Showing 21 results for Size
H. R. Karimzadeh, A. Jalalian,
Volume 6, Issue 3 (10-2002)
Abstract
For the study of field wind erosion and the design and evaluation of wind erosion control techniques, detailed observations of soil particle transport and vertical destribution of eroded soil particles are needed. The objectives of this study were: 1) To describe one device for soil transport particle measurement, i. e. the BSNE sediment catcher and 2) To assess vertical distribution of wind–eroded sediment with height in eastern Isfahan. The BSNE sediment catcher is a wind erosion sampler that traps eroded material at seven heights of 0.24, 0.60, 1.08, 2.00, 3.00, and 4.00 m above the soil surface. Each trap consists of a steel container with an inlet and outlet, mounted on a wind vane that rotates about a central pole. Before using the sampler in the field, it was tested and calibrated in the wind tunnel. The results showed that the average trapping efficiency with speeds ranging from 5.2 to 7.2 m sec-1 for 4 different wind–eroded sediments was 0.44 to 0.68. However the trapping efficiency depended on wind speed, particle size distribution, particle density and type of sediment. The sampler had the lowest efficiency for particles < 44 μm. A BSNE sediment catcher was installed in Babaii Air Base. After a sampling period, the sediment in each trap was collected and weighed. The trapped materials were a mixture of saltation and suspension particles. Vertical distribution of wind–eroded sediment showed that the amount of soil collected decreased with increased height and the percentage of fine particles (<63μm) increased with height. The amount of trapped materials for each cm2 frontal intake with increased height were 12.00, 3.42, 1.44, 1.56, 0.75, 0.21, and 0.39 g cm-2, respectively, for the one sampling period.
H. R. Fooladmand, A. R. Sepaskhah, J. Niazi,
Volume 8, Issue 3 (10-2004)
Abstract
To obtain soil-moisture characteristic curve experimentally is time-consuming and usually subject to considerable errors. So, many investigators have tried to predict soil-moisture characteristic curve by different models. One of these models predicts soil moisture characteristic curve based on soil particle size distribution and bulk density. In this model, soil particle size distribution curve is divided into a number of segments, each with a specific particle radius and cumulative particle mass greater than that of the radius. Using these data, soil-moisture characteristic curve was estimated. In this model, a scale factor, α, is used which may be considered as a constant, or obtained by logistic or linear procedures. The average values of α for clay, silty clay, sandy loam, two loam soils, and two silty clay loam soils were 1.159, 1.229, 1.494, 1.391, 1.393, 1.253 and 1.254, respectively. For most conditions, soil particle size distribution curve is not available, but only the percentages of clay, silt, and sand could be obtained using soil textural data, which is not enough to draw a precise soil particle size distribution curve. In this situation, a precise soil particle size distribution curve must be initially developed on the basis of which the soil moisture characteristic curve can be predicted. In this study, using soil textural data of seven different soils, soil moisture characteristic curve of each was estimated. In these estimations, logistic and linear methods were used to obtain the α value. Then, the results were compared with those of measured soil moisture characteristic curve. For estimation of soil particle size distribution curve, two extreme values for soil particle radius, 125 and 999 m, were used. The results indicated that using particle radius of 999 µm is more appropriate. On the other hand, it was found that for clay, silty clay, and sitly clay loam texture, it is more appropriate to employ a linear equation to determine for estimating soil-moisture characteristic curve while the logistic equation can be more appropriately used for loam and sand loam textures.
A.m. Mohammadi, S.j. Khajeddin, S.a. Khatoonabadi,
Volume 11, Issue 40 (7-2007)
Abstract
Northern watershed of Kouhrang River with the area of 68437 hectares is located in northwestern Chahar Mahal and Bakhtiary province within 49ْ 54ً to 50ْ 9ً E longitude and 32ْ 83ً to 32ْ 36ً N latitude.Making a balance and equilibrium between the number of ranchers, the rangeland production potential and appropriate flock size in each utilization unit is a necessary task. It is a matter of importance to determine suitable ranch size based on pastoral household but suitable household livelihood as well. The main goal of this study is to determine utilization unit size based on ecologic and socioeconomic factors for each household. Along with detecting the ranch allotments, the range capacity and its productivity potential were studied. Then, based on expenses and the revenues resulting from herdship,(on ranges), the suitable flock size for fulfillment of the household expenses regarding the range utilization periods, the suitable range size per household was determined. 10 vegetation types with 0.91 AUM per hectares grazing capacity were detected in studied area. There are 46 range allotments and some parts of other 6 range allotments in studied area with average area at 1510 hectares. Average pastoral household is 36.8 per unit range allotments. Pastoral households share at rangelands is 41 hectares now. The minimum and suitable ranch area for each pastoral household which can provide annual needs and costs is 520 hectares and 142 animal unit at a mix flock at 3 to 2 ratio of sheep to goat for a 100 – dayes grazing season. The result of this study showed that production potential at each range unit is influenced by flock size, household share on farming lands, and the household numbers on each ranch unit. Ranch unit and the livelihood level, have significant influence at 5% level on suitable ranch size per household.
H. R. Fooladmand,
Volume 11, Issue 41 (10-2007)
Abstract
Soil particle size distribution and bulk density are used for estimating soil-moisture characteristic curve. In this model, soil particle size distribution curve is divided into a number of segments, each with a specific particle radius and cumulative percentage of the particles greater than that radius. Using these data, soil-moisture characteristic curve is estimated. In the model a scale factor, a , is used which may be considered as a constant, or obtained by logistic or linear procedures. F or most conditions, soil particle size distribution curve is not available, but only the percentages of clay, silt and sand could be obtained using soil textural data. In this situation, at first a precise soil particle size distribution must be developed, based on which the soil-moisture characteristic curve can be predicted. According to the previous studies, using particle radius of 999 µ m is more appropriate than radius 125 µ m. Also, adjusted coefficients for estimating soil particle size distribution curve for radii 1 to 20 µ m was obtained. In this study, using the soil textural data of 19 different soils from UNSODA database, soil-moisture characteristic curve of each was estimated with logistic and linear methods based on initial and adjusted soil particle size distribution estimation. The estimated values were compared with the measured data. The results indicated that for most soils, using the combination of logistic and adjusted particle size distribution estimation procedures is more appropriate than the previous methods.
A. Karimi, H. Khademi, A. Jalalian,
Volume 12, Issue 44 (7-2008)
Abstract
Despite the existence of highly silty soils in southern Mashhad, there is no information about the aeolian and /or in situ formation of these soils. The main objective of this study was to determine the source of silt generation in this area. Granitic hilly lands in southern Mashhad have been covered by silty deposits. Based on the soil origin, four profiles including a residual soil covered by a silty layer, a residual soil with low amount of silt, a highly silty soil and an alluvial soil as well as a deep profile containing a succession of silty and alluvial materials were studied. Cumulative particle size distribution curve (CPSDC), depth distribution curves of silt/sand ratio (Si/S), Folk inclusive graphic standard deviation, Folk inclusive graphic skewness (SKI) and sand grain morphology analyzed by scanning electron microscopy (SEM) were determined and used to identify the source of the silty materials. Based on the results obtained, silty (L), residual-silty (R-L), residual (R), alluvial (A) and alluvial-silty (A-L) horizons were identified. CPSDC of L horizons is sigmoidal in shape and is easily distinguishable from that of the other horizons. In contrast, the CPSDC of alluvial and residual horizons is spherical in shape. CPSDCs for R-L and A-L horizons are neither sigmoidal nor spherical, but something in between. The L horizons have the highest SKI (very skewed to fine particles) and the lowest Folk inclusive graphic standard deviation (very badly sorted). In this regard, alluvial and residual horizons are intermediate. Because of the silt addition to R-L and A-L horizons, these horizons have a nearly zero SKI (symmetrical) and the highest Folk inclusive graphic standard deviation (very badly sorted). Particle size distribution histograms of R-L and A-L horizons are bimodal, a mode for sand and a mode for silt, suggesting two different sources. Depth distribution of Si/S, SKI and Folk inclusive graphic standard deviation of highly silty and other horizonz show a drastic change between L horizons and the other horizons-an indication of lithologic discontinuity and difference in origin. In conclusion, despite the possible contribution of granitic parent rocks to silt generation in the area, loess deposits recognized appear to have mostly been transported by aeolian movement.
M Ebrahimi, S.m Khayam Nekoei, S Kadkhodaei,
Volume 12, Issue 46 (1-2009)
Abstract
Somatic embryogenesis is affected by several factors. In this research project, we studied the effect of explant size, wounding and desiccation treatments on somatic embryogenesis and their conversion into plantlet among three genotypes of soybean. The explants were sampled from immature embryos of soybean in three different sizes (3, 5 & 7 mm) with wounding treatment on half of each, and then were cultured on the somatic embryogenesis medium. In order to determine desiccation effect on conversion amount of embryos into plantlets, the produced embryos were affected by three levels of desiccation treatments (2, 4 & 6 days). The increase ratio of callus mean weight, percentage of embryogenic calli, embryo number per explant and percentage of embryo conversion to plantlet were used for treatment evaluation. Variance analysis of the data showed significant differences (P<0.01) between treatments regarding the variables. The results indicated that BP was a superior genotype with embryogenic capability (24.19 %) and the best explant size for somatic embryogenesis was immature embryo with 3 mm length. The six day desiccation treatment caused highest percentage of embryo conversion into plantlet (74.7 %). Wounding increased callus production on explants and number of embryos per explant (20.28), but it did not show any significant effect on percentage of embryogenic calli. Germinated somatic embryos were transferred to pots containing peat-moss. Somatic embryogenesis is an efficient method for the plant regeneration and genetic transformation. However, this method still offers low percentages of plant regeneration, and is perhaps related to the maturation process and high morphological abnormalities of the matured embryos. This study aimed to find some solutions for soybean somatic embryogenesis problems.
H Arzani, M Mosayebi, A Nikkhah,
Volume 12, Issue 46 (1-2009)
Abstract
Information on animal requirements for determination of rangeland grazing capacity is essential. Animal requirements depend on its live weight, age, physiological condition and quality of available forage. There are more than 20 sheep breeds with different body sizes grazing in various climatic zone's rangelands of Iran, so animal unit equivalent of each breed should be determined independently. In this research, live weight of animal unit of Fashandy sheep based on average live weight of 3 and 4 year old ewes was determined. Three herds with more than 100 Fashandy ewes among existing herds in Taleghan region were selected. In each herd, 15 three year old ewes, 15 four year old ewes, 5 three year old rams, and 5 four year old rams were selected. They were weighed three times including at the time of beginning of grazing in highlands, end of grazing season in highlands, and once in winter. In each herd, also 5 three month old lambs in the beginning of grazing season and 5 six month old lambs at the end of grazing season were weighed. The amount of daily forage requirement according to live weight and energy requirement of animal unit equivalent for maintenance condition was calculated using NRC (1985) tables and MAFF (1984) formula. It was multiplied by 1.5 because of mountainous condition of rangelands and distances from watering points and villages. The SAS statistical software was used for data analyses according to factorial experiment in the form of completely random design. According to the results, the live weight of animal unit of Fashandy breed was 60.7 Kg. The average live weight of 3 and 4 year old rams were 80.3 and 85.3 kg, respectively. Live weights of 3 and 6 month old lambs were 21.4 and 37.8 kg, respectively. Therefore, animal unit equivalents for rams, 3 and 6 month old lambs were 1.36, 0.35 and 0.62 respectively. According to NRC tables, daily metabolisable energy requirement was 13.8 Mj, and based on MAFF formula it was 11.8 Mj (including that multiplied by 1.5).
E. Nabizadeh, H. Beigi Harchegani,
Volume 15, Issue 57 (10-2011)
Abstract
Selecting an appropriate particle size distribution (PSD) model for a particular soil may be important for a precise estimation of soil hydraulic properties. Various models have been proposed for describing soil PSDs. The objective of this study was to compare the quality of fitting of eight PSD models (Fredlund, Gompertz, van Genuchten, Jaki, Logarithmic, Exponential, Logarithmic-Exponential and Fractal) in 71 soil samples collected from Lordegan and Saman in Charmahal-va-Bakhtiari province, Iran. Coefficient of determination ( ) and Akaike’s information criterion ( ) were used to compare the goodness-of-fit of the models to the experimental data. Results showed that Fredlund model is best for describing PSD of silt loam, silty clay loam, silty clay and sandy loam soil textures. While Fractal, Exponential and Logarithmic-Exponential models produced the poorest-fit in silt loam, silty clay loam and silty clay, they had the best performance in sandy loam texture. The performance of Fredlund and Gompertz models improved with an increase in clay and silt content from 25 and 40 percentage, respectively. The performance of Fractal, Exponential and Logarithmic-Exponential models improved by increasing the sand content. Reverse correlation was observed between silt content and the performance of the Fractal model.
M. Mansourzadeh, F. Raiesi,
Volume 16, Issue 59 (4-2012)
Abstract
The application of herbicides as organic chemical compounds to control pest and weeds may affect the population and activity of microorganisms, and this may have an influence on biochemical processes that are important for soil fertility and plant growth. The primary objective of this study was to evaluate different loading rates of eradican (EPTC) on soil microbial biomass C and N, microbial biomass C/N ratio and the activities of urease and arylsulphatase under field conditions. In this experiment, loading rates of 6 and 9 L ha-1 eradican were applied to a calcareous soil cultivated with corn (Zea mays L.) and left uncultivated using split-plots arranged in a completely randomized block design with three replications. The experiment was conducted in the Kabootarabad’s Agricultural Research Center, Isfahan. Soil microbial biomass C and N were determined at 30th and 90th days after the onset of experiment and the activities of urease and arylsulphatase were assayed at 30th, 60th and 90th days. Results showed that in soils cultivated with corn microbial biomass C increased with increasing eradican levels and in both cultivated and uncultivated soils microbial biomass N and microbial biomass C/N ratios were increased over the control. At 30th day, urease activity at 6 L ha-1 level reduced, while at 9 L ha-1 level it increased compared with the control soils. At 60 day, there was no significant difference in the urease activity between the treatments. At 90th day, the activity of urease showed slight fluctuations. There was a reduction in arylsulphatase activity of the cultivated soils by increasing the loading rates of eradican during the experiment, and in uncultivated soils no trend was observed. Briefly, the use of eradican can cause either reduced or increased microbial biomass sizes and enzyme activities in calcareous soils These changes, however, depend largely upon the application rate of eradican, time elapsed since eradican application (i.e., sampling date) and the presence or absence of plant
N. Ghorbani Ghahfarokhi, Z. Kiani Salmi, F. Raiesi, Sh. Ghorbani Dashtaki,
Volume 17, Issue 63 (6-2013)
Abstract
Free and uncontrolled pasture grazing by animals may decrease soil aggregate stability through reductions in plant cover and subsequent soil organic C, and trampling. This could expose the soil surface layer to degradation and erosion. The objective of this study was to determine the influence of pasture management (free grazing, controlled grazing and long-term non-grazing regimes) on aggregate-size distribution and aggregation parameters by wet and dry sieving methods in two native pastures, protected areas in Chaharmahal va Bakhtiari province. The studied pastures were 1) SabzKouh pastures protected from grazing for 20 years, and 2) Boroujen pastures protected from grazing for 25 years. Soil samples were collected from 0-15 cm depth during the grazing season in summer 2008. Samples (finer than 2 mm) were analyzed for aggregate-size distribution and aggregation parameters by wet and dry sieving methods. Results showed that pasture management had a significant influence on aggregate-size distribution and aggregation parameters in the two areas. The two methods indicated that macro-aggregates in non-grazing and controlled grazing regimes were higher than those in free grazing regime, whereas in free grazing management micro-aggregates showed an opposite trend, and were greater compared with the other grazing regimes. Similarly, soil aggregate stability indices (i.e. mean weight diameter, aggregate geometric and ratio mean diameter) were all improved by non-grazing regimes, suggesting that animal grazing and trampling break down large soil aggregates due largely to compaction and reduced plant coverage. However, the extent to which grazing affects soil aggregation depends in large part on grazing intensity and duration, and the area involved.
H. Beigi. Harchegani, G Banitalebi,
Volume 18, Issue 70 (3-2015)
Abstract
Texture fractal dimension is a physical index to describe soil particle size distribution having a variety of applications. Fractal dimension may be calculated from three relations of mass-time, mass-diameter and modified mass-diameter (Kravchenko-Zhang) with two linear and nonlinear options for fittings. The aim of the present study was to compare methods and select an appropriate one and fitting option for determining the fractal dimension using hydrometer data. Sixty soil samples were collected from four fields of Taqanak, near Shahrekord. After removal of organic matter and other initial treatments, hydrometer readings were obtained at 0.67, 1, 2, 5, 15, 30, 60, 120, 180, 1440 and 2880 minutes and were converted to mass-time or mass-diameter data. Nonlinear fitting of the Kravchenko-Zhang mass-diameter relation was selected as the most appropriate method of calculating the fractal dimension of solid particles, due to its highest coefficient of determination and smallest mean square error and lowest Akaike Information Criteria. Error analysis also confirmed this conclusion. There was a significant, though not very strong, relationship between the fractal dimension obtained by linear and nonlinear fitting of mass- diameter and Kravchenko-Zhang mass-diameter methods. These relationships can be used to correct the fractal dimension determined by other methods and fitting options.
M. Farzadian, S. Hojati, Gh. A. Sayyad , N. Enayatizamir,
Volume 19, Issue 72 (8-2015)
Abstract
One of the major problems associated with petroleum-contaminated soils is water repellency, especially in arid regions of the world. Hence, a variety of methods such as clay addition has been proposed to improve the hydrophobicity of soils. This research was conducted to evaluate the influence of zeolite application on water repellency of an oil-contaminated soil from Khuzestan Province under various treatments including initial soil moisture content (0, 10, 20, and 30 weight %), the amount of applied zeolite (2, 4 and 8 weight %), size (25-53 and <2 μm), and exchangeable cation (Sodium and Calcium). The hydrophobicity of soil sample was determined using Water Drop Penetration Time (WDPT) method. The results showed that by increasing the amount of applied mineral WDPT decreased, where the application of 2 percent of zeolite led to the reduction of WDPT by about 27 percent less than the control. The results also indicated that soils treated with sodium-saturated zeolite had less WDPT than the calcium-treated samples, where the average of WDPT in sodium and calcium treatments decreased by 23% and 5% compared with the control, respectively. The initial moisture content of 30 percent showed the best performance with the decreasing WDPT of about 67 percent. Furthermore, the effect of mineral particle sizes showed a meaningless reduction in WDPT.
A. Holisaz, B. Ahadi Dos, M. Kamangar, A.n Ameli1,
Volume 20, Issue 76 (8-2016)
Abstract
The last two decades have seen increasing applications of digital terrain modeling in hydrological, geomorphological, pedagogical, and biological research, aided by rapid advancement of geographic information system (GIS). Hydrologic models are sensitive to change in the input values to the model, so the change of pixel size input data affects the output values of the model and produces different significant results. In this study, using topographic maps 1:25000 and 1:50000 and choosing ten pixel sizes (10, 15, 20, 25, 30, 50, 75, 80, 100, and 200) and software Arc GIS and HEC-HMS, output values of HEC-HMS model have been studied. Results of this study indicate that accuracy of peak discharge calculated by HEC-HMS model in the spatial scale map 1:50000 is more than the peak discharge calculated by HEC-HMS model in the spatial scale map 1:25000. Also accuracy of the calculated peak flows in a smaller pixel sizes (20 to 50) is more than the larger pixel sizes.
M. Tayebi, M. Naderi, J. Mohammadi,
Volume 21, Issue 3 (11-2017)
Abstract
The aim of this work was to study distribution of some heavy metals in different soil particle-size fractions and to assess their spatial distribution. The study was carried out in Kafe Moor (Kerman, Iran) where the Gol-Gohar Iron Mine is located. One hundred twenty composite soil samples were randomly collected and transferred to the laboratory in bags. After air-drying, the samples were fractionated into six classes including 2- 0.5, 0.5-0.25, 0.25-0.125, 0.125- 0.075, 0.075-0.05 and <0.05 mm. Elemental concentrations (Fe, Mn, Cu, Zn, Pb and Ni) were determined using acid digestion method (HNO3, 4.0 N) and an atomic absorption spectrophotometer in each class. Ordinary Kriging technique was used for predicting spatial distribution of heavy metals. The results showed that content of metals in soil increased with decreasing particle size. The results also showed that the concentration of Fe, Mn, Cu, Zn, Pb and Ni in <0.05 mm size fraction were 2.13, 1.70, 4.79,2.43, 1.42, and 3.47 times higher than in 2-0.05 mm size fraction, respectively. In addition, mapping the concentrations of heavy metals with kiriging showed that metals pollution decreased with increasing distance from mines area.
A. R. Vaezi, Z. Bayat, M. Foroumadi,
Volume 22, Issue 2 (9-2018)
Abstract
Soil erosion by surface runoff introduced as surface erosion is one of the main mechanisms of land degradation in the hill slopes. Slope characteristics including aspect and gradient can control the differences of soil properties along the hillslope. This study was conducted to investigate the effect of slope aspect and gradient on variations of some soil properties in the short slopes. Five hills including both north and south aspects with different gradients (9-10%,
13-16%, 17-22%, 29-31% and 33-37%) were considered in a semi-arid region with 30 ha in area, in the west of Zanjan, northwest of Iran. The hills were weakly covered with pasture vegetation covers. Soil samples were collected along the slopes from two depths (0-5 cm and 5-15 cm) in four positions with 2 m distance along each slope with two replications. A total of 160 soil samples were analyzed for particle size distribution (sand, silt and clay), gravel and bulk density. Surface erosion was determined based on the variation of grain size distribution and bulk density. Differences of the grain size distribution and surface erosion between the two slope aspects and among the slope gradients were analyzed using the Tukey test. No significant difference was found between slope aspects in surface soil erosion. Nevertheless, surface soil erosion was affected by slope gradient in each slope aspect (R2= 0.78, p< 0.05). Surface erosion in the north slopes was more dependent on the slope gradient, as compared to the corresponding south slopes. In the south slopes, surface erosion was affected by the movement of silt particles from soil surface, while in the north slopes, it was significantly affected by the loss of clay particles.
S. Rahmati, A. R. Vaezi, H. Bayat,
Volume 23, Issue 1 (6-2019)
Abstract
Saturated hydraulic conductivity (Ks) is one of the most important soil physical characteristics that plays a major role in the soil hydrological behaviour. It is mainly affected by the soil structure characteristics. Aggregate size distribution is a measure of soil structure formation that can affect Ks. In this study, variations of Ks were investigated in various aggregate size distributions in an agricultural soil sample. Toward this aim, eight different aggregate size distributions with the same mean weight diameter (MWD= 4.9 mm) were provided using different percentages of aggregate fractions consisting of (< 2, 2-4, 4-8 and 8-11mm). The Ks values along with other physicochemical properties were determined in different aggregate size distributions. Based on the results, significant differences were found among the aggregate size distributions in Ks, particle size distribution, porosity, aggregate stability, electrical conductivity (EC), organic matter and calcium carbonate. The aggregate size distributions with a higher percentage of coarse aggregates (4-8 and 8-11 mm) also showed higher Ks as well as clay percentage. A positive correlation was also observed between Ks and clay, aggregate stability and EC, whereas sand showed a negative correlation with Ks. No significant correlations were found between Ks and silt, porosity and organic matter. Further, multiple linear regression analysis showed that clay and aggregate stability were the two soil properties controlling Ks in the aggregate size distributions (R2=0.80, p<0.01). Aggregate stability was recognized as the most important indicator for evaluating the Ks variations in various aggregate size distributions.
N. Sadeghian, A. Vaezi,
Volume 23, Issue 2 (9-2019)
Abstract
Sediment selectivity during transport may provide basic information for evaluating on-site and off-site impacts of the soil erosion. Limited information is, however, available on the selectivity of sediments in rill erosion, particularly in the rainfed furrows. Toward this, the sediment selectivity was investigated in three soil textures (loam, loamy sand sand clay loam) under 10% slope using 90 mm.h-1 rainfall intensity for 40 min. Soil samples were passed from a 10 mm sieve and packed in to the erosion flume with 0.4m × 4 m in dimensions. Particles size distribution (PSD) was determined in the sediments (PSDs) and compared with the original soil PSD (PSDo). The proportion of PSDs and PSDo was stated as PSDs/PSDo to show the selectivity of soil particles by rill erosion. Based on the results, all three soils appeared as the coarse particles (coarse sand and very coarse sand) in sediments with the PSDs/PSDo>1, indicating the higher selectivity of these particles by rill erosion. Loamy sand was the most susceptible soil to rill erosion among the studied soils, which generated a higher runoff (0.0035 m2.s-1) and sediment load (0.1 kg.m-1.s-1) during rainfall. The PSDs of this soil were similar to those of the original soil PSD. This study revealed that the stability of aggregates could be regarded as the major soil factor controlling rill erosion rate and the sediment selectivity in the semi-arid soils. With an increase in the water-stable aggregates, soil infiltration rate and as a consequence, shear stress of flow could be decreased in the rills.
N. Shahabinejad, M. Mahmoodabadi, A. Jalalian, E. Chavoshi,
Volume 24, Issue 3 (11-2020)
Abstract
Wind erosion is known as one of the most important land degradation aspects, particularly in arid and semi-arid regions. Soil properties, by affecting soil erodibility, can control the wind erosion rate. The aim of this study was to attribute the soil physical and chemical properties to the wind erosion rate for the purpose of determining the most important property. To this aim, wind erosion rates were measured in-situ at 60 points of Kerman province using a portable wind tunnel facility. The results indicated that wind erosion rates varied from 0.03 g m-2 min-1 to 3.41 g m-2 min-1. Threshold wind velocity decreased wind erosion rate following a power function (R2=0.81, P<0.001). Clay and silt particles, shear strength, mean weight diameter (MWD), surface gravel, dry stable aggregates (DSA<0.25mm), soil organic carbon (SOC), calcium carbonate equivalent (CCE) and the concentrations of the soluble Ca2+, K+ and Mg2+ were inversely proportional to the wind erosion rates following nonlinear functions. On the other hand, Wind erosion was significantly enhanced with increasing the sand fraction, soluble Na+, electrical conductivity (EC) and sodium adsorption ratio (SAR). According to the final results, among the studied soil properties, SAR and MWD were s the most effective properties controlling wind erosion in the soils of Kerman province. Therefore, it is recommended to consider suitable conservation practices in order to prevent the sodification and degradation of arid soils.
A.r. Vaezi, E. Mohammadi,
Volume 25, Issue 4 (3-2022)
Abstract
This study was conducted to investigate the temporal variations of runoff and rill erosion in various soil textures under different slope gradients. So, a laboratory experiment was set up in three soil textures (loam, clay loam, and sandy clay loam) and four slope gradients (5, 10, 15, and 20%) using the completely randomized design with three replications. Runoff production and rill erosion were measured at a flume with 4 m×0.32 m in dimensions using a simulated water flow with 0.5 lit min-1 in discharge during 30 min. Results indicated that runoff and rill erosion and their interaction were significantly affected by soil texture and slope gradient (P < 0.001). Significant relations were found between rill erosion and runoff both in three soils and four slope gradients, and the strongest relations were in loam (R2= 0.86) and 15% slope gradient (R2= 0.94). Runoff and rill erosion varied considerably in the soil textures and slope gradients during the experiment. A 10-min pick time was found for runoff and rill erosion. In contrast to runoff, rill erosion appeared an irregular and gradual increasing pattern during the experiment which was associated with the frequency of transportable soil particles. Clay loam had more sensitive particles due to a higher percentage of fine particles and weaker structure, and most of them were washed in early times, and finally, rill erosion was reached to a constant pattern. This study revealed that temporal variation patterns of runoff and rill erosion are influenced by soil type (texture and structure) and slope gradient.
M. Eskandari, M. Heidarnejad, A. Egdernezhad,
Volume 27, Issue 3 (12-2023)
Abstract
The formation of vortices behind the gates of diversion dams is an operational challenge. Such vortices lead to vibration and corrosion in the gate, reducing the lifetime and raising the operational cost of the dam. This study investigated these vortices and their formation. It was found that the gate or cutoff wall was not the only explanation for the vortices; the closed side gates also contribute to vortex formation. Furthermore, an increase in the gate width reduced vorticity; the vortex size experienced a 200% reduction as the gate size increased by 200%. The cutoff wall diameter was another determinant. An increase in the cutoff wall diameter raised vorticity. The vortices increased by 50% as the wall diameter increased by 150%.
