
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Introduction: Surface Solar Radiation (SSR) as the largest source of land-surface energy is an important parameter in meteorological and climatological studies. Limitations in ground-based measurements have encouraged the users to approach low cost and reliable methods to estimate radiation components, for the regions where the ground-based radiation data are sparse. Different methods have been developed for estimating SSR including empirical models, radiative transfer models, semi-empirical models, and models based on satellite and reanalysis products. In most studies in Iran, empirical methods have been investigated. Despite the simplicity of these models, they do not accurately represent SSR variations because of not considering all the parameters affecting radiation variations, at large spatial scales with different climates. The Global Land Data Assimilation System (GLDAS) is a combination of measured and satellite data that uses advanced land surface modeling and data assimilation methods. One of the strengths of this model that makes GLDAS unique is that it has global coverage, high spatial-temporal resolution and is available for free. GLDAS is a terrestrial modeling system uncoupled to the atmosphere. This work was aimed to evaluate SSR derived from GLDAS using ground measurements over Iran from 2012 to 2015 on a daily basis.
Materials and Methods: In this study, measured SSR in 24 radiometer stations of Iran from 2012 to 2015 was extracted. Since the measured data are associated with some errors, the quality of the data must be checked and screened before use. In this study, Moradi's proposed method was used to control data quality. The studied areas were classified into three zones of coastal, arid and semi-arid climates based on Digital Elevation Model (DEM) and UNESCO climate classification approach. The GLDAS SSR outputs were extracted with a spatial and temporal resolution of 0.25° grid cell and 3-hourly from 2012 to 2015. The GLDAS is one of the LDAS projects and has been extended jointly by the National Aeronautics and Space Administration (NASA) Goddard Space Flight Center (GSFC) and the National Oceanic and Atmospheric Administration (NOAA) National Centers for Environmental Prediction (NCEP). The purpose of GLDAS is to produce high quality temporal and spatial land surface data. GLDAS drives three land surface models: Mosaic, Noah, and CLM. GLDAS assessments SSR at the land surface using a method and cloud and snow products from the Air Force Weather Agency's (AFWA) Agricultural Meteorology modeling system (AGRMET). Since the GLDAS data are created using the gridded Binary format, the nearest neighborhood interpolation method was used to match these data with ground-based data and GLDAS datasets were generated for station points using CDO software. In this study, GLDAS datasets were compared against measured SSR datasets by four validation metrics. The metrics used are determination coefficient (R2), the mean bias error (MBD), the mean absolute error (MABD), relative mean absolute error (RMABD) and root mean squared error (RMSE).
Results and Discussion: Statistical analysis showed that the performance of GLDAS in SSR evaluation is reasonable in Iran with a high-efficiency coefficient of 0.88. Also, it was shown that the GLDAS has a higher ability to estimate SSR under clear sky (warm seasons) conditions than cloudy conditions (cold seasons). Similar to the obtained results, Träger-Chatterjee et al. (2010); Jia et al. (2013); Boilley and Wild (2015) and Heidary Beni and Yazdanpanah (2017) also showed that the ERA- Interim, NCEP-DOE, RegCM4 and angstrom model are also more capable of estimating SSR in warm seasons. Seasonal bias variations at three studied areas showed that the most changes occurred in summer and least changes in winter. The highest overestimation was also observed in the coastal areas in summer and the lowest overestimation in the semi-arid regions in spring. The evaluation of the GLDAS performance against the site measured SSR data suggests that the GLDAS tends to underestimate in 71% of the studied stations. Moreover, the stations located in the arid region provided a better estimation of SSR as compared with semi-arid and coastal locations. These results were compared with those of Boilley and Wald (2015) that showed ERA-Interim and MERRA reanalysis models have high uncertainty in areas with tropical humid climates, and in regions with arid climates, models perform better in SSR estimation. Our findings were also in good agreement with their results.
Conclusion: GLDAS SSR outputs can be used for agricultural studies. This is due to the facts that arid and semi-arid climates are dominant in Iran and the growing season is mostly in the warm season.
