A Lysimeter Experiment to Assess Environmental Impacts of Soiled Water Application to Grassland Soils.

Soiled water is produced on dairy farms through the washing-down of milking parlours and holding areas. These effluents contain nutrients that are potentially available to plants, but they are also a potential threat to water quality and a potential source of greenhouse gas (N₂O) emission, if not managed correctly. Current management in Ireland is regulated primarily by the Nitrate Regulations which limit rates but allow spreading year-round. A lysimeter experiment was established to measure nitrate leaching and N₂O emissions from soiled water applied to grassland soils and assess the effect of application timing and soil type. 32 lysimeters (30 cm diameter x 70 cm depth) were constructed with undisturbed monoliths and established pasture from two contrasting grassland soils (a well drained Acid Brown Earth and a poorly drained Gleysol). There were 4 treatments, consisting of a control (no soiled water) and soiled water applied at 3 time periods: May-August, September-December and January-April. Soiled water was applied at the legal maximum rate of 50,000 l/ha every six weeks. Application periods correspond to key stages in the grass growth curve and precipitation and soil drainage conditions, and associated N loss risks. Nutrient management accounted for total N in soiled water applications with mineral N fertiliser applied to all lysimeters to achieve a total N loading of 198 kg total N/ha for each lysimeter. Concentrations and total fluxes of nitrate were monitored in leachate and N₂O emissions were monitored using the static chamber method. This poster presents an overview of the experiment and results for the first five months.