The unit plot of the Universal soil loss equation (USLE): Myth or reality?

Abstract

Soil erosion by water is a natural phenomenon involving landscape changes that can be accelerated by anthropogenic actions. Notwithstanding many mathematical models have been developed to estimate soil loss at different spatial and temporal scales, the Universal Soil Loss Equation (USLE) and its revisions remains the most applied one. The mathematical structure of the USLE was deduced using a reference condition, named unit plot, that was defined as a 22.1 m long plot, with a 9% slope, maintained in a continuous, regularly tilled, fallow condition with up and down hill tillage. The unit plot concept was used to compare soil loss data collected on plots having different slopes, lengths, cropping and management and conservation practices. The importance of the unit plot concept and its centrality in the field measurement of the dimensionless factors of the USLE has received little attention. In particular, the availability of soil loss measurements on unit plots is somewhat uncertain. This paper gives an overview on the unit plot concept, its origin, the availability of soil loss measurements in the unit plot conditions and its use for the determination of the USLE factors.