Summary. This study investigated whether changing
phosphatic fertiliser type affects the accumulation of cadmium (Cd) and
fluorine (F) in pasture herbage. North Carolina phosphate rock, and partially
acidulated fertilisers derived from this rock, generally have higher Cd and F
concentrations compared with single superphosphate currently manufactured in
Australia.
Clover herbage from sites of the National Reactive Phosphate Rock trial was
collected and analysed for concentrations of Cd (11 sites) and F (4 sites). A
comparison was made between pastures fertilised with 4 rates of single
superphosphate, North Carolina phosphate rock, and partially acidulated
phosphate rock having Cd concentrations of 283, 481 and 420 mg/kg P
respectively, and F concentrations of 170, 271 and 274 g/kg P
respectively. One site used Hamrawein (Egypt) phosphate rock (HRP) having a Cd
and F concentration of 78 mg Cd/kg P and 256 g F/kg P respectively. To
help identify differences in herbage Cd concentrations between sites,
unfertilised soils from each site were analysed for total and extractable Cd
contents. At one site Cd concentrations in bulk herbage (clover, grasses and
weeds) were related to infestation of the pasture by capeweed
(Arctotheca calendula L. Levyns).
There were no significant differences between F in herbage from plots
fertilised with either single superphosphate, partially acidulated phosphate
rock or North Carolina phosphate rock, or between sites. Concentrations of F
in herbage were low, generally less than 10 mg/kg. However, there were
large differences in Cd concentrations in herbage between sites, while
differences between fertiliser treatments were small in comparison. The site
differences were only weakly related to total or extractable (0.01 mol
CaCl2/L) Cd concentrations in soil.
Significant differences in Cd concentrations in clover due to fertiliser type
were found at 5 sites. North Carolina phosphate rock treatments had
significantly higher Cd concentrations in clover compared with single
superphosphate at 2 sites. Partially acidulated phosphate rock treatments had
significantly higher Cd concentrations in clover compared with single
superphosphate at 4 sites. At the site where Hamrawein was tested, this
treatment had significantly lower Cd concentrations in clover compared with
both single superphosphate and North Carolina phosphate rock treatments.