Assessment of nitrification inhibitors in a glasshouse experiment to investigate nitrogen-loss pathways in sugarcane

Nitrogen (N) loss is an important issue for the sugarcane industry in tropical Australia because of offsite environmental impacts. Enhanced efficiency fertilisers (EEFs) (which include nitrification inhibitors and nitrogen stabilisers) have the potential to reduce nutrient losses leading to improvements in nutrient-uptake efficiency, productivity gains and improved environmental outcomes. A glasshouse experiment compared fertiliser N lost in drainage and as nitrous oxide (N 2O) for conventional urea, urea treated with DMPP (3,4-dimethylpyrazole phosphate) (traded as Entec™) and urea with two levels of nitrapyrin (traded as eNtrench™ Nitrogen Stabiliser) applied at a rate equivalent to 100 kg N/ha. Yield indicators, soil properties and losses of N as leachate and N 2O emissions were measured at 50, 100 and 150 days after planting. There was no yield benefit in using EEF products, but they did show a significant potential to reduce N losses especially in leached and waterlogged conditions. This trial demonstrated that EEF products reduced soil NO 3 - -N concentrations by more than 50% in leaching and waterlogged conditions compared to conventional urea at 50 days after application. Similarly, under field-capacity conditions, DMPP and nitrapyrin 2.5 L/ha reduced soil NO 3 - -N concentrations by 39% at 50 days after application. Despite these reductions in soil NO 3 - -N, there was no significant difference in losses of N in leachate and N 2O emissions. Inability to fully capture all N losses, especially as N 2O, was thought to be the reason for these discrepancies. This study highlights how difficult it is to assess all N loss pathways and the potential of EEFs to reduce these losses. Further research is required to improve the understanding of the role of EEFs to support better management decisions for sustainable farming systems Key words Nitrification inhibitor, enhanced efficiency fertilisers (EEFs), Nitrapyrin, DMPP, Entec™, eNtrench™ nitrogen stabiliser