The potential of L. scoparium, K. robusta and P. radiata to mitigate N-losses in silvopastural systems

Abstract

Silvopastoral systems aim to enhance economic, cultural and social principles by sustainably combining forest management with agriculture. In these typically high-nitrogen (N) environments, plant species selection can profoundly influence N fluxes. For grazed pastures, plants may be exposed to urine patches that have received the equivalent of up to 1000 kg N ha^-1. We aimed to determine the growth and N fluxes in three potential trees that may be used in silvopastoral systems: L. scoparium, K. robusta and P. radiata. Plants were grown in a greenhouse lysimeter experiment, with controlled irrigation and temperature and exposed to N at rates of 200 kg ha^-1 equiv. for 15 weeks, followed by the addition of 800 kg ha^-1 N equiv, to simulate a urine patch. Urea produced a positive growth response of all plant species. Treatments containing L. scoparium and K. robusta leached lower amounts of nitrate (NO₃^-) (2 kg ha^-1 NO₃^-) compared to P. radiata (53 kg ha^-1). Measurements of N₂O over 20 days after the application of 800 kg N ha^-1 indicated an inhibitory effect of L. scoparium and K. robusta on denitrification, hence loss of N via N₂O. Both L. scoparium and K. robusta demonstrated that they have potential to reduce N-losses in silvopastural systems, while producing valuable biomass.

Keywords: Kānuka; Leaching; Mānuka; Nitrous oxide; Pine; Urea.