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STRATEGIES TO REDUCE CADMIUM ACCUMULATION IN PEANUTS

M.J. Bell1, G.C. Wright1, M.J. McLaughlin2 , and A. Cruickshank1

1 Queensland Department of Primary Industries, PO Box 23, Kingaroy, Qld 4610
2 CSIRO Division of Soils, PMB No.2, Glen Osmond, SA 5064

The Australian peanut industry is expanding from traditional rainfed production into irrigated areas with acidic, sandy soils that have a long history of P fertiliser application (e.g. sugarcane and horticultural areas). These soil conditions have been associated with excessive accumulation of cadmium (Cd) in the harvestable portion of other crop species. Surveys of peanut kernel from some new areas have shown Cd levels exceeding the maximum permissable limit (MPL, 0.05 mg/kg). Preliminary experiments were undertaken to understand the mode of Cd uptake (pods v roots) in peanut, and to determine if genotypic differences in Cd accumulation exist.

MATERIALS AND METHODS

Pot experiments with cv. Streeton were undertaken to determine mode of Cd uptake. Cd was differentially applied to physically separated pod and root zones, using DAP with <5 (-Cd) or 75 (+Cd) mg/kg Cd content. Two soil types were used (a Kingaroy Ferrosol and the A horizon of a Bundaberg red podsolic), with additional pod zone treatments of acid-washed sand included to provide a reference with high available Cd. Plants were grown to maturity and kernel Cd content determined. A field study was also undertaken, with kernel Cd content of 30 diverse genotypes grown on the Bundaberg red podsolic used to indicate genetic variation in Cd accumulation.

RESULTS AND DISCUSSION

Despite initial soil EDTA Cd levels which were greater in the Kingaroy Ferrosol (0.07 mg/kg) than in the Podsolic (0.04 mg/kg), high levels of Cd sorption in the Ferrosol resulted in minimal Cd uptake (Trt 1, Table 1). Cd levels exceeded the MRL when available Cd was present in the pod zone (Trt 3), and by a much greater margin when available Cd was present (Trt 4) and/or added to (Trt 5) the root zone. This result suggests that Cd is primarily taken up via the root system before re-translocation to developing pods, although direct uptake of limited quantities via pods may also be significant. Agronomic solutions to the problem will therefore involve consideration of both pod and root zones.

A large range in kernel Cd concentration was observed among peanut genotypes (0.16- 0.50 mg/kg) in the field study. Although no genotype had levels below the MPL, the extent of variation suggests screening for low Cd accumulating lines may be possible

Table 1. Cadmium concentration of peanut kernel (mg/kg) from the pot trial .

Pod zone

Root zone

Kernel Cd

1. Kingaroy Ferrosol, -Cd

Kingaroy Ferrosol, -Cd

0.007 a

2. Acid wash sand, -Cd

Kingaroy Ferrosol, -Cd

0.012 a

3. Acid wash sand, +Cd

Kingaroy Ferrosol, -Cd

0.067 b

4. Acid wash sand, -Cd

Bundaberg Podsolic,-Cd

0.185 c

5. Bundaberg Podsolic,-Cd

Bundaberg Podsolic,+Cd

0.306 d

ACKNOWLEDGMENTS

This research was partly funded by Peanut Company of Australia, Kingaroy.

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