Comparison and quantitative assessment of two regional soil erosion survey approaches

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Regional soil erosion surveys are the first step of soil conservation planning. Grid and sampling approaches are commonly used for soil erosion surveys at the regional scale. With the grid approach, the region is divided into grids (e.g., 1 km × 1 km), and the soil erosion rate of each grid was calculated. With the sampling approach, a small portion of the area (typically 4% or less) was taken and then the soil erosion rate was calculated. Based on the above calculation, both approaches evaluated the soil erosion area (which is the area where the soil erosion rate is greater than the soil loss tolerance (t)) and its distribution in the whole region. The purpose of this paper is to compare the assessment results of the two approaches and analyse their practicality using Yunyang County, Chongqing, China (area is 3636 km2). The soil erosion rate, percentage of soil erosion area (PSEA, which is the ratio of the area where the soil erosion rate is greater than the soil loss tolerance (t) to the area of the total study region) and its spatial distribution were compared between the two approaches. The results showed that the grid approach overestimated the average soil erosion rate and PSEA overall for all 33 sample units and the whole region in comparison to the sampling approach. The sampling approach can yield a reasonable spatial distribution of the soil erosion rate in the whole region. In addition, the soil erosion regions were more clustered than those using the grid approach, which can be more suitable for soil conservation planning. Therefore, the sampling approach is an efficient and practical approach in regional soil erosion surveys. The results can provide insights into regional soil erosion surveys.