Concentrations of arsenic, cadmium, copper, lead, and zinc in New Zealand pastoral topsoils and herbage

Abstract

A national survey of agricultural topsoils and pastures was undertaken in the early 1990s to establish benchmark heavy metal concentrations. In total, 398 sites were sampled covering the major soil groups throughout the North and South Islands of New Zealand. Both pastoral farmed (312) and non‐farmed (86) sites were sampled. Composite soil samples were taken from two depths, as well as pasture samples from the same area, and analysed for arsenic (As), cadmium (Cd), copper (Cu), lead (Pb), and zinc (Zn) concentrations. There was significant (P < 0.05) enrichment of Cd at the 0–7.5 cm depth in five of the eight soil groups on farmed sites (0.44 mg kg^–1), over background non‐farmed soils (0.20 mg kg^–1). Total soil Cd was highly correlated (P < 0.001) to total soil phosphate (P) suggesting Cd enrichment in pastoral soils was related to fertiliser P applications. There was no enrichment of As, Cu, Pb, or Zn at the 0–7.5 cm depth on farmed soils compared with non‐farmed soils. Results showed that soil concentrations of these elements were either typical of worldwide averages, or at the lower end of these ranges. There was, however, a significant (P < 0.05) increase in Cu concentrations in the 0–2.5 cm depth on most farmed soils (14.3 mg kg^–1), compared with non‐farmed soils (11.4 mg kg^‐1). The main difference in heavy metal concentrations between non‐farm and pastoral pasture species was in the weed component. In general, the Cu, Zn, Pb, and As concentrations were essentially pedogenic in origin.

Keywords:

• arsenic
• cadmium
• copper
• zinc
• lead
• pastoral agriculture
• soil groups
• pasture species
• grass
• legume
• weed
• heavy metals
• total phosphorus

Notes

Present address: Ravensdown Fertiliser Co‐Op Ltd, P.O. Box 608, Pukekohe.