EFFECT OF FERTILIZER TYPE ON CADMIUM AND FLUORINE CONCENTRATIONS IN CLOVER HERBAGE

This study investigated whether changing phosphatic fertiliser type af fects the accumulation of cadmium (Cd) and fluorine (F) in pasture her bage. North Carolina phosphate rock, and partially acidulated fertilis ers derived from this rock, generally have higher Cd and F concentrati ons compared with single superphosphate currently manufactured in Aust ralia. Clover herbage from sites of the National Reactive Phosphate Ro ck trial was collected and analysed for concentrations of Cd (11 sites ) and F (4 sites). A comparison was made between pastures fertilised w ith 4 rates of single superphosphate, North Carolina phosphate rock, a nd partially acidulated phosphate rock having Cd concentrations of 283 , 481 and 420 mg/kg P respectively, and F concentrations of 170, 271 a nd 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 concen trations between sites, unfertilised soils from each site were analyse d for total and extractable Cd contents. At one site Cd concentrations in bulk herbage (clover, grasses and weeds) were related to infestati on of the pasture by capeweed (Arctotheca calendula L. Levyns). There were no significant differences between F in herbage from plots fertil ised with either single superphosphate, partially acidulated phosphate rock or North Carolina phosphate rock, or between sites. Concentratio ns of F in herbage were low, generally less than 10 mg/kg. However, th ere were large differences in Cd concentrations in herbage between sit es, while differences between fertiliser treatments were small in comp arison. The site differences were only weakly related to total or extr actable (0.01 mol CaCl2/L) Cd concentrations in soil. Significant diff erences in Cd concentrations in clover due to fertiliser type were fou nd at 5 sites. North Carolina phosphate rock treatments had significan tly higher Cd concentrations in clover compared with single superphosp hate at 2 sites. Partially acidulated phosphate rock treatments had si gnificantly higher Cd concentrations in clover compared with single su perphosphate 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 tre atments.