Sawdust and bark to treat nitrogen and faecal bacteria in winter stand-off pads on a dairy farm

New Zealand farmers are increasingly using improved management systems including moving animals out of paddocks to protect wet soils from damage during winter. The cows can be held for up to 20 h a day on specially constructed unroofed outdoor stand-off pads. Afield study was undertaken to investigate excreta nitrogen (N) transformations, N and faecal bacterial transport to drainage, and denitrification N losses when Pinus radiata bark or sawdust were used as filling materials in stand-off pads. About 3 months after use only 4.0% of the N that was deposited on the bark or sawdust pad by cows had been transported to the drainage. Sim ilarly, after the 3 months of use only 9.8% of the Escherichia coli bacteria that were deposited on the bark pad had been transported to the drainage and with even less, 0.3%, leached from the sawdust pad. The sawdust pad tended to retain more Campylobacter than the bark pad. About 6 months after use, gaseous N losses due to denitrification from the sawdust or bark pad accounted for about 4.5 and 1.7% of the deposited excreta N, respectively. Denitrification activity was limited by the available nitrate in the pad materials, and decreased after cows were moved out of the pads.