Reclamation of Quartz Sand‐Tailings from Phosphate Mining: III. Summer Annual Grasses

Abstract

AbstractQuartz 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 × sudangrass hybrid (Sorghum bicolor (L.) Moench subsp. bicolor × 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 × sudangrass hybrid (S × 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 × 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 × 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.