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13 <br />• These data indicate that several methods are available for stabilizing <br />dill tailings at costs of less than $400 per acre, The chemical-vegetative <br />procedure appears to be cheapest and wherever applicable should be a preferred <br />method. Both the chemical-vegetative .and hydroseeding methods appear to be <br />cheaper than the matting or soil-covering procedures, However, for difficult <br />areas these latter methods may be mandatory. <br />ONGOING BUREAU OF MINES RESEARCH <br />Development of several different vegetative procedures has provided satis- <br />factory stabilization for many of the mill tailing accumulations scattered <br />across the country. However, means of reducing maintenance costs on vegetated <br />tailings is desirable, and more economical-procedures are needed for vegetat- <br />ing highly saline, acid, or alkaline tailings. Reduction of fertilizer <br />requirements is being studied to reduce maintenance costs. To overcome the <br />salinity and other problems, work is being done on seedbed preparation, plant- <br />ing, and watering practices. Research also is continuing on making synthetic <br />soils from the tailings. by adding sewage sludge or refuse compost. <br />Reducine Maintenance Costs <br />Practically all mill tailings are deficient in fertilizer elements, espe- <br />cially nitrogen, Nitrogen not only is low in most tailings, but it is also <br />readily depleted from vegetated wastes containing heavy metal salts. Lack.of <br />nitrogen can be overcome by planting nitrogen-fixing legumes, but legume <br />growth on tailings is difficult to perpetuate, <br />Growth of nitrogen-fixing native plant species that may be compatible <br />With the harsh environment of tailings is being investigated. Particular <br />attention is being given to Indian ricegrass, a desert-type plant that fixes <br />nitrogen in a root sheath of sand particles invaded by bacteria or other micro- <br />organisms, Obtaining growth from Indian ricegrass, however, is difficult to <br />achieve in that the seeds contain a natural inhibitor that limits germination <br />[0 1 percent or less on newly matured or up to 2-year-old seeds. Ricegrass <br />seeds have been gathered during the past 3 years and germination studies made <br />in an effort to break the dormancy. Treatments by attrition grinding with <br />quartz to break the seed covering, sulfuric acid and water soaking and boiling, <br />and cool and below freezing incubation were all ineffective when treating both <br />newly matured and 2-year-old seeds. When soaking seeds less than a year old <br />in 70-percent-by-volume sulfuric acid for 25 minutes at 25° C, germination was <br />nil; and with a subsequent 24-hour soaking in 10-a molar gibberellic acid or <br />kinetin hormones in a solvent of 9 parts of dichloromethane and 1 part ethanol <br />C1 cc solution per 100 seeds), the germination was still less than 5 percent, <br />However, when using an acid soak followed by a soak in both gibberellic acid <br />and kinetin, the germination after 2-, 4-, and 6-week intervals, was respec- <br />tively, in percent, 55, 75,,and 90. When treating 2-year-old seeds, treat- <br />ments with an acid soak plus respective treatments with kinetin, gibberellic <br />acid, or gibberellic acid plus kinetin gave S-week germination percentages <br />respectively of 5, 80, and 80. After 2 years of aging, the inhibitor effect <br />decreases and kinetin treatment is no longer necessary. <br />:I <br />~! <br />r. <br />~~ <br />1 <br />~; - . <br />C;. <br />~~7 <br />~: <br /> <br />.r i <br />:: ~. <br />>! <br />