Colin Gutcher, Jason Krompart, & Peter Nowell
Objective 1: Identify the factors relating to soil erosion
| The USLE outlines the factors that influence the rate of
soil erosion and is defined by Equation 1 (Stone & Hilborn 2000,
Erdogan et al. 2006).
A = R × K × LS × C × P (1)The following is a detailed description of the factors that influence the rate of soil erosion and in turn, make up the USLE:
A) Total potential annual soil loss
The total potential annual mobilised soil, is measured in tons per acre per year. An increase in A, implies a greater rate of soil loss and, by extension, a greater risk of contaminant mobilisation (Stone & Hilborn 2000, Erdogan et al. 2006).
R) Rainfall and runoff factor
The rainfall and runoff factor is used to quantify the effect of precipitation, and its ability to initiate detachment and transport of sediment, on a field. The longer or more intense a storm event, the greater the risk of erosion and, in turn, contaminant mobilization will be (Stone & Hilborn 2000, Erdogan et al. 2006).
K) Soil erodibility factor
The erodibility factor is based primarily on a soils texture as well as its organic matter content. Soils with sandy textures have a higher erodibilty than soils with loamy textures or high clay contents. Furthermore, soils with low organic matter content or soils in which the structure is poor will have a higher erodibilty than soils with high organic matter content and good structure (Stone & Hilborn 2000, Erdogan et al. 2006).
LS) Slope length gradient factor
The slope length and gradient factor takes into account the steepness and length of the slope on which the field is located. The values are based on an empirical standard of a 9% slope that is 76.5 feet long. Slope angle affects how easily and quickly sediment is mobilised by flowing water. An increase in the length or steepness on a slope creates a greater potential for surface transport (Stone & Hilborn 2000, Erdogan et al. 2006).
C) Crop and management factor
The crop and management factor is determined by the crop type and the tillage methods utilised on agricultural fields. Crop values are based on a crop’s ability to impede erosion. For example, plants with extensive root complexes or high leaf to shoot ratios work to stabilise the surrounding soil by promoting soil aggregation or intercepting rainfall respectively. In addition, various tillage practices have different impacts on soil erosion based on the amount of soil disturbance they incur (Stone & Hilborn 2000, Erdogan et al 2006).
P) Support factor
This factor is characterised by the cropping patterns used by farmers which can directly influence erosion rates. For example, farmers may employ management practises, such as contour cropping, or install grassed waterways which work to reduce soil erosion intensities by slowing down the rate of runoff down slopes and across bare soil.