End of Project ReportVariability of heavy metal trace/element amounts in soil and
herbage from 3 farms encompassing 26.5, 33.6 and 21.6 ha
and in a 230 km2 surrounding area has been estimated.
Variability was least in the farm with the greatest soil physical
uniformity. It increased in line with increasing sampling
area. In soil, variability was least (CV 10%) for sesquioxide
metals, iron and aluminium, and elements chromium and
nickel. It was highest where there was evidence of
geochemical contamination with cadmium and selenium. In
general, variability was higher (>20% CV) for extractable
components including copper, zinc and manganese.
Regression analysis of elements in soil showed up a number
of useful associations particularly for the volatiles selenium,
sulphate sulphur, mercury, cobalt, vanadium and fluorine
with soil organic matter. Associations were also found
between fluorine, vanadium and chromium.
• Elements in herbage exhibited two types of associations (i)
those reckoned to be within the plant and confined mostly to
major elements and (ii) those involving metals associated
primarily with soil and indicative of the extent to which
herbage was contaminated by soil.
• Elements that showed lower variability in soil exhibited large
variability in herbage. These included iron, aluminium,
chromium, vanadium and fluorine, where the cause was
attributed to contamination of herbage by soil. It was
suggested that iron could be used almost equally as well as
titanium as an indicator of the degree to which herbage has
been contaminated by soil.
• Long term monitoring of herbage for selenium content
highlighted the unreliability of relying on a single
determination to characterise the selenium status of pasture