Assessing the production and economic benefits from preventing cows grazing on wet soils in New Zealand

On a North Otago dairy farm in New Zealand, eight experimental plots (10 m x 25 m) were monitored for four years to assess whether preventing dairy cow grazing of wet pastures (deferred grazing) during the milking season would improve soil structure and pasture production compared to an unrestricted access to pastures (control). Although the Pallic soil type was highly vulnerable to treading pressure, the landscape and climate in North Otago limited the number of wet days, resulting in only a few deferred grazing events each milking season. Although soils under deferred grazing management had significantly higher total porosity, no significant improvement in macroporosity was apparent throughout the four years of research with values ranging between 0.112 and 0.146 m3/m3, which was always above the minimum guideline value of 0.100 m3/m3 for optimal pasture production. Annual pasture production did not differ between the control and deferred grazing treatments, averaging 17.0±3.8 and 17.9±4.1 t DM/ha/yr, respectively (P>0.05). The DairyNZ Whole Farm Model was used to scale-up results from the plot trial to a farm system level and ascertain the cost-benefit of deferred grazing management. An additional scenario was also tested in which cows were allowed to graze for only 8 hours when soils were wet (short duration grazing). Modelling indicated that removing cows from wet soils using either deferred or short duration grazing during the milking season in North Otago was not effective in increasing farm operating profit. However, short duration grazing was associated with a higher whole farm operating profit compared to deferred grazing and was only marginally less profitable than the control.