مجله تحقیقات آب و خاک ایران
سال چهلم شماره 1 (پیاپی 2، بهمن و اسفند 1388)

Regarding the role and importance of subsurface drainage in water table control, many studies have been made throughout the world to find out new techniques and more economical solutions, especially as related to different pipe envelope material and their installations. This research was conducted to investigate the use of rice husk, as drain envelope material, in drainage installations. In addition, it was also compared with the standard gravel envelope material. Therefore, some such physical and hydraulic properties of rice husk as bulk density, void ratio, gradation curve and hydraulic conductivity were needed to be assessed. Also, a 2-side wall physical model that simulated a part of drain trench (enabling water table control) was used to simulate land drainage in the laboratory and as well to test for the filtration and water conductivity of rice husk envelope. This experiment was carried out in two soils which definitely require envelope material as base on standard methods. The results in this study showed that the hydraulic conductivity of rice husk even in its compact form is more than necessary to guarantee the hydraulic function of rice husk envelope. Also, rice husk envelopes have possess the appropriate filtering function as compared to mineral envelope. Discharge rate of drain through rice husk envelope is however, lower than that in gravel envelope, but because of more cost involved in mineral envelope, the use of rice husk as envelope is reasonable and recommended.

The purpose of this research was an evaluation of the performance of subsurface drainage system in date palm gardens of Abadan. Four cases of drain envelopes including local gravel, standard gravel, and synthetic envelopes (polypropylene 700 and polypropylene 450) were employed and a comparison with the traditional drainage (tide) made. To achieve the purpose, 16 laterals (subsurface drains) installed in a 12 hectare area of date palm gardens in Irrigation and Drainage Project of Abadan Subsurface Drainage system were employed. Four laterals each equipped with one of the four different envelopes were constructed. In order to determine and evaluate hydraulic resistance, water table curves along with other parameters, a number of pizometers were either made connected to the drains or installed in between them at the distances of 0.25L, 0.5L and 0.75L (L is length of lateral). Parameters evaluated were: 1. Performance of subsurface drainage system for controlling water table and salt soil profile, 2. Design parameters of subsurface drainage system. Methods that present a better performance of controlling water table and salt soil profile in comparison with the traditional drainage (tide), were finally determined. With regard to all the results obtained and according to importance, the fallowing two acceptable methods are proposed: construction of subsurface drainage system using synthetic envelope polypropylene 450; construction of subsurface drainage system using standard gravel envelope.

Studies by the US Salinity Laboratory, using Gapon rule, led to the value of 0.01475 (mmol L-1)-0.5for the modified Gapon selectivity coefficient (KG). Nevertheless, the results of subsequent research reveled that KG isn’t constant and could take on a wide range of values depending on soil properties. The aim of this study was to determine the relationship between Exchangeable Sodium Ratio (ESR) and Sodium Adsorption Ratio (SAR) in some salt-affected soils of Tabriz plain. To follow this, thirty composite soil samples were taken from the area. For the soils in the study area with SAR < 100 (mmol L-1)0.5 the ESR-SAR relationship was of the form: ESR=0.011+0.0072 SAR(r2=0.86) which didn’t follow the traditional USSL equation. After correction of the data for anion exclusion, this relationship was modified: ESR=-0.041+0.0120 SAR (r2=0.90). As a result, taking into account the anion exclusion increased the KG value considerably. However, KG value was still lower than 0.01475(mmol L-1)-0.5.This may be attributed to the high salinity level of the investigated soils which can lead to an increase in the affinity of clay minerals for calcium and magnesium through other mechanisms (compression of DDL and/or the formation of quasicrystals) in addition to the anion exclusion mechanism. In a multiple regression procedure, ECe was negatively while ESP positively associated with KG (r2=0.73). After correction of the data for anion exclusion the association was merely with ESP (r2=0.49).

In the Universal Soil Loss Equation (USLE), Soil erodibility factor (K) is estimated through nomograph. Using the nomograph in calcareous soils may lead to uncertainty in estimating the erodibility factor. This study was conducted in Hashtrud, (north west of Iran) from March 2005 to March 2006. Field measurements were carried out in an agricultural area of 30 km × 30 km. Thirty six land grids were considered in the study area and three standard plots installed in a dry-farming land of each grid. K value was assessed based on soil loss per unit of the rainfall erosivity factor (R) and estimated using the USLE nomograph. Results indicated that the measured K value (0.0042 t h MJ-1 mm-1) was on the average 10.98 times lower than the estimated value (0.0360 t h MJ-1 mm-1). Mean Percentage Error of the estimation was 974.6. These results reveal that using the nomograph leads to uncertainty of the soil erodibility factor in the study area. Regression analysis showed that the soil erodibility factor is affected by mineral soil particles, organic matter, lime, and gravel (R2=0.85, p<0.001). Lime is a main factor in causing the uncertainty in the estimation of K.

Accurate information concerning soil hydraulic characteristics is needed for an understanding of the process of water flow and solute transport through soils. One of the soil hydraulic characteristics is its hydraulic diffusivity in unsaturated conditions. A simple method of determining soil hydraulic diffusivity is a simple procedure in which soil moisture measurement is not required and instead only by measuring the wetting front versus time, cumulative infiltration versus wetting front as well as infiltration rate versus inverse wetting front, soil hydraulic diffusivity function can be determined. In this method, the depth of soil column affects the accuracy of the results. Therefore, in this investigation one dimensional horizontal infiltration soil column was used to determine the minimum length (depth) of soil column for three soil textures (light, medium and heavy) employing the above mentioned simple method. Results indicated that for lighter soils, a deeper column of soil would be needed. So that a minimum column length (depth) for heavy and medium soils would be 8, and 15 cm respectively, and while for a light type of soil the column length must be more than 60 cm. Mean diffusivity coefficients for soils with varied initial moisture contents and for different soil textures (in different infiltration and evaporation states) have been presented. Mean hydraulic diffusivity coefficient decreased from light to heavy soil, the same way as did the hydraulic diffusivity coefficient.

The release of Fe from soil solid phases into soil solution is a dynamic process that regulates the continuous supply of this element to growing plants. To ascertain the pattern of Fe release, the kinetics of Fe release from six soils by diethylenetriaminepentaacetic acid (DTPA) solution were investigated using soil samples taken from two different agroclimatic regions of Iran. All soils were calcareous with CaCO3 equivalent content in the range of 2.26 to 49.54%. The kinetic experiments were performed under a moisture condition within the range of field moisture content, i.e. %35 of saturation moisture. The release pattern was generally characterized by an initial fast reaction followed by a slower one. The slow release of Fe continued even after 960 hours in all soils. Different kinetic equations (zero-, first, and second order, parabolic diffusion, simplified Elovich, power function, shell progressive film and particle diffusion equations) were employed to describe the rate of release of soil Fe by DTPA solution. Comparisons of coefficients of determination (r2) and standard errors of the estimate (SE) indicated that the power function, parabolic diffusion, first order and shell progressive particle diffusion equations adequately described Fe release, whereas the zero-order, second-order, simplified Elovich and shell progressive film diffusion equations did not. However, the first order kinetic equation inadequately described the release data at short reaction times. Conformity of the shell progressive particle diffusion equation to the kinetic data may indicate that the release rate is controlled by diffusion of Fe and/or DTPA molecules through a reacted soil particle or aggregate rather than diffusion through the film surrounding soil particles.

An evaluation of the relationship between crop yield and soil properties would be useful in estimating the fluctuations in yield, and in an implementation of correct field management. The study was conducted in farmer operated wheat fields in Sorkhankalateh district, 25 km northeast of Gorgan, Golestan province, Iran. Soil samples (0-30 cm depth) were collected just after crop planting at the end of autumn 2004 from a 100 × 180m plot as a nested grid (n=101). A 1 m2 plot of wheat was harvested at each 101 previously sampled sites at the end of spring. Statistical results showed that frequency distribution of the data was normal. ESP had the variability of CV=12.36% while pH was of the lowest variability (CV=0.59%). For principal component analysis, 7 principal components were used in the study. Selection criterion then was employed for explaining the effective parameters in each component. The eigenvector for each PC, therefore was selected on the basis of having a value larger than the SC value. The results showed that such soil fertility parameters as available P (0.847), OM% (0.810), total N (0.742), available K (0.727) and CEC (0.725) bore larger loadings and therefore had the major role in soil variability. The results suggest that soil and crop yield variability were affected by management. The results of principle component analysis indicated that variability within the field was mostly derived from fertility parameters with multi-regression models explaining 57% of total variability of the yield in wheat.

Digital Elevation Model (DEM) is increasingly used these days as an effective tool to extract elevation data in quantitative environmental and land management studies. The improvement of sensors and land resource satellites has made it possible to generate DEM from remotely sensed data. DEMs which are produced from these data are applied not only in the two dimensional (2D) but also in the three dimensional (3D) interpretations of the earth surface. The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), which is designed to capture along-track stereo images, was selected in this study for DEM generation, and its accuracy assessed, to be applied in land management studies. PCI Geomatica software and Toutin rigorous model were applied for DEM generation. Using accurate and well-distributed ground control points, DEM with a RMSE (Root Mean Square Error) of about 20m was extracted from the data. Image profiles, spatial correlation and statistical parameters were used to assess both the planimetric and vertical accuracy of the produced DEM. Interpretation of the image profiles showed that the generated DEM is very accurate in nearly flat regions and on smooth slopes with either no or sparse vegetation. Errors were generally less than 10m in such areas. Errors increase in dense vegetation, steep slopes and deep valleys because of the shadows. An evaluation of the results showed that the extracted DEM can be successfully employed in land management studies especially in soil-landscape relationship and land evaluation for mapping such elevation parameters as slope, aspect, hypsometry and physiographic as well as catchments discrimination at medium scales of: 1:50000 and 1:100000. It would also be suitable for orthorectifying the satellite images and aerial photos.

Circular- crested weirs are employed for flow measurement among their other wide applications in hydraulic engineering. They can also be used to control water level in farm ponds and reservoirs. Advantages of the circular crested weirs as compared to other weirs include the stable overflow pattern, the simplicity of design and their associated lower costs. In this study, the curvilinear flow past a circular-crested weir is analyzed using simplified Euler equations to determine the discharge coefficient. Also, velocity distribution profile and theoretical method were evaluated through physical models of circular-crested weirs of various radii and heights. It was found that the proposed method agrees well with the experimental observations. Also, it was seen that the estimations of discharge coefficient are close to their experimental values within 3 percentage of error.

The morphological diversity of arbuscular mycorrhizal fungi (AMF) at the Anguran Zn and Pb mining region (Zanjan province, Iran) were studied along a transect from the mine to 4500 m away. Within each plot, a composite sample of root and rhizospheric soil from a dominant indigenous plant was collected. The soil samples were analyzed for their physico-chemical characteristics. Spores were extracted, counted and after trap culturing, identified at species level. Isolatation frequency, spore density and relative abundance of AMF species were calculated for the soils with high, moderate and low levels of Zn and Pb as well as for non-polluted soils. A total of 10 AMF taxon were morphologically identified, which nine of them belonged to Glomus (Glomus mosseae, G. intraradices, G. versiforme, G. ambisporum,G. constrictum, G. fasciculatum, G. geosporum, G. sinosum and Glomus sp.) and one of them belonged to Acaulospora (Acaulospora sp.). Glomus was the dominant genus in all plots. Isolation frequency, spore density and relative abundance of AMF species were different in heavy metals (HMs) polluted and non-polluted sites. G. mosseae was the taxon most commonly observed in different plots, with higher spore density and relative abundance at high level of HMs pollution. G. mosseae, G. intraradices and G. versiforme were more abundant than other AMF species in the soils with moderate and low levels of Zn and Pb contents. Isolation frequency, spore density and relative abundance of G. intraradices were higher than those of other AMF in the non-polluted soils. The Shannon-Weiner index of AMF decreased from 1.55 to 0.52, but the evenness of species (distribution of individuals among the species) had not consideration variations, as the HMs contents of soils increased. The Sorenson similarity index of AM fungi and plant community between non-polluted soils with those of the other pollution levels decreased with increasing soil heavy metals contents and was higher for AM fungal populations than plant community

Expansible soils are those which will suffer considerable swelling and volume change when subjected to water. The resulting swelling pressure may cause complete destruction of such light structures as irrigation canal linings, floor slabs, etc. Based upon previous investigations, swelling of clayey soils has been blamed for failure of many irrigation canals in Iran and in other countries of the world. The main factor in these damages is the variation in moisture content which in turn would cause volume changes. In the present research, effects of cyclic wetting and drying on swelling potential of clayey soils has been investigated. For this purpose, three different clay samples were collected from three locations in south, northwest and central parts of Iran. The samples were tested for determination of their index properties, including grain size distribution, Atterberg Limits, specific gravity, and compaction. The swelling tests were conducted in odometer cells, where percent swelling was measured in five wetting and drying cycles. To investigate the effects of initial moisture content on swelling potential, the samples were tested at shrinkage limit, below shrinkage limit as well as above the shrinkage limit. Each sample was prepared to undergo five treatments of three replications. The results indicated no matter what the initial moisture content of the samples tested, the swelling potential was considerably reduced due to the imposed wetting and drying cycles. For some samples, reduction in swelling potential was observed in the second cycle, while for others it occurred in the third. Therefore it is concluded that one can control the negative aspects effects of the swelling soils. To perform the wetting and drying cycles before any canal lining would notably reduce the swelling potential and prevent the next probable forthcoming destructive effects of soil swellings.