Infiltration and runoff rates in coastal grazing land were tested through a rainfall simulation arranged by the Reef Catchments Paddock to Reef program in Proserpine this past April. This is the first trial to examine infiltration and runoff on the Mackay Whitsunday coastal grazing land.
The trial was designed by Michael Boyd and Belinda Billing from Reef Catchments along with DERM rainfall simulation lead, Bruce Cowie, to measure infiltration rates on alluvial flats and plains as well as eucalypt hills and ranges. Trials were carried out at the end of the wet season on both A/B class and C condition pastures within both land types. The trials also looked at nutrient loads in runoff. Fertiliser (DAP) was applied three weeks prior to the simulation, which replicated very heavy rain over a prolonged period of time.
Initial results showed that infiltration on alluvial flats and plains (cane soils) was rapid, with very slow to almost zero runoff. Conversely the hills and ranges run-off almost immediately showing poor infiltration, despite high levels of ground cover. Further information will come following analysis of the samples collected, including nutrient loads in runoff. The results will be used to better inform models that represent our coastal grazing land, which has seen very little research to date. “I think we will get a lot of good information out of these trials,” said Michael.
The Paddock to Reef Program has commissioned numerous rainfall simulation trials, on cane, grazing, grains and horticultural production systems across the Great Barrier Reef catchments. The trials look at various herbicide, soil and nutrient management practices across a variety of soil, climate and land types. Rainfall simulation imitates a heavy rainfall event giving an indication of how much runoff will leave a property, how quickly the runoff event will be generated and what loads (herbicide, nutrient and/or soil) will be carried away in the runoff.