Improved Water Quality Outcomes from On-Farm Nitrogen Management

Mike Bell
Led by: Prof Mike Bell, UQ


Project Summary

The sugar industry occupies 350,000ha in Reef catchments, applied 58,000t of nitrogen (N) fertilizer in 2014 and is a major contributor of dissolved inorganic nitrogen (DIN) to Great Barrier Reef receiving waters. There are many potential mechanisms for reducing on-farm N usage. However, the comprehensive review of N use in sugarcane (SRA/DoE 2014) identified widespread over-use of N fertilizer and recommended adopting production unit yield potential (PUYP) combined with enhanced efficiency fertilizers (EEFs) to reduce ’surplus N’ (where applied N>crop requirements). This project will combine with existing farm trials at identified N loss ‘hot spots’ to test PUYP as the basis for determining fertilizer N rates and compare EEFs with standard N fertilizers for minimizing N losses, and to examine the water quality benefits that derive from such practice changes. Productivity, economic and environmental indicators will validate these strategies for reducing surplus N and produce recommendations for enhanced BMP’s.

Problem Statements


Dissolved inorganic nitrogen (DIN) from agriculture is a major contributor of DIN to the Great Barrier Reef (2015 Scientific Consensus statement). The ‘Review of Nitrogen Use Efficiency in Sugarcane’ (SRA/DoE, 2014) identified widespread over-use of N fertilizer in the industry and recommended the use of production unit yield potential (PUYP) and commercially available enhanced efficiency fertilizers (EEFs) to improve the efficiency of sugarcane N use. The combination of these approaches will allow lower fertilizer N application rates, reduced ’surplus N’ (where applied N>crop requirements) and contribute to major reductions in DIN loss off farm whilst maintaining industry productivity. Current ‘best’ practice nitrogen management recommends rates based on target yield. Fundamentally this approach is sound; however the current recommended target is the district yield potential, a yield reached in only a few percent of fields (Schroeder et al. 2010, ISSCT 27). Applying nitrogen fertilizer at rates appropriate for district yield potential to consistently lower-yielding fields creates hot-spots for nitrogen contaminant export. For this reason there is a push towards using more spatially-specific yield potentials for a sugarcane ‘production unit’ (PUYP), whether this be a whole farm, a number of similar blocks within a farm, an individual block, or a sub-block unit, as the basis for determining N rate (Bell 2015, NUE Review).

There is good logic that changing to PUYP and EEF should reduce or eliminate N hot-spots, mitigating nitrogen losses from sugarcane farms. However the extent of this mitigation has not yet been measured in the field. This is an important knowledge gap that needs to be addressed. Quantifying the water quality improvement resulting from production unit-specific nitrogen rates will provide a foundation for the further development, promotion and adoption of this new paradigm in sugarcane nitrogen fertilizer management.

How Research Addresses Problem

This project will focus in two key topical areas:

1.) Recommended practices and benefits of adopting the use of Enhanced Efficiency Fertilisers. At identified N loss hot spots undertake replicated on-farm N experiments comparing EEFs with standard N fertilizers and measure key agronomic (crop N demand at different growth stages), productivity (cane and sugar yield response to reduced N application rates), economic (incremental marginal return from fertilizer N applied) and environmental (crop N uptake efficiency; off-site N movement by runoff, drainage and/or denitrification) indicators to validate these strategies for reducing surplus N, and understanding the longevity of nitrification inhibition and the dynamics of the controlled release products at the various field trial locations. Results will be used to develop a predictive index for nitrification inhibitor longevity. Findings will be incorporated into the decision support tools, one possible example being SafeGauge for Nutrients (DSITI) that can be used by growers/advisors to adjust fertilizer management on a site/soil specific basis to minimize risk of off-site N movement.

2.) Moving from District to PUYP. By linking with grower groups and research projects defining the appropriate nitrogen rates for PUYP to: (1) measure the reduction in off-site N loss impacting water quality/greenhouse gas emissions from this new management approach, (2) assess the longevity of the improvement and sustainability of production, and (3) assess the region-wide potential benefits from moving to production unit-specific nitrogen management. We will then use this information, together with information of yield variability, appropriate yield targets and modelling to determine regional-scale potential water quality benefits. These activities will also serve to demonstrate the benefits of this fertilizer management approach and provide a platform for influencing behavioural change to improve water quality outcomes.

Alignment with NESP Research Priorities

Aligns with the following priorities nominated by the TWQ Hub for this round:

1c) On-farm nutrient and sediment loss mitigation and capture and land management practices to improve water quality outcomes.

1d) Practical methods for minimizing nutrient and sediment movement off-farm.

1e) New methods for encouraging behaviour/practice change/improved compliance with BMP.

This project aligns with the above NESP priorities because it will test the ability of two key onfarm N-management strategies to reduce water quality and greenhouse gas emission impacts via reductions in the amount of N-fertiliser applied to farms. By demonstrating that yield can be maintained whilst reducing the rate of N application, this should encourage practice change toward the adoption of enhanced efficiency fertilisers and production unit yield potential rather than district yield potential.

Project Keywords

Nitrogen use efficiency; Sugarcane cropping system; Enhanced efficiency fertilizers; Productivity unit; Yield potential.

Project Funding

This project is jointly funded through UQ, DSITIA, DEHP, CSIRO, DNRM, Sugar Research Australia, Farmasist and the Australian Government’s National Environmental Science Programme.

Project Publications
Conference Presentation
Media Release




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