Erosion processes and erodibility of cultivated soils in North Rhine‐Westphalia under artificial rain. I. Site characteristics and results of laboratory experiments

Soil erosion by water causes substantial on‐site degradation and off‐site damages in the densely populated state of North Rhine‐Westphalia (Germany). Measures of soil conservation should be adjusted to soil erodibilities and should be based on an understanding of the processes involved in water erosion including aggregate breakdown, rainsplash erosion, surface sealing, and soil loss. For a state‐wide assessment of erosion processes and erodibilities, we tested representative cultivated soils of North Rhine‐Westphalia in laboratory and field experiments with artificial rain. In the laboratory experiments described in this paper, rainsplash erosion, sealing susceptibility, and interrill erodibility of 25 topsoils filled in 0.5 m² boxes were investigated. Results of different aggregate‐stability tests correlate with organic‐matter contents but not with parameters of rainsplash or soil loss. On most soil materials, rainsplash increases or maintains constant rates in the course of the simulation runs indicating that the soil surface did not attain a higher shear resistance. High sealing susceptibilities are found for soils of quite different textures ranging from loam sand to silt clay, whereas other silt clays, clay loams, and some clay silts maintain high infiltration rates. A trend of increasing sealing susceptibility and total soil loss with increasing clay content is observed for the loam sands to sand loams. Dynamics of soil loss is largely governed by runoff rates. Total soil loss is also determined by sediment concentration in surface runoff, which is low on most clayey soils, on loam sands poor in clay, and on a sand loam, and high in the case of highly erodible clay silts, loam sands, and sand loams. The most crust prone soils are not necessarily the most erodible. On most soils, soil‐loss rates do not stabilize until the end of the rainfall experiments. For comparing the interrill erodibilities of the soils, total soil loss is preferred instead of interrill erodibility factors (K_i, K_iq) published in the literature.