Reducing Leachates with Native Plants

May 2014

Research at Lincoln University looking at the efficacy of native plants to reduce farm run-off

New Zealand native plants can be incorporated into farming systems to increase profits and reduce harmful contaminants entering waterways.

Brett Robinson is part of a team from the Departments of Ecology and Soil Science at Lincoln University looking to develop planting systems that not only improve the landscape but also maximise the innate potential of the root systems of some New Zealand species to intercept environmental contaminants before they enter waterways.

The potential of native plants to manage nutrients and contaminants has been given added emphasis as our waterways come under increasing pressure from the intensification of farm systems.

It’s been established that a well-managed riparian margin can filter out some contaminants from farm run-off. This is said to help improve water quality and in turn, stock are likely to benefit from improved animal health.

This research looks at native species to see if they can not only improve the aesthetic and conservation benefits of the farming landscape but also reduce contaminants and provide economic benefits for the farmer.

Phytomanagement describes the use of plants to improve environmental outcomes while at the same time producing something valuable.

Good examples of these among NZ native plants would be manuka and kanuka.  Both plants are Biological Nitrogen Inhibitors (BNI) which means they inhibit the transformation of the ammonium in the soil into nitrate, which can leach into groundwater. Both also have value as economic crops – manuka for honey and oil and kanuka for firewood and oils.

Other examples of potentially profitable species include native species such as the broadleaf and akeake that can be used as a fodder supplement to provide high concentrations of essential micronutrients that are often lacking in New Zealand farms. As the species mature, they also provide windbreaks and shade for stock.

Critical to the success of such plantings is an understanding of the belowground processes that occur in the soils beneath the native trees.

The research team from Lincoln are using advanced techniques to measure the movement of nutrients and contaminants under native ecosystems to develop optimal planting strategies for a variety of New Zealand farming landscapes.

Preliminary research indicates that planting native species on agricultural land definitely offers some advantages in terms of nutrient and trace element management.