Cadmium Accumulation by Forage Species Used in New Zealand Livestock Grazing Systems

Little data exists on cadmium (Cd) accumulation in many plant species now commonly used as animal forages in New Zealand livestock grazing systems. A glasshouse trial was undertaken on 12 forage species to address this knowledge gap. Mean tissue Cd concentration decreased in the order chicory > plantain > turnip > lucerne > sheep’s burnet > strawberry clover > kale > perennial ryegrass > haresfoot trefoil > red clover > crimson clover > white clover. Chicory and plantain had significantly greater mean tissue Cd concentrations (1.639 and 0.734 mg kg -1 DM, respectively) than all other species. Cadmium in ryegrass and white clover (0.103 and 0.035 mg kg -1 , respectively) was similar to that reported in other field and laboratory studies. A survey undertaken across a range of commercial farms with varying soil type, land use and phosphorus (P)-fertiliser history validated the results of our glasshouse trial; chicory had a mean Cd concentration of 1.82 mg kg -1 (range 0.40-4.50 mg kg -1 ) and plantain had a mean Cd concentration of 0.80 mg kg -1 (range 0.23-2.40 mg kg -1 ). Modelling of lamb kidney Cd accumulation indicated that food standard maximum levels may be exceeded in animals younger than the current meat industry 30 month offal discard age. With increased use of chicory and plantain as specialist forage crops in New Zealand, this information will be important for improving livestock Cd accumulation risk assessment models. Introduction Cadmium accumulation in New Zealand agricultural soils has been strongly correlated to history of P-fertiliser usage (Bramley, 1990; Roberts et al., 1994). As Cd retains high bio/phyto-availability in the soil for extended periods, and since plants have little ability to regulate Cd uptake, plant tissue Cd concentration tends to increase with increasing soil Cd concentration (Adriano, 1986; Smolders and Mertens, 2012). As elevated Cd in the human diet has been associated with human health disorders (Chaney et al., 1999), Cd accumulation in agricultural land and plant species is undesirable. In New Zealand agriculture, considerable research was carried out on plant Cd accumulation in the 1990s. Aside from a few significant food crops (potatoes, onions, lettuce and wheat (Roberts et al., 1995; Gray et al., 2001)) the majority of this work focused on ryegrass and