Reclamation of Quartz Sand-Tailings from Phosphate Mining: II. Forage Legumes
1981
Quartz sand-tailings are a waste product from the phosphate mining industry in southwest Florida. A split-plot field experiment was conducted to study the performance of the tropical forage legumes: (i) ‘Siratro’ (Macroptilium atropurpureum (DC.) Urb.), (ii) ‘Florida’ Carpon desmodium (Desmodium heterocarpon (L.) DC), (iii) ‘Caribbean’ stylo 7303 (Stylosanthes hamata (L.) Taub.), (iv) ‘Stylo mix’ (31 cultivars) (Stylosanthes spp.), and (v) ‘Florida 66’ alfalfa (Medicago sativa L.), a temperate legume, on four amended sand-tailing treatments. These treatments were: (i) sand-tailings control (SC), (ii) colloidal phosphate (CP) at 336 metric tons/ha incorporated, (iii) CP at 336 metric tons/ha + oven-dry sewage sludge (SS) at 45 metric tons/ha incorporated, and (iv) CP at 336 metric tons/ha + top soil (TS) at 1,460 metric tons/ha incorporated. Siratro, stylo mix, and alfalfa all demonstrated rapid emergence and development on sand-tailings, especially when seeded on the SC and CP treatments. These three species also produced the highest (P < 0.05) yields during the initial harvest season. The first winter after establishment, a freeze at the experimental site killed all entries except alfalfa and Siratro. Throughout the remainder of the study alfalfa outyielded siratro by 250% on all treatments except CP + TS treatments, where alfalfa plants died in 1977. Forage quality measurements (in vitro organic matter digestion and crude protein) of alfalfa were higher (P < 0.05) than those for Siratro, with little difference in forage quality between sand-tailing treatments. The P, K, Ca, Mg, Mn, Cu, and Zn concentrations in the forage of both legume species were more than adequate for good animal performance. The double-acid-extractable P (4,520 kg/ha) and Ca (8,540 kg/ha) were extremely high on all treatments.
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