APPLICATION OF INCREASING LEVELS OF ZINC TO SOIL REDUCED ACCUMULATION OF CADMIUM IN LUPIN GRAIN

Abstract

Yellow lupin (Lupinus luteus L.) and narrow-leafed lupin (L. angustifolius L.) are grown as grain legumes in rotation with spring wheat (Triticum aestivum L.) on acidic sandy soils of south-western Australia. Yellow lupin can accumulate significantly larger cadmium (Cd) concentrations in grain than narrow-leafed lupin. A glasshouse experiment was undertaken to test whether adding increasing zinc (Zn) levels to soil increased Zn uptake by yellow lupin reducing accumulation of Cd in yellow lupin grain. Two cultivars of yellow lupin (cv. ‘Motiv’ and ‘Teo’) and 1 cultivar of narrow-leafed lupin (cv. ‘Gungurru’) were used. The soil was Zn deficient for grain production of both yellow and narrow-leafed lupin, but had low levels of native soil Cd (total Cd <0.05 mg kg−1) so 1.6 mg Cd pot−1, as a solution of cadmium chloride (CdCl2·H2O), was added and mixed through the soil. Eight Zn levels (0–3.2 mg Zn pot−1), as solutions of zinc sulfate (ZnSO4·7H2O), were added and evenly mixed through the soil. Yellow lupin accumulated 0.16 mg Cd kg−1 in grain when no Zn was applied, which decreased as increasing Zn levels were applied to soil, with ∼0.06 mg Cd kg−1 in grain when the largest level of Zn (3.2 mg Zn pot−1) was applied. Low Cd concentrations (<0.016 mg Cd kg−1) were measured in narrow-leafed lupin grain regardless of the Zn treatment. When no Zn was applied, yellow lupin produced ∼2.3 times more grain than narrow-leafed lupin, indicating yellow lupin was better at acquiring and using indigenous Zn from soil for grain production. Yellow lupin required about half as much applied Zn as narrow-leafed lupin to produce 90% of the maximum grain yield, ∼0.8 mg pot−1 Zn compared with ∼1.5 mg Zn pot−1. Zn concentration in whole shoots of young plants (eight leaf growth stage) related to 90% of the maximum grain yield (critical prognostic concentration) was (mg Zn kg−1) 25 for both yellow lupin cultivars and 19 for the narrow-leafed lupin cultivar. Critical Zn concentration in grain related to 90% of maximum grain yield was (mg Zn kg−1) 24 for both yellow lupin cultivars compared with 20 for the narrow-leafed lupin cultivar.