EFFECT OF SHEEP TREADING AND GRAZING ON PASTURE AND SOIL CHARACTERISTICS OF IRRIGATED ANNUAL PASTURES

The two experiments reported examined the effects of sheep treading on pasture growth and soil characteristics on autumn-irrigated subterranean clover-Wimmera ryegrass pastures and their subsequent influence on winter production. Treading only (experiment 1) increased the bulk density of soil by 40% as the stocking rate increased from 0 to 39.2 sheep ha-1. This caused a 33% reduction in late winter production (July), the decline (675 kg ha-1) being due mainly to a reduction in the proportion of ryegrass in the pasture. The combined impacts of treading and grazing (experiment 2) proved more detrimental to subsequent pasture recovery. At the July measurement, treading reduced production by 20% when the stocking rate was increased from 0 to 19.6 sheep ha-1, while the combined effect produced a 58% loss in yield. In addition to stocking rate, the length of the pre-grazing establishment period proved critical, with greater compaction evident in plots stocked 24 h after irrigation. This compaction affected the botanical composition, significantly more ryegrass being present in compacted plots, although increased tillering was encouraged by intense defoliation at high stocking rates which intensified this effect. © 1979 CSIRO.