Determination of soil erodibility using fluid energy method and measurement of the eroded mass

Publication date: 15 December 2016
Source:Geoderma, Volume 284
Author(s): Derege Tsegaye Meshesha, Atsushi Tsunekawa, Nigussie Haregeweyn
The resistance of soil to erosional processes, especially in hillslopes is generally well recognized and documented in many researches, however, the full implications of tillage (soil disturbance) and slope degree on erodibility of a soil are not considered and well investigated. Thus, in this paper we particularly examined the impact of tillage (soil disturbance) and surface slope on the erodibility of four types of soils (Masa, Oxisols, Andosols, Sand soil), and determined their thresholds of soil water content (SWC) and erosivity that initiate soil erosion. The soil samples were obtained in disturbed form, where the natural conditions of the soils such as structure, density and shear strength were changed. Hence, systematic compaction (soil pressing) treatment was carried out for a couple of months with the concept that the treated soil will be a surrogate of the soil at field condition (untilled-fallow soil) and the disturbed soil represents the soil in its tilled condition. We used dripper type of rainfall simulator to generate runoff and the suspended sediment concentration (SSC) in the runoff was measured using optical backscatter sensor, and the infiltration rate was measured with Mini disk portable tension infiltrometer. We used optical disdrometer under simulated rainfall to measure raindrop size, splash kinetic energy and erosivity of rain events; thereby, we applied fluid energy method to determine erodibility of different soils. The results revealed that both in disturbed and treated conditions, erodibility of Oxisols was the highest followed by Andosols, Masa and Sand soil. After the treatment, erodibility and threshold of SWC significantly decreased in most of the soils while their threshold of erosivity increased; and this implies that the treated soils had better resistance to erosion than disturbed soils. Slope had also notable impact on erodibility (thah/MJmmha) of all soils, where the measured soil erodibility varied from 0.08 to 0.21 in the gentlest slope (5.2°) and from 0.21 to 0.49 for the steepest slope (35.3°). Particularly, the erodibility of Oxisols and Andosols showed a remarkable increase in the steeper slope. Furthermore, the finding showed that erodibility, thresholds of SWC (%) and erosivity were different for different soils considered in the study. Masa soil had the lowest threshold of SWC and erosivity to initiate erosion followed by Sand soil, Oxisols and Andosols. In general, the treated soils had lower erodibility than the disturbed soil. The erodibility of all soils increased with slope, however, Oxisols and Andosols showed a significant increase towards higher slope degree. Thus, tilling steep slope areas of the latter two soils might cause significant erosion and soil loss due to their substantial increase in erodibility towards higher slope.