Evaluation of enhanced-efficiency fertilisers in Queensland sugarcane

Enhanced-Efficiency Fertilisers (EEFs) are purported to reduce nitrogen (N) losses by better matching N supply to crop demand over the growing season. The EEF60 project was designed to evaluate EEF performance across regions, rainfall conditions, soil types and fertiliser application times. EEFs were tested on 74 sugarcane farms, located between Mossman and Bundaberg, with the lifespan of trial sites ranging from one to three ratoons. Four treatments, including two urea and two EEF treatments, were tested. One urea treatment had N applied at the SIX EASY STEPS Step 4 (6ES) recommended rate (Urea 6ES), while the three other treatments applied 20% less N. Applying urea at 20% less N decreased cane yield in medium and high rainfall conditions but improved profitability in low rainfall conditions. Urea treated with nitrification inhibitor (NI) and blends of 20% controlled release fertilisers (CRF) with 80% urea applied with 20% less N maintained similar productivity and profitability to urea applied at 6ES. Blends with high proportions of CRF applied at 20% less N also maintained productivity but cost more, which generally made them less profitable to apply. Nitrogen-use efficiency indicators, such as crop-N content, partial factor productivity of applied N and N-uptake efficiency, were improved when EEFs were applied at 20% less N. These findings indicate that NI-urea and blends of 20% CRF with 80% urea at N rates 20% less than 6ES can be applied at any time during the season without loss of productivity or profitability in comparison to Urea 6ES. EEFs appeared to obtain higher yields than Urea 6ES in some situations under high rainfall conditions, which corresponds to past EEF research. These findings suggest that the EEF option could be endorsed as a recommended nutrient management strategy, particularly when high rainfall is expected.