نشریه دانش آب و خاک
سال بیست و دوم شماره 2 (تابستان 1391)

Drought and low rainfall are arising problems in recent years in many countries that limit agricultural production. An appropriate solution to overcome water deficit stress in sustainable agriculture is establishment of mycorrhizal symbiosis in plants. Mycorrhizal fungi affect plant growth by widespread activity in roots and soil. A greenhouse experiment was carried out using tomato (Lycopersicon esculentum L. cv. Behta) plants inoculated with two species of mycorrhizal fungi Glomus intraradices (Gi) and Glomus etunicatum (Ge) in a sterile soil. The experiment was factorial based on a completely randomized design with three replications. After plants establishment, three ranges of soil moisture: (0.9FC–FC) [D0] and (0.7FC-0.8FC) [D1] and (0.55FC-0.65FC) [D2] were applied to the pots. In both fungal species root mycorrhizal colonization decreased by decreasing soil moisture. Inoculation of plants with Gi and Ge increased shoot dry weight by 14.5% and 16.2%, respectively, compared to non-mycorrhizal plants but shoot dry weight declined by decreasing soil moisture. Mycorrhizal fungi significantly (P<0.01) increased leaf relative water content (RWC), leaf water potential (LWP) and stomatal conductance (gs) but these parameters were decreased by decreasing soil moisture. Mycorrhizal plants at all levels of soil moisture had more shoot P concentration than the control plants, but Ge significantly increased shoot K concentration. Thus, both P and K contents decreased by decreasing soil moisture. Based on the results, it can be concluded that the arbuscular mycorrhizal fungi can increase tomato growth and nutrient uptake under water deficit stress.

The bed and sidewall average shear stresses in smooth trapezoidal open-channels are determined by solving the continuity and momentum equations. The isovels and orthogonals for a trapezoidal channel section with 1:1 sidewall aspect ratio were obtained by using conformal mapping technique. New equations were drived by determining a portion of bed shear stress from total shear stress. As a first approximation, the boundary shear stress equations were obtained after neglecting the secondary currents and assuming a constant eddy viscosity. In comparison with laboratory measurements, the first assumption overestimated the average bed stress by 20% but it underestimated the average sidewall shear stress by -24%. The second approximation was then presented by introducing two lumped empirical correction factors for the effects of secondary currents, variable eddy viscosity and other unexpected effects. Comparison between laboratory measurements and those from the second approximation, showed an excellent agreement (R2>0.993 and average relative error less than 1.2%) between them with experimental measurements over a wide range of width-depth ratios.

In this study, 14 strains of A. chroococcum isolated from wheat grown fields around the city of Tabriz, in northwest of Iran, were assayed for siderophore production using chrome azurol-S agar (CAS-agar) method under in-vitro conditions. Results showed that some strains had relatively higher ability in siderophore production. In a pot culture experiment with sterile soil, wheat plants (Triticum aestivum L.CV. Falat) were inoculated with 14 bacterial strains. Positive control received nitrogen fertilizer without bacterial inoculation and negative control was left un-inoculated and without N- fertilizer. Totally, 16 treatments with four replications were arranged in completely randomized design. Concentartions and contents of Fe, Cu, Zn and Mn in shoot and root as well as translocations of these elements from root to the shoot were determined at the harvest time. Results showed that the inoculation with Azotobacter had significant effects on concentrations and contents of Fe, Zn and Cu in shoot and root. Translocations of Fe, Zn and Cu from root to the shoot were markedly increased in bacterial treatments compared to the positive and negative controls. Mn concentration and content as well as its translocation from root to the shoot were not significantly affected. In-vitro assessment of siderophore production revealed that the higher siderophore production in bacterial stains was in accordance with higher Fe in plant tissue and its translocation as well.

Land leveling and consolidation of paddy soils is a key approach in precision agriculture for water management improvement, weed control and agricultural mechanization. However, nutrients spatial variability in these fields is affected by land leveling. The objective of this study was to determine land leveling effect on the degree of spatial variability of soil fertitility. Land leveling caused significant spatial variability and spatial distribution of soil fertility properties. Clay content significantly increased, while soil organic carbon, total nitrogen, available phosphorous and available potassium significantly decreased. Alteration of spatial distribution was due to cut off the top soil at higher locations and its deposition on the low areas. The post-leveling evaluation of soil several fertility status with geostatistics demonstrated that leveled field faced with deficiency in one or several nutrients. The traditional fertilizer recommendation for whole field would accelerate non- uniformity in soil fertility status and would not lead to realization of the potential.

In this paper, the MSM2 model was evaluated based on the field data measured at the agricultural research station of the University of Tabriz. The model was evaluated by data obtained from cultivated SC704 hybrid maize in a lysimeter. Comparisons between measured values of soil water content, maize evapotranspiration, grain yield and top dry matter with those predicted by the model showed the good estimation accuracy of the model. Also the comparisons between evapotranspiration estimation method of MSM2 model with conventional methods, considering single and dual crop coefficients, showed that the MSM2 model method had better accuracy than the conventional methods.

The technique of submerged vanes (Iowa vanes) is a new and efficient method for sediment management in rivers. This method has positive environmental effects. The performance and efficiency of a submerged vane is related to its shape. In the past, using of simple rectangular vanes was common. Recently some studies are in progress to reduce the vanes dimension and optimize their shape. The ultimate goal is to lower the costs and improve the vanes performance by reduction of local scour that occurs around the submerged vanes. The present paper attempts to address these issues. In the present study, physical hydraulic model testing was performed to investigate four shapes of vanes: a simple rectangular vane, and three vanes that are beveled at leading edge of =30, 45, and 60 with respect to the base, respectively. The experiments were carried out at four Froude numbers of Fr = 0.14, 0.16, 0.18, and 0.20. Clear water scour occured at Fr = 0.14 and 0.16 and live bed scour arised at Fr = 0.18 and 0.20. Results determine the performance and effectiveness of the vanes based on local scour occurred around the vanes and sedimentation pattern at downstream of the vanes. Results showed that maximum decrease of the depth of scour hole, for =60 and respect to the baseline rectangular vane, was 33%, 49%, 43% and 28% at Fr = 0.14, 0.16, 0.18 and 0.20 respectively. The maximum reduction of scour depth at leading edge of the vanes was observed at =60. The estimated decreases were 41%, 48%, and 61% at Fr of 0.14, 0.16 and 0.18 respectively. At Fr = 0.2 the scour depth at the leading edge of the vane reduced to zero.

In this research a numerical model has been presented which simulates the 1-D open channel flow over an erodible bed. For calibration and improving the model, solution procedure of the governing equations has been investigated. Comparison of the model results with the experimental data shows that the simultaneous solution procedure of the complete governing equations decreases the computational errors and improves the simulated results. Due to complexity and uncertainly in determining the friction factor of alluvial channels, an optimization technique and the proposed model have been coupled to dynamically identify the Manning roughness parameter by using the experimental data. The study shows that application of the optimized roughness coefficient increases the accuracy of flow simulation over an erodible bed.

In this study the effect of chute bed roughness height on energy dissipation has been investigated. To do so first general non dimensional relationship was developed. Then series of experimental tests were conducted in a physical model using three different bed slopes (15, 22.5 and 30 degrees) and three different uniform roughness heights (1.1, 1.43 and 2.1cm). Total of 48 tests were conducted with flow discharges ranged between 15 and 45 lit/sec. Results show that in comparison with the smooth bed, nearly 12 to 48 percent of the flow energy was dissipated on the roughened bed chute. Maximum energy dissipation occured for slope of 22.5 degrees and the minimum energy was dissipated on 30 degrees chute. A relationship was developed for prediction of energy slope on this type roughened bed chutes and the results obtained were compared with the results of previous works.

In earth dams, the rapid drawdown process creates a pressure gradient between the embankment and reservoir. This pressure gradient which is due to the temporal delay that is required for dissipating excessive pore water pressure existing in the upstream slope, may let the upstream slope to be prone to failure. In this research, the effect of length and thickness (of horizontal drain) on upstream slope stability under rapid drawdown conditions were considered in a model of homogeneous earth dam. The factor of safety for different drain dimensions immediately after drawdown ranged within 1.5-2.6 and 1.3-2.2 for superficial and deep slips, respectively, and increased with time to 2-3 and 2.2-3 for the drain with maximum effective length and thickness. Moreover, for drawdown ratio of less than 0.3, drain with the length ratio (drain length to water depth in reservoir) of 0.43 assured the stability. For the greater ratios of drawdown, drain length ratio of 0.71 with medium thickness provided the stability against sliding.

Iron is one of the most essential and effective elements in soil forming processes. The amount and distribution of extractable Fe forms in profile indicate the stage and degree of soil development. Because of the physiographic unit importance in pedogenic processes, the effect of physiographic unit in soil forming and development can be investigated based on the amount and distribution of iron forms. This research has been is done in two different physiographic units of piedmont (slope of %2-5%) and hill (slope of %8-15%) as low and highland, which are located in southern Ahar, East Azerbaijan province. For this purpose, various forms of iron in three profiles of each unit (totally six profiles) were measured by pyrophosphate, oxalate and dithionate extractants. The average amount of crystallized iron was obtained 2.876 g kg-1 for downstream physiographic unit and 4.76 g kg-1 for upstream physiographic unit which statistically means comparison is significant. The mentioned results confirm increment of crystalline iron oxides and decrease of amorphous forms and bounded with organic matter in highland in comparison with lowland. Also in this research, some of soil physical and chemical characteristics were measured using standard methods and correlation between different forms of iron was evaluated. According to the relationship between soil age and different forms of iron, it can be said that the highland soils are more developed than the lowland soils, and these results are accommodated with geomorphologically unit type, clay percentage, solum depth, and relative amount of kaolinite mineral.

This study was carried out at tobacco Research Institute in Rasht during the cultivation year 2008 in order to investigate on the effects of nitrogen fertilizer level and Azotobacter chroococcum on quantitative and qualitative characteristics of tobacco as a factorial trial and randomized completely block design (RCBD). Four levels of nitrogen fertilizer (non fertilizer, 15, 30 and 45 kgha-1) and three levels of Azotobacter chroococcum (non inoculation and 1 and 2 kgha-1) with three replications were applied. Results indicated that application of nitrogen fertilizer had significant effect on quantitative characteristics (except number and width of leaf and leaf area index), nitrogen uptake and qualitative characteristics. Application of nitrogen significantly increased dry weight of tobacco in comparison with control treatment (non nitrogen fertilizer). Inoculation of roots with Azotobacter had significant effect on dry weight of priming, the price per kg, nitrogen uptake and qualitative characteristics. Moreover, application of nitrogen fertilizer and Azotobacter significantly increased nitrogen uptake and nicotine and significantly decreased sugar in comparison with the control. In addition, N4B3 (with 45 kgha-1 N fertilizer and 2 kgha-1 bacterium) treatment had maximum content of nicotine in priming, and minimum content of sugar in tips. Furthermore, N3B2 (with 30 kgha-1 N fertilizer and 1 kgha-1 Azotobacter) led to maximum price per kg tobacco. Azotobacter inoculation was economically most efficient at lower doses of fertilizer nitrogen which increased tobacco yield qualitative characteristics.

Combined structure of weir-gate is used in order to measure both flow rate and to prevent accumulation of sediment behind the weir. Combining weir with gate leads to alterations in discharge coefficient. In the current study, five models of combined structure of triangular sharp crested weir-rectangular gate were designed and constructed, and then the effects of hydraulic parameters such as flow depth above the weir crest (h) and geometric parameters such as gate height (d), gate width (b) and the vertical distance between the lower edge of (y) on the discharge coefficient were investigated. The discharge coefficient was found to be inversely proportional to h/d, b/d and h/y. The results indicated that the combined structures were functionally similar to the gate and a regression equation with R2 = 0.97 was developed to predict discharge coefficient. The sensitivity analysis showed that the equation was more sensitive to h/y. The presented equation was compared with those introduced in the literature indicating the accuracy of the developed equation and the shared ranges for using the equations with other studies.

Groundwater is the largest available resource of fresh water on the earth. But due to its limitation and also consumption augmentation, the world would face with crisis of water resource shortage. Since Iran is located in an arid and semi-arid region, the situation is more serious for the country. According to the reports published by the Ministry of Energy in Iran, there is 4.8 billion m3/y excessive depletion of groundwater in the country. Ajabshir plain is an important agricultural area in East Azarbaijan. This plain has been faced with deficiency and shortage of water supplies along with steadly falling water table level in the aquifer. Therefore, studies about the consumption manner and proper management of water resource usage seem to be very crucial. Management based on the extraction cost is one of the most adapted methods in ground water exploitation management. In this procedure, water utilization is based on the equality of net benefit and cost. The extraction path was determined by execution of the mentioned model in this aquifer. The results showed that the aquifer would be useful for the next 8 years. After that it would face with salt water layer. Subsequently, by saving of water and use of alternative resources the agricultural sector, it would cause the aquifer to be built-up and get improved.

Modeling of water table depth fluctuations because of uncertainity in its parameters is rather complicated and was studied in the current work. For this purpose temporal variability of water table depth at 22 piezometric wells and precipitation data at 3 rainfall stations in the Malayer plain were evaluated from 1989 to 2007. Trends in data series of monthly, seasonally and annually with Sen's estimator nonparametric method was calculated and interpreted based on the defined constraints and trend start time by using Mann-Kendall test. The results showed that at monthly time scale 79.5% of the wells had significant positive slope. The remaining 16.3% had positive and 4.2% negative slope. At seasonal time scale 80.7% of trends had significant positive slope; 14.8% of the rest encountered with positive and the remaining 4.5% with negative slopes. At the annual time scale, analysis indicated that the trend in 81.8% of the wells was significant with positive slope. The tredn in 13.6% was non-significant with positive slope and the 4.6% was negative. Overally, the trends of piezometerc wells showed rapid decreasing in the water table depth at the sudied area and presenting unwise utilization of the ground water resources in the area.