Soil Physics, Erosion and Conservation
E. Karami; S. Ghorbani Dashtaki; Bijan Khalilimoghadam
Abstract
Introduction Soil erodibility can be viewed as the integral result of the processes determining the infiltration of rain into the soil and of the processes determining the soil’s resistance to the detachment of its particles and their subsequent transport (Lal, 1988). It is generally considered ...
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Introduction Soil erodibility can be viewed as the integral result of the processes determining the infiltration of rain into the soil and of the processes determining the soil’s resistance to the detachment of its particles and their subsequent transport (Lal, 1988). It is generally considered as an inherent soil property with a constant value for a given soil type and widely adopted as an important factor in soil erosion prediction models, such as the Universal Soil Loss Equation (USLE), and the Revised USLE (RUSLE). The erodibility factor, commonly known as the K factor, in the USLE was defined as the average rate of soil loss per unit of rainfall erosivity index from a cultivated continuous fallow plot, on a 9% slope 22.1 m long. Soil erodibility factor K is not only an internal factor indicating the amount of soil loss, but also the basis for the quantitative study of soil erosion. Soil erodibility is closely related to the basic physicochemical characteristics of soils. The total aggregate content, 1–10 mm aggregate content, aggregation degree, aggregate dispersion coefficient and erosion rate are indexes for the analysis of soil anti-erosion capability. Not only may soil erosion be different for various types of soils, but also it is different for the same type of soil under different climate conditions or land use management. Different land use systems might alter several soil properties and processes. Kosmas et al. (2000) reported that land use change could impact soil physical, chemical, and biological properties. Studies by Duiker et al. (2001) showed that land use changes from natural and semi-natural vegetation to cultivated and grazed lands affect soil bulk density, porosity and water storage, water infiltration and water flow characteristics and surface runoff. Abbaszadeh Afshar et al. (2010) found that organic matter content and bulk density were greater in pasture soils than in dry farm soils. Kay (2000) showed that large aggregate sizes and high organic matter content protect soils against splash detachment. Although there are many studies on land use impacts on soil erodibility, to the best of the authors’ knowledge, no study has of yet been reported on the effects of land use change on soil erodibility in Zayandeh-Rood watershed. Therefore, the objective of this study was to investigate the impacts of different land uses on soil erodibility in a part of Zayandeh-Rood watershed. Materials and Methods For this purpose, soil properties including particle size distribution, gravel percent, bulk density, permeability of soil profile, Structure code and permeability code, organic matter, calcium carbonate equivalent, mean weight diameter of aggregates and surface shear strength were measured. Soil erodibility was measured with a rainfall simulation device with rainfall intensity of 30 mm h-1 and 30 min duration in a plot with 0.25 m2 area and 9% slop in two land uses, namely pasture and degraded pasture. A completely randomized design was used in which soil texture and the land use changes were analyzed. The multiple-linear regression analysis was used to relate soil erodibility factor to different soil parameters. Results and Discussion The influence of land use change on soil erodibility was investigated based on simulated rainfall in field conditions. The findings of this study demonstrated that a considerable amount of soil erodibility occurred in the study region characterized by low organic matter and mismanagement. On average, soil erodibility was significantly affected in the Zayandeh-Rood watershed, Iran, by the land use system (i.e., soil structure and management practices) rather than by the soil textural class. Average soil erodibility was obtained in pasture land use 0.05 (ton h MJ-1 mm-1) and in degraded pasture 0.09 (ton h MJ-1 mm-1). Low soil organic matter content in the degraded pasture land is probably caused by livestock overgrazing and ultimately grazing. Based on the results obtained of the transfer functions in each land uses, it was observed that clay and coarse sand particles (R2=0.86) in pasture land uses and surface shear strength and permeability code (R2=0.90) in degraded-rangeland at the 5% level compared to other soil properties were more suitable parameters for estimating of soil erodibility. Thus, vegetation cover protection was recommended to soil conservation in this region.
Maryam Jamshidsafa; Bijan Khalili Moghadam; Siroos Jafari; Shoja Ghorbani
Abstract
Introduction: Wind erosion is not only a basic geomorphic process of eroding and altering landforms but also one of the main causes of sandy desertification in arid and semiarid areas (Chepil 1945; Nordstrom and Hotta 2004). Single-grained, fine sand dunes are usually composed of none-strength materials ...
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Introduction: Wind erosion is not only a basic geomorphic process of eroding and altering landforms but also one of the main causes of sandy desertification in arid and semiarid areas (Chepil 1945; Nordstrom and Hotta 2004). Single-grained, fine sand dunes are usually composed of none-strength materials with a low water retention that make them susceptible to wind erosion. They lack organic matter and are inherently of low fertility (Ahmadi, 2002). Therefore, sand dunes and drift areas require non-oil artificial covers for their stabilization and that of the vegetation cover (Rezaie, 2009). The covering material types include oil (Rezaie, 2009), flat crop residues (Chepil, 1944; Bilbro and Fryrear, 1994), standing residues (Siddoway et al., 1965; Bilbro and Fryrear, 1994), pebble (Li et al., 2001), cotton gin trash, clay, gravel, picket fence, brush, straw, and hay (Fryrear, 1985). Soil properties including compressive strength, plasticity, compactibility, strength characteristics, elastic modulus, crushing strength, unconfined compressive strength, erodibility, shear strength, and permeability have been investigated for evaluating mulch effectiveness. Improvements have been achieved in sand dune stabilization by decreasing permeability and enhancing strength properties. The effect of soil properties on wind erosion has been studied through shear strength of soil surface which includes a frictional term (due to inter-particle frictional strength) and a cohesive term (due to intrinsic bonds among particles) (Koolen and Kuipers, 1983; Alizade, 2009). As regards the factors influencing soil shear strength, soil particle diameter, bulk density, cohesion, aggregate index, water content, crust, and organic matter have all been found to influence wind erosion (Raji et al., 2004; Homauoni and Yasrobi, 2011). Based on these observations, it may be hypothesized that soil cohesion caused by mulching operations could be effective in reducing wind erosion. Filter Cake is residue produced in huge amounts by the agro-industry that is composed of cellulosic substances, CaCO3, N, P, K, organic matter, and clay. The objective of this research is feasibility of Filter Cake using as a Khuzestan sugarcane residues for adopted-environmental mulch production. Materials and Methods For this purpose, Factorial experiments in completely random design form were conducted that factors included mulch kind(5 organic mulch and oil mulch), thickness(1 or 2 layers) and precipitation. In this study, Filter cake and clay soil samples (Albaji-Ahvaz) were used to make sugarcane mulches. A sand dune sample was selected as bed for applying the mulch. To select the right ingredient and treatments, Filter cake, clay samples were mixed with water in try and error, and producted suspension sprayed on sand dune bed. Surface surface soil shear strength, penetration resistance, soil adhesion and mulch’s internal frictional angle and erodibility were measured by shear vane, penetrometer, Zhang’s shear device, wind tunnel respectively. Results and Discussion The results determined that there is significant effect (p<0.01) on surface shear strength and penetration resistance in different much and thickness. But there is no significant effect on soil adhesion and mulch’s internal frictional angle because Zhang’s shear device hasn’t essential sensitive to differentiate them. Based on this research, Mulch 1(50g clay+150 g Filter Cake) is selected as superior mulch in Ahvaz sand dune stabilization because of higher surface shear strength and penetration resistance rate. It is defined as the resistance soil materials can offer against shear stress. This property is directly related to the cohesive and friction forces between soil particles (Koolen and Kuipers, 1983; Knapen et al., 2007; Khalilmoghadam et al., 2009) and, thereby, related to soil intrinsic properties such as clay content, salinity, and organic matter content (Horn et al., 1994). Sugarcane residues due to their effects on cohesive forces affect soil strength via the physical and chemical properties of Filter Cake. In this study, increases in SAR were found to be inversely proportional to SSS and PR. With identical values of SAR, treatments with higher EC values exhibited greater saturated SSS and PR. This shows the adjusting effect of EC on SAR effects. It is, therefore, concluded that the combined Filter Cake and clay soil could strongly affect soil resistance to erosive shearing stresses and wind erosion under environmental conditions. Conclusion Sugarcane mulches were shown to be effective in stabilizing sand dunes as compared to oil mulches. It is, therefore, concluded that the combined Filter Cake strongly influence to erode under environmental conditions.