Fertiliser management effects on dissolved inorganic nitrogen in runoff from Australian sugarcane farms

Abstract

Dissolved inorganic nitrogen (DIN) movement from Australian sugarcane farms is believed to be a major cause of crown-of-thorns starfish outbreaks which have reduced the Great Barrier Reef coral cover by ~21% (1985–2012). We develop a daily model of DIN concentration in runoff based on >200 field monitored runoff events. Runoff DIN concentrations were related to nitrogen fertiliser application rates and decreased after application with time and cumulative rainfall. Runoff after liquid fertiliser applications had higher initial DIN concentrations, though these concentrations diminished more rapidly in comparison to granular fertiliser applications. The model was validated using an independent field dataset and provided reasonable estimates of runoff DIN concentrations based on a number of modelling efficiency score results. The runoff DIN concentration model was combined with a water balance cropping model to investigate temporal aspects of sugarcane fertiliser management. Nitrogen fertiliser application in December (start of wet season) had the highest risk of DIN movement, and this was further exacerbated in years with a climate forecast for ‘wet’ seasonal conditions. The potential utility of a climate forecasting system to predict forthcoming wet months and hence DIN loss risk is demonstrated. Earlier fertiliser application or reducing fertiliser application rates in seasons with a wet climate forecast may markedly reduce runoff DIN loads; however, it is recommended that these findings be tested at a broader scale.

Constructed Wetlands Suitability for Sugarcane Profitability, Freshwater Biodiversity and Ecosystem Services

“…It remains unexamined whether the scheme resulted in a net increase or decrease in nitrogen loading to the downstream Great Barrier Reef (GBR). An expansion and intensification of cane farming, along with increased drainage, may result in greater nitrogen leaching and runoff (Thorburn et al 2011 ; Fraser et al 2017 ). However, the constructed lagoon has the potential to denitrify runoff and offset any increased nitrogen losses (Land et al 2016 ; Adame et al 2019b ; Wallace and Waltham 2021 ), while the increased cane growth, reduced tillage from longer cane cycles (increased ratooning) and reduced fertiliser loss (from flooding) may contribute to lower nitrogen losses (Webster et al 2012 ; Skocaj et al 2013 ; Thorburn et al 2017 ).…”

Validation and calibration of Source water quality models in the Great Barrier Reef catchments

“…Improvements were made to the sugarcane paddock model which subsequently impacted on DIN loads generated within the catchment model (note: outputs from the paddock models are aggregated for a landuse within a subcatchment and uploaded into the catchment models). Firstly, a modification was made to the DIN generation algorithm which improved the correlation between fertiliser inputs and DIN runoff concentration (Fraser et al 2017). This was derived from the GBR wide pool of experimental data (collected as part of the paddock scale monitoring (Masters et al 2017)) to improve the prediction of DIN in runoff across a season.…”

Trans-Tasman Cumulative Effects Management: A Comparative Study

“…Coastal marine systems are also impacted by sediments, nutrients and other pollutants derived from landbased activities. In the GBRMP, CE operate on local and global scales (Ortiz et al, 2018), including nitrogen inputs (Fraser et al, 2017), crown-of-thorns starfish outbreaks (Fraser et al, 2017;Vercelloni et al, 2017;Ortiz et al, 2018), climate change and extreme weather events such as cyclones (Fuentes et al, 2011;Ortiz et al, 2018), and degraded water quality and warming leading to coral bleaching (Ortiz et al, 2018).…”