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Reclamation of Quartz Sand-Tailings from Phosphate Mining: III. Summer Annual Grasses¹

ABSTRACT

Quartz sand-tailings, a waste product from the Florida phosphate (PO₄) mining industry, amount to about 90 million metric tons annually. These sands contain no phytotoxic substance but are low in several nutrients, organic matter, and water retention capacity. A split-plot field experiment was conducted to determine the production, quality, and nutrient concentration of four summer annual grasses: (i) full season corn (Zea mays L. ‘Dekalb XL 395’), (ii) mid-season corn (Zea mays L. ‘Funks G. 4864’), (iii) grain sorghum Sorghum bicolor (L.) Moench ‘Dorado M’, and (iv) sorghum x sudangrass hybrid (Sorghum bicolor (L.) Moench subsp. bicolor x Sorghum bicolor (L.) Moench subsp drummondii (Steud.) deWet ‘Dekalb SX 16’), grown on four amended sand-tailing treatments. These treatments were: (i) sand-tailings control (SC), (ii) colloidal phosphate (CP) at 336 metric tons/ha, (iii) CP at 336 metric tons/ha + oven-dry sewage sludge (SS) at 45 metric tons/ha, and (iv) CP at 336 metric tons/ha + top soil (TS) at 1,460 metric tons/ha. Forage dry matter (DM) and grain yields of corn and sorghum tended to decrease with the following treatments: CP + TS > CP + SS > CP > SC. The sorghum x sudangrass hybrid (S x S) produced higher (P < 0.05) total forage DM yields (13.4 metric tons/ha) than other grasses in both 1976 and 1977. Highest grain yields (3,370 kg/ha at 15.5% moisture) were obtained from the full-season corn hybrid. In vitro organic matter digestion was highest both years for corn (67%), followed closely by S x S hybrid (61%) and grain sorghum (62%).

The P and K concentrations increased in grain sorghum forage while P, K, Ca, Mg, Mn, Cu, Zn, and Fe increased in the S x S hybrid as the root system expanded over harvests. Data indicated that relatively low forage yields, of good quality and adequate nutrient concentrations for beef cattle, can be produced.

Key Words: soil amendments • Zea mays (L.) • Sorghum bicolor (L.) Moench • corn • sorghum • sorghum x sudangrass hybrid

¹ Contribution of the University of Florida Agric. Res. Ctr., Ona, FL 33865, and Univ. of Florida Soil Sci. Dep., Gainesville, FL 32611, as Journal Series no. 2747.

² Associate Professor of Agronomy, Univ. of Florida Agric. Res. Ctr., Ona, and Professor of Soil Fertility, Soil Sci. Dep., Univ. of Florida, Gainesville, respectively.

Received for publication November 29, 1980.