The potential of native plants to manage nutrient and contaminant fluxes from New Zealand dairy farms

Abstract

This study investigates the elemental composition of components from the soil-plant continuum of 6 New Zealand native plant species. These components have been evaluated to determine if the plants have potential uses in trace element management and if there are any potential capabilities of these plants to attenuate contaminant flux from soil and soil leachate resulting from New Zealand dairy paddocks. Plants were selected based on their compatibility with riparian plantings, root morphology, plant structure and physiological traits. An initial investigation included collection and analysis of vegetation, soil and rhizon soil leachate samples from each sample site to collect baseline data. New Zealand native plant species are found to have distinct patterns of elemental accumulation when comparing native monocots and dicots as well as to exotic ryegrass. Foliage concentrations of N, P, K and S were highest in ryegrass (L. perenne), although significant differences between native plant species were found. Foliage concentrations of Cd were up to 10 fold higher in native plant species when compared to ryegrass. Significant differences in elemental concentrations were found between the soils of the paddock margin and adjacent intensively managed paddock soils.

Dairy cattle effluent was then applied to the soil surface adjacent to each plant at a volume equivalent to 50 kg N ha⁻¹. Soil leachate samples were collected for a period of one month following the effluent application to evaluate the influences of each plants rhizosphere on the leaching of the effluent through the soil profile. Significantly higher concentrations of nitrate were found beneath C. richardii. However, differences found in soil leachate chemistry may be attributed to differences in plant physiology and root morphology. Soil temperature and moisture had little apparent effect on rhizosphere chemistry over the early spring months. Soluble nitrogen mobility through native plant rhizospheres is probably not a major nitrogen flux pathway. Some native plants exhibit elemental properties that could potentially be suitable as fodder supplements.