In the mining industry place, tailing dumps remain, which contain toxic substances. For their rehabilitation, it is proposed to use local zeolite-containing clays of North and South Ossetia Eredvit and Dialbekulit containing a complex of minerals with an alkaline reaction of the environment. In addition to clays, peat with a high content of humic substances is introduced into the substrate. The prepared substrate is irrigated with mineral sulfur-containing water of the Tamisk spring. Accumulating toxic substances and herbs are sown on the surface of the densified area: annual and perennial herbs, for example, amaranth, legumes, winter camelina. Before sowing, grass seeds are mixed with the husk of winter camelina. Such remediation of contaminated sites reduces the toxicity of tailings to 90 % and restores soil fertility.

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The article contains a retrospective of the development of extraction of mineral resources in the mountain ecosystem of the Eastern Caucasus; the stages of environmental tension growth in various components of the biosphere of the region are also shown. It has been proved that in the areas of dislocation of existing mountain objects, landscapes and soils, which are an integral part of ecosystems, are distinguished by a pronounced zoning, each of which has certain components that influence the formation of ecological situation. The studies have shown that pollution of the soil horizon with heavy and toxic metals leads to depletion and degradation of the natural environment, a radical transformation of the landscape, leading fragmentarily to its steady destruction. It is shown that the ecological technical capacity of the territory depends on the volume of the air basin (in mountain canyons, gorges it reaches 200 meters height from the base), the totality of reservoirs of drains, land areas and soil reserves, the bulk of flora and fauna species; biochemical circulation flow rates (speed, mass of gas exchange, pure water increment, soil formation processes and biota productivity). The ecological situation formed under such conditions needs to be improved by adopting special scientifically grounded organizational, technical and technological measures to reduce the ecological load to the ecosystem of mountain landscapes and restore sustainable forms of its functioning. The results of the research given in the article can be useful for environmental agencies, design institutions and existing mining enterprises for taking necessary environmental measures to ensure sustainable development of the natural-technical system under the conditions of mountain landscapes of the Caucasus. Keywords-extraction of mineral resources; landscape degradation; heavy metals; soil horizon; ecological technical capacity of territories; region biosphere; components of the biosphere; landscape properties.VIII

The article presents the results of a study of vital activity of nodule bacteria of Trifolium praténse, Trifolium hibridum, Trifolium alexandrinum and Trifolium incarnatum as environmentally friendly bioindicators in soil toxicity assessment. The study focused on the number of nodules and their stain with leghemoglobin. The materials were taken from the plots artificially contaminated with heavy metals (lead (Pb), arsenic (As), mercury (Hg), fluorine (F), zinc (Zn) and cobalt (Co)). The results of the experiments showed that environmental distress occurs when the nitrogen-fixing nodules are stained pink or red in the range of 8-15%, which indicates that the lead content in the soil exceeds the threshold limit value (TLV) by 1.2-1.5 times. A significant decrease in nodule activity and weak or no stain were observed with an increase in mercury concentration by 1.1 times. It was found that the mass of rhizobium or the supply of organic nitrogen obtained by plants from fixation from the air is directly dependent on the grass density. At high concentrations of heavy metals in the soil, the nodule bacteria lose the amount of leghemoglobin, therefore the stain of bacteria is disrupted, so this indicator can be used as a bioindicator in soil toxicity assessment.

The article presents the results of studies on the seeding time of perennial forage crops in the foothill area of North Ossetia-Alania. An agricultural method which is necessary is the pre-sowing treatment of seeds with natural agronomic ores in a ratio of 1:2 and simultaneous seed scarification. The studies revealed that the most optimal seeding time in terms of field germination and plant safety for harvesting for all the studied crops was the variant of the middle seeding time in the second ten-day period of May, when the soil temperature was warmed up to 12-14 °C. Also, when seeded late, the plantings of the studied crops significantly decreased in terms of leaf area—by 1.9 thousand m2/ha for burnet, by 1.2 thousand m2/ha for clover, by 1.5 thousand m2/ha for medicago, by 1.5 thousand m2/ha for sainfoin, by 1.5 thousand m2/ha for galega, by 0.8 thousand m2/ha for festulolium. Over four years, the average biochemical composition of perennial grasses of different seeding periods did not differ significantly in the content of forage units, digestible protein and metabolic energy. Thus, depending on the seeding time, fluctuations in the content of forage units were as follows: 2.21-2.24 t/ha for clover; 2.09-2.21 t/ha for medicago; 2.34-2.46 t/ha for sainfoin; 2.69-2.79 t/ha for galega; 2.27-2.41 t/ha for festulolium; 2.56-2.74 t/ha for burnet. The digestible protein content, respectively: 0.37-0.44 t/ha for clover; 0.51-0.55 t/ha for medicago; 0.49-0.54 t/ha for sainfoin; 0.43-0.57 t/ha for galega; 0.38-0.44 t/ha for festulolium; 0.57-0.64 t/ha for burnet. The output of metabolic energy was: 48.9-51.7 GJ t/ha for clover; 38.4-43.2 GJ t/ha for medicago; 39.3-42.4 GJ t/ha for sainfoin; 41.7-46.3 GJ t/ha for galega; 48.7-52.3 GJ t/ha for festulolium; 40.5-42.7 t/ha for burnet. Moreover, the crops of early and medium time of seeding had the highest values of biochemical composition.