Effect of exotic tree species on the fertility of pasture soils in Canterbury: A dissertation submitted in partial fulfilment of the requirements for the degree of Bachelor of Agricultural Science (Honours) at Lincoln University

Abstract

An experiment was conducted into the effects of different exotic tree species on the fertility of two pasture soils at Orton Bradley.Park (Charteris Bay) and Glentunnel. This involved sampling soil to depth under pasture and adjacent forest. At Orton Bradley Park, macrocarpa (Cupressus macrocarpa) and eucalypt (Eucalyptus nitens) had minor effects on soil fertility, with slightly lower total nitrogen (N) levels in the topsoil (0-12cm) and increased levels of available magnesium (Mg) and sodium (Na) compared with pasture. The latter was related to the combined effects of atmospheric filtering and stemflow. At Glentunnel, topsoil (0-10cm) pH decreased by up to 0.8 units under Douglas fir (Pseudotsuga menzieii), European larch (Larix decidua), eucalypt (Eucalyptus nitens) and western red cedar (Thuja plicata) compared with pasture, while carbon (C):N ratios increased under all tree species. Mineralisable N levels increased under Douglas fir and European larch by 31% and 33% respectively compared with pasture, but decreased under eucalypt and western red cedar by 57% and 24% respectively. Available phosphorus (P) levels under European larch, eucalypt and Douglas fir increased by up to 12 μg P g⁻¹ (or 52%) compared with pasture, but decreased by 5 μg g⁻¹ (or 15%) under western red cedar.