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

Dairy cow effluent from a loose-housed barn was applied to a series of large infield plots (400 m2) using low rate and low depth (LRLD) application methods. Applications were scheduled over two winters, at times when soil moisture content was often at or very near to field capacity. Losses of nitrogen (N), phosphorus (P) and the faecal indicator 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 > 12 mm per application). The annual quantities of nutrients applied to the treatments and the grazing managements imposed were similar. Although winter fluxes of N were significantly greater for the LRLD treatment (15 kg N/ha v 8 kg N/ha for the SP treatment), on an annual basis fluxes were similar between treatments (approximately 20 kg N/ha/yr). 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 two year period indicated that the LRLD management system did not lead to a significantly greater risk to water quality compared to stand practices.