مجله آب و خاک (Feb 2016)
Effects of Fire on Soil Splash Erosion in Semi-steppe Rangelandof Karsanak Region,Chaharmahal and Bakhtiari
Abstract
Introduction: The detachment process can be conceptually divided in two sub-processes included aggregate breakdown (Le Bissonnais, 1996) and movement initiation of breakdown products(Kinnell, 2005). soil detachment depends on raindrop size and mass(Elison, 1944; Bisal, 1960), drop velocity(Elison, 1944; Bisal, 1960), intensity rainfall (Ting et al, 2008), kinetic energy (Kinnell, 2003; Fernandez- Raga et al, 2010), runoff depth(Torri et al, 1987; Kinnell,1991 and 2005), crop covers(Bancy, 1994; Ghahremani et al, 2011), wind speed( Erpul et al, 2000) and experimental area (cup size) (Leguedois et al, 2005; Luk, 1979; Torri and poesen, 1988). Many of studies have been conducted to evaluate the relationship between splash and slope (Bryan, 1979; Torri and Poesen, 1992; Wan et al, 1996).Torri and Poesen (1992) expressed that in steep slope the gravity force adds to the drop detaching force and decreases of soil resistance, consequently increases splash erosion rate with increasing slope. Soil splash erosion is also strongly influenced by soil properties including soil particles size distribution (Mazurak and Mosher, 1968; Legout et al, 2005; fan and li, 1993), soil shear strength(Cruse and Larson, 1977; Al-Durrah and Bradford,1981; Ekwue and ohi; 1990 ), soil cohesion(Torri et al, 1987), soil organic matter content and aggregate size (Ekwue and Maiduguri, 1991; Qinjuan et al, 2008), soil aggregates stability(Qinjuan et al, 2008), surface crust (Qinjuan et al, 2008). Fire, play an important role in splash erosion. The absence of vegetation cover in disturbed lands accelerates splash erosion rates by as much as several folds compared to undisturbed sites (Lal, 2001; Thomaz and luiz, 2012).The detachment of soil particles by splash depends on several raindrop characteristics, including raindrop size and mass, drop velocity, kinetic energy, and water drop impact angle (Sharma et al., 1993; Singer and Le Bissonnais, 1998; Cruse et al., 2000, Bhattacharyya et al., 2010). Detachment rate is strongly influenced by soil properties, including soil texture and thickness of the water layer at the soil surface (De Ploey and Savat, 1968; Moss and Green, 1983; Sharma et al., 1991; Kinnell, 1991, Jomaa et al., 2010), soil strength, bulk density, cohesion, soil organic matter content, moisture content, infiltration capacity (Nearing et al., 1988; Owoputi, 1994; Morgan et al., 1998, Planchon et al., 2000, Ghahramani et al., 2011), soil initial water content, surface compaction and roughness (Planchon et al., 2000), the nature of soil aggregates and crust, porosity, capacity of ionic interchange, and clay content (Poesen and Torri, 1988). Several studies have shown that splash detachment rate is mainly related to surface rock fragments in soils with sparse vegetation cover (Jomaa et al., 2012). The present study was conducted to investigate the effects of fire on splash erosion and some erosion depended properties in semi-steppe rangeland of Karsanak region in Chaharmahal and Bakhtiari province which affected by man-made fire during 2008, 2009, 2010 and 2011. Materials and Methods: Soil samples were obtained on 2012 from the mentioned regions (8 samplesfrom the burned area and 8 samples as a control (unburned) in the adjacent burned area) from 0-7 cm depth. Splash erosion under simulated rainfall intensity of 2 mm per minute was measured using multivariate splash cup apparatus considering the slope of 5 and 25 degree. Soil pH, soil electrical conductivity, equivalent calcium carbonate, soil organic matter, sand size fraction particulate organic matter (SSF POM), mean weight diameter and, geometric mean diameter of aggregates, percent of macro and micro-aggregates, percent of clay, silt, sand, water dispersible clay and soil bulk density were measured. Statistical data analysis was performed by t-test at 5% level. Results Discussion: The results showed that soil splashing increased significantly in treatment 1 year after the fire in both slope 5 and 25 degree and in treatment 2 year after the fire in slope 25 degree. The amounts of increase in soil splashing compared to control treatment were 22, 24 and 15 percent in treatment 1 year after fire in slope 5 and 25 degree and in treatment 2 years after the fire in slope of 25 degree respectively. Comparison of the total soil splash on slopes of 25 degree at 1, 2, 3 and 4 years after the fire, showed a significant increase in the level of five percent relative to the slope of 5 degree at 1, 2, 3 and 4 years after the fire. The other measured soil properties (except equivalent calcium carbonate) was affected by fire. Also, the differences between many of the mentioned properties in the first 2 years after the fire was significant compared with the control area, but they have been reached to the initial values in the third and fourth years after the fire. Conclusion: Time was shown to be effective factor inrecovering soil propertiesin Karsanak region of Chaharmahal and Bakhtiari province which affected by man-made fire during 2008, 2009, 2010 and 2011. Fire accelerates splash erosion rates by as much as several folds compared to control in this area.
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