Wambiana grazing trial Phase 2: stocking and spelling strategies for improving carrying capacity and land condition in North Australian grazing lands

Summary

In Phase 2 of the Wambiana trial (2010-2014) some treatments were modified to determine whether flexible stocking +/- wet season spelling could sustainably deliver higher profitability than constant moderate stocking (MSR), moderate stocking with rotational spelling (R/Spell) or heavy stocking (HSR). Due to wet conditions and a controlled burn, new treatments were only fully implemented for two seasons.
Despite seven good-average years, pasture condition was worst in the HSR but best in the MSR and R/Spell, followed by the two flexible strategies. Bothriochloa pertusa has increased dramatically in all treatments, with the greatest increase in the HSR. The decline in land condition in the HSR has reduced carrying capacity but not rainfall use efficiency. Individual animal performance (weight gain, carcass grade) was highest in the R/Spell and MSR, followed by the flexible strategies, but lowest in the HSR. Conversely, LWG/ha was greatest in the HSR. Despite recent good years, accumulated gross margin in the HSR remains far below that of the other treatments. The present short term results indicate that flexible stocking (+/-spelling) is no more profitable or sustainable than constant moderate stocking (+/- spelling) at long term carrying capacity.
Enterprise level bioeconomic modelling with breeders confirmed that profitability and pasture condition are maximised at moderate stocking rates under either constant or low flexibility stocking strategies. However, the optimum stocking rate varied with climate window reinforcing the need to adjust stocking rates with rainfall.
While there has been insufficient time to fully assess the new Flex and Flex+S strategies, the trial results and bioeconomic modelling, both indicate that profitability will be maximised and land condition maintained/improved by adjusting stocking rates as seasons change in a flexible, risk averse fashion, around long term carrying capacity.