Field transect evaluation shows elevated particulate organic carbon under tree clusters on dairy farmland, suggesting margin plantings enhance soil carbon storage without trade-offs.
Key Points
To evaluate how soil organic carbon stocks and particulate organic carbon concentrations differ between pasture and three distinct tree plantings on an intensively managed dairy farm.
Sampled soil along transects from open pasture into three planting types: mixed native species, hybrid willow (Salix matsudana × S. alba), and kānuka/mānuka (Kunzea robusta and Leptospermum scoparium) on a pastoral dairy farm in Lincoln, New Zealand.
Quantified soil organic carbon stocks and particulate organic carbon fractions at depths of 0–0.1 m and 0.1–0.3 m across pasture, canopy dripline, and interior tree stand locations.
Soil organic carbon stocks at 0–0.3 m depth were significantly higher 12 m inside the mixed native planting (114 t C ha−1) compared to the dripline and pasture (95 t C ha−1), representing a 20% increase, while willow and kānuka/mānuka stocks did not differ significantly from pasture.
Particulate organic carbon at 0–0.1 m was significantly higher beneath all tree plantings (mean 0.22 to 0.35 g per 100 g soil) than under adjacent pasture (0.06 to 0.11 g per 100 g soil).
Carbon concentrations did not peak at the dripline in any planting, and exotic willow stands accumulated no more carbon than native plantings, disproving dripline-peak and exotic-superiority hypotheses.