Hydraulic thresholds for erosion of fourteen upland mineral and organic soils were determined in a hydraulic ยฏume. These soils are from areas to be aorested in the United Kingdom. Some of the group are erosion resistant but others are susceptible to erosion once denuded of vegetation; for example, by preaorestation ploughing. These threshold data were required to calibrate a hydraulic model for eective design of preaorestation drainage networks on a variety of soils. However, simple ยฎeld measures of soil properties indicative of erosion potential would be of value to the forestry industry for management purposes. Consequently, hydraulic threshold data were related by linear regression methods to basic soil properties, including organic content, grain size, bulk density, compression strength and penetration resistance.
The investigation concluded that four peat soils are not eroded by clear water velocities up to 5ร7 m s ร1 , although a mineral bedload might induce erosion at lesser current speeds. Penetration resistance is a good ยฎeld indicator of the degree of humiยฎcation of the peat soils. Although selected physical parameters contribute resistance to water erosion, an increased organic content is pre-eminent in reducing erosion susceptibility in both organic and mineral soils. Although compressive strength was not indicative of soil erodibility, ยฎeld measurements of penetration resistance on a variety of soils could be related to hydraulic thresholds of erosion; albeit through the construction of discriminant functions interpolated by eye. Consequently, organic content (laboratory) or penetration resistance (ยฎeld) might form the basis of classifying upland soils in terms of erodibility.
Mineral soils dier widely in terms of their erodibility, so that subject to further consideration, the use of ploughing for forestry cultivation might be appropriate in wider circumstances than presently recommended by the Forests and Water Guidelines. Ploughing should be acceptable on deep peat providing the underlying mineral soil is not exposed in the bottom of the furrow, and furrows are not led from mineral soils on to deep peat. # 1997