Author:
McLaughlin M. J.,Bell M. J.,Wright G. C.,Cruickshank A.
Abstract
Production of summer grain legumes like peanut, soybean, and navybean is
expanding into irrigated or high rainfall areas on more acid, lighter textured
soils in coastal areas of north-eastern Australia. A history of intensive use
of phosphatic fertilisers, combined with soil properties 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 examine the effect of grain legume species and
variety on Cd accumulation when grown across a range of soil types. Results
clearly show that both peanut and soybean accumulate Cd in seeds at levels
greater than the maximum permitted concentration (MPC, 0·05 mg
Cd/kg) even on soils with 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 uptake. Cadmium concentrations in plant tops always exceeded
that in seeds or kernel, and the testa in peanut kernel was shown to contain
Cd concentrations that were 50 times greater than that in the embryonic axis
and cotyledons.
Significant (P < 0·05) variation in Cd content
(at least 2-fold) was recorded among peanut varieties, with lesser variation
evident among a limited sample of commercial navybean varieties. Comparison of
results for 11 peanut varieties grown at each of 2 locations suggested strong
genotype environment interactions determining kernel Cd concentration.
Highly significant (P < 0·01) linear
relationships 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. However, 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 reproduced in field trials. Kernel
Cd concentrations from field-grown peanut plants were generally higher than
those from 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 pHw 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 partly due to Cd uptake from deeper soil layers.
Subject
General Agricultural and Biological Sciences
Cited by
54 articles.
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