Grazing strategies to protect soil physical properties and maximise pasture yield on a Southland dairy farm

Intensive dairy cattle grazing on wet soil can have a detrimental effect on soil physical quality and consequently on pasture production. Soil physical properties (porosity, bulk density, saturated hydraulic conductivity) of a Pallic soil (Pukemutu silt loam) and pasture production were assessed on a dairy farm in Southland, New Zealand, under a number of different cattle grazing strategies: (i) normal grazing management on undrained land, (ii) normal grazing practice on drained land, (iii) restricted autumn grazing, (iv) restricted grazing when soil conditions were wet, (v) never pugged, and (vi) never grazed. A hand-pushed cone penetrometer determined treatments (iv) and (v). Soil macroporosity was significantly greater (P < 0.05) on the never grazed plot than all other treatments at post-spring sampling each year. There were no significant differences in any soil physical properties measured on cattle grazed treatments. Spring pasture yield from the never grazed treatment was greater (P < 0.05) than the drained and undrained standard practice grazing treatments for one of the three seasons. The lack of treatment differences in soil physical properties and pasture yield from grazing treatments suggests that the never pugged grazing strategy failed to prevent soil compaction by dairy cows. To some extent this is expected as soil compaction occurs at soil water contents lower than the thresholds for pugging damage. However, the large number of grazing events when soil conditions were considered safe according to the never pugged treatment protocol, but when soil water content was greater than the plastic limit, probably contributed to both soil treading damage and compaction during the traditionally wet early spring period.