Effect of cattle and sheep treading on surface configuration of a sedimentary hill soil

Abstract

Pastures with a 6-year history of grazing by cattle (cattle pasture) and sheep (sheep pasture) were used to measure the effects on soil disturbance of a single severe grazing/treading event by sheep (S), one by cattle (C1), or 2 events within 3 weeks by cattle (C2). Treatments were stocked at 35 500 kg LW 0·9 /ha (≡ 200 cattle/ha) for 48 h when the soil was wetter than the plastic limit. A control plot (untrodden, U) was grazed only lightly by sheep to control pasture cover while causing minimal observable surface damage. Change in surface contour, random roughness, soil surface damage, and pasture cover were determined with a ‘contometer’. The construction and use of the contometer to measure change in microtopography and to describe the soil surface and vegetative state by grazing is described. Disturbance was calculated as the change in height (mm) of soil level at fixed positions along transects within treatment plots. Both sheep and cattle pastures were affected similarly (P > 0·05) in relation to absolute and net disturbance of soils. Averaged across both pasture types, very little absolute surfacesoil disturbance was measured on S, whereas cattle-treading caused significant upward and downward movement of soil. Mean ( s.d.) absolute surface disturbance (sum of upward and downward movement on a transect) was greater by cattle (C1, 11·2 8·1; C2, 9·9 5·0 mm) than by sheep (5·1 1·8 mm) (P < 0·01) after the single treading and 9·0 4·1 mm for C2 after the second treading. Net disturbance (average of upward and downward movement on atransect) was 1·9 4·0, 1·8 4·0, and 3·0 1·8 mm for C1, C2, and S (P > 0·05), respectively, after the first treading and 4·1 3·7 mm for C2 after the second treading. Cumulative net disturbance resulting from C2 on sheep pasture was greater than on cattle pasture (P <0·05), especially after the first treading, suggesting sheep pasture was more susceptible to compaction than the previously damaged cattle pasture. Random roughness and percentage of surface soil penetrated by hooves, based on observation, was greater following cattle than sheep treading. Random roughness tended to increase more (P < 0·07) following treading of sheep than of cattle pastures, which were already rougher. It was concluded that the effect on soil surface configuration of severe short-term treading events on wet soils was greater by cattle than by sheep stocked at the same metabolic liveweight per hectare and that this occurred irrespective of the previous grazing history. Although absolute disturbance in each of the 2 cattle treadings in C2 was similar, net disturbance (compaction) on sheep pasture was more than twice that on cattle pasture (P < 0· 05).