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 p astures at Flaxley, South Australia, accounted for <15% of April-Octob er rainfall in 1996; 88-96% of runoff was overland flow. A range of ch emicals, including carbon (C), phosphorus (P), and sulfur (S), was mea sured 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 o f other chemicals ranged from 0.6 g/ha (boron) to 39.8 kg/ha (aluminiu m). 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 d issolved form. Relatively high losses of P and dissolved organic C are important to a dairy industry which is under increasing pressure to d emonstrate minimal environmental impact from farming practices.