TOWARDS INNOVATIVE MANAGEMENT OF NITROGEN FERTILISER FOR A SUSTAINABLE SUGAR INDUSTRY

THE MANAGEMENT of nitrogen (N) fertiliser is important to the Australian sugar industry, as it has significant production and environmental consequences that need to be balanced in N management recommendations. This paper reports results from 12 on-farm experiments established from Mossman to Broadwater in 2003 or 2004 to examine the concept of replacing N lost from a field through harvested cane and environmental processes as a way of determining N fertiliser needs. This N replacement concept was compared with the farmers’ current N management and, at seven sites, a lower rate of N fertiliser. In general, yields were similar and profitability (assessed by partial gross margins) higher in the N replacement than the current N management. At only one site in one year was yield with the farmers’ N management significantly higher than with N replacement. CCS was little affected by N treatment. Trends in soil mineral N through time at the sites differed more between sites than between treatments, and suggested that yields in the N replacement treatments were not being sustained by ‘mining’ N from the soil. Yields with low N were little different from the other treatments, although there was some evidence of depletion of soil N at two sites with this treatment. The surplus of N, i.e. the difference between N applied and that lost through crop harvest (and trash burning at some sites), was estimated to be 85% lower in the N replacement treatment than with farmers’ current N management, indicating a potentially much reduced environmental impact of this management system. The results to date provide the first field evidence that the N replacement concept may be an economically and environmentally sustainable innovation in N management for sugarcane production.