Regional total phosphorus budgets for sugar production in Queensland

Historical fertiliser phosphorus (P) rates, averaged over the crop cycle, are presented for the four sugar producing regions of Queensland. Rates of application of P increased sharply in the 1960s and began to decline in the 1980s and 1990s in response to increased P fertility of sugar cane soils. Regional P budgets for 1993/94 suggest that there was a net input of P equivalent to 8, 9 and 13 kg P/ha for the northern, central, and southern cane growing regions, respectively. It was estimated that historical P fertiliser additions (1930-1994) account for 22% to 27% of the total P in the top 30 cm of soils in these areas. In contrast, P inputs in soils of the Burdekin region equal P losses. Accordingly, there was no net P build up in Burdekin soils. In all regions and on average, present-day additions of P fertiliser increase total P concentrations in the top 30 cm of caneland soils by up to 1 % annually. This suggests that reducing fertiliser P inputs will only slowly change the total soil P reserves and thus the total flux of P moving to the sea via erosion. However, the bio-availability of P in the eroded sediments has not been assessed.