Wambiana Grazing Trial: Water Quality Update to Burdekin Dry Tropics NRM

Abstract

Aside from the obvious issues of animal production, pasture condition and economic performance, a key issue in savanna management is that of soil loss and runoff. Increased sediment and nutrient inputs from grazing lands have been identified as major threats to the Great Barrier Reef (GBR) lagoon and water quality is obviously of major relevance to the grazing industry. However, an aspect usually given lesser prominence is that excessive loss of runoff and nutrients will inevitably compromise long term pasture and animal production.
Previous studies conducted on grano-diorite and sedimentary landscapes in the Burdekin catchment showed that runoff and sediment loss increased sharply as cover declined (McIvor et al., 1995; Scanlan et al., 1996). However, neither study addressed the issue of nutrient loss from these systems. Furthermore, both studies were conducted on relatively small plots: under these conditions much of the sediment moved is likely to be redeposited before entering water ways, making it difficult to extrapolate sediment losses to larger catchment scales.
Major knowledge gaps thus exist concerning the relationship between management and runoff in extensive grazing lands. These are firstly, how runoff and water quality are affected by grazing management on the relatively flat, infertile, tertiary sediments, which make up c. 20% of the Burdekin catchment. Secondly, how grazing management affects water quality. And thirdly, the extent (if any) of the trade-off between reduced soil loss and economic productivity in grazing management.
To test the effects of grazing management on soil and nutrient loss, five 1 ha minicatchments were established in December 1997 under different grazing strategies on a sedimentary landscape near Charters Towers. The objectives of the trial are to:
1. Assess the relative ability of different grazing strategies to cope with rainfall variability in terms of their effects on animal production, economics and resource condition.
2. Develop new and practical sustainable management strategies based on seasonal climate forecasting to cope with present and future rainfall variability, and
3. Promote the adoption of these strategies through direct demonstration of the benefits of sustainable management.