NITROGEN FERTILISER GUIDELINES IN PERSPECTIVE

SUBSTANTIAL advances in fine-tuning nitrogen (N) fertiliser recommendations have recently been made in the Australian sugar industry. Traditionally N recommendations were general in nature for use across regions and soils. Modified recommendations promote the concept of an integrated or ‘whole-ofsystem’ approach to ensure that N inputs are appropriate for specific sites, soils and farming systems. The N requirement of a particular block of cane is now determined from a combination of regional/district yield potential (to establish a base-line N rate) and a set of N mineralisation indices (to take into account N released from soil organic matter). The concept also takes account of other possible sources of N such as legume crops and fallows, mill by-products, and residual mineral N in the soil profile following small-crop production. The efficacy of the approach to the wider Australian sugar industry is illustrated using the N mineralisation potentials of soils from various districts. The modified N guidelines are validated using data from recent field trials conducted in the Bundaberg and Herbert districts. The integrated approach is effective in providing recommendations for growers that are all encompassing, with a firm basis for tailoring inputs to suit specific conditions. Information is provided on current investigations aimed at further enhancement of the system, particularly in relation to the incorporation of N loss pathways and their impact on environmental and temporal risk.