جستجوی مقالات مرتبط با کلیدواژه "ساختمان خاک" در نشریات گروه "آب و خاک"

Water erosion can be affected by land use change and soil degradation by agricultural activities. This study was conducted to investigate the effects of land use change in poor pastures on soil physical degradation and water erosion in semi-arid regions. Experiments were performed in 42 soil samples taken from seven areas covering the two land uses: poor pasture and rainfed agriculture, which have different soil textures (clay loam, silty clay loam, sandy clay loam, silt loam, loam, sandy loam, and sandy loam). The physical characteristics of soils were measured in the samples of both types of land use and its changes were expressed as physical degradation of the soil. The soil's susceptibility to water erosion was measured under simulated rainfall with 50 mm h-1 intensity for 60 min. The results showed that the land use change in pastures leads to the physical deterioration of soils; so bulk density, porosity, macropore, field capacity, saturated point, aggregate size, and aggregate stability were degraded with a rate of 28, 22, 41, 11, 5, 62, and 63 percentages. The structural characteristics of soil (aggregate size and stability) had the highest physical deterioration due to the land use change in the pastures. The change in land use change greatly increased the sensitivity of soils to water erosion. A significant relationship was found between the susceptibility of water erosion and the soil's physical degradation. The soils with coarser and more stable aggregates have higher physical degradation by the land use change and in consequence show more susceptibility to water erosion.

Many researchers have investigated the role of organic matter in the soil aggregation process, but each of them has used these characteristics for a limited area. In this research, the aim was to evaluate the effects in several climates and with two different types of organic fertilizers in different soil textures and in crop rotation for two years.

In order to investigate the effect of organic matter on the soil granulation process in this research in three types of soil texture and in 6 weight ranges of soil grain diameter including 75-105, 105-250, 250-500, 500-1000, 1000-2000 and 2000-4750 Micron, which has a relatively high comprehensiveness, including the smallest to the largest diameter of soil grains, was carried out under the influence of alternating years of cultivation (wheat and corn) on the weighted average of the diameter of soil grains in 11 regions of the country. Also, changes in the average weight of the diameter of the soil grains in the control state (before cultivation) and the first and second year of cultivation in wheat and corn plants were investigated. In this experiment, the effect of organic matter on the soil granulation process was investigated in 5 treatments: 10, 20 tons per hectare of animal manure, 10, 20 tons per hectare of compost and control in a factorial experiment in a completely randomized design.

The results indicate the predominant accumulation of clay in the range of 250-500 (40% by weight) and 500-1000 (30%) for clay loam texture, 105-250 (25% by weight) and 250-500 (30% by weight) for loam texture. and 105-250 (40% by weight) for the texture of sandy loam before the start of cultivation, this range is due to the completely effective and positive role of clay in increasing soil granulation, improving soil structure and consequently the stability of soil pores. The increase of organic fertilizers increased the weight average diameter of soil grains and caused the formation of soil grains with sizes of 250-500 and 500-1000 microns. The results of the effect of alternative crops of wheat and corn on the weight average values of the diameter of soil grains compared to before cultivation, especially in the first year of cultivation, showed that with the increase of organic fertilizers, the formation of soil grains with a diameter of 500-1000 microns increased and the percentage of abundance of soil grains with Diameter 105-250 and 250-1000 decreased. Also, the results showed that the improvement of soil granulation with the increase of organic fertilizers was the highest in soil with sandy loam texture and the lowest in soil with clay loam texture. Also, in different treatments of animal manure and compost in none of the diameters of soil grains and in any of No significant difference was observed between tissue classes. And the results indicate that the application of different treatments of organic fertilizers has the greatest effect on sandy loam soil compared to loam and clay loam soil.

Generally and according to the statistical results, the addition of organic matter improves the soil granulation process, and also the soil with sandy loam texture is the most effective for the increase of organic fertilizers

Adding organic matter to the soil is an important method to solve the problem of compaction and consequently penetration resistance and fertility reduction. Mushroom substrate compost (MSC) has many properties that are required for growing organic crops and environmental management. Considering that the ingredients of mushroom substrate compost (including heavy soil, light soil, root soil, wheat straw and stubble, limestone and chicken manure) are different from other types of organic materials, it is necessary to carry out new research to investigate its effect on the physico-chemical properties of the soil. Although different textures behave differently but, the effect of MSC on the penetration resistance and aggregates size distribution in different soils, has not been studied, so far. Therefore, the purpose of this study was to investigate the short-term effect of MSC on the penetration resistance, mean weight diameter of aggregates, aggregates size distribution and organic matter content in three soil types.

A factorial experiment was conducted in a completely randomized design with three replications. Factors consist Soil texture at three levels (sandy loam, loam and clay) was the first factor, and MSC at three levels (0, 3 and 6% W/W) was the second factor. After treatment of the soils, samples were then incubated for 120 days, and they were saturated and dried with urban water, regularly, once a month (saturated from above), during this period. At the end of the incubation period, disturbed and undisturbed soil samples were taken by 5 cm in diameter and 4.5 cm in height steal cylinders. The penetration resistance was measured by a micro-penetrometer on the core samples at the matric suction of 0.3 bar. Organic matter, mean weight diameter of aggregates and aggregates size distribution were measured.

The results showed that the use of 6% level mushroom substrate compost in the sandy loam soil caused a decrease in the penetration resistance compared to the level of 3% and the control, due to the interaction between the compounds in the compost and the creation of stable soil aggregates. Also, the results showed that highest amount of organic matter and mean weight diameter of aggregates at 6% level of MSC was found in loam texture. Also, the order of the mass of aggregates in classes 4-8 and 2-4 mm, was in loam> sandy loam> clay, with significant differences between the textures. Application of MSC at 3 and 6% levels in the loam texture significantly increased the mass of aggregates of 0.25 – 0.5 and 0.5-1 mm in comparison with control. These aggregates did not show significant differences in sandy loam and clay soils at different application levels of the MSC Organic matter, mean weight diameter of aggregates, mass of aggregates of 0.5 to 1, and 0.25 to 0.5 mm increased in the range of 27 to 66%, 16 to 34.5%, 4 to 117.5% and 4 to 170%, respectively, by increasing MSC application levels at different soils. Conclusion This compost is different from other modifiers and can have different effective mechanisms in different textures. The simultaneous addition of lime, clay and organic matter (through compost) to soils with different textures causes cation exchange reactions in the soil. Lime as one of the main additives that has the ability to improve the behavior of fine-grained soils has been noticed for a long time. In this way, in clay and loam soils, the interaction between lime and clay with organic matter plays an important role as soil accumulation factors by forming cationic bridges. The use of lime and gypsum directly improve soil resistance. Therefore, the use of mushroom substrate compost in agricultural lands is useful for improving the soil structure.

The use of agricultural and industrial wastes as a organic materials are increased. In order to evaluate of the effect of sawdust and nitrogen on soil quality indices under bean cultivation, an experiment was conducted on split plot with RCBD design with three replications. Sawdust in 4 levels 0, 5, 10 and 15 ton/ha as a main factor and nitrogen fertilizer in 3 levels 75, 150 and 225 kg/ha. and then mixed with soil. In the use of nitrogen,the maximum grain yield was 1302.8 kg/ha were obtained of 225 kg/ha of urea application. In traits of soil properties, sawdust in all traits and nitrogen fertilizer on some traits had meaningful effects. With increasing of sawdust, all of trait increased, but the increasing of traits with increasing of nitrogen showed some of traits. The investigating of rates of sawdust on MWDwet showed the difference between 5 and 10 ton/ha of sawdust was not significant, but by applying of 15 ton/ha difference and was significant. The maximum effect of MWDwet was 0.84 mm were obtained of 15 ton/ha of sawdust, in compared with 10 ton/ ha and control increasing was 100 and 265% respectively. This research indicates that sawdust as an organic conditioner and nitrogen fertilizer improved the quality of soil and the use of this treatments increased porosity, water holding capacity in FC and PWP points and organic carbon. Thus, sawdust can be used as a suitable organic fertilizer to improve the organic matter of soil and unsuitable condition of soil.

Land leveling is a conservation solution to create a uniform slope to integrate, facilitate irrigation and drainage of paddy lands. Despite the positive effects of land leveling, it destroys the physical properties of the soil. The purpose of this study was to investigate the impact of land leveling on the physical characteristics of the soil. This work compares traditional and leveled lands, Balagafsheh and Limuchah areas, which have been leveled for two and five years, respectively. A total of 80 samples were taken, 20 soil samples from each traditional and land leveled plot in the two areas at depth of 0-20 cm by a grid method with dimensions of 20 by 20 meters.  Mean comparison was performed using an independent t-test and SPSS software. The results of comparing the mean showed a significant increase in the percentage of clay, bulk density, penetration resistance in the leveled lands of Limuchah, but in Balagafsheh area, the opposite results were observed. In general, the results indicated changes due to land leveling, such as changes in particle size distribution, structure destruction, and soil compaction without proper management after the implementation of the project, and the reversibility of soil properties is not adjusted solely by relying on the role of the time factor.. Proper management practices such as growing cover crops and returning them to the soil, such as the Balagafsheh area, can exploit the benefits of the land consolidation plan and control the destructive effects of it.

Soil water content (SWC) is an important physical factor that plays an essential role in many processes such as infiltration and soil erosion. This study was conducted to investigate the effect of SWC on runoff and soil detachment from rills in coarse-grained soils in the semi-arid region. For this purpose, furrows with 6 m in length were installed in five rainfed farms with different slope steepness (6.1, 10.6, 14.8, 20.7 and 27.1%) treated with four moisture levels including air-dried (AD), between air-dried and field capacity (AD-FC), field capacity (FC) and saturation point (SP) in a completely randomized design witht three replications. Flow rate with a discharge of 2 L min-1 was used to investigate soil detachment from the farms. The soils were coarse texture (having 56-75% sand) and rocky (having 22-57%) with unstable structure and high infiltration rate. Based on the results, soil detachment decreased with increasing SWC in 6.1, 14.8 and 20.7 % slopes. The highest soil detachment rate (g m-2s-1) in these lands was observed in AD-FC (0.01), AD (0.306) and AD (0.0045), respectively. By increasing SWC, the continuity and stability of soil mass of furrow increased, and runoff occurred mostly as subsurface flow in the rills. Surface runoff as well as the soil particle detachment decreased in the rills. Therefore, in the semi-arid slopes with coarse-grained soil, soil detachment rate decreases with increasing SWC.

The drought crisis reveals the necessity of saving and optimal use of water in various sectors, especially in agriculture. One of the strategies to optimize use of water resources is the application of organic materials and natural (bio) and synthetic sorbents. The purpose of this study was to investigate the effect of polyvinyl acetate polymer, wheat straw biochar and cellulose hydrogel on the water retention capacity (at suctions 33, 100, 300, 500 and 1500 kPa), bulk density, aggregate stability and amount of organic carbon in the sandy soil. Therefore, a factorial experiment was conducted in a completely randomized design with three replications. A sandy soil was collected from the southeast Ahvaz. The factors included (1) amendment (Polyvinyl Acetate polymer, biochar and cellulose hydrogel of wheat straw), (2) amendment concentration (Polyvinyl Acetate polymer: 5 and 10 g/L, biochar and cellulose hydrogel: 1 and 3 % w/w) and (3) time duration (21, 42, 63 and 126 days). The results showed that all experimental treatments, at all pressure heads, increased soil water retention significantly (p<0.01). The addition of amendments reduced the soil bulk density and increased the organic carbon and aggregate stability. Minimum bulk density was observed in the cellulose hydrogel and biochar treatments at 126-days and in the polyvinyl acetate polymer at 21-days. Maximum organic carbon and aggregate stability were observed in the cellulose hydrogel treatment at 126-days. In hydrogel treatments with passing time, aggregate stability and water retention increased, but water retention of polyvinyl acetate polymer decreased with increasing time. Moisture absorbent biopolymer is a suitable replace to super absorbent synthetic polymers because not only increase soil organic matter but also enhance soil aggregate stability and water retention capacity.

Wind erosion is known as one of the most important land degradation aspects, particularly in arid and semi-arid regions. Soil properties, by affecting soil erodibility, can control the wind erosion rate. The aim of this study was to attribute the soil physical and chemical properties to the wind erosion rate for the purpose of determining the most important property. To this aim, wind erosion rates were measured in-situ at 60 points of Kerman province using a portable wind tunnel facility. The results indicated that wind erosion rates varied from 0.03 g m-2 min-1 to 3.41 g m-2 min-1. Threshold wind velocity decreased wind erosion rate following a power function (R2=0.81, P<0.001). Clay and silt particles, shear strength, mean weight diameter (MWD), surface gravel, dry stable aggregates (DSA<0.25mm), soil organic carbon (SOC), calcium carbonate equivalent (CCE) and the concentrations of the soluble Ca2+, K+ and Mg2+ were inversely proportional to the wind erosion rates following nonlinear functions. On the other hand, Wind erosion was significantly enhanced with increasing the sand fraction, soluble Na+, electrical conductivity (EC) and sodium adsorption ratio (SAR). According to the final results, among the studied soil properties, SAR and MWD were s the most effective properties controlling wind erosion in the soils of Kerman province. Therefore, it is recommended to consider suitable conservation practices in order to prevent the sodification and degradation of arid soils.

A challenge of sustainable development is related to agriculture, food security, and conservation of water and soil resource, under the current crop production paradigm. Increasing crop yields often have negative environmental impacts. Soil salinization and sodication are major environmental hazards that limit agricultural potential and are closely related to agricultural unsuitable management and water resources overexploitation, especially in arid climates. In this study, we investigated the negative impacts of saline and sodic irrigation water on soil properties that it is necessary to study the factors affecting the degradation of soil structure to implement proper land management and we intended to help the farm producer or landowner to understand the fundamental differences between these two problems. Samples of clay loam and sandy loam soils were treated in 5 wetting and drying periods with different types of water quality (which combinate different levels of EC and SAR). Soil water content of samples was achieved at soil matric suctions of 0, 10, 20, 40, 60, 100, 300, 1000, 2000, 4000 and 15000 cm. Also, dispersible clay and saturated hydraulic conductivity were determined. Results showed that increasing of SAR caused dispersion of clay and saturated hydraulic conductivity was decreased with increasing of dispersed clay. Increasing SAR caused some macropores and mesopores changed to micropores and as result enhanced water retention especially at high matric suctions. Water retention capacity was enhanced by increasing in water EC as that flocculated soil particles and created new soil pores.

Destruction of soil structure and reduction of soil organic matter are major problems of cultivated soils which result from improper tillage operations, excessive consumption of chemical fertilizers and low consumption of organic and green fertilizers. One method for maintaining sustainable agriculture is to add organic and inorganic amenders. By producing resistant aggregates, organic matters improve soil structure and enhance soil permeability, FC moisture and water availability capacity. Furthermore, through enhancing organisms’ activities, especially earthworms, organic matters improve soil hydraulic conductivity and reduce bulk density. Organic matters may be added to soil through different way, however, the effect of each one on the soil’s physical properties is different. Chicken feather (CF) is readily available through henhouses and slaughterhouses, however, significant amounts of CF are destroyed by burning and burying them. Potassium Humate (PH) is a potassium salt from humic acid. Humic acid is extracted from various natural sources such as humus, peat, lignite and coal. Vermicompost (VC) is a compost which is produced by a non-thermal process. The impact of CF on different soil properties has not been studied yet. Accordingly, we investigated the impact of adding differing weight percentages of three types of amenders (PH, CF and VC) on the physical properties of soil under wheat cultivation at different moisture levels.

The experiment was conducted in factorial form based on randomized complete block design with 27 treatments in three replications. The first factor included the above-mentioned amenders; the second factor included three weight levels of these amenders (0%, 2.5% and 5%); the third factor included three moisture levels (0.5FC, 0.7FC and 0.9FC). The amenders were uniformly mixed with the soil up to the depth of 10 cm; then, wheat seeds were planted and moisture treatments were carried out during the growth period (from late April 2016 to September 2016). The soil moisture of the plots was controlled during the experiment period using the gravimetric method. For investigating the changes in the soil’s physical properties, samples (disturbed and undisturbed) were taken from the plots before and after the experiment. The following physical parameters were measured: bulk density (BD), soil moisture in field capacity (FC), permanent wilting point (PWP), wet aggregate stability (WAS), saturated hydraulic conductivity (KS), penetration resistance (PR), retention curve slope at inflection point (Si), mean weight diameter of aggregates (MWD) and mass-size fractal dimension of aggregates (Dm). Statistical analysis was done by SPSS software and means were compared via Duncan test. Tables and graphs were generated by Excel software.

Variance analysis and means comparison indicated that using amenders reduced bulk density for 89%. Reduced bulk density was caused by high keratin (91%) in CF, high porosity and the production of coarse pores in soil. On the other hand, VC with many pores led to increased aggregation and reduced bulk density.
Results revealed that consuming CF increased soil moisture to field capacity (FC) (87%). CF had more significant impacts on increasing FC at high moisture levels. Thanks to its keratin structure, feather operates like a sponge which enhances soil porosity; hence, it absorbs more moisture and improves FC. Furthermore, results indicated that increasing the amounts of amenders led to increased soil moisture in PWP (91%). By increasing the amount of amenders in soil, aggregation and soil porosity increased which led to enhanced PWP.
Large amounts of CF, PH and soil moisture (0.9FC) resulted in 3.7 times enhancement of Ks. CF led to the production of large soil pores and reduced soil density which resulted in improved soil structure and increased Ks. Thanks to its adhesion properties, PH increased Ks.
Increasing the amount of amenders and the level of soil moisture in all three types of organic matters (especially CF) caused the 2.5 times enhancement of WAS.
The results revealed that increasing soil moisture and amenders led to reduced Si (101%). Given all three types of amenders, PH had the highest impact on the reduction of Si. Moreover, soil penetration resistance (PR) was reduced as a function of increasing the soil moisture level.
Contrary to the expectation, MWD was reduced as a result of increasing amenders. Furthermore, it was found that, given little soil moisture, increasing the amount of amenders resulted in increased Dm; however, given high soil moisture, increasing the amount of amenders led to decreased Dm. Thus, it should be noted that adding amenders improved the stability of aggregates over long time periods and at high soil moisture levels.

One major strategy for improving soil physical and chemical properties is using modifiers, especially organic matters. In this study, we investigated the impact of chicken feather on physical properties of soil and compared its effect with those of potassium humate and vermicompost under different levels of soil moisture and wheat cultivation.
The results indicated that consuming amenders resulted in reduced Bd but increased FC, PWP, Ks and WAS.
In other words, it improved physical properties of soil. Moreover, Si decreased as a result of increasing soil moisture and organic matters. Among the three types of amenders, potassium humate had the highest impact on reducing Si. PR was reduced as a function of increasing soil moisture. However, increasing organic matter led to decreased MWD. Furthermore, it was unexpectedly found that, given low soil moisture, Dm increased as a result of increasing the organic matters weight. Nevertheless, in high levels of soil moisture, Dm ​​decreased as a function of increasing organic matter. Thanks to positive impacts of organic matters (especially CF which is cheaper and more accessible than other amenders) on soil’s physical properties, they are highly recommended for soil improvement. Regarding future studies, investigation of the effect of these amenders on soil chemical properties under different soil textures is suggested

Soil aggregates refers to groups of soil particles which attach to each other stronger than neighbour particles. Aggregate stability shows the capability and strength of soil aggregates to tolerate breakup when disruptive stresses and destructive forces via mechanical agricultural operation such as tillage and water or wind erosion are applied. Wet aggregate stability shows how well a soil can withstand raindrop impact and water erosion, while size distribution of dry aggregates can be used to predict resistance to abrasion and wind erosion. Aggregate stability changes can act as the first indicators of recovery or degradation of soils. Aggregate stability is an indicator of organic matter content, biological activity, and nutrient cycling in soil. Generally, in small aggregates (< 0.25 mm), the particles are bound by older and more stable forms of organic matter. Microbial decomposition of fresh organic matter releases products (that are less stable) that bind small aggregates into large aggregates (> 2-5 mm). Although, there is not a unique acceptable methodology that serves and applies the entire world up to now, aggregate stability has been introduced as a soil physical quality indicator. Difficulties remain when comparison of aggregate stability from different methodologies are done. The objective of the present study was to assess appropriate and satisfactory aggregate stability tests that enable to distinguish the soil physical quality condition of both arid and moist medium textured soils. A total of 120 soil samples which contained 60 wetland samples from Guilan province with a very humid climate, average annual rainfall of 1285 mm, and average annual temperature of 16°C, and 60 samples from Fars province with dry climate, average rainfall of 225 mm, and the average annual temperature of 27°C were provided. Soil sampling was performed from surface layer (0-20 cm). Each 10 soil samples with similar texture were mixed and one soil sample for each texture was finally obtained. After air drying and sieving, soil texture and organic carbon were determined by pipette and oxidation methods, respectively. Also, undisturbed samples were taken using metal cylinders from surface layer of 5-15 cm for determination of soil saturation coefficient, soil moisture curve, and soil bulk density. Also, in order to determine the aggregate stability, Kemper and Rosenau, de Leenheer and de Boodt, as well as Le Bissonnais were used. Among different tested methods, wet sieving using the well known fast wetting methods of Kemper & Rosenau and of Le Bissonnais presented similar results in both climates. The mean weight diameter value of both methods for assessing aggregate stability can be considered as a dependable indicator of soil structure status for comparing soils. These aggregate stability tests were in correspondence with only one out of the eight soil physical quality indicators when the entire soils were used. It was concluded that the aggregate stability should be used judiciously and in accordance with other indicators for an overall assessing of the soil physical quality condition. The great differences in the estimation of aggregate stability between KRSW and LB2 with other methods confirm that aggregate stability increases with increasing soil moisture content. This involves reducing the amount of air condensed, which results in the reduction of compressive forces on the aggregates during rapid wetting. But the lack of similarity between the KRSW and LB2 methods in terms of MWD suggests that the results of these two methods are not comparable to dry and wet soils. The difference in aggregate size distribution from all three treatments of LB method was higher in dry areas than wet areas. Only dry soils based on LB (LB1 and LB3 treatments based on MWD) (P <0.05) are comparable. In dry soils, the LB3 method is very efficient. This method involves the use of ethanol that protects the aggregate structure against dryness stresses. The lack of similarity between the MWD and other soil quality indicators describes the complexity of the soil structure, which is dependent on the location. It seems that SOC can be considered as an indicator with high correlation with the aggregate sustainability index of LB and KRFW methods, at least in the studied medium-textured soils. Since only a soil quality index (SOC) had a similar trend to the sustainability index derived from these two methods (LB1 and KRFW), it can be concluded that aggregate stability should be judged and recognized correctly, along with other used soil physical indicators for a general assessment of the conditions. In case of arid land soils, efficiency of pre-wetted methods of Kemper and Rosenau and of Le Bissonnais as well as pre-wetted Le Bissonnais with mechanical slaking and shaking were similar. If a simple and rapid analysis of the structure status is needed, single tests such as fast wetted Kemper and Rosenau and Le Bissonnais can be used.

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.

Knowledge of the change of soil properties in each event during sequence rainfalls is very important for recognition the critical period of that the soil would be susceptible to erosion processes is vital. This study was conducted to investigate the effect of sequence rainfalls on the changes of soil properties, runoff and soil loss in eighteen different soils with the same aggregate size (from 4 to 6 mm) using the simulated rainfalls. The experiments were performed at small erosion plots with 80 cm long and 60 cm wide under 9% slope steepness during seven sequence rainstorms with 80 mm h-1 in intensity for 30 min and 5-day interval. The results indicated that significant differences were among the soils in bulk density, water retention, runoff and soil loss (p

Fractal geometry concepts have been widely applied as a useful tool to describe complex natural phenomena, in particular,for a better understanding of soil physical systems. However, limited information is available on the fractal characteristics of soil properties or soil aggregation. A soil aggregate is made of closely packed sand, silt, clayand organic particles building upsoil structure. Soil aggregation is a soil quality index integrating the chemical, physical, andbiological processes involved in the genesis of soil structure. Soil structure and its stability are important issuesfor many agronomic and environmental processes. Thus, quantitative description of soil structure is very important. Soil forming factors in different soils (various orders) and forms affect the soil structureformation. Characterizing aggregate size distribution for different soil orders using fractal theory is necessary for evaluating the impact of soil forming factors on soil structure and quantifying the relationship between fractal dimension and other important soil properties. Therefore, the aims of this research were quantifying the structure of different soil orders using fractal geometry, mean weight diameter of aggregates (MWD)and geometric mean diameter of aggregates (GMD). In addition, MWD and GMD indices and fractal parameters of soil aggregate size distribution were compared toevaluate soil structure and determinethe relationship between fractal parameters with MWD, GMDand other soil properties.
Fractal models which simulate soil structure are also used to better understand soil behaviors. Aggregate size distribution is determined by sieving a fixed amount of soil mass under mechanical stress and is commonly synthesized by the MWD, GMDand fractal dimensions such as the fragmentation fractal dimensions. Therefore, aggregate size distribution and its stability variation were evaluated using some fractal models and MWD and GMD (empirically indices).In the current study, the original data were obtained from analysis of diagnostic horizons of seven important soil orderslocated in Fars Province in the Southern Iran. Soil samples were collected from diagnostic horizons of seven soil orders includingEntisols, Vertisols, Aridisols, Mollisols, Alfisols, Histosols and Inceptisols. The measured physico-chemical properties of soil were aggregate size distribution, soil particle size percentage (sand, silt, and clay), saturation percentage (SP), organic carbon (OC), pH, calcium carbonate equivalent (TNV), gypsum content, soil electrical conductivity (EC) and soil bulk density (BD). The MWD and GMD indices, the fractal dimensions and fractal parameters of aggregates were then calculated. Relationships between soil properties with MWD, GMD and the fractal dimension were also determined.
The results showed that there was a significant correlation between fractal dimension of Riue and Sposito and Taylor and Wheatcraft models and soil aggregate stability indices (MWD and GMD indices of aggregates) with the other soil characteristics. This correlation between fractal parameters with organic matter, bulk density, clay and sand percentage was stronger than other soil properties. There was a significant and negative correlation (p The results indicated that fractal theory can be used to characterize soil structure at different soil orders and fractal dimensions of soil aggregate seems to be more effective in this regard, except forHistosols. Fractal dimension can be estimated using some easily available soil properties. Fractal theory can be applied to characterize and quantify soil structure in different soil orders of Fars Province.

Marls are the most susceptible geological formation of erosion and keeping a permanent crop cover on the soil of this formation is difficult due to some limitations such as the instability of soil
structure, poor soil productivity and low soil moisture storage. Polymers can be investigated as one of options to protect soil resources in these formations. This study was conducted to compare the effects of polyacrylamide (PAM) and polyvinyle acetate (PVAc) on improving soil properties and germination rate in the marl formations. PAM and PVAc were sprayed on the soil surface with 0.0, 33.3, 66.6, 100.0 kg ha-1 amounts in three splits. In total 32 boxes of polymerized soil were provided and wheat seeds were planted in them. The soil physical properties along with the wheat germination percentage were evaluated in the polymerized soils after five rainfall simulations (40 mm h-1 for 30 min). The experiment was conducted as factorial using a completely randomized design with three replications. With an increase in the two polymers rates, aggregate size, aggregate stability and saturated hydraulic conductivity were significantly improved whereas bulk density and soil surface resistance were strongly decreased in the prepared marl soil. Water holding capacity and available water of the soil decreased after the application of PAM while no significant differences were found after treating with the PVAc. This study revealed that the PVAc had the same role with the PAM in improvement of soil physical properties and in contrast it had no negative effect on the water holding capacity. Therefore, the PVAc can be successfully considered as a replacement for the PAM in the marl areas.

Soil erosion by water is the most serious form of land degradation throughout the world, particularly in arid and semi-arid regions. In these areas, soils are weakly structured and are easily disrupted by raindrop impacts. Soil erosion is strongly affected by different factors such as rainfall characteristics, slope properties, vegetation cover, conservation practices, and soil erodibility. Different physicochemical soil properties such texture, structure, infiltration rate, organic matter, lime and exchangeable sodium percentage can affect the soil erodibility as well as soil erosion. Soil structure is one of the most important properties influencing runoff and soil loss because it determines the susceptibility of the aggregates to detach by either raindrop impacts or runoff shear stress. Many soil properties such as particle size distribution, organic matter, lime, gypsum, and exchangeable sodium percentage (ESP) can affect the soil aggregation and the stability. Aggregates size distribution and their stability can be changed considerably because of agricultural practices. Information about variations of runoff and sediment in the rainfall events can be effective in modeling runoff as well as sediment. Thus, the study was conducted to determine runoff and sediment production of different aggregate sizes in the rainfall event scales.
Toward the objective of the study, five aggregate classes consist of 0.25-2, 2-4.75, 4.75-5.6, 5.6-9.75, and 9.75-12.7 mm were collected from an agricultural sandy clay loam (0-30 cm) using the related sieves in the field. Physicochemical soil analyses were performed in the aggregate samples using conventional methods in the lab. The aggregate samples were separately filed into fifteen flumes with a dimension of 50 cm × 100 cm and 15-cm in depth. The aggregate flumes were fixed on a steel plate with 9% slope and were exposed to the simulated rainfalls for investigating runoff and soil loss (sediment). Ten same rainfall events with 60 mm h-1 in intensity for 30 min were applied using a designed rainfall simulator in the lab. The rainfall simulator had a rainfall plate with a dimension of 100 cm × 120 cm which has been fixed on a metal frame with 3m height from the ground surface. Runoff and sediment samples were collected using a plastic container placed the out-let of the flumes. Runoff generation of each flume was determined based on multiplying total content volume of the tank by volume proportion of water in the sample. Soil loss for each event was determined using multiply the container volume and sediment concentration of the uniform sample. Initial soil moisture was measured in the aggregate samples before each rainfall event in order to investigate its effect on the runoff and sediment variations in the event scales. Runoff, soil loss and initial soil moisture data were evaluated for normality before any statistical analysis using SPSS version 18 software. Differences of runoff and soil loss among different rainfall events were analyzed using the Duncan's test.
Based on the results, the soil was calcareous having 16% equivalent calcium carbonate. Low amount of organic matter (0.6%). The measured aggregate stability showed to be very low, indicating high susceptibility of the aggregates to water erosion processes. Significant differences were found among the rainfall events in runoff (p

Soil structure is an important indicator for optimal management of soil and water resources. Because it directly influencing several physical characteristics of soils such as soil water status، hydraulic conductivity، heat and air contents، soil porosity and bulk density. However، due to complexity of soil structure، its quantitative description is rather difficult. One of the relatively new methods proposed to explain soil structure in a quantitative manner is the so-called fractal geometry concept. In this concept، by determining the fractal dimension of bulk soil، the stability of aggregates can be quantitatively analyzed at different scales. The objective of this study was to quantify soil structure stability using some classic indicators and fractal approach in a large scale. Consequently، 41 intact soil samples were taken from an agricultural area and their particle size distribution، soil bulk density and aggregate bulk density، were measured. The weighted mean diameter and geometric mean diameter of both dry and wet aggregates were measured using dry and wet sieving method. The fractal dimensions of all dry and wet aggregates were obtained using fractal models of Mandelbrot، Tyler-Wheatcraft and Rieu-Sposito. The results indicated that fractal dimensions of the number-size model of Mandelbrot for dry sieve series and the number-size model of Rieu-Sposito in the wet sieve series perform quite well. These two models could also provide reasonable agreement with classical geometric mean and weighted mean diameters of aggregates.

Soil aggregate stability is a key factor in soil resistivity to mechanical stresses, including the impacts of rainfall and surface runoff, and thus to water erosion (Canasveras et al., 2010). Various indicators have been proposed to characterize and quantify soil aggregate stability, for example percentage of water-stable aggregates (WSA), mean weight diameter (MWD), geometric mean diameter (GMD) of aggregates, and water-dispersible clay (WDC) content (Calero et al., 2008). Unfortunately, the experimental methods available to determine these indicators are laborious, time-consuming and difficult to standardize (Canasveras et al., 2010). Therefore, it would be advantageous if aggregate stability could be predicted indirectly from more easily available data (Besalatpour et al., 2014). The main objective of this study is to investigate the potential use of support vector machines (SVMs) method for estimating soil aggregate stability (as quantified by GMD) as compared to multiple linear regression approach. The study area was part of the Bazoft watershed (31° 37′ to 32° 39′ N and 49° 34′ to 50° 32′ E), which is located in the Northern part of the Karun river basin in central Iran. A total of 160 soil samples were collected from the top 5 cm of soil surface. Some easily available characteristics including topographic, vegetation, and soil properties were used as inputs. Soil organic matter (SOM) content was determined by the Walkley-Black method (Nelson & Sommers, 1986). Particle size distribution in the soil samples (clay, silt, sand, fine sand, and very fine sand) were measured using the procedure described by Gee & Bauder (1986) and calcium carbonate equivalent (CCE) content was determined by the back-titration method (Nelson, 1982). The modified Kemper & Rosenau (1986) method was used to determine wet-aggregate stability (GMD). The topographic attributes of elevation, slope, and aspect were characterized using a 20-m by 20-m digital elevation model (DEM). The data set was divided into two subsets of training and testing. The training subset was randomly chosen from 70% of the total set of the data and the remaining samples (30% of the data) were used as the testing set. The correlation coefficient (r), mean square error (MSE), and error percentage (ERROR%) between the measured and the predicted GMD values were used to evaluate the performance of the models. The description statistics showed that there was little variability in the sample distributions of the variables used in this study to develop the GMD prediction models, indicating that their values were all normally distributed. The constructed SVM model had better performance in predicting GMD compared to the traditional multiple linear regression model. The obtained MSE and r values for the developed SVM model for soil aggregate stability prediction were 0.005 and 0.86, respectively. The obtained ERROR% value for soil aggregate stability prediction using the SVM model was 10.7% while it was 15.7% for the regression model. The scatter plot figures also showed that the SVM model was more accurate in GMD estimation than the MLR model, since the predicted GMD values were closer in agreement with the measured values for most of the samples. The worse performance of the MLR model might be due to the larger amount of data that is required for developing a sustainable regression model compared to intelligent systems. Furthermore, only the linear effects of the predictors on the dependent variable can be extracted by linear models while in many cases the effects may not be linear in nature. Meanwhile, the SVM model is suitable for modelling nonlinear relationships and its major advantage is that the method can be developed without knowing the exact form of the analytical function on which the model should be built. All these indicate that the SVM approach would be a better choice for predicting soil aggregate stability. The pixel-scale soil aggregate stability predicted that using the developed SVM and MLR models demonstrates the usefulness of incorporating topographic and vegetation information along with the soil properties as predictors. However, the SVM model achieved more accuracy in predicting soil aggregate stability compared to the MLR model. Therefore, it appears that support vector machines can be used for prediction of some soil physical properties such as geometric mean diameter of soil aggregates in the study area. Furthermore, despite the high predictive accuracy of the SVM method compared to the MLR technique which was confirmed by the obtained results in the current study, the advantages of the SVM method such as its intrinsic effectiveness with respect to traditional prediction methods, less effort in setting up the control parameters for architecture design, the possibility of solving the learning problem according to constrained quadratic programming methods, etc., should motivate soil scientists to work on it further in the future.

Stratification ratio of soil organic matter and aggregate stability are considered as indicators of soil quality under different conditions such as burning rangeland vegetation. The objective of this study was to investigate the impact of fire on stratification ratio of soil organic matter and aggregate stability and distribution of organic matter in two macro and micro fractions in semi-steppe rangeland of Karsanak region in Chaharmahal and Bakhtiari province. Several sites which were affected by fire three، two، and one years before this study (i. e. 2008، 2009، and 2010، respectively) were chosen. Since the soil samples were taken from two depths (0-10 cm and 15-25 cm) of each site with 9 replications، the numbers of soil samples for laboratory analysis were 108. Independent t-test (P= 5%) was used to assess the difference between the measured properties at the burned and control sites. The results showed that the soil organic matter and mean weight diameter of aggregates (MWD) in the surface layer decreased significantly in 1 and 2 years after fire. Particulate organic matter (POM) significantly decreased in surface layer of the burned areas compared with the control areas. The effects of fire on stratification ratio of soil organic matter in 1- and 2-years after fire were significant compared with control areas، and stratification of soil organic matter decreased 26% and 22 percent in 1 and 2 years after fire، respectively. Stratification ratio of aggregate stability was lower in all burned areas compared with control areas، but the differences were not significant. Macro organic matter of both surface and subsurface layers in 1 year after fire was significantly reduced compared with the control، while، micro organic matter of subsurface layer showed significant increase. The study results showed that the effect of fire on physical and chemical soil properties in the surface layer were more than subsurface layer، because of higher-severity fire in surface layer. Furthermore، due to reduction of organic matter and aggregate stability after fire، rangeland soil quality decreased.

Runoff production along with rainfall characteristics and soil properties is affected by the soil type. This study was carried out to investigate runoff variations as affected by the same rainfall events in different soil textures in Zanjan province. After initial tests، ten soil textures were recognized in the area and accordingly soil samples were taken from 0-30 depth. The experiment was done in the randomized complete block design with ten treatments at three replications. The soils were filled within the plots with a dimension of 60 × 80cm and 20 cm-depth on a sloped land (8%). Experimental plots were exposed to 10 simulated rainfalls with 55-mm h-1 intensity and 30-min duration. Soil moisture content was measured at the plots before each event using the weighted method. The initiation time and volume of the generated runoff were measured at the plots in each rainfall event. The results showed that there was significant differences among the soils in the initial soil moisture (P<0. 001)، runoff initiation time (P<0. 001) and runoff depth (P<0. 001). Rainfall events also significantly affected the moisture content (R2=0. 98، P<0. 001)، initiation time (R2=0. 95، P<0. 001) and runoff depth (R2=0. 96، P<0. 001) in the soils. From the first rainfall event to the forth event، the soil moisture content and runoff depth significantly increased and the runoff initiation time considerably declined. After the fifth event، the runoff parameters did not significantly vary probably due to the stop of the aggregates breakdown. Based on the results، both the runoff production and the runoff initiation time were remarkably related to the soil moisture content (R2=0. 96، P<0. 001 and R2=0. 94، P<0. 001، respectively).