Assessing the environmental implications of applying dairy cow effluent during winter using low rate and low depth application methods

Dairy cow effluent collected over winter from a loose-housed barn was applied to a series of large infield plots (400 m(2)) using low rate and low depth (LRLD) application methods. Applications were confined to the winter period, at a time when soil moisture content was often at or very near to field capacity and was applied over two seasons. Cows were confined to the housing facility during winter only, and outside of this period they remained on pasture. Losses of nitrogen (N), phosphorus (P) and the faecal indicator bacterium Escherichia coli (E. coli) in surface runoff and subsurface drainage from the LRLD treatment were compared with losses from effluent applications that occurred during spring to autumn, at an application depth not exceeding the soil water deficit, i.e. a standard practice treatment (SP, typically 10-15 mm per application). The annual quantities of nutrients applied by the treatments and the grazing managements imposed were similar. Although winter losses of N were significantly greater for the LRLD treatment (15 vs. 8 kg N ha(-1) for the SP treatment), on an annual basis fluxes were similar between treatments (approximately 20 kg N ha(-1) year(-1)). Effluent management had no significant effect on the annual fluxes of P and E. coli although the latter varied considerably. Average contaminant fluxes over a 2-year period indicated that the LRLD management system did not lead to a significantly greater risk to water quality compared with standard practices.