جستجوی مقالات مرتبط با کلیدواژه « پایداری خاکدانه » در نشریات گروه « آب و خاک »

Organic matter is one of the important indicators of soil quality. Organic matter increases water retention in the soil and helps to transport water and air in the soil. Organic matter increases crop growth and provides nutrients needed by plants and soil microorganisms. The amount of soil organic matter in nature depends on factors such as climate, soil properties, and agricultural management, especially in the plowing stage. This is although in many cultivated and undisturbed soils, the amount of soil organic matter reaches a constant value after some time and becomes balanced.On the other hand, most regions of Iran the arid and semi-arid and have low organic matter. The chemical composition of organic matter is approximately 50% of carbon, 5.0 % of nitrogen, 0.5% of phosphorus, 0.5% of sulfur, 39% of oxygen, and 5.0% of hydrogen, and these values change from one soil to another. The management of compost and plant waste is one of the most essential aspects of soil fertility management in the direction of sustainable agriculture. The research results showed that organic matter and carbohydrates are two factors related to the stability of soil structure. Considering the role and effect of using organic fertilizers (from animal sources and urban waste compost) on the physical characteristics of the soil, it is necessary to improve the productivity of soil and water, changes in the physical characteristics of the soil in different crop management (rotation) in fixed plots and in several years to be reviewed and evaluated consecutively.

This research has been done to investigate the effect of applying organic manure from animal sources and urban waste compost in different and conventional crop rotations in fixed plots and also to investigate the changes in the physical characteristics of the soil due to the application of the following treatments in Alborz Province (at the research station of the Soil and Water Research Institute, Karaj) was implemented from November 2016. After planting wheat in 2016 and harvesting it in 2017, the land alternated with fallow. Wheat was planted again in the fall of 1997 and corn was planted in July 1998. In the fall of 1998, wheat was planted again and then the land was alternated with fallow. This research was conducted in the form of randomized complete blocks in five treatments and three replications in plots with an area of 200 square meters. The treatments include 1- no planting (T1), 2- control without fertilizer use (T2), 3- application of nitrogen, phosphorus, and potassium chemical fertilizers based on soil test (T3), 4- annual application of 20 ton/h of animal manure (T4) and annual application 20 ton/h of compost (T5). By taking soil samples from the surface layer, the physical characteristics of the soil, including field capacity, permanent wilting point, bulk density, final infiltration of soil, and aggregate stability of soil were measured in different treatments. Soil physical characteristics were measured after harvesting each product from a depth of 0-30 cm in three replicates. By removing the soil surface layer, the aggregate stability was determined by the wet sieve method.

Treatments T1, T2, and T3 did not show significant changes in field capacity. The mean values of the field capacity of these treatments T1, T2, and T3 are about 17.8% and the treatment using animal manure (18.1%) and compost (18.3%) increases the field capacity by about 1.0 and 2.0 %, respectively, compared to the average treatments without the use of organic fertilizers. The values of bulk density changes in the treatments for the desired periods are not significant and it indicates that there is no specific trend in each period due to the changes in soil surface conditions for the treatments. The values of changes in the soil aggregate stability values have become significant only in the treatments of organic fertilizer consumption (from animal sources and compost) in the desired periods. The soil aggregate stability index in the treatment of using compost and manure increased by 27 and 18%, respectively, compared to the average of treatments without fertilizer use (1.1 mm), which indicates the role of organic fertilizer use in increasing the aggregate stability. The average final infiltration rate in the treatments without using fertilizer is about 28.1 mm h-1 and the average rate of final infiltration in the treatments using manure and compost is about 32.7 and 33.3 mm h-1, respectively. The average rate of final infiltration in the treatments using manure and compost has increased by about 16 and 19%, respectively, compared to the average of other treatments.

According to the obtained results and the changes in the physical characteristics of the soil affected by the use of manure and compost in the cultivation periods, the role of the use of these materials in improving the physical characteristics of the soil is generally evident. The average bulk density of treatments T1 to T5 was equal to 1.47, 1.52, 1.54, 1.54, and 1.54 g cm-³, respectively, indicating a relative increase in bulk density in organic fertilizer treatments. The soil aggregate stability index in the treatment of using compost and manure increased by 27 and 18%, respectively, compared to the average of treatments without fertilizer use, which indicates the role of organic fertilizer use in increasing the aggregate stability. The average final infiltration rate in manure and compost treatments has increased by about 16 and 19%, respectively, compared to the average of other treatments, which indicates the effect of manure and compost application in increasing the final soil infiltration rate. Because for each crop rotation, the soil is subjected to tillage operations, therefore destruction of the surface layer of the soil (with more organic matter) and as a result intensifying the activity of microorganisms, from the effect of organic matter on the characteristics, the physical properties of the soil are reduced and it even causes that no special trend can be seen in the physical characteristics of the soil during the cultivation periods. Therefore, it is necessary to use a set of management strategies to improve the amount of organic matter or the physical characteristics of the soil.

The surface seal formation can have destructive agricultural, hydrological and environmental effects. Seal formation is a complex mechanism that controlled by a wide range of factors such as soil properties, rainfall characteristics, and flow conditions. The present research was conduct in order to identify an efficient index to determine the sensitivity of soil to the seal formation in the soil of Kowar plain region of Fars province.

In the present study, according to the area of the region, 160 sampling points selected, then according to the characteristics of the studied area and type of land use, to achieve the goals of the research, first, the land use, geology and topography maps of the area is prepared and by doing several times of field work in different seasons of the year, the topographies and shapes in the maps and pictures were adapted to the environmental conditions. To carry out this research, 80 composite soil samples (0-20 cm) were prepared from the Kovar plain of Fars province. Then the parameters of soil particle size distribution, mass moisture, organic matter, electrical conductivity and pH of saturated mud extract measured. Then the parameters of soil particles size distribution, volume wetness, organic matter, electrical conductivity and pH of saturated mud extract, measured. Also, mean weight diameter(MWD), geometric mean diameter(GMD), calcium carbonate equivalent, fractal dimensions, saturation percentage, sodium, calcium, magnesium, sodium absorption ratio (SAR), saturated hydraulic conductivity (Ks) and bulk density were determined. Assessing the sensitivity of the soil to the surface seal formation by comparing the regression equations of seven different indices, including the soil structural stability index (SSI), crusting index (CI), water aggregate stability (WAS), crusting susceptibility index (CSI), consistency index (C5 - C10), penetration resistance (PR) and relative sealing index (RSI) carried out in data preprocessing, Descriptive statistics of variables such as mean, maximum, minimum and variance, data distribution diagram and data distribution obtained using Minitab- 19 software. In addition, in case of remote data or mistakes in entering the data, appropriate measures taken and a table of descriptive information was prepared. The normality of the frequency distribution of these features evaluated using the significance test of skewness. To explain the ability of indicators and statistics in seal formation, First, linear correlation between variables determined by SPSS-22 software and by using Pearson's correlation coefficient (r), the correlation relationship between the indices and early characteristics of the soil was obtained and for data analysis, Pearson's correlation method and ridge multiple linear regression were used by stepwise backward method and using Statistica, SPSS-26 and Minitab-19 software.

In terms of the soil structural stability index, the studied area was in the danger range of aggregate destruction, which can considered relevant to the high percentage of silt in the region. The sodium surface absorption ratio of the majority of soil samples in the study area, had a non-sodium rating. 95% of the samples with agricultural land use in terms of organic matter were located in the weak to medium with structure and structure stability group. The majority of samples had more than 20% clay. Most of the measured variables had a low coefficient of variation and in terms of data distribution and dispersion, had a relatively favorable situation. Clay was the common variable in five regression equations of the indices, which refers to the importance and dual role of clay in the aggregates stability and reducing the sensitivity to compaction. The relatively low value of the standard deviation in the soil structural stability index indicated the greater accuracy of this model in estimating the coefficients. In the present study, the best-fitted regression model, to describe the sensitivity of the soil to the surface seal formation, compared to other models, belong to the soil structural stability and crusting indices.

Based on the results obtained, the soil aggregate stability index with the modified coefficient of explanation R2=0.92 had a high capability in predicting the sensitivity of the soil to the seal formation and is the most effective index in expressing the changes in soil aggregate stability and the surface sealing. The results of the data analysis expressing the extreme limitation class of the mean weight diameter was in the soil of the region.

Soil erosion in upstream areas has an important role in sediment entry to dams. Sediment accumulation result in decreases of dam service life, environmental problems, and acceleration of floods. In addition to climate, topography, vegetation cover and land management, soil erosion amount depends on soil characteristics and its erodibility.  In this research, soil erodibility factor and its special distribution was assessed by using of various pedotransfer functions including KUSLE, KEPIC and KDg in a part of Aliabad watershed of Roodbar, located at upstream of Sefidrood dam. The soil samples were collected from 0-10 cm depth and size distribution of soil primary particles, organic carbon content, and aggregates stability were measured. The KUSLE was calculated in two ways without codes of soil structure and permeability, and with respective codes, named as KUSLEi, and KUSLEf, respectively. The results showed that studied soils generally had coarse texture, and KUSLEi was estimated low to moderate in range of 0.11 to 0.040 ton h MJ-1 mm-1. The least soil erodibility factor belongs to KDg, which was significantly lower than the soil erodibility factors calculated by other pedotransfer functions. All of the calculated erodibility factors had significant negative correlation with mean weight diameter of aggregates which KUSLEi and KDg showed the most and least correlation with MWD, respectively. All of the erodibility factors had moderate spatial dependence, however KUSLEi showed strong spatial dependence. Therfore, it generally can be concluded that zoning map of KUSLEi  generated via kriging can be a suitable indicator of the studied soils erodibility.

Changes in land quality factors were investigated according to the change in land use of two conventional cropping systems in Khuzestan (Dimcheh region, periodic cultivation system, sugarcane, forest, and deforesting in Zaras region). The results showed that by the change of forest land use, organic carbon from 0.93 to 0.55%, cation exchange capacity (CEC) from 19.6 to 13.3 cmol/kg, C/N from 7.4 to 3.8%, the mean weight diameter of aggregate (MWD) from 1.7 to 1.3%, and microbial respiration from 0.11 to 0.06 mg of CO2 /gr of soil per day decreased and in contrast, the dispersible clay from 4.6 to 19.3% increased. PCA analysis for the parameters showed that five factors justified more than 90% of the variance in the values of FC, PWP, AW, and AF. In the Dimcheh region, the average volumetric moisture content of FC from 31.3% to 27.3%, available water from 12.9% to 9.8%, dispersible clay from 56.1% to 12.3%, and bulk density reduced from 1.6 to 1.4%, organic carbon from 0.45 to 0.78%, C/N from 6.3 to 10.0%, microbial respiration from 0.01 to 0.04 mg of CO2 /gr soil per day and MWD of aggregates increased from 0.77 to 1.3 mm. Five factors including FC, AW, BD, DC, and OM explained more than 90% of the variance.

Although the use of fertilizer in poor soils is essential for increasing soil fertility and optimal growth of plant, but in recent years, chemical fertilizers have caused a lot of environmental damages. Thus, this study was conducted to investigate the effect of organic matter (Rice Husk) and mineral modifiers (Clinoptilolite Zeolite) on some soil properties. For this purpose, an experiment was performed in 2020 in the greenhouse faculty of the agricultural and natural resources of lorestan university. Test treatments include: 1- organic modifiers with three level (1, 3, 5 wool weight) and mineral modifiers with three level (3, 5, 10 wool weight) and control treatment 2- three different incubation time (30 as control, 60, 90 days). Before starting the proposed times, one month incubation was applied to the soil to adjust the soil material. The result showed that the use of both modifiers increased average weight of the aggregate diameter, porosity, weight moisture, electrical conductivity, total nitrogen, acidity, carbon ratio to nitrogen and microbial respiration compared to the control. The average weight of aggregate diameter increased by 26.7% compared to the control. But, the amount of bulk density and the hydrophobicity of the samples were decreased as compared to the control treatment. 10% weight of zeolite and 3% weight of rice shell treatment reduced hydrophobicity by about 37.8% compared to the control. Over time, the amount of bulk density, porosity, electrical conductivity, organic carbon, total nitrogen and microbial respiration showed a reduction trend, but the soil acidity and carbon ratio to nitrogen had an increasing trend. The carbon/nitrogen ratio during the incubation period of 60 and 90 days, significantly increased by 7.04 and 17.32% compared to the control. The result of data analysis showed that the effect of time on hydrophobic and average weight of the aggregate diameter and weight moisture was not significant.

Nowadays, vast areas of forests have been changed to farmlands, and the change in land use is one of the important factors reducing soil quality. The purpose of this research is to investigate the effect of land use change from forest and pasture to agriculture on some soil characteristics in Sarab Badia area (Kermanshah province). Sampling was done in 2018 from points with the same slope in the form of a nesting site. For this purpose, four areas near each other that have the same landscape and include 3 uses of forest, pasture, and agriculture and also two depths of 0-20 and 20-40 cm were considered. Composite samples were prepared from each depth. After transferring the samples to the laboratory, the important characteristics of the soil were measured based on standard methods. The results showed that among the physical characteristics of the soil, MWD was affected more than the other physical characteristics due to the change in land use, so that by changing the land use from forest to agriculture in the subsoil layer (20-40 cm), MWD decreased by 51.04%. Among the soil chemical properties, organic carbon and total nitrogen with 52.95% decrease in top layer of the soil (0-20 cm), had the most variability due to the change of land use from forest to pasture. The metabolic coefficient was sensitive to the change in land use from forest to agriculture, as its value decreased by 92.92% in the sub layer (20-40 cm). Characteristics such as; MWD, organic carbon, total nitrogen, and metabolic coefficient are highly sensitive to changes of management conditions at the field level, so these characteristics can be used to monitor soil quality.

Vegetation type changes some soil properties such as bulk density, nutrient absorption and soil organic carbon. Nutrition management of lawn plant is an important factor which affects soil properties in lower layers. The application of biofertilizers enhance the quality of soil and enhance the growth of lawn plant and in addition they are ecofriendly. The purpose of this study was to investigate the effect of urea and biofertilizer containing nitrogen-fixing bacteria (Pantoea agglomerans) on some quality characteristics of soil under lawn plant cultivation. This experiment was conducted in a completely randomized design in a greenhouse condition with three replications. Treatments include: 1-Control (Br), 2- lawn plant cultivation (Speedy Green) by conventional method (Gr), 3- lawn plant + urea (GrU), 4- lawn plant + bio-fertilizer containing Pantoea agglomerans (GrPA), and 5- lawn plant + Pantoea agglomerans + growth promoting bacteria (GrPP). The fresh weight of lawn plant was measured along with some soil properties. The results showed that lawn plant and application of biofertilizer containing Pantoea agglomerans shaped larger soil aggregates than control but they had no significant effect on aggregate stability. Biofertilizers and urea increased the growth of lawn plant. Cultivation of lawn plant increased soil organic carbon, total nitrogen, phosphorus and potassium uptake, but the effect of biofertilizers was not significant. The highest amount of total nitrogen and soil organic carbon observed in urea fertilizer treatment. In general, the use of biofertilizers in lawn plant cultivation is recommended.

Most of the soils in arid and semi-arid regions of Iran contain less than 1 % organic matter, which lead to reduce the quality of some physical properties of the soil, including decreasing the stability of aggregates, destruction the soil structure and reducing saturated hydraulic conductivity. Considering to the importance and role of organic matter and the presence of sodium and potassium in cattle manure and their destructive effects on soil structure, this research was performed to study the effect to investigate the effect cattle manure, sewage sludge and potassium chloride on soil structure stability indices.

In this research, the effects of cattle manure and municipal sewage sludge at three rates (0, 1 and 2 %) and potassium cation (potassium chloride) at three salinity levels (1, 3 and 5 dS/m) and 3 replications as a completely randomized design and factorial arrangement were studied to compare the treatments on soil structure stability indices. Treatments of 1 and 2 % (weight) cattle manure and sewage sludge were applied to soil and treated soil filled in pots (1 kg weight). To saturate the soil, all pots were irrigated with 300 ml of urban water. Then, irrigation was made by KCl solutions and 200 ml of KCl was added to each pot every week for the period of 8 weeks. After then, soil structural stability indices including normalized stability index (NSI), geometric mean diameter of wet aggregates (GMD), and percentage of aggregate destruction (PAD) were measured. The statistical analysis of data was made by JMP8 software and comparison of means based on LSD test at P < 0.001 was performed.

the results of structural stability showed that sewage sludge treatment had a positive effect on aggregate stability, percentage of aggregate destruction and geometric mean diameter of wet aggregates, while manure application due to high concentration of sodium and potassium and their destructive effects on aggregate stability had the negative effect on most structural stability, except for the normalized stability index. In general, geometric mean diameter of wet aggregates in treatment with no organic matter and salinity level of 3 dS/m was the lowest value and it showed the highest value in 1 % of sewage sludge and salinity level of 3 dS/m. Also, amounts of normalized stability index were the highest and lowest values in salinity of 1 dS/m + 1 % of manure, and salinity of 3 dS/m + no organic matter, respectively. Percentage of aggregate destruction significantly decreased at salinity levels less than 3 dS/m when organic matter increased, while it was not significantly changed at salinity of 5 dS/m due to increment of potassium and its destructive effect on soil structure.

Considering the positive effect of organic matter on stability of aggregates in short term, and the cost effectiveness of sewage sludge, it is suggested that the application the sewage sludge on soil structure indices in agricultural lands will be studied during several years.

This research was conducted to evaluate the effect of land use changes on the land quality under deforestation in semi-arid regions. Soil quality of the top layer (0-15 cm) was compared for two land uses. The results show that the organic matter (OM), aggregate stability (AS) and dispersible clay (DC) were changed from 1.19, 2.22, and 2.4% in oak forest to 0.67, 2.08, and 22.8% in deforestation area, due to land use change. These results showed a severe decrease in soil quality due to deforestation. Aggregate stability was decreased and dispersible clay was increased due to deforestration. In addition, the canopy cover and soil organic matter were reduced. With increasing the DC, it was increased the soil surface crust and accelerate the splash erosion. Bulk density increased, since the OM decreased. Also, the percentages of gravel, sand, coarse and fine silt changed from 6.3, 56, 12.6, and 5.4% to 35.6, 64.3, 14.6, and 2.5%, respectively, due to deforestration. Direct sunlight and higher soil heat, especially in hot seasons, accelerated the volatilization of soil nitrogen and despite the addition of nitrogen fertilizers to the farmland, the amount of nitrogen in the farmland decreased. Data analysis by PCA method showed that the different factors affect the varimax due to land use changes. Deforestation was the main factor changing the soil characteristics and seriously reducing the land quality. Land use change not only does not benefit the production of more food, but also destroys the quality of the land, causing floods and increasing sediment from these areas.

Nano-particles can be used for the soil conservation practices due to high specific area and high efficiency in low volume. Nano-particles cannot perform well individually similar to the lime. So, in this study nano-SiO2 in combination of lime was used for slope stabilization.

In this study, control treatment (without nano-SiO2 and lime) and different combinations of nano-SiO2 and lime including 0.05% nano + 2% lime, 0.1% nano + 4% lime, 0.6% nano + 6% lime, 0.4% nano + 8% lime, 0.8% nano + 10% lime, 2% lime, 6% lime, 10% lime, 0.05% nano and 0.1% nano were sprayed on 0.25 m-2 plots. Treatments were conducted in three replications on cutslopes with gradient of 100% in Bahramnia forest roads. After the curing times of 7 and 28 days, soil samples were collected to measure the stability indices of soil structure using wet and dry sieving.

In this study, there wasn’t significant trend in aggregate stability indices versus increasing the concentrations of lime and nano-SiO2. Maximum values of MWDwet, MWDdry and AS was detected for treatment 3 (0.6% nano + 6% lime) in curing time of 28 days which was 66.24%, 51.01% and 72.98% higher as compared with control. Minimum rate of AS was observed for treatment 8 (10% lime) which was 82.36% lower as compared with control. All of the treatments cause to decrease DI except for treatments 1 (0.05% nano) and 8. Minimum DI was observed for treatment 3, which was 257.61% higher than control.In this study, there wasn’t significant trend in aggregate stability indices versus increasing the concentrations of lime and nano-SiO2. Maximum values of MWDwet, MWDdry and AS was detected for treatment 3 (0.6% nano + 6% lime) in curing time of 28 days which was 66.24%, 51.01% and 72.98% higher as compared with control. Minimum rate of AS was observed for treatment 8 (10% lime) which was 82.36% lower as compared with control. All of the treatments cause to decrease DI except for treatments 1 (0.05% nano) and 8. Minimum DI was observed for treatment 3, which was 257.61% higher than control.

Results of this study showed the positive effect of mixed treatment of lime and nano-SiO2 on stability of soil structure. 0.6% nano+6% lime had better influence on reduction of aggregate destruction percentage.Results of this study showed the positive effect of mixed treatment of lime and nano-SiO2 on stability of soil structure. 0.6% nano+6% lime had better influence on reduction of aggregate destruction percentage.

Wind erosion is one of the most important environmental issues in the world. This phenomenon could have hazardous effect on weather, water quality and human health. In recent years, the use of mulch has been considered for controlling wind erosion and soil stabilization. The aim of this study was to use Montmorillonite Nano clay, Polyvinyl Acetate polymer and wheat straw biochar as a natural mulch for controlling wind erosion and soil stabilization. A factorial experiment was conducted in a completely randomized design with three replications. The factors included (1) mulch (three types), (2) mulch concentration (Nanoclay: 0, 16 and 32, Polyvinyl Acetate polymer: 0, 8, and 16 and biochar: 0, 65 and 200 g/m2) and (3) time duration (21, 42 and 63 days). Two soil samples (sandy and loamy sand) were collected from the dust source of southeast of Ahvaz (center Number.4). Trays with a 500×300×50 mm were filled by the soils. Then, the emulsion of Nanoclay, and Polyvinyl Acetate were sprayed uniformly on the soil surface. The biochar also was uniformly mixed with the soils. The trays were placed on wind tunnel channel and wind erosion test was performed at a speed of 20 m/s for 5 minutes. Then, aggregate stability (MWD), penetration resistance (PR), shear strength (SS) and their changes were measured at all duration times. The amount of soil loss at first duration time in nanoclay, polymer and biochar treatments were decreased in sandy soil 98%, 97% and 43.65%, and in loamy sand soil 97%, 95% and 58%, respectively as compared to the control treatment. Maximum MWD, PR and SS was obtained in the nanoclay treatment. In general, the results showed that the use of nanoclay, polymer and biochar materials significantly reduced wind erosion at different duration times, compared to the control treatment.

Soil saturated hydraulic conductivity is one of the most important physical characteristics of soils that affects water movement in soil. . The aim of this study was to determine the most important parameters in prediction and modeling of saturated hydraulic conductivity from conveniently available parameters, using the decision tree and error estimator cross validation and re- substitution. In this study, 72 soil samples with six different textures were collected from the village of Morgmalek and Shahrekord District. Conveniently available soil properties were introduced into software in 4 scenarios (the first scenario: pH, EC, % sand, % clay, OM%, CaCO3, mean weight diameter of dry aggregate (MWD dry), mean weight diameter of wet aggregate (MWD wet), BD; the second scenario: CaCO3 , OM%, % sand, % clay, BD, % gravel, electrical resistivity, dielectric constant, root penetration resistivity; the third scenario: pH, EC, Geometric mean diameter )dg(, Geometric standard  deviation )σg(, OM%, CaCO3, mean weight diameter of dry aggregate (MWD dry), mean weight diameter of wet aggregate (MWD wet), BD; and the fourth scenario: CaCO3, OM%, dg, σg BD, % gravel, electrical resistivity, dielectric constant, root penetration resistivity). Saturated hydraulic conductivity was measured with single ring. The results showed that moisture followed by structural features such as (σg) in the first scenario, and OM and BD in the second scenario, BD and MWD in the third scenario, and OM and BD in the fourth scenario were the most important parameter affecting saturated hydraulic conductivity. Correlation between predicted data by decision tree and measured data in the second and fourth scenarios were 0.83 and 0.82, respectively, and 0.79 in the first and third scenarios. All four scenarios were successful in modeling with respect to error rate and %RMSE. However, the %RMSE in the second and fourth scenarios was lower and the correlation coefficient was higher than the other two scenarios. The RMSE values in the four scenarios were 0.79, 0.83, 0.79, and 0.82, respectively.

Changing land use is one of the most important human interactions in natural ecosystems that affect ecosystem processes, especially soils. In the present study, the effects of forest (natural forest and oak plantation) and non-forest (garden, rangeland and agriculture) land sues on the variability of soil quality indices and carbon dioxide emission dynamics have been considered. In each of the proposed land uses, 16 soil samples (0-10 cm depth) were collected and transferred to the laboratory. According to the results, the highest amounts of soil organic matter were allocated to forest habitats and the highest bulk density was belonged to rangeland and agricultural areas. However, the variation of soil particle density among the various land uses was not significant, but the highest soil porosity was found under oak plantation. The natural forest has the most stable aggregates, and following deforestation and the land use change, their stability was significantly reduced. The highest amount of sand was belonged to rangelands and the highest amount of clay was allocated to natural forest, while the content of silt did not show significant differences among different land uses. The highest amount of coarse root biomass was observed in the natural forest and oak plantation, while the fine root biomass in the natural forest was the highest amount. Greater amounts of soil moisture content were found in the forest habitats (especially in winter and autumn), while the highest soil temperature was assigned to agriculture and rangeland areas (especially in summer). The emission of carbon dioxide from the soil was highest during the summer, under the oak plantation. According to the PCA output, the amount of soil organic matter, moisture content and porosity in the oak plantation have had an important role in increasing carbon dioxide emission from the soil of this type of land use compared to other sites. The results of this study confirm the protection of natural forests in order to increase the soil quality characteristics and health.

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.

There are controversial reports about the physical, chemical and biological properties of biofilms modified soils. Although there is no report on comparing the effects of Arabic gum on different soil textures, reports of different biopolymer effects as potential analogues of biofilms in different soils are contradictory. We assume that the soil texture class, as its intrinsic property, may affect the effects of various soil amendment. Therefore, in order to evaluate the performance of Arabic gum in two different soil texture classes, the present study was conducted to investigate the effects of Arabic gum as a similar to biofilm (extracellular polysaccharides) on several soil characteristics in loam and clay loam soils. For this study, two different soil types including clay loam and loam texture classes, a factorial experiment in a completely randomized design (CRD) were carried out with two factors including soil type and different amounts of Arabic gum (0, 5 and 10 g per kg of soil) and three replications and two observations. Then, after the incubation stage of the treated soils, the disturbed and undisturbed soil samples were collected from the pots and prepared for measuring the bulk density, soil moisture content, hydraulic conductivity, saturated water content, soil aggregate stability (WAS), mean weight of aggregate diameter (MWD), mass fractal of aggregates, soil acidity (pH), organic carbon content, cation exchange capacity, and microbial respiration. The results showed that the effect of Arabic gum on saturated moisture content, soil bulk density, saturated hydraulic conductivity, and microbial activity in loam soil was lower than that of clay loam. The use of Arabic gum in clay loam soil increased by approximately 12, 18 and 317 percent, respectively, in the saturated volumetric and gravimetric water contents and the saturated hydraulic conductivity. While having very little effect on these properties in the loam soils. The use of Arabic gum also reduced the bulk density of clay loam soil, while no changes were found in the loam soils. Also, in treated soils, Arabic gum showed positive changes in soil organic carbon and the stability, size, and mass fraction dimension of aggregates, being independent from soil type. Considering that less variation was observed in the properties of loam texture (which is courser than clay loam soils), we recommend the use of a higher amount of Arabic gum (greater than 10 g kg-1) in coarse texture soils or its use with residues of organic matter to have significant effects on these soils.

Soil structure stability refers to the ability of a soil to hold up the solid particle arrangement and the spaces among them when face to different stresses. According to the important role of organic matters in formation and stability of soil aggregates; it appears that the different fractions of them may also have significant effects on soil aggregate stability. Furthermore, separating the different fractions of organic matter helps the identification of the sensitive and sustainable parts and their locations in aggregate structure. The purpose of this study is to evaluate the effect of different fractions of organic matters on the soil macro (>0.25 mm) and micro (
Fifteen soil samples were taken from the surface (0-10 cm) using a supervised random method in three different land uses including forest, range, and agricultural lands (totally, 45 points) in Rabor region, Kerman province. After air-drying the samples and passing them through a 4 mm sieve, mean weight diameter (MWD) of soil aggregates was measured using the wet sieve method for the macro and micro aggregates. Then, different fractionations of organic matters in the macro and micro aggregates were determined using the density method. Finally, the amount of organic carbon in different fractions of organic materials and also the total amount of soil organic carbon were identified using the Walkley-Black method and then the percentage of total organic matter existed in each fraction was calculated by considering the weight and percentage of organic matter in each fraction,. Afterward, the organic matter data were used as input to the artificial neural network model. Besides, the regression relationships among the variables and soil aggregate stability were investigated.
The results showed that the free light fraction of organic matter (F1) in the macro-aggregates was greater than in the micro-aggregates. Also, the F1-amount in the forest was greater than the other two investigated land uses due to the higher organic matter content. The amounts of occluded light fraction of organic matter (F2) in the agricultural lands were lower than other land uses which might be due to tillage operation, soil aggregate destruction, and release of the trapped organic matter inside of them. The parts of organic matter which were associated with mineral fractions (F3) were allocated with the largest percentage of the total soil organic matter as compared to the other two fractions. The amount of last mentioned fraction was higher in the micro-aggregates than the macro-aggregates in all three investigated land uses. Results also revealed that the linear regression was not able to identify the interrelationship between the studied variables and aggregates stability index. In contrast, the diagrams related to artificial neural network model showed that all input variables to the model have influenced the MWD, although the important coefficients of the input variables were different.
Different fractions of soil organic matter were more sensitive to the land use type than the total organic matter. The macro and micro aggregate percentages were different depending to the land use type; however, the micro aggregates with greater organic matter contents were more stable against entered stresses than the macro aggregates. Artificial neural network model had more efficiency in estimating the soil aggregate stability than the linear regression method indicating that there is a non-linear relationship between different fractions of organic matter and MWD. By considering the accuracy and efficiency of artificial network model, it appears that this method can be used to determine the linear and non-linear relationship among different soil properties, with higher precision and lower cost and time.

Soil water repellency (SWR) is a soil characteristic that creates strong resistance to water penetration and decreases infiltration time from a few seconds to hours, days or weeks. The undesirable consequences of SWR have received interest from the scientific literature. However, the SWR has some beneficial aspects like increasing aggregate stability. Although several authors have reported the soil organic carbon as the origin of SWR but it seems only some parts of the soil organic carbon are hydrophobic and are involved in SWR. Thus, the aims of this study were: (a) to determine which soil organic carbon pools are linked with SWR, (b) to assess the impact of SWR on aggregate stability and (c) to determine which vegetative cover produce more hydrophobic organic compounds and contribute to SWR.
Soil samples were collected from the 0-5, 5-10 and 10-20 cm layers of the lands under different forest tree species including Populus caspica, Oak (Quercus castaneifolia), Alder (Alnus glutinosa), Bald cypress (Taxodium distichum), Loblolly pine (Pinus taeda) and Juniper (Juniperus polycarpos). The soil samples were analyzed for organic carbon content, pH, water repellency and aggregate stability (MWD) and were also separated to different organic matter pools based on particle size fractionation. The experimental variables were soil depth and kinds of vegetative cover and the data obtained from the soil samples were analyzed statistically by a two-way analysis of variance (ANOVA) using a factorial experiment with completely randomized design and 30 replications. Also Pearson linear correlation was used to indicate the relationships between the measure characteristics.
The vegetative covers and soil depths had significant impacts on SWR and the measured soil properties. The highest water drop penetration time (WDPT) was measured for the surface soil layer (0-5 cm). About 13.33 and 3.33 % (n=30) of the samples collected from the soil surface under P. taeda and T. distichum had the more than one hour WDPT (extremely repellent class). In contrast, the lowest SWR classes were mostly observed under the vegetative covers of P. caspica, Q. castaneifolia and A. glutinosa which were broadleaves tree species. The water repellency decreased with soil depth and 82.22% of the soil samples collected from the 10-20 cm layer of all tree species (n=180) determined as wettable soil (WDPT The strong correlation between SWR and the organic carbon content of the sand fraction indicates that this fraction contains organic compounds that contribute to SWR. Increase in soil pH and extent of decomposition of soil organic matter, however changes the solubility of soil organic matter and decrease SWR. As the soil aggregation depends on the total soil organic carbon content, the stability of aggregates is affected by hydrophobic fraction of soil organic carbon. Despite the extreme SWR in coniferous, Considering the undesirable quality of soil under coniferous trees such as low pH, MWD and organic carbon content, it is recommended to use discretion in the selection of these species for afforestation and reforestation projects.

Degradation of forest lands by fire is one of the major bioenvironmental problems in northern Iran that significantly changes the vegetation attributes and visible features at the soil surface and therefore, affects aggregate stability against erosive forces. The complete information from aggregate stability at the micro scale and type of features related to soil erosion at the plot and watershed scales leads to a perfect judgment about erosion risk in an area. The objective of this study was to evaluate the effect of fire on aggregate stability, surface visible features and vegetation cover at the micro, plot and watershed scales in some parts of forest lands in west northern zone of the Guilan province.
Material and In parcels separated in 15 fire-affected forests and 15 unburned forests adjacent to the fire-affected forests, in five geomorphological units, aggregate stability indices at the micro scale and microtopographic erosion features and litter percentage at the plot scale were measured. In addition, some vegetation attributes, drainage density index, and the presence of some morphodynamics features of soil erosion were evaluated at the watershed scale.
The results of analysis of variance showed that all aggregate stability indices as well as litter percentage and drainage density had significant differences within subjects (within burned and unburned forests). Among studied parameters, only litter percentage showed significant differences between subjects (geomorphological units). Results also revealed that the time reversibility for aggregate stability indices and drainage density to condition before fire was about four to five years. Also, increasing the fire severity from low to high and changing of fire type from surface to canopy had the most effect on mean weight diameter of aggregates. Assessment of microtopographical erosion features at the plot scale revealed that some of them had variations in burned sites compared with the control sites. At the watershed scale, the rills, gullies and landslides were more abundant in the burned sites than the unburned sites. The correlation coefficients between measured properties related to different scales showed that there were significant correlations between some of them at the various scales.
The soil aggregate stability indices are very useful to evaluate the power of formation of many microtopographic and morphodynamics features of soil erosion at the plot and watershed scales. The results of this study can be used for assessment of soil erosion risk in forest lands and can be useful for management of woodland.

Aggregate, as the basic unit of soil structure,represents a collection of primary particles which their adherence to each other is more than their connection to environ soilparticles. Aggregate stability is a highly complex parameter influencing a wide range of soil properties, including carbon stabilization, soil porosity, water infiltration, aeration, compatibility, water retention, hydraulic conductivity andresistance to erosion by water and overland flows. Maintaining high stability of soil aggregate is essential for preserving soil productivity, minimizing soil erosion and degradation and thus minimizing environmental pollution as well. Nevertheless, aggregate stability is described as one of the soil properties that can serve as an indicator of soil quality.The main purpose of this study is to determine the most important component of soil aggregate (macro and/ormicro) in estimating the soil structural stability in the Rabor region, Kerman province, using geostatistical method.
Ninetysurface soil samples (0 to 10 cm) were taken on a 200 m square sampling grid in the study area for the geostatistical studies.After air drying the soil samples and passing them through a 4 mm sieve, the percentage of aggregates belong tothree parts of total, macro, and micro classes and aggregate staility were calculated in both dry and wet conditions.Some stability indices were calculated and their spatial variabilities were investigated using two variography and estimation stages methods. Finally, the kriged map of each aggregate stability indicator was produced. To determine the compatibility of kriged maps of the soil aggregates stability indices calculated for the macro and micro aggregates with aggregates stability index (i.e., AS index) calculated forthe total aggregates, the overall accuracy related to each aggregate component (i.e., macro and micro) was calculatedafter creating an error matrix.
The results showed that total aggregate stability in the dry condition and macro aggregate stability in the wet condition had the lowest and highest coefficients of variability,respectively. The highest percentage of total aggregate stability (i.e., 89.90 %)was observed in the north and southeast positions of the study areain the dryconditionwhich had the highest amount of organic matter(i.e., 2.30 %). Also, the variograms of all investigated variables were exponentially and their ranges were varied between 380 to 450 m. Although the obtainedranges were different, a sampling distance more or less equal to 420 m is reasonable to study the most of the variables in the area. This can be a good indicator to decrease the sampling tasks for monitoring of these parameters in future.An overall look at the obtained root mean square standardized error (RMSSE) values indicated a high correlation between the measured and estimated values of all investigatedvariables (except for macro aggregate stability in the wet condition). However, all variables had a strong spatial correlation class. The percentage of overall accuracy obtained from crossing the total and macro aggregate kriged maps in the dry condition (i.e., 51.75 %), was more than its percentage for similar maps in the wet condition (i.e., 32.17 %). In return, the percentage of overall accuracy obtained from crossing the total and micro aggregate kriged maps in the wet condition (i.e., 17.31 %)was greater than its percentage for the mentioned maps in the dry condition (i.e., 10.93 %). Because of macro aggregate sensitivities to the amount of pressure imposed on them (as in the wet sieving method, the aggregates are under pressure caused by water energyin addition to tensions related to mechanical motion of sieving), the conformities of above two mentioned maps were less than those in the dry sieving method.
In general, the soil aggregates stability depends strongly on the amount of pressure imposed on them. Besides, the study of spatial variability of macro and micro aggregate stabilities and relative effects of each on the soil structure stability can be useful for choosing proper land management activities in future studies. According to theeffect of aggregation on nutrient cycling, capture, storage and water movement, and also other soil characteristics affecting plant growth and sustainable agriculture on one hand, and the effect of organic matter on aggregation on the other hand, it can be concluded thatall human activities that have a role in reducing or removing organic matter from the soil (e.g., grazing, deforestation, and intensive cultivation etc.) may reduce soil aggregate stability and finally can jeopardize human life in a near future.

Amongst different habitats, fire is an ecological factor and determinant that affects many physico-chemical soil factors. In addition, among natural disturbances, fire plays an important role in plant diversity conservation and in some areas around the world, the presence of some plant species depends on natural fire. The extension of fire influences on soil is related to the fire severity. In fact, fire severity encompasses of two characteristics: extension and time of burning. On the other hand, fire extension and burning time are affected by humidity, air temperature, wind speed, topographical characteristics. Despite high frequency of fire in natural habitats and high level of fire effectiveness on soil parameters, study of fire impacts on soil characteristics were rarely reported in Iran. In addition, most previous studies were conducted in forest habitats, ignoring the severity of fire on soil.
In order to investigate the effect of fire severity on some soil physico-chemical characteristics, Yeylagh Dasht area (rangeland habitats) was selected in southern-east of national Golestan Park with three different plant covers, viz. grass, shrub and cushion. Many fires occurring have been reported in this park in each year. For the current study, we tried to select the habitats in which the fire was occurred at least one year before. A control area without burning with similar ecological parameters was also selected adjacent to the burnt area. in fact unburnt area was isolated by a road from burnt area, unable to extend the fire into unburnt area due to the road. Fire had been occurred in the burnt area in September, 2014. Soil samples with 15 replications in burnt area and 15 replications in unburnt were collected within a depth of 0-5 cm and then transported to the soil laboratory to measure some qualitative soil characteristics i.e. soil organic matter (SOM), particulate organic matter (POM), total nitrogen (TN) and aggregate stability (AS). All statistical analyses were done by R software. Before ANOVAs (one and two-ways) and unpaired t-test, we tested data for normal distribution by Shapiro-Wilk test and homogeneity of variance by Flinger Test.
The results of two-way ANOVA showed that the main effect of fire on soil was not significant while the main effect of fire severity and the interaction of fire and fire severity on SOM and POM were significant (Table 1). The results of one-way ANOVA showed that the content of SOM was significantly different between three different treatments in unburnt area (control area) while there were no significant differences between the three treatments (three fire severities) in burning areas. Therefore it can be discussed that the kind of vegetation (grassland, shrub or cushion) could affect SOM while the fire increased the spatial homogeneity of SOM. The same pattern of SOM was occurred for POM in burnt and unburnt areas. However, the results of unpaired t-test showed that POM was drastically decreased after high and intermediate fire severities. Aggregate stability and POM were significantly decreased in the intermediate and high severities of fire (cushion and shrub plant cover). Fire in the intermediate and high severities increased TN (Figure 1). We concluded that fire occurring by plants might be decreased POM and AS significantly. In addition, mineralization probable increased TN after burning. We also compared soil characteristics among three fire severities in burnt area and in unburnt area separately.
This study showed that the variation of soil characteristic was mainly affected by different fire severities. Therefore, we emphasized that fire severity should be considered in the studies of the impact of fire on soil in different habitats. Fire can decrease the spatial heterogeneity of soil parameters among different sites. We showed that soil POM is a characteristic more sensitive than total SOM in confronting with fire.