Minimising Nutrient Loss - Where Best to Tweak

This paper explores challenges that are being faced by land treatment system managers, investigating which components of land treatment/farm management practices can be altered to provide nutrient loss mitigation, while maintaining viable farming systems.

Overseer® modelling was carried out to assess the effects of various management options on reducing nitrogen leaching for a conceptual Waikato combined dairy farm and land treatment system. Various soil properties have also been modelled to assess potential mitigation of nutrient losses when selecting new land treatment sites.

Modelling assessment results indicate mitigation through further wastewater treatment can be limited and that expanding irrigation area to reduce hydraulic and nitrogen loading may provide very little benefit depending on the surrounding land use. Modelling indicates that standoff pads and stocking rate reduction are more significant factors for lower nitrogen leaching.

The results of the modelling indicated that nitrogen losses can be higher for well drained soils. This shows that conventional thinking, where well drained soils are generally preferred for hydraulic management in land treatment systems, does not necessarily provide optimum land treatment for nitrogen removal. In addition, variables such as shallow free draining layers and limited rooting depths have a significant bearing on nitrogen leaching potential.