Iranian Journal of Soil and Water Research
Year:2019 | Volume:50 | Issue:4 |Papers Count:20

There are various parameters which are important in determining the dispersion coefficient in rivers, e. g. hydrodynamic parameters and river geometry. Thus it is a challenging task to determine this coefficient accurately. There are different empirical formulas to estimate the dispersion coefficient in rivers. These formulas are mostly accurate in the range of conditions they validated. It is important to know the conditions in which the dispersion coefficient effect is significant in rivers. Thus, in this conditions, one should determine it with more accuracy. The main purpose of this study is to present a new method for determining the situations in which, dispersion coefficient has significant effect on solute transport mechanism. The proposed method is based on the Monte Carlo simulation method. The method was verified and validated using several hypothetical and also a real test cases. The results show that the time pattern of pollution source is a key factor in the dispersion coefficient effects on solute transport mechanism. The main finding of the study is that, sometimes it is possible to consider the dispersion coefficient with large errors and no significant changes occur in results of the solute transport simulation.

An accurate estimation of precipitation is important and necessary for flood simulation, drought monitoring and water resources management. Currently, most parts of the world are suffering from the lack of the rain gauge observations and the spatial coverage of ground observations aren’ t enough and continues. One of the most important precipitation datasets is the model-based precipitation datasets, by which the satellite techniques, the general circulation models (GCMs) and the land surface models (LSMs) are integrated to provide high temporal and high resolution datasets for all parts of the world. This datasets can compensate the lack of adequate ground observation gauges or can be considered as an alternative for ground observations, especially in ungauged regions. In this research the accuracy of the most important reanalysis datasets, called ECMWF, for estimation of daily and monthly precipitation over the SefidRood watershed for the time period of 2000-2008 was investigated. In addition, for better assessment of the proposed precipitation datasets, TRMM dataset was used. Findings on daily and monthly time scales, show that the correlation coefficient (CC) between observed and ECMWF dataset is so remarkable, especially in south, central and west parts of the study area. For instance, the CC values of the average precipitation of ECMWF data versus gauge datasets in both daily and monthly time steps were estimated to be about 0. 83, 0. 94, respectively, while the CC values for TRMM dataset versus gauge datasets were estimated to be 0. 32 and 0. 57, respectively. In contrast to reanalysed datasets, one of the most important weakness of the precipitation datasets such as TRMM is that they estimate the rainfall only based on the cloud thickness and its available water. Moreover, according to the categorical verification statistics in both time spans, ECMWF due to having low value of false alarm ratio (FAR) and high values for accuracy and probability of detection (POD) yields acceptable results over the SefidRood watershed. SefidRood watershed is a large scale region and contains different climate and topographical conditions and hence the results of this research can be used as an appropriate guidance for other similar areas. Based on the findings in this study it’ s highly recommended for using this rainfall dataset as one of the best alternatives for ground observations, especially in data sparse regions that accessing to ground datasets is so hard or almost impossible.

In this study, the effect of equal matric and osmotic potentials was investigated separately and simultaneously on water uptake and yield of corn. A factorial experiment with two factors; potential type (osmotic, matric and combined) and potential levels (-0. 46,-1. 12,-1. 91, and-3. 63 bar) was performed on the basis of completely randomized design with 4 replications in greenhouse conditions. Increasing in osmotic stress (from-0. 46 to-3. 63 bar) resulted a reduction in water uptake by 36. 6%. Potential reduction reduced root dry mater 40 and 36. 6% in osmotic and combined potential treatments, respectively. Slight drought stress increased root dry matter by %26. Among the treatments and potential levels, the highest water use efficiency was observed with 1. 12 g/l for the potential level of-1. 12 bar in the combined stress. The results showed under the same levels of osmotic and matric potential, the salinity stress causes more damage to plant growth with decreasing water uptake. At low potential levels (-0. 46 to-1. 12) of combined treatments, the partially irrigation system increases water use efficiency, due to relative improvement in root growth. At low potential level (-3. 63 bar) of combined treatment (with equal suction at two sides of the root), the plant uptakes less water than the condition where total root experiences the same level of potential by salinity. At least for low salinity leves, the osmotic and matric potential values cannot be considered as two additive parameters; On the other hand, the sumation of them cannot show the real stress conditions of the root environment. The results of such studies can be used to accurately manage the quantity and quality of irrigation water under the salinity and drought stress in arid and semi-arid regions.

In order to study the effect of magnetic field and different levels of saline irrigation water on cumin yield, a factorial experiment with a completely randomized block design with three replications was carried out in Kashmar Higher Education Institute in 2016. In this experiment, four salinity levels of irrigation water; 0. 5 (S1) as control, 6 (S2), 8 (S3), and (S4) 10 dS m-1, and two levels of magnetic field; magnetic water (M1) and nonmagnetic water (M2) Were used. The results showed that the magnetized water increased the yield of cumin compared with non-magnetized water. So that the maximum grain yield of cumin (1085 kg. ha-1) was corresponded to S1M1 treatment and the lowest one (530 kg ha-1) was corresponded toS4M2 treatment. Also, the maximum and the minimum biological yields (2215 and 1295 kg ha-1) were corresponded to the same treatments (S1M1 and S4M2) respectively. The yield reduction rates for 6, 8 and 10 dS m-1 saline waters were calculated to be 7. 8, 14. 7 and 32%, respectively for the magnetic field and 6, 15. 7 and 44. 5%, respectively for the non-magnetic field as compared to the control treatment. In addition, the average water use efficiencies of saline and magnetic water treatments (0. 5, 6, 8 and 10 dS m-1) were estimated to be 8. 8, 6. 5, 10. 3 and 17. 4% greater than the ones of saline and non-magnetic water treatments, respectively. Therefore, the use of magnetic water can increase the yield of cumin under salt stress conditions.

The soil of rangelands is an important global carbon sink, in which any change makes a high impact on the CO2 emissions to the atmosphere and global warming. The capacity of this sink is controlled by complex interaction functions among various factors, including climate, soil properties, vegetation type, and management practices. For understanding the effect of these factors on soil carbon in long term, the soil carbon models have a vital role. The soil carbon models must be correctly validated for a specific region and ecosystem, then they can be used to simulate and predict changes in soil carbon. The main objective of this study was to evaluate the performance of RothC and Century models as the most widely used models in the soil carbon studies for semiarid rangelands of Bajgah in Fars province. The R2 (determination Coefficient), r (correlation coefficient), RMSE (root mean square error), MAE (mean absolute error), MD (mean difference) and t-student test between simulated and measured values of soil organic C were used to evaluate the performance of RothC and Century models. Results showed although the Century model negligibly simulated SOC lower than the RothC model, but based on the statistical analyses, both models represented satisfactory results and their simulated values were consistence well with the measured values. Also the results of simulations by Century and RothC models showed that the SOC stocks will be increased during the years of 1987 to 2050 by 7. 92% and 12. 92%, respectively.

Estimating the soil physical indices requires determination of soil moisture content at field capacity (FC). Therefore, the aim of this study was to evaluate the effect of various soil suctions according to field capacity on different soil physical quality indices and subsequently to evaluate the soil physical quality based on the calculated indices. In this study, 35 soil samples from agricultural lands of Alborz province were used to calculate Dexter's S, air capacity, plant available water and relative field capacity indices. The results showed that only 20 % of the soil samples were in weak soil physical quality groups (S < 0. 035) and the rest of soil samples had a good or better soil physical quality (80 %) on the basis of Dexter's S index. However, the results of other indices showed by assuming a FC moisture content at soil suction of 100, 330 cm and calculated suction based on the negligible drainage rate concept, 12, 44 and 70% of soil samples, respectively had a good physical quality in terms of soil aeration, water availability and microbial activity. There was no significant difference between the average FC at equivalent soil suction of 330 cm and the proposed approach based on the negligible drainage rate. Hence, the soil physical indices based on FC at soil suction of 330 cm can be used to evaluate the soil physical quality of the studied soils. Moreover, the results showed that despite of good ability of S index, use of other soil physical quality indices leads to a more comprehensive assessment of soil physical limitation on crop growth. However, determination of the soil quality indices requires an accurate estimation of soil moisture content at the field capacity.

Soil moisture characteristic curve (SMCC) is an important hydraulic properties in modelling of water movement and solute transport in unsaturated zone of soil, which its direct measurement in a laboratory is expensive, time-consuming and laborious. Therefore, the objective of this study was to compare the fitting capabilities of several SMCC fractal (Tyler and Weatcraft, 1990; Rieu and Sposito, 1991; Perfect, 1999 and Bird et al., 2000) and empirical models (Brooks and Corey, 1964; Campbell, 1974 and van Genuchten, 1980) to the observed data and to select the appropriate models. For this purpose, fifty-four soil samples were randomly collected from Ghorveh-Dehgolan plain and some important physical and chemical properties of soils were measured in the soil laboratory. The SMCC fractal and empirical models were fitted to the measured data based on the least esquare error approach using the solver toolbox of EXCEL software. In order to evaluate fitting quality of the proposed models, three statistical parameters including coefficient of determination (R2), root mean square error (RMSE) and Akaike information criterion (AIC) were used. The results indicated that all models did well with R2 ranging from 0. 75 to 0. 99. Bird et al., (2000) and van Genuchten (1980) models are selected as the best models, respectively, based on the highest R2 and the lowest RMSE and AIC. Rieu and Sposito (1991) model was the weakest, although the average R2 was greater than 0. 75 and the average RMSE was smaller than 0. 071 cm3/cm3.

In order to study the effect of various irrigation water and fertilizer levels on water use efficiency, grain yield and protein percentage, a two-year field experiment was conducted in agricultural and natural resources research station of Broujerd. The experiment was carried out in a split-split plot design with three replicates. The main plot was involved three irrigation water levels (I0=4000, I1=5000, I2=6000 m3) and three levels of fertilizer including F1=NPK+ME, F2=NPK+1. 3ME and F3=NPK+0. 7ME allocated to sub plots. "ME" means microelements consumption including iron, zinc, manganese, copper and boron. Sub-sub plots were included three wheat cultivars; Marvdasht, M-75-7, M-75-10. Two-year results of the studied treatments showed that the highest grain yield is corresponded to M-75-10 cultivar with F1 fertilizer and I1 irrigation water level. The highest water use efficiency is corresponded to Marvdasht cultivar with F2 fertilizer and I0 irrigation water level and the highest protein content is corresponded to M-75-7 cultivar with F0 fertilizer and I0 irrigation water level.

Infrared thermometer is one of the proper irrigation scheduling tools that can be used in fields or gardens with different soil texture. In order to schedule irrigation of maize (SC704) in Urmia climate conditions, using a difference in temperature of canopy cover of plant and air in 2017, a research was conducted at research farm of Urmia University college of agriculture under drip irrigation. In this research, the effects of various irrigation water treatments were investigated. The experimental design was carried out in a randomized complete block design with three levels of irrigation I1, I2 and I3 of 50, 75 and 100 percent of water requirement in three replications, respectively. Based on the results, the average values of CWSI for maize during the growth period for treatments of I1, I2 and I3 were calculated to be 0. 53, 0. 44 and 0. 28, respectively. The results showed that the CWSI index increased with decreasing water requirement. The threshold of water stress index (0. 28) of I3 treatment (no stress treatment) was the basis for irrigation scheduling. Then, some relationships were presented to determine the irrigation time of maize, using the CWSI index in Urmia climate for July, August and September as  c a  c T  T  3. 4617  0. 1553(AVPD),  c a  c T  T  2. 5536  0. 0556(AVPD) and  c a  c T  T  7. 2806  0. 1572(AVPD) respectively.

Abruptly expanding stilling basins are often used at downstream of structures such as overflows, gates and spillways to increase energy loss in hydraulic jumps. Increasing the jump length, decreasing the depth ratio and asymmetric flow are among the characteristics of jump in a sudden expanding channel. The channel bed roughness is one of the method that can reduce the secondary depth and jump length. Therefore, in this study, the effect of sand bed with median size 1. 9 cm on S-jump characteristics was investigated. Whole of the experiments were performed at expansion ratios of 1, 0. 67, 0. 5, and 0. 33 and within the range of Froud numbers; 4 to 12. The results showed that the abruptly expansion stilling basins with a rough bed in all the expansion ratios reduced the depth ratio with an average of 12 to 16 percent, compared to an abruptly expansion stilling basins with smooth bed. Also, the average jump length reduction for all expansion ratio in the abruptly expanding stilling basin with the rough bed was obtained 20 percent.

In most countries, agricultural sector is the main user of water resources (surface and ground water). The process of exploitation of water resources to explain the sustainability and continuity of exploitation in each region, especially in arid and semi-arid areas, which is faced with the shortage and severe competition of water resources use in different sectors is necessary. The purpose of this study was to investigate the status of water resources in the Marvdasht-Kharameh range (covered by two modern irrigation networks in Dorodzan and traditional Korbal) in Fars province during the statistical period of 2006-2016, based on the stability analysis indexes proportional to the volume of water allocated in comparison with excessive withdrawal of groundwater resources, as well as the relationship between rainfall and the amount of variations in the level of stagnation. For this purpose, by using Dorodzan weather data and Persepolis stations, as well as Kheirabad, Pulkhan and Zarghamabad hydrometric stations and the irrigation networks data, the available water resources in terms of surface and groundwater were estimated. According to the average level of stagnation and changes in aquifer volume, excess water harvesting were calculated in two areas covered by Dorodzan and Korbal irrigation networks. The amount of runoff coefficient in plain, altitudes and total range was calculated to be 6. 9, 14. 1 and 9. 9 percent, respectively. The average amount of excess withdraw in the area covered by two modern Dorodzan and Korbal networks is 96. 33 and 16. 2 MCM /year, which according to available water resources is 8. 2% and 5. 2%, respectively. The Average standardized precipitation-evaporation-transpiration12-month SPEI index for Droodzan and Persepolis stations was calculated to be-0. 33 and-0. 43, indicating the mild drought in the area and during the proposed time period, and this is in good agreement with the Water table drawdown. The result of linear regression between the independent variable of rainfall and the dependent variable of the average water table changes showed a significant increasing linear relationship (p < 0. 001) with R2 = 0. 95 and RMSE = 0. 99. This result for the independent variable of rainfall with the dependent variable of water allocation volume, indicated an incremental linear relationship (P = 0. 110), with R2 equal to 0. 29 and RMSE equal to 245. 6. Indicators of water resource sustainability analysis, such as Falcon Mark (FI), United Nation (UN) and Water Tension Index (WSI), were calculated for the region. The values of the Indicators of water resource sustainability analysis including Falcon Mark (FI), United Nation (UN) and Water Tension Index (WSI) were 1983 cubic meters per person, 210 percent and 2. 93, respectively. By comparing the values of these indexes, it was found that based on the FI index, the area is close to tension. The UN and WSI indicators are indicative of the fact that the study area is under severe crisis and excessive use of water resources and the pattern of exploitation of water resources should be managed in order to eliminate surplus withdrawals and sustainability of water resources.

The first step in management of available water resources is to maintain their quality, due to the limited usable water resources. Conservation of water resources quality requires the correct understanding of the fate of water quality and its proper modeling. The QUAL2Kw Model is a numerical model that can simulate water quality issues. However, this model cannot be used before calibration and validation for a given river. In this research, the calibration of the QUAL2Kw model was performed using the Water Cycle Algorithm (WCA). For this regards, the qualitative data of Yamuna River in India including CBODs, CBODf, organic nitrogen, ammonia and nitrate during the period of ten years (1999-2009) were studied. The results of calibration with GA and WCA algorithms were compared together. The average R2 value was 97 percent for all the variables. RMSE ranges for WCA and GA algorithm were 0. 32 to 4. 2 and 0. 4 to 8. 2, respectively. In general, it can be concluded that the WCA algorithm has a better performance and accuracy than GA in calibration of the QUAL2Kw model and can be used to calibrate the model.

Soil contamination is one of the most important problems of modern societies. One of the serious pollutants in this area is nickel. Phytoremediation is one of the proposed methods that allow pollutants to be removed from the contaminated soils with pollutant accumulation in plants. In the case of heavy metal contamination, the use of soil chelating agents can increase the efficiency of this method. The aim of this study was to investigate the uptake of nickel from soil by maize (Zea maize) and sunflower (Helianthus annuus) in the presence of two levels of citric acid (5 and 10 mmol kg-1 soil), two levels of nitrilotriacetic acid (NTA) (2. 5 and 5 mmol kg-1 soil) and two levels of anion polyacrylamide (APAM) (0. 07 and 0. 14 g kg-1 soil). Control treatment was performed without chelate. This experiment was conducted as a completely randomized design with three replications in soils contaminated with nickel (200 mg Ni kg-1 soil, added as Ni (NO3)2) under greenhouse conditions. The results showed that the most effective chelate in increasing the yield of maize (plant height, fresh and dry weight of shoot and root) was NTA chelate at its highest concentration. The highest increase of sunflower yield was obtained by applying CA chelate. NTA at high concentrations had the greatest effect on nickel available, nickel accumulation of shoot and total absorption in both plants compared to CA and APAM treatments. Based on the results, the use of maize and application of NTA at highest concentrations resulted a higher accumulation of nickel and increased transfer and refinement factors in the proposed plants.

Disturbance in nitrogen cycle balance has a negative impact on the overall trend of sustainable development and the use of soil amendments is necessary to reduce these hazards. In order to investigate the effect of some amendments and irrigation water salinity on mass nitrate balance, a factorial experiment in a completely randomized design with three replicates was conducted. The treatments consisted of three levels of soil amendments (zero, 7. 5 g/kg of raw pistachio residues and 7. 5 g/kg of its biochar) and four salinity levels of irrigation water 0. 5 (tap water), 5. 5, 8 and 10. 5 dS/m. Two pistachio seedlings were transferred to all columns and then in three stages and in each stage, 25 mg/kg N of potassium nitrate was added to the soil. After adding nitrogen, nitrate measurements were done in different times. The results indicated that the pistachio residuals and its biochar increased nitrate outflow from the soilby 9% and 52%, respectively. The nitrate concentration with the exit of about 60% of the drainage water (about 7 hours later) reached the lowest, then remained constant until complete exit.

Fine-grained soils with a high percentage of clay minerals are used for covering sanitary landfill and for earth dams' cores because of their low permeability. One of the key factors affecting the behavior of these soils is pore fluid chemistry, so that changes in fluid viscosity and type of cations change the engineering properties of these soils. In this study, the effect of water salinity has been investigated on Atterberg and compaction characteristics, shear strength, pore water pressure of fine-grained soils. For this purpose, Atterberg limits, compaction and undrained triaxial tests were conducted on the fine-grained soils, used in the cores of Shahid Madani and Malekian dams, with different pore fluids. Distilled water, project salty water, NaCl solutions with 0. 2, 0. 4, and 0. 8 molar are used as a pore fluid. The results showed by increasing the salinity of water, the liquid limit, plastic limit and plasticity index decrease in both soils, but these changes are not considerable. The results of the triaxial tests showed increasing NaCl salt concentration does not always increase the shear strength of the soils. The maximum increase in the soil shear strength values in both Malekian and Madani soils was obtained with 0. 2 molar which is mentioned as an optimal point. In both soils, by increasing the salinity of water, the excess pore water pressure decreases and there is not any meaningful effect on the deformation modulus secant of soils. The cohesion parameter in both soils are reduced up to 0. 4 molar and after that increased by increasing salinity. The saline water with concentration between 0. 2 and 0. 4 molarraised the internal friction angle of soil and beyond these concentration did not have a positive effect on the friction angle.

Water is the most important limiting factor for plant growth in dry and desert regions. Addition of soil amendments is one of the most important practices to reduce water shortage by improving soil physical properties and water use efficiency. In this study, the effect of natural and urban waste-compost biochars on the soil physical properties (e. g., bulk density, particle density, field capacity, permanent wilting point, available water, saturated hydraulic conductivity, and irrigation interval) as the most effective parameters on irrigation were investigated. This experiment was conducted as factorial and in a completely randomized blocks design with three factors and three replications in greenhouse condition. The proposed factors were consisted of four levels of natural biochar (0, 1, 3, and 5 % of weight) and four levels of municipal waste-compost biochar (0, 1, 3, and 5 %) and a plant factor at one level (Calligonum species). The results showed that the addition of biochars to the soil had a significant increasing effect on the field capacity, available water, and irrigation intervals and a significant decreasing effect on the saturated hydraulic conductivity, bulk and particle density. Field capacity, permanent wilting point, available water and irrigation interval had an average incremental rate of 17. 2, 16. 8, 17. 4, and 3. 2% respectively and hydraulic conductivity, bulk and actual density had an average decremental rate of 39. 4, 4. 4 and 11. 7 % respectively as compared to the control treatment. Treatment No. 13 (soil+5% natural biochar+5% urban waste compost biochar) had the most effectiveness on the above mentioned parameters.

The main objective of this research is to optimize the type and location of Best Management Practices (BMPs) to reduce the amount of nutrients entering the lake Zrebar in order to improve lake conditions. In this regard, Simulation-Optimization approach derived from the integration of the SWAT model and a spatial optimization model of BMPs based on multi-objective genetic algorithm (NSGA-II) was used. In this approach, the optimal model of management practices was determined with respect to three objectives: maximizing the net profit of the agricultural sector, minimizing the nitrogen loads and minimizing the phosphor loads. In this research, a wide range of BMPs was investigated and the optimal spatial pattern of the management practices such as fertilizer, irrigation and tillage managements were determined. Results showed that by applying the selected management practices with the optimal spatial pattern, the total amount of phosphorus and nitrogen in the basin outlet decreased by 2. 8% and 22. 1% respectively and consequently the concentration of nitrate in the lake will be greatly reduced. Also the net income of the agricultural sector decreased by 16. 4%. The results indicated that applying the selected management practices with the optimal spatial pattern can help to improve the environmental condition of the lake.

The infiltration parameters, used in the surface irrigation simulation models, are not measured directly and their estimations are difficult and uncertain. Therefore, after calibration of model parameters, the uncertainty due to error in the model and the strategies should be considered to reduce and control the uncertainty of the results. For this reason, Monte Carlo simulation approach has been used in this study. Nowadays, the Monte Carlo simulation approach is used as a simultaneous and integrated approach to identify different types of uncertainty with various objective functions. Therefore, this research was conducted to analyze the uncertainty of the simulation results of the runoff hydrograph and the advance trajectory modeled by the WinSRFR software by developing the posterior analysis of the infiltration equation parameters and simulation of 1000 Monte Carlo samples. The results of the analysis indicated a high degree of uncertainty (bandwidth over 4) in initial selection of furrow irrigation infiltration parameters, Nash-Sutcliff criteria was considered to district behavioral and nonbehavioral simulations and the acceptable threshold value for NSE criteria defined as NSE>0. 9. By applying NSE>0. 9, the behavioral simulations were detected and used for uncertainty analysis of the model. The uncertainty analysis of the model was performed based on 5% and 95% confidence levels of behavioral simulations errors. In this case, the uncertainty band width (d-factor) of two response variables was less than one indicating a good calibration result. The results of uncertainty analysis showed that the uncertainty of model parameters wasconsiderably decreased with application of Monte Carlo method. Therefore, the use of this method in the modeling and management of surface irrigation systems is recommended.

Land use change is one of the major human interactions in natural ecosystems that affect ecosystem processes, especially soils. In the present study, the effect of land use change on the dynamics of microbial and enzymatic activities in the Gerdkooh-Safak area of Mazandaran province was investigated. For this purpose, soil sampling was carried out by systematic-random method from two depths of 0-5 and 5-10 cm. Totally, 240 soil samples were collected from six land uses (i. e. natural forests of hornbeam-ironwood, degraded natural forest, alder plantation, sequia plantation, improved follow and home garden), in four seasons of spring, summer, autumn and winter. According to the results, alder plantation and natural forest had the highest basal (0. 49 and 0. 44 mg CO2-C g− 1 day− 1) and substrate induced respirations (1. 40 and 1. 40 mg CO2-C g− 1 day− 1); in contrast, the sequia plantaion and improved follow had the least basal (0. 21 and 0. 24 mg CO2-C g− 1 day− 1) and substrate induced respirations (1. 02 and 1. 07 mg CO2-C g− 1 day− 1). Alder plantation and natural forest had the highest amount of nitrogen microbial biomass (70. 20 and 67. 38 mg kg-1), nitrate (32. 92 and 30. 49 mg kg-1) and ammonium (30. 04 and 27. 95 mg kg-1). The highest levels of enzymes activity of urease, phosphatase, arylsulphatase and invertase were found in alder plantation and natural forest (145. 8, 144. 8 μ g NH4+– N g− 1 2 h− 1, 651. 2, 629. 6 μ g PNP g− 1 h− 1, 142. 4, 141. 4 μ g PNP g− 1 h− 1 and 217, 214. 8 μ g Glucose g− 1 3 h− 1) respectively and the least activity was detected under improved follow, degraded sites and sequia planation (127. 22, 128. 86, 128. 08 μ g NH4+– N g− 1 2 h− 1, 273. 2, 261. 2, 272. 8 μ g PNP g− 1 h− 1, 107. 2, 109. 6, 108/8 μ g PNP g− 1 h− 1 and 151. 4, 155. 4, 158. 8 μ g Glucose g− 1 3 h− 1). Due to the variability of soil microbial and enzymatic characteristics in different seasons of the year and the proposed depths, the highest values of these characteristics were allocated to the seasons of summer and spring and the upper layer of soil. According to the evaluation of land uses and following the natural forest, the establishment of the alder species in the degraded forest areas of the northern Iran can be considered as the selected species for land uses with similar conditions to improve the soil quality and health.

In many plains of Hamedan province, free distribution and low water subsidies paid by farmers have led to its overexploitation at the fields, which can threat the existing water resources and agricultural sustainable development in the region. Undoubtedly, one of the most important tools for optimal allocation of water resources is economic valuation, which emphasizes the long-term development strategy of the country. In this regard, the purpose of this study was to determine the economic value of agricultural water in potato fields in Razan-Ghahavand plain of Hamedan province using two approaches; production function and willingness to pay farmers using conditional valuation method (CVM). The required information was collected by completing a questionnaire from 150 potato farmers using a two-stage cluster sampling method in 2015-2016. In order to achieve the research objectives, the estimation of various forms of production functions was used, and the best form of the function was determined according to the results obtained by the transcendental production function. The results of the production function method showed that the average economic value of water producing potato crops was 2461 Rials per cubic meter. Also, the average willingness to pay farmers of this product after estimating the Logit model was 3452 Rials per cubic meter. Regarding the reported results, better achievements can be derived, if the water pricing policy is depended on effective factors, including the willingness to pay farmers, as well as the farmers' participation in decision-making.