Effect of sheep and cattle treading damage on soil microporosity and soil water holding capacity

With the recent introduction of a large scale district irrigation scheme into the North Otago Rolling Downlands (NORD) of New Zealand, land use has intensified including a shift from dryland sheep farming to irrigated dairying. Land use change and intensification has lead to considerably greater physical pressure on soils and has been associated with a decline in soil physical condition. A farmlet trial was established in the NORD to compare the influence of four farm management systems; cattle irrigated, cattle dryland, sheep irrigated and sheep dryland on soil structure. Soil compaction under irrigated cattle grazed pasture caused a significant decline in readily available water (RAW) relative to all other treatments. A decline in total porosity and pore size indicated a lower irrigation volume applied more frequently will be required to maintain soil matric potential between irrigation trigger point (−100 kPa) and field capacity (−10 kPa). Changes in soil water release characteristics under animal grazing may also limit the rate of natural soil structural recovery thereby increasing the risk of repeated soil damage with on-going grazing, particularly under cattle irrigated pasture, where the initial damage was most severe.

► Land use intensification is associated with a decline in soil physical condition.
► Readily available water significantly lower under irrigated cattle grazed pasture.
► Soil compaction means reduced irrigation depths to avoid surface water run-off.