Sugarcane industry mill mud management will not report nutrient saving for individual projects

November 2022 release

The dissolved inorganic nitrogen (DIN)savings from mill mud management are represented in catchment models rather than the P2R projector tool. Mill mud is a by-product of the sugar milling process and the majority of it is spread across cane paddocks. There are significant amounts on nitrogen (N) in mill mud and by reducing the application on one farm, it may reduce DIN generation and loss from that farm.

However, the remaining mill mud can be applied elsewhere in the catchment, meaning landholders cannot guarantee that there is a net reduction in DIN to the Reef by farm scale mill mud management programs.

Previous versions of P2R Projector (up to Nov 2022) accounted for the use of mill mud as part of the farm scale N balance for determining potential N surplus. P2R Projector would account for reported changes in ‘before’ and ‘after’ mill mud application rates to determine the overall N budget and potential DIN savings. Changing the mill mud application rate between the ‘before’ and ‘after’ surveys results in no estimated DIN load reductions in the P2R projector tool. The ‘before’ mill mud application rate is the default value used for both the before and after case (as of Nov 2022 release).

The mill mud use questions have been retained in the sugarcane practice survey because they are used in the collective Paddock to Reef Integrated Monitoring, Modelling and Reporting program (Paddock to Reef program). The Paddock to Reef program level modelling considers the collective impact of all previously reported practice change, and as such the modelling approach has the capacity to include the impact of spatial patterns of changes in in mill mud use.