Abstract
The first part of this research project focuses on the measured effects of sheep trampling on a pastured surface soil under varying moisture levels. The results of changes in bulk density, bearing capacity and moisture retention capacity are used to formulate a 'drainage criterion' for the Otokia silt loam. This proposes a minimum depth to water table of 40 cm. Trampling at this level marks the achievement of a surface soil stability index. Both bulk density and bearing capacity values reach a maximum at this level and remain unchanged even when trampled at greater depths to the water table.
Sheep trampling effects on a convex/concave hillslope sequence are also measured. Water table surveys show that in winter the lower concave slope segments are permanently wet. Surface soil bearing capacities are correspondingly low. The upper convex slope segments are generally drier and mechanically more stable than their lower counterparts. Despite this however, significant variations in both depths to water tables and surface bearing capacities are a feature of these slopes. It is therefore concluded that all yellow/grey fragipan soils are likely to benefit from artificial drainage, irrespective of topographic contour.