RA-226 AND CALCIUM-UPTAKE BY CROPS GROWN IN MIXTURES OF SAND AND CLAYTAILINGS FROM PHOSPHATE MINING

Radium-226 is a naturally occurring radionuclide found in reclaimed cl ay and sand tailings from phosphate mining. Field studies were conduct ed to investigate the effects of sand/clay ratio (SCR), Ca supplement, and organic amendments on the Ra-226 concentration in turnip (Brassic a rapa L.), ba-na pepper (Capsicum annum L.), cabbage (Brassica olerac ea var. capitata), yellow squash (Cucurbita pepo L.), mustard [Brassic a juncea (L.) Czern & Coss.] and alfalfa (Medicago sativa L.). For veg etables, treatment effects included SCR (2:1, 4:1, 6:1, and 8:1), phos phogypsum (PG) (0, 22, and 134 Mg ha-1), and peat (0, 100, and 200 Mg ha-1). For alfalfa grown in a 1:1 SCR mixture, treatments included org anic amendments (control, peat, sewage sludge, sawdust, composted sewa ge sludge, composted garbage and humate) applied at 44.8 Mg ha-1 (2.2 Mg ha-1 for humate). Plant Ra-226 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 Ra- 226 concentration in vegetables and alfalfa. Mean Ra-226 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 Ra-226 kg-1. A quadratic relationship based on 631 observations was ob served between Ra-226 and Ca concentration in plant tissues. The Ra-22 6/Ca ratio in plant tissues ranged from 0.85 to 2.13 kBq Ra-226 kg-1 C a and decreased with increasing plant Ra-226. Results indicated that w ide differences in plant 226Ca concentration were related more to diff erences in plant Ca levels than to soil factors.