Impacts of sugarcane (Saccharum sp.) soil and fertiliser management practices on nutrients and sediment in plot-scale runoff from simulated rainfall

Abstract

Runoff of nutrients and sediment from agricultural catchments can impair the health and resilience of aquatic ecosystems in receiving waterbodies. The sugarcane (Saccharum sp.) industry in Australia has adopted strategies to improve farm runoff water quality. Rainfall simulation trials were conducted to quantify the relative effectiveness of some sugarcane soil and fertiliser management practices on nutrient and sediment loss in runoff. The trials were conducted within the Herbert River catchment in the Wet Tropics of Queensland. Simulated rainfall (~76 mm h–1) was used to generate runoff from 1.70 m2 plots in first ratoon sugarcane on well-drained Ferralsols at Abergowrie and from 1.55 m2 plots in sugarcane planted into furrows and mound beds on an imperfectly drained Luvisol at Trebonne. At Abergowrie, the practices studied were; crop residue retention after harvest (green cane trash blanketing), applying a liquid rather than a granular fertiliser, and applying fertiliser to the sub-surface rather than to the surface on ratoon phase sugarcane. At Trebonne, sub-surface fertiliser placement was studied on plant cane and after varying amounts of time and repeated rainfall after fertiliser application. Comparisons were made with a similar study in plant cane at Macknade. Particulate nitrogen (N), particulate phosphorus (P), and suspended sediment losses in runoff were reduced by crop residue retention, which was expected. Dissolved inorganic N (DIN) loads (but not concentrations) were also reduced by residue retention. Dissolved inorganic N and filterable reactive P concentrations in runoff were reduced by sub-surface fertiliser placement, as expected, and by the liquid fertiliser that was studied. In contrast to expectations, DIN concentrations increased in mound beds (but not in furrows) with increasing time and rainfall after fertiliser application. The increase was attributed mainly to increases in soil mineral N and runoff volume. The practice that was most effective at reducing DIN loads in runoff (64–85% reduction) was sub-surface rather than surface placement of fertiliser.