Identifying critical soil water thresholds to decrease cattle treading damage risk.

Dairy cattle grazing on wet soils can have a negative effect on soil physical quality and future pasture production. A laboratory based method, ‘the proctor test’, has been used to identify the critical water content (CWC) at which the onset of cattle treading damage occurs in two Pallic soils collected from North and South Otago, New Zealand. The sampling locations were contrasting in their climate and topography yet similar in their landuse (dairying). We have attempted to relate the CWC to simple field–based metrics (the soil plastic limit [PL] and a critical soil water deficit [SWD]) that can be deployed by farmers at a given location. The PL was a poor indicator of the compaction risk (i.e. the CWC) which in the Pallic soils assessed occurred at SWCs less than field capacity (FC). To avoid compaction in these soils, the use of a threshold SWD, in this case 3mm, is expected to be a useful metric to guide grazing practices that reduce the impact of cow treading damage.