Improved water quality outcomes from on-farm nitrogen management

Mike Bell
Led by: Prof Michael Bell , UQ


Project Summary

The sugar industry occupies 350,000ha in Reef catchments, applies >55,000t of nitrogen (N) fertilizer annually 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 zone yield potential (PZYP) combined with enhanced efficiency fertilizers (EEFs) to reduce ’surplus N’ (where applied N>crop requirements). This project is utilizing existing farm trials at identified N loss ‘hot spots’ to test PZYP as the basis for determining fertilizer N rates and for comparing EEFs with standard N fertilizers for minimizing N losses. Water quality benefits that derive from such practice changes are being evaluated. Productivity, economic and environmental indicators will validate these strategies for reducing surplus N and produce recommendations for enhanced Best Management Practices.


Project Description

Problem Statement

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 PZYP and commercially available 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 should contribute to major reductions in DIN loss off farm whilst maintaining industry productivity. Current ‘best’ practice nitrogen management recommends rates based on target yield, but the current recommended target is the district yield potential (DYP), a yield reached in only a few percent of fields (Schroeder et al. 2010, ISSCT 27). Applying N fertilizer at rates appropriate for a DYP target to consistently lower-yielding fields creates hot-spots for N contaminant export. There is a need to adopt more spatially-specific yield potentials for a sugarcane ‘production zone’ (PZYP), 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). Changing to PZYP and EEF should reduce or eliminate N hot-spots, mitigating N losses from sugarcane farms, but the extent of this mitigation has not yet been quantified and is an important knowledge gap. Quantifying the water quality improvement resulting from production zone-specific N rates will provide a foundation for the further development, promotion and adoption of this new paradigm in sugarcane N fertilizer management.

Project Activities

The project is active in four specific areas: (i) Establishing and maintaining experiments using a common design at field sites in Freshwater (1), Tully (2), Silkwood (1), Burdekin (1) and Mackay (2). These experiments are comparing standard urea fertilizer applications to the same N rates derived from combinations of the best available EEF products in the market. Fertilizer N rates are based on the conventional DYP yield target, as well as on more site-specific PZYP, with measurements of crop productivity (both cane and sugar yields) and NUE, as well as quantifying N in runoff water at two sites; (ii) A PhD project that is looking at the efficacy of various chemical inhibitors and controlled release fertiliser technologies when each of these products are applied in bands at high N fertiliser rates – the situation in sugarcane fields; (iii) Technical interactions with the fertiliser industry (product efficacy and use strategies), including comparative testing of the efficacy of different products under standard conditions; and (iv) Scientific leadership of the CANEGROWERS/Sugar Research Australia  Reef Trust Phase 4  ’EEF60’ project (as the designated Technical Steering Group for this project that involves conducting 60 EEF trials on participating cane farmer’s properties).

Significant project findings 2016-2018

The first field crop season provided evidence that EEFs are more efficient than conventional urea at increasing crop N uptake, with the second harvest due in late 2018. Differential yield responses have generally not been evident due to the high initial soil N status in most commercial cane fields. However, the higher fertilizer N uptake from the EEF treatments should deliver advantages at lower fertiliser N rates as soil N reserves decline during the 2-year project extension.

N losses in runoff at both Silkwood and Freshwater sites have been lower with lower N rates. N losses were also lower under EEF management compared to urea at the same N application rate. In combination, lower rates and EEFs have reduced runoff losses by up to 60%, an outcome that if replicated in all cane growing regions with high N losses, would see the sugar industry contribute significantly to meeting Reef 2050 Plan DIN targets.

The laboratory studies have shown that the chemical environment in and around an N fertilizer band appears to be a serious limitation to the effectiveness of either controlled release or inhibitor technologies deployed to slow N release and match crop N demands. This has significant implications for the development of new fertiliser products and for use of inhibitor technology, and has generated considerable interest from the fertiliser industry. Results suggest that blending technologies may moderate these effects, but this has yet to be tested.

Strong linkages have been developed with a large number of fertiliser manufacturers and distributors, with indications that greater industry involvement in, and financial support of, research into effective EEF use may develop in the future.

Project staff are the designated Technical Steering Group for the Reef Trust 4/EEF60 project, which is in its first year of experimentation and proceeding well.

Planned activity 2019-2020

During the additional two years the project will (i) Extend the duration of field sites to cover a full crop cycle that experiences a broader range of wet season conditions. This will allow better testing of the water quality benefits of EEFs and the cane crop responses to differential N products and rates; (ii).Validate the estimates of fertiliser N recovery derived from biomass sampling and mass balance calculations from the field sites using natural isotope relative abundance techniques; (iii). Using the techniques and methodologies developed in the PhD program to study N dynamics in bands of urea or specific EEF products, explore the benefits and risks associated with blending EEFs with differing modes of action in fertiliser bands. This will provide the scientific knowledge to interpret results from field trials in this project and Reef Trust4/EEF60; (iv). Identify (through modelling and the development of a simple user-friendly decision support framework) and communicate to industry the circumstances (climate, harvest date, fertilising date, soil type etc) where EEF use and reduced N application rates provide the greatest water quality benefits at minimal risk of productivity losses; and (v) Continue to provide scientific leadership to the Reef Trust Phase IV/EEF60 program and guidance to the commercial fertiliser manufacturers and retailers servicing the sugar industry.

Project inclusions and exclusions

Inclusions – Effective engagement with end-users and stakeholders on project outcomes, with a focus on the Wet Tropics, Burdekin and Mackay-Whitsunday regions.

Exclusions – Training of end users in any decision support tools developed as project outputs.

Links with other projects and hubs

The projects listed below are using consistent methodology to measure nutrient bioavailability, enabling results to be integrated from source (production zone to sink (GBR lagoon).

  • NESP TWQ Hub Project 2.1.5 Steve Lewis et al., ‘What’s really damaging the Reef? Tracing the origin and fate of the environmentally detrimental sediment’
  • Burton et al., ‘RP128G Sources of Bioavailable Particulate Nutrients Phase 1 and Phase 2’ EHP Reef Water Quality Science Program
  • Moody et al., ‘2015/069 Decision support for informed nitrogen management: Soil nitrogen mineralization tests and assessment of soil N contribution to crop N requirements’ SRA N Use Efficiency Program.

Salter, Ashburner et al., ‘Reef Trust 4/EEF60’ project, testing EEF products and reduced N rates at 60 field sites across GBR catchments.


NESP 2017 Research Priority Alignment

This project aligns with TWQ Hub Research Theme 1 (Improved understanding of the impacts, including cumulative impacts, and pressures on priority freshwater, coastal and marine ecosystems and species) and specifically to Sub-theme 1.2 (Develop practical improvements to land management practices that will influence behavioural change and improve outcomes for tropical water quality and ecosystem health) in the NESP 2017 Research priorities.

Project activities also directly address two priority knowledge needs of the Reef 2050 Water Quality Improvement Plan RD&I Strategy (2017–2022): N.1- Knowledge, data and tools to underpin a Nutrient Decision Support Tool, and N.3 – Improved understanding of the complexities of paddock-scale nutrient budgets and the effect on water quality.


Project Keywords

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


Project Funding

This project is jointly funded through UQ, CSIRO, Dept of Environment and Science (Office of the GBR), Dept of Environment and Science (Science Div.), Dept of Natural Resources, Mines & Energy, Sugar Research Australia, Farmacist and the Australian Government’s National Environmental Science Program.


Project Publications
Peer Reviewed Paper