RRRD009 Progress Updates

November 2012

Science Summary:

-  During the 2010 and 2011 hydrological years, total nitrogen loads from the butterfly pea pasture have exceeded those of brigalow scrub, grass only pasture and grass/leucaena pasture on a kg/ha basis. A lower EMC for butterfly pea in 2011 compared to 2010 indicates that the establishment phase of the pasture may be particularly susceptible to nitrogen loss.

-  Bias in the load estimation techniques previously used in the 2011 hydrological year have been removed with new methodology, and the refined data is now ready for provision to users including the Paddock to Reef program. Using the refined load estimation techniques, data from the 2011 hydrological year shows similar or lower loads of TSS and nitrogen (total and species) from buffel grass and leucaena pastures compared to native Brigalow Scrub. Orthophosphate load from buffel grass pastures continues to be greater than that of virgin Brigalow Scrub. Loads of TSS, nitrogen (total and species) and phosphorus (total and species) from young (<5 year) butterfly pea ley pasture continue to equal or exceed all other catchments.

-  The extension of this work into the Burnett-Mary and Burdekin catchments was undertaken using rainfall simulation. Post-wet season simulations at both sites demonstrated that more rainfall was required to generate runoff from legume based pastures compared to grass only pastures. This “sponge” effect of cracking clay soils calls in to question the suitability of rainfall simulation in these landscapes.

-  Estimation of sediment and nutrient loads over time were obtained by applying EMC data collected from 2000 onward to modelled daily flow data from the catchments covering the period 1984 to 2004. Cumulative sediment loads from cropping over the 21 year period are an order of magnitude greater than pasture, with both land uses showing an increase in sediment load due to land use change. A reduction in the rate of cumulative load for cropping post 1998 coincides with a switch to minimum tillage and opportunity cropping. Total nitrogen loads over the same period show an increase in load from cropping as a result of land use change. However, loads from pasture show a reduction compared to loads from the native brigalow vegetation. The reduction of load from pasture is an order of magnitude larger than the increase in load from cropping.

Progress Update:

-  A late break to the 2011 wet season resulted in no new water quality data until 2012. One communication activity has been held over into 2012 due to this lack of data. All other scheduled data collection, analysis and communication activities were completed as proposed.

-  Quarterly soil and pasture sampling for the end of winter period have been completed. Sample processing is continuing and samples will be submitted for analysis in January.

-  Field operations to July 2012 and data available since project commencement were reported in a combined progress report.

-  The rainfall simulation component of the program has been completed well ahead of schedule. The final simulation was the Burdekin Catchment site, end of dry season, and was done in this reporting period. First cut analysis of the flow and water quality data is being undertaken.