Aspects of temporal N management in sugarcane in sub-tropical Queensland : ASSCT peer-reviewed paper
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The proximity of the Australian sugar industry to the Great Barrier Reef (GBR) has resulted in ongoing concerns about elevated concentrations of the dissolved inorganic nitrogen (DIN) in the near-reef environments due to sugarcane production practices on-farm. Although the nitrogen (N) guidelines within the SIX EASY STEPS nutrient-management program are generally appropriate, scope exists for fine-tuning of N application rates for specific circumstances. In particular, enhanced-efficiency fertilisers (EEFs), such as urea coated with 3,4-dimethylpyrazole phosphate (DMPP-urea) and polymer-coated urea (PC-urea), offer promise potentially to improve nitrogen-use efficiency (NUE) in sugarcane production and reducing DIN losses to the GBR. Temporal N-management strategies using these EEFs were assessed within a randomised complete-block field trial conducted in a sub-tropical environment on a well-drained soil supported by a concurrently run shorter-term pot experiment. There were no significant yield responses to applied N, split applications or use of EEFs in the trial in either the plant or first-ratoon crops. Rainfall measured during these seasons would not have resulted in excessively wet conditions at the trial site and may have contributed to the lack of responses to EEFs. Increased N-uptake by the crop, due to the use of N strategies away from the standard practice (i.e. by using EEFs or split applications of urea), improved NUE values based on crop N, but this did not always translate into any improvements in yield. The highest partial net returns in the plant and first-ratoon crop corresponded to the control treatments. Urea applied at 120 kg N/ha in a single application resulted in the next best partial net returns in both crops. This appeared to be the most appropriate strategy to minimise risk to growers. The cost of EEF fertilisers negatively affected the partial net returns, with DMPP-coated urea being more affordable than the poly-coated urea. The results of the pot experiment that included two sugarcane cultivars supported these outcomes. Further work, across seasons (dry, wet and 'normal'), is needed to evaluate more fully the potential of EEFs for use in specific circumstances.