A comparison of the temporal relationship between liquid P application and P concentration in surface runoff for two contrasting Tasmanian pasture soils: a rainfall simulation study

Food processing wastewaters commonly do not contain harmful contaminants and can provide viable alternatives to supplement traditional fertilisers for optimising pasture growth and their use may contribute to conservation of Phosphorus (P) resources. As with all fertiliser use, wastewater irrigation must be managed to prevent runoff and leaching of nutrients that may be detrimental to surface and ground water quality. This issue becomes critical when wastewater is being irrigated to meet wastewater disposal needs and it is applied in excess of pasture requirements or in wet conditions when infiltration to the soil and plant uptake cannot occur. Run off events that occur close to fertiliser applications are known to create higher nutrient concentrations in runoff (Burkitt et al 2011). This temporal relationship is investigated here for liquid P applications on two contrasting Tasmanian pasture soils - a high P sorbing Ferrosol (clay loam) and low P sorbing Hydrosol (sandy loam). In Tasmania Ferrosol soils are used extensively for dairy and vegetable cropping. Recent increases in dairy pasture conversions are occurring on hydrosol soils in north east Tasmania. Hump and hollow land forming is used to extend viable pasture areas on these seasonally waterlogged soils. The study investigated the properties of these soils (Table 1.). The Ferrosol has very high iron oxide content which drives a strong P sorption capacity. The Hydrosol has a relatively inert quartz dominated chemistry and lacks mechanisms to strongly sorb phosphorus. To investigate the change in P availability to runoff with time rainfall simulation experiments were conducted on miniswards of perennial ryegrass to measure P concentration in runoff generated at 1, 2, 5 and 10 days after a P solution application.