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Radium-226 and Calcium Uptake by Crops Grown in Mixtures of Sand and Clay Tailings from Phosphate Mining

College of Agric., Univ. of Hawaii at Hilo, Hilo, HI 96720-4091 (currently Environ. Horticulture, Fifield Hall, P.O. Box 110670, Univ. of Florida, Gainesville, FL 32611);

J. B. Sartain

Soil Sci. Dep., Univ. of Florida, Gainesville, FL 32611;

R. X. Gonzalez and W. D. Carrier, III

Bromwell & Carrier, Lakeland, FL 33807-5467.

^* Corresponding author (caba{at}gnv.ifas.ufl.edu).

ABSTRACT

Radium-226 is a naturally occurring radionuclide found in reclaimed clay and sand tailings from phosphate mining. Field studies were conducted to investigate the effects of sand/clay ratio (SCR), Ca supplement, and organic amendments on the ²²⁶Ra concentration in turnip (Brassica rapa L.), banana pepper (Capsicum annum L.), cabbage (Brassica oleracea var. capitata), yellow squash (Cucurbita pepo L.), mustard [Brassica juncea (L.) Czern & Coss.] and alfalfa (Medicago sativa L.). For vegetables, treatment effects included SCR (2:1, 4:1, 6:1, and 8:1), phosphogypsum (PG) (0, 22, and 134 Mg ha^–1), and peat (0, 100, 200 Mg ha^–1). For alfalfa grown in a 1:1 SCR mixture, treatments included organic amendments (control, peat, sewage sludge, sawdust, composted sewage sludge, composted garbage and humate) applied at 44.8 Mg ha^–1 (2.2 Mg ha^–1 for humate). Plant ²²⁶Ra concentration tended to be higher in the 4:1 than in the 2:1 SCR mix but this depended on the crop and the season. Organic amendments and PG had no effect (p < 0.05) on the ²²⁶Ra concentration in vegetables and alfalfa. Mean ²²⁶Ra concentration in plant tissues ranged from 3.4 Bq kg^–1 in banana pepper fruit to 31.1 Bq kg^–1 in turnip leaf. Sand-clay mixtures contained 289 to 592 Bq ²²⁶Ra kg^–1. A quadratic relationship based on 631 observations was observed between ²²⁶Ra and Ca concentration in plant tissues. The ²²⁶Ra/Ca ratio in plant tissues ranged from 0.85 to 2.13 kBq ²²⁶Ra kg^–1 Ca and decreased with increasing plant ²²⁶Ra. Results indicated that wide differences in plant ²²⁶Ca concentration were related more to differences in plant Ca levels than to soil factors.

Grant support from Florida Institute of Phosphate Research.

Received for publication February 3, 1992.