Nitrogen losses via subsurface flow from sugar cane on floodplain soils in the Australian wet tropics

Nitrogen losses via subsurface flow from sugar cane were quantified for a range of floodplain soils in the Ripple Creek area in the Lower Herbert (Queensland, Australia). Apart from leaching losses to groundwater via recharge, a special focus was on the quantification of losses via lateral flow from shallow perched watertables (0--1 m depth) to the drain system (interflow). Although the study was carried out over two relatively wet years with high recharge, the N losses were relatively small. Average N losses to groundwater were about 17 kg N/ha/yr and average loss to the drain via interflow was about 5 kg N/ha/yr. These results indicate that subsurface flow is not the major loss pathway on floodplain soils in this region of the Australian wet tropics. Exceptions were the sandy soils of the riverbank, where high losses to groundwater (up to 70 kg N/ha/yr) occurred under plant cane. Differences in N losses between the years indicate that the rainfall distribution in the early wet season (after fertiliser application) might play an important role.