WATER AND SOIL SCIENCE (AGRICULTURAL SCIENCE)
Year:2012 | Volume:22 | Issue:1|Papers Count:14

Salinity and sodicity are expressed in a number of ways, depending on the method and purpose of the measurements. Some researchers attempt to estimate the parameters which can be time consuming, expensive and linked with error from easy- to- obtain parameters. However, these relationships are not universal and, may also vary depending on the type of soil. The aim of this study was to find simple equations in order to estimate the salinity and sodicity parameters for the salt-affected soils of Tabriz plain. For this purpose 30 composite soil samples were taken from the area. According to the results, salinity (TSS, ionic strength and concentration of chloride and sodium ions) and even sodicity (SAR and ESP) parameters are in close relation with the ECe. The following equations are proposed for estimating parameters of ionic strength (mmol L-1) TSS (mmolc L-1) and SAR (mmol L-1 )0.5 from ECe (dS m-1): I=19.1 ECe (R2=0.991, SEE=57), TSS=7.56 ECe1.13 (R2=0.994, SEE=3.9) and SAR=1.44 ECe0.925 (R2=0.916, SEE=11.3).The data showed that there is a significant positive relationship between pH of saturation extract (in contrast to pH of saturation paste) and bicarbonate concentration. Moreover, this pH may be greater or lower than the pH of saturation paste, depending on the degree of salinity.

Spatial variability of infiltration parameters were investigated in about 4000 ha of Kavar plain, east of Shiraz, Iran. For this purpose, infiltration was measured on a systematic squared grid pattern with 500 by 500 m in 161 sites using double ring infiltrometer. Soil bulk density (BD), initial soil water content, soil texture, organic carbon content (OC), saturation percentage (SP), pH, and EC were also measured. The interpolation of infiltration parameters in non-sampled areas were predicted using kriging, inverse distance weighted, and co-kriging methods. The experimental semi-variograms were fitted to linear, exponential, gaussian, and spherical models. Cross validation method using statistical parameters of MBE, MAE, MSE, and RMSE was used to choose the most accurate interpolation method. The spatial distribution map of parameters was obtained using the best interpolation method. Estimating the coefficient of a in Kostiakov model using co-kriging method (spherical model) and co-factor of BD with R2=0.99, nugget effect of -0.002, and range of 3380 m was superior to kriging method. The power b of Kosiakov was estimated by exponential mode and kriging method with R2=0.97, nugget effect of 0.005 and range of 14410 m. To estimate sorptivity parameter (S) of Philip model, the co-kriging method with spherical model and co-factor of BD with R2=0.99 and range of 2973 m was preferred to kriging method. Likewise, estimation of transmissivity parameter of Philip model using co-kriging method (Gaussian model) with R2=0.996, nugget effect of 0.0003, and range of 3862 m showed high accuracy. Using soil moisture content, BD, texture, SP, and organic carbon as co-factors of co-kriging method, resulted in relatively better estimation of infiltration model parameters.

Acquiring knowledge about land use effect on soil properties is essential for maintenance and increase of soil fertility and productive ity in sustainable agriculture. In the present study, soil physical, chemical and mineralogical properties in southern Ahar area as affected by crop (wheat) and orchard (apple) land use were studied. Two profiles on the crop land use and two profiles on the orchard land use were selected to classify according to keys to soil taxonomy 2010. Profiles located on the orchard land use showed higher rate of leaching. It can be related to the irrigation water on the orchard and dry farming of crop land use, and also deeper root of orchard in comparison with crop. Changes of cation exchange capacity in orchard were higher than crop, while e lectrical conductivity and total calcium carbonate percentage increased in crop land use. The maximum changes in soil carbonates were shown in orchard land use. With increase of soil depth, in spite of increase of pH in soils on the both land use, organic carbon decreased in these soils. Mineralogical analysis using XRD spectrums showed that chlorite, montmorillonite, illite, kaolinite and quartz were dominant clay minerals in soils of the study area, and detected clay minerals were not affected by different land use.

Livestock grazing may directly and indirectly make changes in plant cover and soil properties, with a consequence for alterations in soil microbial activity, growth and biomass. The primary objective of this study was to assess the effects of pasture management (grazing and ungrazing) on soil N and C contents, and the amounts of microbial biomass C and N in the natural pastures of Chaharmahal Va Bakhtiyari province. Three managerial regimes including: a) long-term ungrazed, b) controlled grazed and c) free (over) grazed in close vicinity were selected at three sites including SabzKouh (grazing- protected for 18 years), Boroujen (grazing-protected for 23 years) and Sheida (grazing-protected for 2 years). Soil samples were collected from 0-15 cm depth and organic C, total N and microbial biomass C and N were measured under standard conditions. Results showed that SabzKouh and Sheida sites had the highest (14.6 mg g-1) and the lowest (4.80 mg g-1) soil C stocks, respectively. Soil N and C contents at SabzKouh were significantly higher when compared to the other sites, probably due to more rainfall and humid climate. The amount of microbial biomass was significantly higher (366%) in ungrazed than grazed soils at SabzKouh, while at Sheida the light grazing pasture had a greater soil microbial biomass, and no change was found at Boroujen site. In brief, degraded pastures at SabzKouh and Boroujen seem to recover rather quickly from the long-term overgrazing with a proper management, while pasture ecosystems at Sheida site with cropping history need a much longer period for steady-state conditions and for improvements in soil quality and fertility after long-term soil degradation and disturbance.

Although many kinds of rainfall-runoff models have been developed by hydrologists, the unit hydrograph methods are still gainful tool for flood estimation in many basins where recorded hydrological data are not sufficient to support distributed rainfall- runoff models. The aim of this paper is to derive the analytical unit pulse response functions of quick and slow runoff of stream flow using a conceptual model containing three serial tanks as well as a parallel hybrid tank. The interrelation of the tanks can be shown using exponentially structured models which their parameters reflect the physiographical characteristics of the basin. Parameters of the model were estimated using Nelder–Mead optimization method. Efficiency and validity of the developed conceptual model were evaluated for various observed events using statistical criteria such as Nash-Sutcliffe, mean relative absolute error for discharge, peak flow and runoff depth. Results showed that the developed model had good capability in predicting rainfall- runoff process considering soil moisture conditions before rainfall occurrence without the need for definition of excess rainfall.

Identifying the parameters affecting discharge coefficient of circular crest weir in an optimum application is very important. Since circular weir crest may be constructed by different materials with different roughness. So in this research influence of roughness on discharge coefficient has been investigated. Without present of roughness, the result of the experimental test on weirs with five different curvature radii (from 2.5 to 7.5 cm) indicated that the most effective parameter on discharge coefficient was the ratio of upstream total head to crest radius. Also discharge coefficient increased with increasing this ratio. On the other hand variation of weir height to upstream total head ratio had no significant effect on the discharge coefficient. The effect of four different sizes of roughness on discharge coefficient, which had been overlooked in previous researches, was also evaluated. Results of the tests showed that with increasing relative roughness, discharge coefficient reduced and lower relative roughness, had the higher influence on reducing the discharge coefficient. Two mathematical relationships based on the affected parameters on discharge coefficient were presented. The first relation that is for the conditions imposed without roughness, discharge coefficient is just a function of upstream total head to crest radius ratio. Applying a correction factor, which is an exponential function of the relative roughness, the final relationship for calculating the coefficient of discharge including the effects of roughness, was obtained.

Vanes are rectangular thin angled flow-training structures that high and low pressure zones are produced on both sides of them. These structures generate a secondary vortex, which is used to modify the near- bed flow pattern and thus redistribute the sediment transport and erosion within the channel cross section. The function of vanes to reduce scour around the bridge piers and sediment movement in the region of vanes due to downflow in front of them are affected by arrays of the vanes. This research reports a laboratory study that examines the effectiveness of submerged vanes as pier scour protection devices. Experiments were conducted in an 8m long and 0.8m wide flume and a cylindrical pier of 6 cm diameter. Clear-water scour tests with u*/u*c=0.9 were performed with two different vane aspect ratios (length to height of 2 and 3), and one placed at streambed level. Dissimilar arrays of vanes with different angles to main flow direction were employed. Results showed that reduction of scour with different arrays of six vanes was 0.4% to 51%. The highest reduction occurred in the layout of each row of vanes with different angles. In the case of application of four vanes, scour depth reduced to 12%. The reduction for two vane case was 1% to 5%. Finally, application of six vanes in the layout of each row with different angles was the best case of scour reduction around the bridge piers in this research.

Nowadays along with development of societies and border extension of cities, their impervious areas increase and therefore higher amount and volume of runoff accrue. Thus control of flood in urban areas has always been a major concern of designers and managers. In this research the performance of East Eghbal urban drainage system located in the south and southeast of Mashhad city was analyzed in a region with area of 71 Km2. To estimate the physical parameters of subcatchments and hydraulic parameters of conduits, and some other computations like calculation of weighted average, subdividion of catchments into sub-catchments and providing land use map, the GIS was used. Because of the complicacy in simulation of urban drainage system, MIKE SWMM was applied for rainfall -runoff simulation and hydraulic response evaluation of the urban drainage system. Finally, 3 suitable places were recognized for retention basins based on topographic maps, flood conduits position and land surveying. Results showed that 6 conduits had difficulty and computed flow was more than the designed flow. Urban drainage system was simulated again by the presence of retention basins and results showed that these basins could reduce the flood peak from 8 to 100% and also infiltrate 12.35 m3/ h and also infiltrate of water.

Zinc is one of the micronutrients for plants and its deficiency is common in calcareous soils. On the other hand, many features of arid and semi-arid soils are affected by the presence of carbonates. To evaluate carbonates influence, Zn sorption was studied in 20 composite soil samples (0-30 cm) collected from the central region of Iran before and after carbonates removal. Carbonates were removed with sodium acetate buffer (pH=4.75). X- ray diffraction (XRD) analysis showed that calcite was the most commonly carbonate found in the studied soils. Original and free carbonate soils described L-curves isotherm and carbonate removal did not change the isotherm type. With increasing the applied Zn concentration, the effect of carbonate removal became more obvious. Upon carbonates removal, specific surface areas of the soils decreased and so did the amount of sorbed Zn (mg Zn/ kg soils). Sorbed Zn in per unit particles surface area (mg Zn/m2 soil) however, significantly increased. Freundlich empirical model (q=KC1/n) adequately described Zn sorption data in both original and carbonate free samples and the K – Freundlich variation was much higher than the n-coefficient. Single site Langmuir sorption model did not properly describe Zn sorption data, but double site Langmuir equation (q=K1b1c/1+K1c+K2b2c/1+K2c) was well fitted to the data. The results showed that, k1 and k2 coefficients considerably decreased after carbonate removal.

Design storm is required for designing of hydraulic structures but its current estimation methods are criticized by hydrologists since these method need many parameters and requires the rainfall data at different durations. Nowadays fractal theory is used to improve the estimation of design storm which has few parameters and the design storm at different durations and with any return periods is estimated only from annual 1-day maximum rainfall series. In this research, fractal theory was used to estimate the design storm in Ghotvan Dam site. The results showed that momofractal model underestimated the design storm, but the estimated design storm by multifractal model was consistant with the observation data.

Arbuscular mycorrhizal fungi in association with plant roots may affect plant growth, nutrition and tolerance to heavy metals in polluted soils. Therefore, this association can play an important role in phytoremediation. In this study, the effects of two arbuscular mycorrhizal fungi species including Glomus intraradices and Glomus mosseae, on the uptake and translocation of Pb in sorghum, were investigated under greenhouse conditions. The experiment was conducted as factorial, completely randomized design including four levels of Pb2+ (0, 200, 400 and 600 mg Pb2+ kg-1) and three treatments of fungi (two mycorrhizal fungi species and a non-mycorrhizal plant) with four replications. Lead were added to the pots as Pb (NO3)2.The Results indicated that symbiosis with G. intraradices increased shoot dry weight at 200 and root dry weight at 400 and 600 mg Pb kg-1 compared to the non-mycorrhizal treatment. There were, however, no significant effects on other growth parameters. Both mycorrhizal fungi caused a significant decrease in Pb2+ translocation from the root to the shoot. However, the shoot and root dry weights, leaf area and chlorophyll content in plants inoculated with G. mosseae at higher levels of Pb2+ were considerably (p<0.05) decreased compared to the non-mycorrhizal plants. At pb levels of 400 and 600 mgkg-1, the ratio of Pb concentration in root to that of shoot in plants inoculated with G. mosseae was significantly (p<0.05) greater than that of plants inoculated with G. intraradices and none inoculated ones.

When the density current smashes into the lower dense fluid mass a plunge region will occur. Since the plunge depth bounds between density current and ambient fluid, determining of this point is important. In this research, the hydraulic parameters of density current and bed slope of stagnant fluid were investigated. To achieve the purpose of this research a physical model was built in the hydraulic laboratory of Shahid Chamran University (SCU) and various experiments were performed. In the experiments, the plunge depth at the different discharge of density current and density difference 6, 9, 13 and 16 kg/m3 at three slopes 8, 12 and 16% was measured. Then using Flow-3D under RNG turbulence model, plunge depth was simulated for the same experimental condition. The comparison of results obtained showed that the predicted plunge depth with Flow-3D under RNG turbulence model had a high and satisfactory accuracy. Finding showed that for the 8% bed slope, the results of RNG turbulence model 14% was more than experimental data. While, for the entire slope, the results of RNG turbulence model was predicted 10.5% in average more than measured data. Generally, the statistical investigations showed that the RNG turbulence model with satisfactory precision estimated the plunge point depth.

In 2007, 91.2 percent of the exploited water in Gazvin province has been consumed in agricultural sector that implies the importance of this input in the agricultural products of this province. So making the scientific and managerial strategies will be important to optimal use of water. Balancing between water supply and demand is the main issue in economic management of water resources. To this end, price or economic value of water has a responsible deterministic role as well as the price of other inputs. The economic stimulus (water economic value calculation) can be used as the motivation and economic factor to control the demand of water. In this respect, this study estimated the water economic value in barley production in Qazvin plane irrigation network from applicant perspective by using residual method and production function approach. The required data was gathered by questionnaire in 2007-08 year. The results indicated that in barley production, the economic value of water was estimated 909 Rials/m3 by using the residual method. Also it was estimated 907 and 546 Rials/ m3 based on market and guarantee prices of barley by utilizing production function approach, respectively.

In this research, the spatial distribution of N, P and K in agricultural lands of Golestan province were evaluated using different geostatistical methods such as Kriging, Inverse Distance Weighting, Radial Basis Function, Inverse Multiquadric and Local Polynomial. For this porpose, 505 soil samples were collected from fields in 2008 and concentrations of these elements were measured for each sample. The performance criteria for evaluation were Mean Absolute Error, Mean Bias Error and Root Mean Square Error with the Jacknife methods. The results showed that Kriging was the best method for estimating N, P and K. Because, it showed the highest accuracy and the lowest error for estimating of these elements. Local Polynomial (degree3) was also found as the most unsuitable method for estimating of these elements. Semivariograms analysis indicated that N and K were the best fitted by Exponential models, also P by Spherical model. Result of zoning showed that amounts of N and P were lower in north and east regions of the study lands.