Mj. Bell et al., INTER-SPECIFIC AND INTRA-SPECIFIC VARIATION IN ACCUMULATION OF CADMIUM BY PEANUT, SOYBEAN, AND NAVYBEAN, Australian Journal of Agricultural Research, 48(8), 1997, pp. 1151-1160
Production of summer grain legumes like peanut, soybean, and navybean
is expanding into irrigated or high rainfall areas on more acid, light
er textured soils in coastal areas oi north-eastern Australia. A histo
ry of intensive use of phosphatic fertilisers, combined with soil prop
erties which generally enhance phytoavailability of cadmium (Cd), have
produced concerns about the likely quality of grain legumes produced
in these areas. This paper reports field and pot experiments which exa
mine the effect of grain legume species and variety on Cd accumulation
when grown across a range of soil types. Results clearly show that bo
th peanut and soybean accumulate Cd in seeds at levels greater than th
e maximum permitted concentration (MPG, 0.05 mg Cd/kg) even on soils w
ith relatively low total or available Cd concentrations (<0.5 mg/kg).
The relative risk of MPC exceedance in marketable seeds or kernels was
peanut > soybean > navybean, with the differences between peanut and
navybean apparently correlated with differences in total plant Cd upta
ke. Cadmium concentrations in plant tops always exceeded that in seeds
or kernel, and the testa in peanut kernel was shown to contain Cd con
centrations that were 50 times greater than that in the embryonic axis
and cotyledons. Significant (P < 0.05) variation in Cd content (at le
ast 2-fold) Ras recorded among peanut varieties, with lesser variation
evident among a limited sample of commercial navybean varieties. Comp
arison of results for 11 peanut varieties grown at each of 2 locations
suggested strong genotype x environment interactions determining kern
el Cd concentration. Highly significant (P < 0.01) linear relationship
s were established between soil Cd in the cultivated layer (0-20 cm; 0
.1 M CaCl2 extraction) and seed Cd content in field-grown soybean. How
ever, despite observations of an apparent relationship between soil Cd
(CaCl2 extraction) and peanut kernel Cd in pot studies, relationships
between soil Cd in the cultivated layer and kernel Cd could not be re
produced in field trials. Kernel Cd concentrations from field-grown pe
anut plants were generally higher than those horn pot trials, despite
using soil collected from the cultivated layer (0-20 cm) of the field
site for the potting medium. The presence of significant levels of Cd
to approximately 60 cm in the soil profile and a general decline in pH
(w) with depth suggest the lack of correlation between soil test Cd in
the top 20 cm and kernel Cd in field-grown plants may be at least par
tly due to Cd uptake from deeper soil layers.