Chemical losses off dairy catchments located on a texture-contrast soil: carbon, phosphorus, sulfur, and other chemicals

Runoff (overland flow and A/B horizon interflow) from 2 grazed dairy pastures at Flaxley, South Australia, accounted for <15% of April-October rainfall in 1996; 88-96% of runoff was overland flow. A range of chemicals, including carbon (C), phosphorus (P), and sulfur (S), was measured in runoff. As much as 2.3 kg P/ha, 10.7 kg/ha of total dissolved C, and 1.8 kg S/ha was lost from the catchments in that year. Loads of other chemicals ranged from 0.6 g/ha (boron) to 39.8 kg/ha (aluminium). Over 92% of P, 76% of total dissolved C, and 93% of S was lost in overland flow. Between 50% and 60% of P, and 60% and 85% of S, was in the dissolved form; 64-96% of total dissolved C was dissolved organic C. Other chemicals varied from 0% (aluminium) to 97% (sodium) as the dissolved form. Relatively high losses of P and dissolved organic C are important to a dairy industry which is under increasing pressure to demonstrate minimal environmental impact from farming practices.