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Soil loss at the field level is mainly due to the actions of water, wind, or activities such as tillage. Top soil normally has a high organic matter and loss of these soils may affect productivity and also have downstream effects such as pollution of adjacent wetlands.
How to operationalize the metric
Method of data collection and data needed to compute the method:
Erosion caused at the plot or field scale has traditionally been measured with Wischmeier plots, where water (runoff) and soil (erosion) that runs off of the plot are captured at the bottom of the field. These plots are expensive to install and it is costly to collect and analyze the materials. They can be useful for comparing the effects of different soil management interventions on different soils and slopes, but are usually done on research plots by soil physicists and not recommended otherwise. This methodology can result in overestimates of erosion losses, because the possible redistribution of soil among small plots within a field is not accounted for and there could be no net losses at the field scale.
Instead we recommend approaching this metric by estimating the different factors that can contribute to erosion by water. These factors include: landscape features, steepness and length of slope of the field, vegetative cover and soils management, and rainfall erosivity. These factors have been combined into the Universal Soil Loss Equation (USLE or Modified USLE) (Wischmeier and Smith, 1978; Renard et al., 1991) where erosion is estimated or modeled. If measures of these different erosion factors are difficult and the models not available, the relative erosion of different interventions within a site (or between sites) could be compared through visual observations of these factors and ranked as to the most to least important for the different interventions.
Unit of analysis:
Tons of soil lost per hectare per year (t/ha/yr) is the unit of analysis for the soil erosion/loss indicator.
Limitations regarding estimating and interpreting:
This method may be costly and may likely overestimates of soil erosion.