PDS Jimbour: Demonstrating and Testing land condition recovery and enhancement strategies in the Jimbour Uplands sub-catchment of the Darling Downs

Summary

Pasture management workshops were organised in late 2007 to establish a common understanding among landholders about pasture ecology and the historical management practices that had contributed to land condition decline in the district. As a result of the workshops, six demonstration sites were established in the Brigalow Jimbour floodplain catchment to trial strategies for improving land condition on degraded, C condition paddocks (using the ABCD condition categories). Five of the six paddocks were old cultivation and all had ongoing problems with broadleaf weeds, patchiness in pasture composition and soil surface condition.
Strategies to address these problems included using broadleaf herbicides, re-sowing pasture, ripping the soil surface and splitting paddocks with a fence. All strategies were underpinned by the proven principles of wet season spelling and maintaining a minimum level of grass stubble throughout the dry season. The quickest pasture recovery time was found to occur when paddocks had broadleaf weeds suppressed early in the wet season and were then given an entire wet season spell. A return to A condition from C land condition was achieved within three years of applying this strategy with average summer rainfalls.
The most improved paddock experienced a change from 0.9% to 4.2% pasture basal area over the project period. This wasalso the best strategy from an economic point of view with a benefit-cost ratio of 1.91:1, which indicates for every dollar invested, $1.91 was generated. Costs were minimised in this demonstration by only treating the worst affected area of the paddock. The slowest returning strategy had a high capital outlay and the least improvement in land condition after three years. Paddocks that were returned to A land condition within three years performed the best economically, regardless of strategy and capital outlay. This effect was accelerated with increasing summer rainfall. Where 3P species still comprised approximately 30% of the pasture and soil surface condition was good, a combination of broadleaf herbicides and wet season spelling gave a quicker improvement in condition than re-sowing pastures. 
The financial benefit of re-sowing pastures is largely governed by achieving a quick return to A land condition. Two of the demonstrations in this project re-sowed pasture, however one returned to A land condition within three years while the other achieved only B land condition within the three years of the project and had higher costs per hectare. The benefit-cost paybacks for these two demonstrations were 1.70:1 and 1.08:1, respectively. An important consideration with re-sowing pastures is also the ability to sustain the improved land condition in the longer term. For both of the strategies implemented, there are issues with how best to maintain land condition in the long term. The paddock which returned quickly to A condition is now dominated by Rhodes grass and is already showing signs of nitrogen deficiency. The risks with this paddock are (1) that with another extended period of dry conditions the Rhodes could die out and once again provide opportunity for broadleaf weeds to encroach and drop the long-term carrying capacity, and (2) with the paddock already showing signs of nitrogen deficiency, pasture yield, liveweight gain and carrying capacity will decline over time without regular fertilising or establishment of a legume. For the second re-sow option, the short-lived perennial silk sorghum was a dominant coloniser in the heavy soils of the paddock. In future years it is likely that the silk sorghum will die out and also provide opportunity for broadleaf weeds to encroach if there has not been adequate density of 3P grass species to seed and spread to the bare areas.