جستجوی مقالات مرتبط با کلیدواژه « Mean weight diameter » در نشریات گروه « آب و خاک »

Aggregate stability of soils informs about their relative strengths against erosive forces and mechanical disruption. In this research, a hybrid Genetic Algorithm-Artificial Neural Network method was used to select the best subset of features affecting the mean weight diameter (MWD. In addition, the ability of ANNs and multiple linear regression (MLR) for quantifying the relationship between the MWD index and some soil properties was assessed. After the modeling process, the importance of the selected features in relation to spatial variability of aggregate stability was investigated. In order to prepare a suitable data set; MWD index and some soil features were measured in collected soils from 90 sampling points. Feature selection results showed that six soil features including clay, sand, organic matter, calcium carbonate, electrical conductivity, and sodium adsorption ratio had the greatest effect on the aggregates stability of the studied soils. According to the MWD modeling results, the obtained values of coefficient of determination (R2), mean absolute error percentage (MAEP), and root mean square error (RMSE) for the ANN model performance were 0.94, 21.39, and 0.07% respectively. These findings indicated that the developed ANN model was able to predict the complex and nonlinear relationships between the MWD index and the soil properties selected by the algorithm. Based on the sensitivity analysis results, calcium carbonate equivalent, sand particles, and organic matter were identified as key factors in estimating aggregate stability. Overall, this study provides a robust framework for the prediction of aggregate stability and identifying the most determinant parameters influencing it in arid and semi-arid soils that could be applied to other regions with similar challenges.

Little is known about the long term effects of nanoparticles on soil properties. Therefore, the objective of this study was to investigate the three years effects of nanoparticles on aggregate stability and some of the soil chemical properties. Different amounts (1, 3 and 5 percentage by weight) of two types of nanoparticle of metal oxides, MgO and Fe3O4 were mixed with a loamy soil in three replications and their possible effects on different properties of the soil after three years were investigated. The results showed that application of nanoparticles, increased the pH of the soil from 7.7 in the control to 8.1- 9.3 and the electrical conductivity from 0.31 in the control to 0.34 -0.56 dSm-1, due to the increase in the alkali cations. The percentage of calcium carbonate increased from 19.75% in the control to 20.5-22.7% due to the accumulation of nanoparticles in the soil, with the highest increase in three variables with 5% magnesium nano oxide. 3% nano iron oxide significantly increased the cation exchange capacity from 23.50 in the control to 24.28 cmolc/kgsoil. Also the nanoparticles increased the mean weight diameter, due to their high specific surface area, with the greater effect of magnesium nano oxide (increased from 33 to 1242 percentage compared to the control) than iron nano oxide (increased from 97 to 173 percentage compared to the control). In general, the results of this study showed that, nanoparticles with specific physico-chemical properties can affect some properties of soil.

Stability of soil aggregates is a result of complex physical, chemical and biological processes in the soil. In many studies, organic matter has been studied as a major factor in formation of aggregates and the effects of symbiosis between mycorrhizal fungi and bacteria largely ignored, however these microorganisms have a great effect in the formation of the aggregates. Plant roots provide a suitable habitat for the activity of many soil microorganisms. In this regard, the symbiosis of plant roots with fungi is one of the most common and long-lived symbiotic relationships that are found in most ecosystems. On the other hand, biological fertilizers can improve soil aggregation through influence the growth of root and plant. Despite the significant effect of fungi and bacteria on the stability of the soil structure, the effect of arbuscular mycorrhizal fungi species Glomus mosseae and Rhizobium species Mesorhizobiumon caesar on the soil structure has been rarely investigated. Therefore, the aim of this study was to evaluate the effect of chickpea inoculation with Rhizobium (Mesorhizobium caesar) and mycorrhizae (Glomus mosseae) on soil structural stability and aggregates size distribution under both greenhouse and field conditions.

The present study was conducted as a randomized complete-block design with three replications in both greenhouse and field conditions. The treatments under field condition were mycorrhizal fungus (Glomus mosseae), Rhizobium (Mesorhizobium caesar), mycorrhizae – rhizobium combined treatment and a control (no inoculation). In the greenhouse condition, sterilized mycorrhiza background material and without plant (without inoculation) treatments were also added. Chickpea was planted at both conditions. Soil sampling was carried out after harvesting. The stability of aggregates using wet sieving method and soil organic carbon content were investigated.

Greenhouse study results showed that mycorrhizae treatment significantly increased the mean weight diameter of the aggregates by 51.6% and 189.1%, in comparison with the control (without inoculation) and control- without plant (without inoculation), respectively. This treatment increased macro aggregates and decreased the fine aggregates. In the greenhouse condition, soil organic carbon content had a high correlation with the mean weight diameter of the aggregates (R2 = 0.53) and mycorrhizal treatment increased organic carbon content from 0.73% in the control (without plant) to 1.02%. However, the mycorrhizae – rhizobium combined treatment had less effect on the stability of the aggregates than their single effects. The mass of aggregates of 1–2 mm are more sensitive to short-term management. In the greenhouse condition all the three biofertilizer treatments significantly increased the mass of the aggregates of 1-2 mm in comparison with the control treatment without plant (without inoculation). On the other hand, the mean comparison results showed that there was no significant difference between the sterilized mycorrhizal background and the control without plant (without inoculation). This may be due to the lower organic matter content in these two treatments compared to others. In the greenhouse condition, increasing the mass of coarse aggregates of 4-8 mm in diameter indicates the suitability of soil structure. On the other hand, aggregates coarser than 0.25 mm are considered as coarse and stable aggregates. It can be concluded that the application of mycorrhiza and rhizobium increased soil structural stability through the increase of the mass of these classes of the aggregates (2-4 and 4-8 mm), probably by affecting the length and volume of the root and plant yield. Under the field condition, the treatments had no impact on the mass of the aggregates in different size classes.

Bacteria and fungi can be effective factors in improving soil structure through increasing organic carbon in soil. The results of the present study indicated that aggregate stability was affected by biological fertilizer treatments under greenhouse condition so that the treatments containing biofertilizers increased soil aggregate stability and improved the soil structure that was probably due to increasing plant yield and root. Also, the less effect of biofertilizers on the stability of the aggregates and the increase of coarse aggregates under the field condition can be due to the uncontrolled climatic conditions compared to the greenhouse and the short duration of the study. In recent decades, the physical and chemical properties of soils have changed due to the use of chemical inputs in agricultural lands.The use of biological and organic fertilizers is an appropriate solution to these problems. It is recommended further study on the efficacy of other species of mycorrhizal fungi and rhizobium bacteria in improving soil physical and chemical quality, especially at the field scale. Also, considering the implementation of this project in the field condition, it is suggested to study the physical, mechanical and chemical properties of soil in the long term.

In order to study the effect of two organic amendments on some physical properties of three soils with different textural class, a greenhouse experiment was conducted as a factorial arrangement in completely randomized design with three replications. Treatments consisted of two types of organic materials (compost and ripe fig fruit waste), four organic material levels (zero, one, two and four % by weight) and three types of soil textural class (Loamy Sand, Loam, and Silty Clay Loam) from Maharloo, Zarghan and Shiraz areas in Fars Province, Iran. Four months after mixing the organic material with soil, some physical properties of the soil including the mean weight diameter (MWD), the final infiltration rate of water in the soil, field capacity (FC), and water evaporation from the soil surface were measured. Results showed that application of 4% ripe fig fruit waste significantly increased the average MWD, infiltration rate, FC moisture by about 32.4, 8.5, and 9.02% respectively, and application of 4% compost significantly increased the average MWD, infiltration rate, and FC by about 69.3, 5.4, and 7.7% respectively as compared to that of control. Moreover, application of 4% ripe fig fruit waste and compost significantly decreased the average of water evaporation from the soil surface by about 10.9 and 22.3 %, respectively as compared to that of control. According to the results, organic waste can be used as an amendment in soils with different textural class to improve soil physical condition. Moreover, results showed that the effect of compost in improving the physical properties of the soil was more than that of ripe fig waste.

The study of physical properties of suspended sediments is one of the main topics in river studies. Sediment size distribution is one of the sediment physical properties which indicate the relation between the sediment source and its sedimentation process in watersheds. It is also important for prediction of the load of non-point source pollution, and for planning sediment trap structures. The Anzali Wetland, located on the southern coast of the Caspian Sea in northern Iran, is a large complex of freshwater lagoons with extensive reed-beds, shallow impoundments and seasonal flooded meadows. Environmental conditions in the Anzali Wetland have been degraded due to the increased inflow of sewerage, wastewater and solid waste from the industry, agriculture and urban area, and sediment from the upper stream mountainous area. The lagoon has decreased in size since the 1930s to less than a quarter of its former extent. The aim of the present study was to assess the changes in size distribution of suspended sediment in Pasikhan River as the most important river interring to Anzali Wetland. Pasikhan River originates from the South Mountains, has two branches namely Siahmezgi and Imamzadeh Ebrahim. The sampling carried out during a seven month time period (October 2013 to April 2014) at two hydrometric stations; Mobarakabad (upstream) and Nokhaleh (downstream). The samples were collected in 15 days intervals by depth-integration technique at normal condition. Particle size distribution was measured by Pipette method based on Stocks law. The mean weight diameter (MWD) of sediment particles was calculated, the sediment size distribution curve was drawn and the median grain size (d50) was calculated. According to the European classification, the particles size distribution was divided into four groups of fine sand (0.2 mm), coarse silts (0.06 mm), medium silt (0.02 mm), and fine silt and clay (equal to and less than 0.006 mm). The data were compared for each sampling time for both Stations. Flow discharge and suspended sediment load were also determined at each sampling date. At the Nokhaleh station, the maximum observed flow discharge and sediment concentration were 51.4 m3/s and 4.162 g/L, occurred in February 4, 2014 and  November 3, 2013, respectively. The highest flow discharge and sediment concentration of the Mobarakabad were 9.8 m3/s and 2.633 g/L which were observed on February 19, 2014 and April 4, 2014, respectively. These changes and differences were partly due to topography and land use differences between upland and lowland and partly due to rainfall pattern. Results showed that the MWD and d50 were 0.062 and 0.052 mm on average, respectively at Mobarakabad station, and 0.055 and 0.051 mm, respectively at Nowkhaleh station. The maximum values of MWD and d50 were observed to be 0.07 and 0.061 mm, respectively at normal condition at Mobarakabad station. The study of sediment size distribution indicated that the particles smaller than 2 mm comprised 83-94 percent of the suspended sediment at Mobarakabad station, and 87-99 percent at Nokhaleh station. The percentage of particles smaller than 0.02 mm were observed to be 12-33 and 10-64 at Mobarakabad and Noukhaleh stations, respectively. Also the amount of fine silt and clay in suspended sediment were 3-16 and 5-24 percent at these stations. There was not any correlation between flow discharge and sediment concentration or sediment size distribution characteristics. In most of the samples, there was not any relationship between the flow discharge and particle size distribution of suspended sediment which emphasize on the non-hydraulic nature of sediment transport and the effects of different factors including sediment sources, the season, transport energy, rainfall erosivity, soil erodibility and deposition process. Generally, the size of sediment particles at Mobarakabad station was coarser than Nokhaleh station. This could be due to the type of soil erosion which is different at upstream and downstream. In upstream regions, mainly because of severity of topography and vegetation cover including forest and rangeland, the occurrence of gully erosion and landslide is higher in comparison with surface soil erosion. But in downstream especially in paddy fields, the soil erosion type is mainly splash and sheet erosion. Also the cultivation practices including plowing and paddling of the field usually provides fine particles entering to the river.  In addition, the river profile is very gentle at the plain before the Nokhaleh station which resulted in deposition of coarser particles.

Land cover type and slope are two dominant parameters in soil and water erosion intensity. Although many studies have been conducted to explore the effects of slope or vegetation cover on soil erosion, but the there wasn’t any report regarding comparison of their effects in sediment generation in run off or derange. The objective of this study was to comparison of sediment in surface runoff and drainage water under influence of cultivation type (Alfalfa and Wheat) and slope (5% and 20%) in a sandy loam soil. The laboratory experiments were conducted using a soil box with dimensions of 100 cm long, 30 cm wide, and 25 cm deep, with one soil drainage outlet and one surface flow outlet, packed with soil in Agricultural Faculty of Bu-Ali Sina University. The result showed that intensive vegetation cover (alfalfa than wheat) can considerably reduce the loss of soil erosion. As under alfalfa cultivation less sediment was observed than wheat cultivation in both runoff and drainage. The current results showed that sediment generation in runoff and drainage vary with slope; as under both alfalfa and wheat cultivations larger sediment was observed in 20% slope in runoff, whereas in drainage the higher amount was observed in 5% slope. The observation of slighter sediment after 60 minute of rainfall in runoff could attribute to the generation of a surface crust that encouraged runoff and reduced soil erosion. Although there were no significantly effects of land cover and slope on mean weight diameter, it was larger under alfalfa as a result of erosion-reducing effectiveness of plant covers.

Fire is a major threat for natural resources in the world and is an important factor in changing physical and chemical properties of soil. Knowledge of the positive or negative effects of fire on soil properties can be a great importance for the management of natural resources. This study was conducted with the aim of the effect of fire on physical and chemical properties of soil in rangelands of Badreh area in Ilam provice and comparison with non-fire areas (control). After field studies in Badreh area in the eastern of Ilam province, soil samples were taken from 0-5 and 5- 20cm depths and collected randomly and transferred to the laboratory. Physical analysis (soil texture, mean weight aggregate diameter, saturation moisture and bulk density) and chemical (organic matter, total nitrogen, phosphorus available, potassium available, calcium and magnesium exchangeable, cation exchange capacity) were carried out on soil samples. The highest amount of sand (46.4%) and soil silt (24.4%) were found in burned pasture and the highest clay content (39%) was found in control rangelands. Fire decreased the stability of aggregates and soil porosity in burned rangelands compared to unprocessed rangelands (14.28 and 8.68%) significantly (α= 0.05). The bulk density of the burned pasture was 9.1% higher than that of the control pasture. In the soil surface layer, the soil moisture content increased 16.98% compared to the control treatment. The fire decreased the amount of soil organic matter from 2.66% in control pasture to 2.19% in burned pasture (α= 0.05). Soil acidity increased significantly in burned pasture (pH=7.45) compared to control pasture (pH=7.07). The highest cation exchange capacity (24.82 cmol kg-1) and the lowest (18.98 cmol kg-1) were obtained in control and burned rangelands respectively. Also, with an increase in soil depth, the cation exchange capacity of soil decreased to 14.10%. The most available phosphorus, magnesium and calcium were obtained in burned pasture at the soil surface. Fire had no significant effect in the subsoil layer, on the amount of soil phosphorus, magnesium and calcium exchangeable. In general, the results indicate that fire in rangelands of Badreh area in Ilam province affected physical and chemical properties of soil. In most cases, soil quality is decreased chemically (decreasing organic matter, nitrogen, cation exchange capacity) and physically (soil texture changing, soil aggregate stability, porosity and bulk density), and in some cases, fire caused to release the nutrient elements such as phosphorus, calcium and magnesium in the soil and improved the nutrient cycling nutrients in the soil.

Soil structure and aggregate stability are physical characteristics that directly and/or indirectly affect the other soil properties and growth of plants. These soil attributes are influenced by factors such as the type and amount of organic matter and soil water conditions. The effects of 0, 0.05%, 0.5%, and 5% organic acid and 1, 4, 8, and 12 wetting-drying (W-D) cycles of 10 days on the soil aggregate stability and size distribution were evaluated in a factorial experiment arranged in a completely randomized design with three replications. Mean weight diameters (MWD) of aggregates increased significantly (by 22%) as compared to the control when 4 cycles of W-D were applied, whereas geometric mean diameter (GMD) of aggregates was decreased by 27% and 23%, respectively, when 8 and 12 cycles of W-D were applied. Application of 4, 8, and 12 W-D cycles resulted in a significant decrease in D10, and application of 8 and 12 W-D cycles decreased D25, D30, D50, D60, and D75, significantly. The uniformity coefficient of the aggregate size distribution curve increased by 13%, 15%, and 11% when, respectively, 4, 8, and 12 W-D cycles were applied. Also, the curvature coefficient of the aggregate size distribution curve decreased by 6% in response to application of 0.05% organic acids. In general, W-D cycles decreased some indices of aggregate size distribution, while organic acids had no significant effect on aggregate stability. Organic acids could mitigate the adverse effects of W-D cycles. Therefore, their application in the regions with W-D cycles is recommended to reduce the adverse effects of wetting-drying process on the soil structure and aggregate stability, and the negative results of the consequent water and wind erosions.

Low organic matter in arid and semi-arid soils results in decreasing physical quality and increasing runoff and soil erosion. Application of organic compounds (sewage sludge) in these regions can improve soil physical and chemical properties. In the present research, effect of different levels of sewage sludge (0, 30 and 60 ton ha-1) on organic carbon, aggregate stability (mean weight diameter, MWD and geometric mean diameter, GMD), and plasticity limits (upper plastic limit, UPL, lower plastic limit, LPL, and plasticity index, PI) was studied over three time periods of 30, 60, and 120 days after application of sewage sludge. Soil organic carbon increased with increasing sewage sludge, but decreased significantly over time as compared to that of the control. Aggregate stability increased with sewage sludge application. Aggregate stability decreased 60 days after experiment as compared to that of 30 days, whereas, there was no significant difference between the aggregate stability at 120 and 30 days after the experiment. Upper plastic limit increased with increasing sewage sludge application. This criterion increased over time and decreased after that; whereas, LPL increased with sewage sludge application and did not vary over time. Sewage sludge did not affect PI significantly, while PI increased over time and then decreased. In general, results indicated that application of sewage sludge could increase soil organic matter and water holding capacity. Furthermore, with application of sewage sludge, soils can be tilled at higher moisture contents without any probable compaction. Of course, in addition to considering the positive effects of sewage sludge in improving soil physical properties, economical issues and the probable adverse effects of excessive application of sewage sludge and environmental risks should also be considered.

Usually, the impact of calcium and magnesium on improving and maintaining soil structure is assumed to be similar. This study was conducted to investigate the effect of different concentrations of magnesium on soil quality indicators. A clay loam soil was treated with fourconcentrations of magnesium (0, 1, 2, 3, 4, and 5 mmol/L) during 4 months in a completely randomized design with three replications. After this period, the mean weight diameter(MWD), wet aggregate stability(WAS) , clay dispersion (DS) and soil saturated hydraulic conductivity(KS )were measured. Analysis of variances showed that aggregate stability, hydraulic conductivity and clay dispersion significantly (p

Anionic polyacrylamide application as an organic conditioner alone or in combination with organic material, can improve soil properties. Improment of soil arregation and increase of aggregate stability by addition of organic matter are the most important ways for improving soil physical properits, which can increase carbon retention and sequestration in soil, water infiltration, porosity, aeration and seed germination and decrease soil compaction, water runoff and erosion of soil surface layers. The objective of this study was to investigate the influence some organic conditioners on mean weight diameter (MWD) and dispersible clay percentage (DCP).
Soil samples collected from the top 30-cm layer of two loamy sand and clay soils were treated with alfalfa and wheat residues ( The addition of plant residues and polyacrylamide decreased the percentage of dispersible clay in the both clay and loamy sand soils. The effect of these organic soil amendments onthe decrease of DCP in soils was synergistic and the lowest percentage was measured in concomitant application of both amendments in soil. The mean weighted diameter in the both soils increased significantly with the addition of plant residues. This beneficial effect in wheat straw treatment was higher. In both soils, we found that in the soil without plant residue, the application of polyacrylamide caused an increase in MWD. But in heavy soil treated with wheat straw and alfalfa straw, the application of polyacrylamide had detrimental effects on MWD. However, this detrimental effect was not significant in the light soil. The mean weighted diameter of the clay soil in all treatments increased during soil incubation up to that measured in the interval time of 10 to 20 day and then it decreased. The percentage of dispersible clay had a reverse change. It had the lowest level in this interval time. The temporal changes of soil MWD and DCP in loamy sand soil were similar to those in clay soil. But the highest levels of MWD and the lowest level of DCP were measured in a later interval time (30 to 45 day).
Although separate application of plant residues and polyacrylamide in soil can increase MWD but in concomitant application they had an antagonistic effect on soil MWD. The application of polyacrylamide decreased soil MWD in heavy soil treated with wheat straw and alfalfa straw. Plant residues by increasing biological activity and polyacrylamide especially in clay soil by physico-chemical reactions can improve soil aggregation and aggregate stability. Thus they do not have a synergistic effect on soil MWD. This occurrence may be related to the reaction of polyacrylamide with clays in soil that inhibits the beneficial effect of biological interaction between plant residue and soil clay particles in aggregation.

The location of extracellular enzyme activities in soil aggregates can be influenced by slope position. This study aims to determine the effect of slope position on aggregate distribution of organic C and L-glutaminase activity. The soils were collected from different slope positions (shoulder, backslope, footslope and toeslope) at two pasture ecosystems (Fereydoonshahr and Chelgerd, central Iran). A wet sieving procedure was used to separate soil aggregates and then mean weight diameter (MWD) was calculated. Soil organic C (SOC) and L-glutaminase activity (LGL) were measured in the separated aggregates. Results indicated that slope position influenced aggregates distribution and stability through its effect on soil physico-chemical properties. The LGL activity significantly influenced by slope position which was consistent with the pattern of SOC content (Fereydoonsahr: r=0.7, P

Soil structural stability affects the profitability and sustainability of agricultural systems. Particle size distribution (PSD) and aggregate stability are the important characteristics of soil. Aggregate stability has a significant impact on the development of the root system, water and carbon cycle and soil resistance against soil erosion. Soil aggregate stability, defined as the ability of the aggregates to remain intact when subject to a given stress, is an important soil property that affects the movement and storage of water, aeration, erosion, biological activity and growth of crops. Dry soil aggregate stability (Mean Weight Diameter (MWD), Geometric Mean Diameter (GMD)) and Wet Aggregate Stability (WAS) are important indices for evaluating soil aggregate stability.To improve soil physical properties, including modifying aggregate, using various additives (organic, inorganic and chemicals), zeolites are among what has been studied.According to traditional definition, zeolites are hydratealuminosilicates of alkaline and alkaline-earth minerals. Their structure is made up of a framework of[SiO4]−4 and [AlO4]−5 tetrahedron linked to each other's cornersby sharing oxygen atoms. The substitution of Si+4 by Al+3 intetrahedral sites results inmore negative charges and a high cation exchange capacity.Zeolites, as natural cation exchangers, are suitable substitutes to remove toxic cations. Among the natural zeolites,Clinoptilolite seems to be the most efficient ion exchanger and ion-selective material forremoving and stabilizing heavy metals.Due to theexisting insufficient technical information on the effects of using different levels of zeolite on physical properties of different types of soils in Iran, the aim of this research was to assess the effects of two different types of zeolite (Clinoptilolite natural zeolite, Z4, and Synthetic zeolite, A4) on aggregate stability indicesof soil. In this study at first, after preparation of two different types of soil with light and medium texture and doing identification tests such as determination of gradation and hydrometer tests and Atterberg limits, zeolite in four levels, 0 (control), 1%, 5%, and 10%w/w, was mixed with two soil textures (sandy loam and silty loam) in three replications. Then, each treatment was saturated for 48 hours in each month, during 6 months. Dry soil aggregate stability (Mean Weight Diameter (MWD), Geometric Mean Diameter (GMD), and Wet Aggregate Stability (WAS)), were determined. The experiment was carried out using factorial method in a randomized complete design. The results showed that, in sandy loam texture, there was no significant difference between two types of zeolites, their level of using and their interaction on MWD (p

Soil aggregate stability is considered as a key indicator of soil quality and health assessments in rangelands. Many factors and properties such as soil texture, organic carbon, calcium carbonate, sodium adsorption ratio, and electrical conductivity might affect soil aggregate stability. The effects of these factors on aggregate stability of 71 soil samples collected from 4 rangeland sites (2 in semi-arid and 2 in arid lands) in Isfahan province were investigated. Aggregate stability was measured using the wet-sieving method. To optimize the trial conditions for the investigated soils, three shaking times (5, 10 and 15 minutes) were used to impose different hydromechanical stresses on the aggregates of ten soils selected out of the studied soils. The structural stability was assessed using mean weight diameter (MWD) and geometric mean diameter (GMD) of the water-stable aggregates. Significant differences of MWD were observed between the shaking times. The 10-min shaking was selected as best for structural stability assessment in the studied regions because it resulted in better differentiation of soils on the basis of structural stability. Among the intrinsic properties, soil organic carbon content had the most important role in aggregate stability in all zones. However, electrical conductivity (in addition to organic carbon content) had an important role in aggregate stability in the arid rangelands. Log-normal distribution and GMD could represent better the aggregate size distribution when compared with normal distribution and MWD in the studied regions. Overall, wet-sieving method with shaking time of 10 min is suggested to assess the soil structural stability in rangelands of Isfahan province. Therefore, soil aggregate stability and the factors affecting this vital indicator can be used efficiently for assessing and monitoring management effectiveness and rangeland functionality trend.

The objective of this study was to evaluate the long-term effects of mechanized sugarcan cultivation on some soil physical properties in several lands of Khozestan Sugarcane Agro-Industries. According to this، the experiment was carried out statistically as a randomized complete block design at 38 points in each of Deabal-Khazaei، Amir-Kabir، Karoon and Haft-Tapeh Agro-Industries with 5، 15، 40 and 50 years service. Measured soil variables included soil texture، electrical conductivity، sodium adsorption ratio، organic matter، equivalent calcium carbonate، acidity، bulk density (BD)، resistance of soil penetration (PR) at 16. 82-17. 96 moisture interval at two depths 0-40 and 40-80 cm and mean weight diameter (MWD) at soil surface and 40 cm depth. The results showed that BD and PR increased with numbers of years service and also، MWD increased caused by improvement soil organic matter content. The PR values increased with depth، which achieved to the greatest value at 55 to 80 depth interval. Also، results showned that the significant effect of number of years service on BD، PR and MWD، so that BD، PR and MWD with increasing the number of years service from 5 to 50 years were increased from 1. 57 to 1. 7 gr/cm3، 0. 98 to 1. 16 MPa and 0. 98 to 1. 76 mm at first depth and 1. 58 to 1. 79 gr/cm3 and 1. 29 to 2. 15 MPa at second depth، respectively. Whereas، non-significant change was found in MWD related to increase the number of years service at first depth.

Cropping practices have considerable effects on soil physical properties by influencing soil structure. The aim of this study was to investigate the effects of two soil textures، namely، clay loam (CL) and sandy loam (SL)، and two crops، namely، alfalfa (A) and wheat (W) managements on soil structure stability. Two structural stability indexes of mean weight diameter (MWD) and tensile strength (Y) were determined at air-dry and 500 kPa matric suction conditions at three depths (0-10، 10-20، and 20-30 cm). Soil texture and crop managements'' combination affected MWD and Y in the order of CL-A> CL-W> SL-A> SL-W at both moisture conditions. MWD decreased with depth due to diminishing the soil organic matter، whereas Y increased with depth as a result of reduced severity of wetting and drying cycles. The soil organic matter content showed the highest impact on aggregate stability indexes followed by clay and calcium carbonate content. The highest R2 obtained for the relation between Y and the intrinsic soil properties was at air-dry condition، whereas for Y and MWD it was found at matric suction of 500 kPa. Our results indicate that the considered indexes are suitable for investigating the effects of soil intrinsic properties and agricultural managements on soil structural stability.

Applying of intensive cultivation especially in marginal and sensitive regions, after conversion of rangelands to cropland farms, commonly causes reduction in soil quality, and thus an increase in soil degradation, erosion and runoff. This study was conducted to evaluate the land use change effects on some soil physical and chemical properties such as mean weight diameter (MWD), soil organic matter (SOM), bulk density (BD) and saturated electrical conductivity (ECe). For the experiment, soil samples were collected from 8 regions (rangeland and cultivated range) from west and southwest of Isfahan. Samples were taken from two soil layers 0-15 and 15-30 cm. Results showed that after conversion of range to cultivated lands, in some regions, SOM content was increased about 39% but in some regions decreased about 26%. This is due to the initial conditions of the regions. The ECe also increased by 41% due to this conversion. However, no changes were observed to the MWD, BD and pH in different treatments. Although there were little change to the physical and chemical properties of soil as a result of this conversion, those properties which were changed, could have a degradation effect and lower the soil quality.

Tillage is one of the important managing factors that can destroy or improve soil structure. Soil structure is affected by the machines and shape of the wheels. Field experiments were conducted at Hamadan Agricultural Research Station on a coarse loamy mixed mesic Calcixerolic Xerocrepts soil to measure and evaluate the effects of tillage and wheel-induced compaction on selected soil physical properties. Treatments included tillage methods (Moldboard Plow and Chisel Plow, (MP, CP)) performed using three customary tractors in Iran [John Deer (J), Romany (R) and Massey Ferguson ( MF) ]. Traffic zone and non traffic zone were other treatments. A split-plot design with three replications was used in a completely randomized arrangement of treatments. Soil samples were taken at the end of wheat growth season in traffic and non- traffic zone and from four layers and compared for bulk density (BD), cone index (CI), and mean weight diameter (MWD). The influence of both tillage methods on BD in most soil depths was not significant, meanwhile, BD was higher in the deeper layers. Wheel traffic did not affect BD significantly, but its effect decreased by increasing the depth. Commonly, conservation tillage increased structural stability as evaluated by MWD. Cone index illustrated the same trend as for BD, with some variation because of it higher sensitivity, so it was significantly was increased in CP rather than in MP for the traffic zone. Such a difference was not observed in non-traffic zone. The CI was also significantly increased in traffic zone compared with non-traffic zone. J significantly increased CI in two first layer in comparing with MF, but there was not significant difference between J and R. The MWD was increased by chisel plow in non-traffic zone and this increment was significant in fourth soil layer (22.5- 30 cm). Wheel traffic caused the increase of MWD in the second layer and significant difference was not observed in other layers. Overall, R caused less destruction in soil structure and tillage methods changed some of soil physical properties.

The increased potential for soil erosion and compaction due to continuous row crop production and intensive tillage is causing some concern and has led to the consideration of reduced tillage techniques as part of the solution. The objective of this study was to investigate the short-term (one-year) influences of different management practices on the physical properties of a sandy loam soil under corn crop. Treatments were the combinations of three tillage systems (no-till, NT chisel plow, CP and moldboard plow, MP) and three composted cattle manure rates [0, 30 and 60 ton (dry weight) ha-1]. The experiment was carried out in a split-plot design. Three replicates of the treatments were applied in a randomized block design. Saturated hydraulic conductivity (Ks), total porosity (TP), macro-porosity (Macro-P), micro-porosity (Micro-P) of soil and mean weight diameter (MWD) of aggregates, were measured to a depth of 22.5 cm when 100 percent of the tassels appeared. Tillage and manure combination had significant effects on Log[ Ks], TP, Macro-P and Micro-P. The MP system increased pore space and continuity due to complete inversion and loosening, and as a result Ks, TP, Macro-P and Micro-P were higher than NT system. Higher Macro-P observed for CP might have caused higher Ks versus MP. Reduced tillage systems increased MWD and the increment of manure caused an increase in MWD over all tillage treatments. The results indicate short-term positive effects of manure application on soil pore size characteristics and aggregate stability under moldboard and chisel plowings in the region.