MEASUREMENT OF RUNOFF AND SOIL-EROSION ON REGULARLY CULTIVATED FIELDSIN SWITZERLAND - SOME CRITICAL CONSIDERATIONS

In field measurements of soil erosion spatial variability is usually n eglected. Due to natural site conditions, however, considerable variat ions of runoff and soil loss can occur even within apparently homogene ous fields. This was observed on large (75 m(2)) erosion test plots in triple replication in a forage-maize cropping experiment. The variabi lity, with mean coefficients of variation ranging from 30% to 50%, par tially obscures the expected differences between the compared treatmen ts. Soil loss computations based on unit area (e.g. single plots) thus hardly allow comparisons among dissimilar sites and treatments or an extrapolation to larger areas. Thus for the presented experimental des ign we suggest as many replications as possible. At a similiar level o f measurement accuracy, this is easier attainable with a flexible set- up and open plots than with permanently installed large experimental s tations.