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

Grant Fraser,Ken Rohde,Mark Silburn

doi:10.1007/s10661-017-6115-z

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.

Highlights

Dissolved inorganic nitrogen and the Great Barrier ReefMovement of dissolved inorganic nitrogen (DIN) from fertilised agricultural lands has been identified as a major water quality issue internationally (e.g. Howarth et al 2002; Schindler et al 2006; Swaney et al 2012) and within Australia (e.g. Mitchell et al 2009; Kroon et al 2012; Thorburn et al 2013)
As sugarcane has the highest concentrations of DIN in runoff and is in close proximity to the Great Barrier Reef (GBR), sugarcane farm management of nitrogen fertiliser has been a major focus of the government initiative
We develop a daily time-step empirical model of DIN concentrations in runoff that can be incorporated into paddock-scale hydrological models and which represent the effects of the main management practices available to sugarcane growers, i.e. N rate, N form and timing of application

Summary

Introduction

Dissolved inorganic nitrogen and the Great Barrier ReefMovement of dissolved inorganic nitrogen (DIN) from fertilised agricultural lands has been identified as a major water quality issue internationally (e.g. Howarth et al 2002; Schindler et al 2006; Swaney et al 2012) and within Australia (e.g. Mitchell et al 2009; Kroon et al 2012; Thorburn et al 2013). Movement of dissolved inorganic nitrogen (DIN) from fertilised agricultural lands has been identified as a major water quality issue internationally Sugarcane production occurs in coastal catchments adjoining the GBR (Fig. 1), and it is estimated that runoff DIN loads to the GBR have increased by threefold since preEuropean times (Kroon et al 2012). Catchments dominated by sugarcane production were found to have the highest median DIN runoff concentrations when compared to a range of other agricultural and non-agricultural land uses (Bartley et al 2012). As sugarcane has the highest concentrations of DIN in runoff and is in close proximity to the GBR, sugarcane farm management of nitrogen fertiliser has been a major focus of the government initiative. There have been a number of experiments monitoring DIN runoff loads from sugarcane farms

Objectives

Results

Conclusion