Refining nitrogen management under different conditions: economic results from preliminary grower-demonstration trials

Abstract

Economic findings are presented on a selection of refined nitrogen (N) rate demonstration trials conducted in the Wet Tropics, Burdekin and Mackay-Whitsunday regions of Queensland. Different N rates were examined to account for nutrients supplied by break crops, mill-by-products and groundwater irrigation. Reduced N rates were also considered in final ratoons, on cane varieties with perceived higher N-use efficiency, and where nitrification-inhibiting fertilisers were applied. Approaches to refined N rates were
aligned to industry-led programs such as SIX EASY STEPS™ (6ES) and the more recent 6ES Toolbox. Past research has identified that applying N rates above 6ES guidelines often reduced grower profitability. Refining N rates to account for organic sources of N and consideration of production characteristics may provide opportunity for growers to improve profitability whilst maintaining or improving production levels. Agronomists supporting Project Catalyst conducted 11 grower demonstration trials between 2018 and
2020. This program aims to reduce dissolved nutrients, sediment and pesticide loss from sugarcane farms using innovative farm practice improvements. The N treatments evaluated in these trials included standard grower rates, 6ES guideline rates (through following the full 6ES rather than simply following the regulated method) or the 6ES Toolbox to account for alternative sources of N. Yields and commercial cane sugar levels (CCS) from different treatments were analysed. Data on revenue and costs were collected to calculate gross margins and relative profitability of treatments. The largest impact on grower profitability was associated with the groundwater-N trials. Despite results showing improved or maintained gross margins for refined N rates in most trials, there were no significant differences. Although demonstration trials provide a good resource to improve practice adoption by growers, longer-term trials and increased replication across a wider variety of sites are needed to validate refined N management and improve confidence in the results.