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16 <br />on other tailings. These opposing effects were deemed to depend principally <br />on two factors: First, if salt-containing tailings produced an appreciable <br />osmotic concentration when watered, the fertilizer appeared to increase this <br />concentration with deleterious effect on the plants. Second, if heavy-metal- <br />containing minerals were solubilized by the ammonia in the fertilizer, the <br />metal ions hindered plant growth. <br />Wercoming Salinity and Acidity Problems <br />Research was conducted to devise means of overcoming the deleterious <br />effects of salts and acids in mill tailings. The following three methods were <br />considered: (1) Percolation leaching of the salts from the tailings; <br />(2) stratification of the sand and slime fractions of the tailings during. <br />deposition; and (3) solar orientation of mounds of tailings to produce differ- <br />ential concentrations of salt on shaded and sunlit sides of the mound. <br />Additional research for overcoming salinity problems only is underway, <br />encompassing the addition of sulfur in various forms to saline soil and tail- <br />ing materials. Native and byproduct gypsum, sulfur, sulfur plus limestone, <br />pyrite, ferrites, and sulfuric acid are under consideration as additives and <br />test plots have been established. Insufficient time has elapsed to properly <br />evaluate the results and the findings are not included in this report. <br />A minimum of work was done on percolation leaching, because an apparently <br />satisfactory means of leaching highly acidic tailings has been reported (5). <br />The work by James showed flooding is not an effective means of leaching acid- <br />ity from tailings because {1) prolonged flooding compacts the materials pro- <br />ducing conditions unfavorable for plant growth, and (2) when flooding is <br />halted, evaporation brings the acid to the surface again. James' investiga- <br />tions indicated that the downward movement of acidity can be encouraged by an <br />extremely fine spray of water which forms a mist over the surface and retards <br />evaporation. If the spray of water applied does not exceed the rate at which <br />it can penetrate the tailings, high acidity can be moved to a sufficient depth <br />to permit vegetative growth within a period of 3 to 4 weeks. If the acid can <br />be moved downward to contact a slime layer with which it reacts, subsequent <br />evaporative movement will not return the acid to the surface. <br />These projections have recently been substantiated by research on the <br />reclamation of saline soils using drip irrigation .and widely spaced deep <br />furrows in planting. Practitioners of drip irrigation indicate that spot <br />irrigation with small amounts of water sufficient to drive the majority of the <br />salts beyond the pickup zone of the plant roots speeds vegetative growth, Siu <br />ilarly, good vegetative growth of grasses and legumes in harsh saline environ- <br />ments has been achieved by planting the seeds in 4- to 6-inch-deep furrows <br />spaced at intervals from 12 to 42 inches apart. The wide spacing between <br />furrows reduces plant competition and the deepness of the furrow permits con- <br />centration of the water and directs the salts to the ridges between furrows. <br />Other studies made by the Bureau indicated that stratification and mound- <br />ing of tailings were effective in ameliorating salinity problems. Comparative <br />vegetative growth tests were made (1) in unstratified plots of tailings <br />