Shaun Lisson^† and Bill Cotching* ^†

^†CSIRO Ecosystem Sciences, PMB 54, Hobart Tas. 7001, Australia.

*Tasmanian Institute of Agricultural Research, PO Box 3523, Burnie Tas. 7320, Australia.

The Panatana catchment in central north Tasmania, Australia (~41°12’S, 146°26’E) is one the most intensively cropped catchments in the state due to a favourable climate, productive soils and ready access to various agricultural processing and port facilities. The high rates of irrigation and fertiliser use in the catchment, combined with typically high annual rainfall totals and soils that have high infiltration rates and rapid permeability, create conditions that are conducive to high drainage and nitrogen leaching losses below the root zone.

This paper reports on desktop modelling studies of the impact of current management practices on the N balance under intensive vegetable-based cropping in the Panatana catchment. Modelling was also used to identify feasible and viable practices for reducing N loss.

Crop water supply was found to exceed crop water use for all crops grown across the 7 crop-based case farms resulting in substantial (i.e. >100 mm) average seasonal drainage figures for each crop. Crop N demand is close to crop N supply for all rotation elements with the exception of potato which has an average surplus of 89 kg N/ha. As a consequence, potato has the highest rate of N loss of 29 kg N/ha (up to 4X greater than other crops). Modelling showed that practicable management options such as deficit-based irrigation and reduced N fertiliser rates have the potential to generate significant financial savings via reduced input costs and reductions in offsite N loss, while maintaining current levels of productivity.