DISTRICT YIELD POTENTIAL: AN APPROPRIATE BASIS FOR NITROGEN GUIDELINES FOR SUGARCANE PRODUCTION

THE QUEENSLAND Government has developed a Reef Protection Package aimed at enhancing the water quality and health of the Great Barrier Reef Lagoon. It has focused on nitrogen (N) and phosphorus (P) inputs within the sugarcane production system as these two nutrients have been identified as posing the greatest risk to water quality in the Great Barrier Reef lagoon. Over the past decade, BSES Limited and its collaborators have developed the SIX EASY STEPS program to underpin the adoption of sustainable nutrient management practices in sugarcane production. The nitrogen (N) guidelines within the SIX EASY STEPS program are based on a combination of district yield potential (DYP) and a soil N mineralisation index. This paper describes the concepts of estimated highest average annual district yield (EHAADY) and DYP and relates these to average annual yields at a range of levels within sugarcaneproducing districts in Queensland. Mill statistics data indicated that the established EHAADY values used within the SIX EASY STEPS program are appropriate for the various districts within the Queensland sugarcane industry. Data from sub-districts indicated that DYP values, determined as EHAADY multiplied by a factor of 1.2, are realistic, particularly when individual farm data are considered. It was found that the average sugarcane yields on a substantial number of farms reached or exceeded the established DYP value during seasons that were characterised by favourable rainfall conditions. DYP was not reached on the majority of farms during seasons with unfavourable rainfall patterns (which could include high, low or unevenly distributed annual rainfall). Sugarcane yield plotted against block numbers for particular soil types illustrated thereason why actual yield should not be used as a basis for determining N input. The difficulty of predicting seasonal weather conditions curtails our ability to formulate N input strategies prior to a particular growing season. This means that the only appropriate management option is to apply fertiliser with the aim of producing an optimum / sustainable sugarcane crop and to assume that the forthcoming season will be characterised by favourable weather conditions (particularly rainfall). Further R&D is required to assess the inclusion of accurate seasonal climate forecasting into the SIX EASY STEPS package to assist in guiding N inputs.