Download - New Zealand Society of Soil Science

soil and ground water quality and livestock health. The rate of F accumulation in topsoils depends on
soil texture, type of minerals, and pH. In most pastoral soils with near-neutral pH, the majority of
fertiliser-derived F remains in the topsoil and little moves below a depth of 20-30 cm and therefore is
unlikely to contaminate ground waters. However, F may pose a risk to shallow ground waters in very
acidic low P-fixing soils.
Pasture forage accumulation of F is very low; therefore, F intake by animals through pasture
consumption is much lower than F intake through soil ingestion. Ingestion of high rates of topsoil
having elevated F concentrations can result in chronic fluorosis leading to bone damage or tooth wear
in livestock.
The bone F concentration of sheep generally increases curvilinearly with age, with the rate of bone F
accumulation greatest in lambs. A recent survey of sheep farms with a long fertiliser history showed
that sheep bone F concentrations observed in these farms (less than 601 mg F/kg DM) were much
lower than the threshold bone F concentration of 2,400 mg F/kg DM reported for chronic fluorosis.
This suggests that the potential risk of chronic fluorosis occurring in sheep grazing most New Zealand
pastures is low. Reducing soil ingestion by maintaining good pasture cover, especially during winter
periods, can reduce F accumulation in livestock.
Concentrations and Species of Cu, Zn and Ni in Soil Solution in
Response to Anthropogenic Impacts
Guodong Yuan
Landcare Research, PB 11052, Palmerston North, yuang@LandcareResearch.co.nz
Human impacts on soils would increase as urban boundary expands, agriculture intensifies, and more
chemicals in larger quantity enter the soils. Understanding the dynamics of introduced chemicals,
including their concentrations and species in soil solution, would help the sustainable use of soil
resource. In this regard, long-term data would be particularly valuable because soil is a complex
system and its ability to cope with human impacts varies. Here I collected soil solution by
centrifugation and analysed copper, zinc, and nickel concentrations in response to a range of human
impacts over years when the soils were under normal pasture, amended with metal-spiked biosolid,
limed, and acidified. The chemical species of the metals were obtained from Windermere Humic
Aqueous Model (WHAM).
Before biosolid amendment in 1997 the baseline concentrations of Cu, Ni, and Zn in soil solution were
0.27, 0.11 and 1.2 µM, respectively, and dominated (>66%) by free ion species, the most toxic one.
Adding metal-spiked biosolid to soil (Cu loading 180, Ni 58, or Zn 296 mg/kg) increased Cu, Ni, and
Zn in soil solution to 3.97, 13.2, and 476 µM in 1998. In the next two years, there was little change in
Cu concentration, whereas both Ni and Zn concentrations decreased with time. Liming the soil to raise
pH from 5 to 7 significantly lowered the concentrations of Cu (1.87–2.36 µM), Ni (0.93–2.21 µM),
and Zn (0.84–2.94 µM) in 2001–2003. Free ion species accounted for