EUTROPHICATION FROM AGRICULTURAL SOURCES - Effects of Agricultural Practices on Nitrate Leaching

Summary: Synthesis Report of the ERTDI-funded project 2000-LS-2.3-M2

Main Message

The objective of this integrated research project was to measure nitrate leaching from an intensively managed dairy farm in a vulnerable area. Mean concentrations of nitrate nitrogen in the groundwater beneath Curtin’s farm during the first and second monitoring years were 15.2 mg/l and 11.9 mg/l, respectively, and exceeded the Maximum Admissible Concentrations (MAC) set in the Nitrates Directive and drinking water legislation. The average nitrate nitrogen concentrations in the soil pore water were less than the drinking water MAC in the three measurement years. However, there was a trend for increased nitrogen loadings to result in elevated concentrations of nitrate nitrogen in soil pore water and groundwater. The results indicated that lower concentrations of nitrate nitrogen in groundwater can be expected where management practices reduce the nitrogen and hydrological loads.

Questions remain as to the specific suite of management practices required to achieve compliance with water quality targets on an intensively managed grassland dairy farm on a vulnerable soil type:

• Will the implementation of the identified management practices which reduce the nitrogen and hydraulic loads achieve compliance with current water quality targets?
• Can models be expanded to provide an evaluation of the relevance of the present results and the possible mitigation strategies required in other less vulnerable circumstances?
• What are the implications of extrapolating these farm scale results to larger catchment scales where the intensity of farming can vary quite considerably?

A number of national research projects have been initiated to address some of these questions.