THE SCIENTIFIC JOURNAL OF AGRICULTURE (SJA)
Year:2005 | Volume:27 | Issue:(Special Issue of Water Science Engineering)|Papers Count:12

The use of a model makes it possible to simulate and identify the process of crop production, thus insuring optimal use of resource and more stable production with higher financial benefits. Since the systematic approach to crop production in plants is a fairly recent innovation, various models have been developed and applied, yet little or no information regarding their infrastructure has ever been provided. The proposed model is capable of simulating the development stages, carbon assimilation, respiration and assimilate-partitioning of wheat crop under different soil moisture regimes. The period of simulation starts with crop germination and lasts until the end of the growth period, using daily time steps. The model uses meteorological data and depth and time of irrigation / precipitation as input parameters. Drought stress assessment is done through its influences on development rate, leaf expansion, acceleration of leaf senescence, leaf rolling and assimilate partitioning. In order to compute related reduction factors as a function of soil water potential, root zone water balance calculations were performed during each time interval. Calibration of the model was performed with existing field data for several wheat varieties grown in the region. Model verification was done with the data collected in a field experiment on the Agricultural Research Station at Shahid- Chamran University, Ahwaz, during the year 2002-2003. Analysis of the results shows a good agreement between the results obtained in the field study and the data obtained from the LAI simulated model and the accumulated dry matter of R2=0.90 and R2=0.88, respectively. Using a t-Test and taking the results obtained from the field study and the model run to be equal, both parameters were shown to have the values of Pvalue> 0.890 and Pvatue> 0.192.

In order to evaluate the effect of initial soil moisture content on soil aggregate stability during leaching with horizontal leaching technique, soil samples from AmirKabir agroindustrial site were subjected to 3 moisture levels of 3, 15 and 19 percent by weight. Hydraulic conductivity of the 3 soil samples was measured as an indicator of soil structure stability in the experiments. Hydraulic conductivity was determined in a special permeameter; and soil structure stability was evaluated on this basis. Results showed that samples with moisture content above 15% showed higher hydraulic conductivity and. There for a more stable structure during their leaching. However below 15% moisture, soil aggregates were not Stable. Therefore, the lowest permissible moisture content for soil structure stability under leaching would be 15%. However, it is assumed that under the given climatic conditions in Khuzestan and for a restructured soil with increased aeration, soil moisture levels will. decrease further under field conditions. Thus final judgment on the application of horizontal leaching method depends on field conditions.  

Infiltration, is one of the most important parameters in design and water management for surface irrigation. Several equations have been developed which are physically or experimental based. Field experiments should be undertaken to select the desired infiltration equations. In this paper Kostiakov, Modified Kostiakov Philip, and SCS Infiltration c equations are tested using fifteen series of data from sugarcane area, in the south of Ahwaz. In this research a computer program has been worked out in Q-basic language. To deter mine of the infiltration coefficients two-point method was used for estimation of infiltration coefficients in the Kostiakov and Modified Kostiakov equations. One point method is selected for determination of infiltration coefficients in the Philip equation. Also basic infiltration rate (ƒ0 ) is obtained using the SCS infiltration equation. Calculated infiltrated volume of water using the infiltration equations is compared with the observed data, and the average errors. (EA)was calculated for each infiltration equations. The results showed the SCS equation with 11.6% average error gives better estimation of the volume of infiltration water compared to the other equations in the tested area.

One of the most effective factors which restricts the crop yeild is environmental stress. Previous studies show that with an optimal irrigation programing, e.g., using crop canopy temperature, the negative effects of these stresses can be decreased to a considerable degree.The current study intends to investigate water stress and irrigation planning of the spring corn (hybrid SC704) in year 2002. Different irrigation regimes were planned on the basis of cumulative evaporation from Class A of the evaporation pan. Irrigation was carried out in five treatments 50, 70, 90, 110 and 130 of cumulative evaporation. The experiments were conducted in Dezful Agricultural Research Center, in a completely randomized blocks design, and pour replications.Crop water stress index was calculated using Idso and Jackson methods along with the parameters measured both before and after the irrigation in growing season.The obtained results showed a good linear relationship between these two methods (CWSIj =1.037CWSIj - .054) with a correlation coefficient of R2=0.999.A good linear equation was also developed using the least square method between the grain yield and the crop water stress index (Jackson method) in the form of Ys =-10.925 CWSIj +13.196 with a correlation coefficient of R2=0.99.This equation may be applied to predict the corn grain yield using the measured CWSI. Another equation was also developed, in which the, relative humidity received solar radiation, depleted soil moisture from the root zoon, and wind speed were related to the canopy-air temperature difference.

In characterizing the flow behavior in the curved channels ƒb(head less coefficient) is a significant source of error in head loss assessment. This coefficient is a function of several geometric and dynamic parameters and the influence of each non-dimensional parameters on ƒb is not well understood. In this investigation, variables such as rc/b , θ, b/y , Rn and Fn were introduced and evaluated in order to define a suitable functional relationship for the head loss in curved channels. This study was conducted for steady-state and subcritical regime occurring in open channels.A general Multi -Variable Nonlinear Model (MVNLM) applied to the functional relation for predicting. ƒb coefficient was introduced. The unknown coefficient in the model was determined using optimization technique in the SPSS statistical analysis software with the experimental data from different sources in the literature. The predictive model gave the best results. The model is capable of determining the. ƒb coefficient and allowing more accurate head loss assessment in hydraulic design practices.

The effects of different irrigation levels and plant densities on vegetative growth and seed yield of three soybean cultivars [Glycine max (L.) Merr.] were studied during 2000-2001. The experimental design used was split-factorial in a randomized complete block design (RCBD) with three replications on the Research Farm of Agriculture College at Shahid Bahonar University of Kerman. Irrigation levels (I1, I 2, I 3 and I4) were considered as the main plot and plant densities (D1, D2, D3 and D4) and soybean cultivars (V1, V2 and V3) as the subplots. The following plant characteristics were studied; plant height, number of nodes per main stem, internodes length in the main stem, leaf area index at flowering stage, plant dry weight, main root length, number of seeds per plant, seed yield per plant and harvest index. Results of this study showed that the highest and lowest rate of seed yield were obtained by irrigation treatments at I2 and I4, respectively (irrigation after 60 and 100 mm. evaporation from Class A pan). The highest rate of seed yield per plant was obtained from 30 plants per m2(D1) in Williams cultivar (V2) and the lowest from 60 plants per m2 (D4) in Hill cultivar (V3). Maximum and minimum plant height, number of nodes in the main stem, internodes length and leaf area index were obtained at I1 (irrigation after 40mm evaporation from Class A pan) and 14, respectively. Increasing the plant per unit area increased plant height, internodes length and leaf area index, but decreased the number of nodes in the main stem, plant dry weight and root length. Harvest index (HI) was highest at I2 level of irrigation, 40 plants per m2 ( D2 ) plant density and Hobbit ( V1 ) cultivar (I2D2V1 treatment), while it was lowest at I4 level of irrigation, D4 plant density and V3 cultivar (I4D4V3 treatment). Number of seed per plant was highly correlated with seed yield per plant, whereas root length was poorly correlated with grain yield per plant.

One of the problems found in the dam reservoirs is the sedimentation of cohesive sediments just upstream of the dam. By increasing the sediment volume, the consolidation process is initiated and the sediments will be consolidated over time. To dredge or flush these sediments either through mechanical or hydraulic processes, it is important to determine the physical properties of consolidated sediments. An experimental study was conducted to investigate the mechanism of consolidation for submerged cohesive sediments. In order to identify and review the sedimentation and consolidation processes for cohesive sediments and to define the required physical parameters, a physical test model consisting of a Plexiglas cylindrical tube with a diameter of 30 cm and a height of 3,5 m was constructed. Experiments were carried out on the cohesive sed. with various initial heights and density. During the initial hours of the test, water within the test cylinder was muddy, yet the sediments gradually began to settle and a visible sediment – water interface was formed and it was possible to measure the consolidation process. in the model. Results of this study show that the sedimentation and consolidation process is not only affected by the type of water and sediment but also the initial height and density of the water and sediment mixture. The developed dimensionless parameters revealed a correlation between various experiments with different initial height and density. The results of the study also reveal a four separate logarithmic relationship between sediment density and time in the sedimentation and consolidation process.

Hydraulic jump is an effective phenomenon which is used for dissipation of excess kinetic energy downstream of hydraulic structures such as drops, spillways, chutes and gates. During the past decades many studies have been conducted on characteristics of hydraulic jump on smooth floor. Recent studies have shown that corrugated bed can reduce the cost of hydraulic jump stilling basins. Therefore, the main goal of this study is to conduct an extensive experimental study program on this subject. Four different beds of trapezoidal corrugated shapes were tested under different Froude number ranging from 4 to 12. The results show that the required tail water depth and the length of jump have been reduced as compared to the jump on smooth floor. Computation of shear stress also shows that the bed shear stress on rough floor is 10 times the shear stress of classical jump. During the experimental tests, the velocity profiles were measured and it was found that the centerline velocity of the incoming jet is reduced which depends on the entrance velocity and the distance from the gate opening. The results of this study reveal that trapezoidal corrugated floor can reduce the cost of stilling basins.

Soil erosion by concentrated overland flow is an important part of water erosion in the South of Iran. Degrading of vegetation cover due to drought and over grazing causes increasing concentrated overland flow and rill erosion. The aim of this research was to compare the impact of vegetation density in a native rangelands on the formation and development of rill erosion in a Silty-loam soil. An open hydraulic flume with 15m length, 0.3m width and 0.5m. depth was used to simulate concentrated overland flow on the native rangeland around Lamerd city. Four treatments including bare land (without vegetation cover), poor (vegetation density less than 20%), moderate (vegetation density between 20 and 40%) and good vegetation (vegetation density higher than 40%) were examined. For each treatment, four to five discharges from low to high were used and hydraulic parameters and number of rills on the bed of flume were measured.Result of this study shows that overland flow was concentrating to points without vegetation cover. Reynols number were large than 5000 (5000<Re<95000) and the flow was completely turbulent. Critical shear stresses for erosion initiation were 27, 29, 3"0and 38 dyne /cmJ\2 for bare land, poor, moderate and good range respectively. With increasing discharge and its duration headcuts were formed in the bed of flume. The number of headcuts were 19,8,5 and 0 for barelands, poor, moderate, and good rangelands respectively.

Constructing intake structures in order to deviate a part of flow from the rivers causes some changes in hydraulic conditions of flow in the front of intake port. The changes, as flow in river bends, reinforce the secondary flows, cause sedimentation in the intake port and erosion in the bank facing intake port. Those conditions finally deviate the river thalweg toward the facing bank. To overcome such a problem in the intake places, a number of solutions the latest of which is submerged vanes have been applied. Submerged vanes have been used for different purposes such as reducing erosion in river bends, bank stabilization, increasing inpoudment efficiency and so on. The vanes are installed with an angle of 15 to 25 agrees to the flow direction and their initial height being about 20% to 50% of the flow depth. The performance of the submerged vanes that is based on making revolving currents in downstream to reduce the effects of secondary flows depends on the longitudinal and widthwise distance, angle of the installation and longitudinal arrangement of the vanes. In this study, the possibility of the use of submerged vanes to control and direct the flow and river thalweg toward the intake port with different longitudinal arrangement has been investigated. Three longitudinal distances 3H, 4H and 6H (H, being the initial height of the vanes) have been considered and the experiments have been done for the regular and zigzag arrangement for different discharges.The results show that the use of the submerged vanes in the longitudinal distance (3H - 6H) in regular and zigzag arrangement make it possible to direct the thalweg toward the intake port and with the use of the submerged vanes, a trench is made toward the intake port which increases the inpoundment efficiency by 36%-95% in regular arrangement and 21%-'65% in zigzag arrangement. The Submerged vanes can also reduce the sedimentation by 15%-40% in comparison with intakes without the vanes. From the total experimental results, it can be concluded that the regular arrangement of the vanes and the longitudinal distance of 4H show the best performance in changing the thalweg of channel increasing impoundment terurn and decreasing the intake sedimentation.

To study the effect of secondary currents on sedimentation processes at water intake, the strength of secondary currents were experimentally investigated. A series of experimental tests were performed in fixed and mobile bed conditions with no vane, and parallel and zigzag vane arrangements. The strength of the secondary current was measured for 10, 20, 30 and 40 vane angles installation. From the fixed bed experimental result, it was found that the 20 degree zigzag arrangement produced minimum strength in the secondary current; Thus, it is selected as the efficient angle for vane installation. From the mobile bed experiments, it was found that the sediment entry into the water intake was reduced by 72.86 percent for zigzag arrangement and by 63.94 percent for parallel arrangement when compared to no vane installation. Therefore, the zigzag arrangement was found more efficient when compared with parallel arrangement due to 9 percent sediment entry reduction into the water intake.

Optimum reservoir performance is the most important discussion in water resources management. Constantly increasing demand for sufficient quantity and quality of water along with drought periods emphasizes the problem. In this study, reservoir performance of Maroon dam simulated with ARSP package for demand supply. Environmental concerns, urban and industrial demand full supply and deficit impose on agriculture demand. Optimum rule curve with scope minimizes deficit on agriculture water calculate based on reservoir performance criteria such as reliability, mean deficit and vulnerability. Optimum rule curve supplies agriculture demand with minimum reliability of 80% and maximum vulnerability of 20%. The rule curve with impose hedging rule can provide full agriculture demand as well.