Land recultivation (restoration) is a complex of engineering, reclamation, agro-technical and other measures aimed at restoring biological productivity, economic value of disturbed lands and improving environmental conditions.
Disturbed lands – lands which have lost their original economic value or have become a threat to the environment by changing the soil cover, hydrological regime and formation of anthropogenic landscape as a result of human industrial activity.
61% of disturbed lands fall on the territories of mineral deposits development, their processing and geological prospecting works, 27% – on peat extraction works. In 1997 the area of disturbed lands from mining operations and geological prospecting works was about 700 thousand ha, peat extraction – more than 300 thousand ha.
According to the data of the State Research Institute of Land Resources, depending on mining and geological conditions of mineral deposits from 2,6 to 43 hectares of land are disturbed per 1 million tons of surface coal mining, from 14 to 640 hectares of iron ore, from 76 to 600 hectares of manganese ore, from 22 to 77 hectares of phosphorites. Land disturbance with deterioration of the environmental situation may also occur during underground development of deposits due to surface deformation, such as sinkholes, storage of excavated rocks, pollution by industrial emissions, oil products, sewage water, drilling fluids and cuttings during drilling and well operation.
Land disturbance occurs when laying main pipelines, building roads and canals. At the same time, landscapes and land use structure deteriorate, erosion processes intensify, the balance of ground and surface waters is disturbed, nearby lands become waterlogged or dry out, and their productivity decreases.
Land disturbance is predominantly pronounced in areas with high population density and developed industry, where the reserves of introducing new lands into agricultural use are almost exhausted. For this reason, the issue of including disturbed lands subject to reclamation in the total balance of agricultural land is relevant.
According to the State Land Records, as of January 1, 1999 the acreage of disturbed lands in Russia made up 1.19 million hectares. The main part of disturbed lands is concentrated in the areas of intensive farming with high population density.
In Russia there is a tendency of increasing the rate of land disturbance in Western and Eastern Siberia, in the Far East by 15-20% per year, in the Central Black Earth zone, especially in Kursk and Belgorod regions. Over 30 thousand hectares of valuable chernozem and gray forest soils have been withdrawn from land use in these zones for the iron ore industry.
Land recultivation (restoration)
Recultivation makes it possible to return disturbed land to agricultural land, to use it for forests, water bodies, recreation areas, housing and industrial construction. Recultivation can be subjected to excavation of quarries, peat mines, rock dumps of mines and quarries, sites of drilling wells, etc.
The problem of recultivation in conditions of a constantly increasing area of disturbed lands acquires great socio-economic and ecological significance. The issue of recultivation should be included in the projects for the construction and reconstruction of enterprises, in the schemes of land management of territorial and production complexes.
If scientifically grounded recultivation technologies are followed it is possible to turn the disturbed lands into highly productive land within 3-5 years. More than 2,200 thousand hectares of disturbed lands have been reclaimed in Russia.
Some rocks are characterized by effective fertility. Achievements of modern agriculture, developed technologies of creation of anthropogenic soils, methods of biological development of recultivated areas and management of soil formation process in anthropogenic landscapes allow to use these rocks in order to create productive farmlands as well as to improve ecological conditions in relation to a specific natural zone or territory.
Depending on the requirements of plants to growing conditions, several ecological and trophic groups of plants have been identified:
Megatrophs are agricultural crops with the highest requirements for soil (edaphic) environment: rye, wheat, oats, barley, corn, sorghum, millet, buckwheat, sunflower, castor bean, water melon, Agropyron, Bromus.
Oligotrophs – crops that can grow under specific conditions, for example, under high acidity and salinity of soil, unfavorable air or water regimes of soil. They are divided into halophytes, argyllophytes, acidophytes, psammophytes, metophytes and others.
Eurythrophs are crops with symbiotic nitrogen fixation ability which allows to ensure productivity at the level of old undisturbed soils. They include: alfalfa, sainfoin, elm, sweet clover, Lotus, astragalus and other leguminous grasses.
The thickness of the recultivated soil layer is determined depending on the biological characteristics of crops, the composition of rocks and the bulk layer. For black earth soils, for example, it is from 1-1.5 to 2-2.5 m, which allows to create conditions for the development of the root system and plants close to normal.
Rocks with phytotoxic properties, i.e. containing excess of readily soluble salts, pyrite, mobile forms of iron and aluminum, rocks of early geological ages, such as the Cretaceous and Jura Mesozoic, Carboniferous and Devonian Paleozoic with unfavorable agrophysical and agrochemical properties are the most problematic for recultivation for agricultural land.
For specific and difficult conditions of the Podmoskov coal basin, where phytotoxic rocks in the overburden strata make up to 40-60%, technologies have been developed to create agricultural plots with yields at the level of zonal indicators in place of disturbed lands. For example, in the Novomoskovsk district of the Tula region, the recultivated lands yield up to 4-4.5 t/ha of grain.
At the quarries of the Moscow region the arable land is created by applying a layer of glauconite sand on the surface of the dumps. Application of nitrogen fertilizers allows to increase the yield of these lands by 30-50%, compared with conventional soils.
The abandoned lands can be used to create large specialized agricultural enterprises.
Egoryevskoye phosphorite deposit is a good example of successful land recultivation. In the conditions of the Kursk Magnetic Anomaly positive results were obtained from the formation of artificial soils on the waste rock and adjacent low-productive lands, which was carried out by applying a layer of chernozem and cultivation of potentially fertile rocks.
Overburden rocks in the zone of the Kursk Magnetic Anomaly according to the degree of suitability for development and introduction into agricultural turnover are divided into:
- High quality rocks suitable for the cultivation of legumes and cereal-legume grasses, some field crops. These include loess-like loams, loess, soil mixture, loams with other rocks.
- Rocks of medium quality, suitable for afforestation and grassing: sands, soil mixture of silts with chalk, loam, marl, colluvium clays.
- Low quality rocks, suitable for afforestation and reforestation after preliminary improvement: Devonian deposits, chalk.
- Pyrite-bearing rocks, highly acidic, unsuitable for biological development.
Stages of land recultivation
Land recultivation is carried out in two stages.
- Technical recultivation consists in preparation of lands for further target use in agriculture: restoration of fertile layer, leveling the surface, removal or neutralization of toxic substances for plants, construction of reclamation and other structures.
- Biological reclamation – measures aimed at restoration of soil fertility, including agrotechnical and phytomeliorative methods aimed at restoration of flora and fauna.
Biological recultivation can be agricultural and forest.
Agricultural recultivation involves the creation of hayfields, pastures, arable land, perennial fruit and berry plantations on the restored land.
Forest recultivation involves planting tree crops on disturbed lands to create forests of different purpose and value.
Methods and techniques of land reclamation are determined by physical and geographic, economic features of the area, mining technologies, properties of minerals, physical and chemical properties of overburden rocks and other conditions. According to legislative requirements, all industrial organizations are obliged to remove the fertile humus layer from the land plots allocated for mining and use it for recultivation. For agricultural use, the top fertile layer with a humus content of at least 1-2%, for black earths 2-2,5% is removed. The humusized layer of soil is stored in stacks or bunches up to 10-15 m high. To protect the stacks from erosion processes they are planned and sown with grasses.
When recultivating lands for agricultural use special attention is paid to creation of a fertile arable layer, optimization of soil treatment, selection of cultivated plants.
Priority objects of recultivation include exhausted peatlands. The drainage network on them is restored in advance taking into account the subsequent agricultural use. Then, a set of cultural and technical works is carried out. Exhausted peatlands can be successfully used for cultivation of agricultural crops and hayfields.
Currently, for all economic zones of the country there are developed methods of disturbed land recultivation, which allow to solve a wide range of issues on cultural transformation of anthropogenic landscapes. However, not all sectors of the economy pay sufficient and timely attention to land recultivation, and the removed fertile soil layer is not fully used, and the volumes of its storage are increasing. The volumes of reclamation of disturbed lands in Russia are insignificant. For example, in 1996 160.1 thousand hectares of disturbed lands were reclaimed.
Methods and technologies of disturbed land recultivation
To perform biological recultivation of disturbed lands it is important to take into account agrochemical and water-physical properties of overburden rocks. That allows to reduce the cost of implementing a set of works on recultivation: covering the surface of dumps, cutting terraces, creating access roads, determining the steepness of slopes, etc.
Modern recultivation technologies developed for different natural zones of Russia, taking into account biological features of crops, compositions of overburden rocks and soil-climatic conditions, establish optimal capacities and designs of recultivated layers, assortment of crops and determine ameliorative crop rotations, technologies of crops cultivation and cultivation of productive forest plantations. For example, for the subzone of southern black earths the recultivated layer thickness is 1-1,5 m, ordinary – 1,5-2 m and typical black earths – 2,5 m.
Application of the humus layer
Recultivation of disturbed lands for arable farmland begins after the stabilization of planned rocks, after which a humus layer of 40-50 cm is applied. In some cases the thickness of the humus layer can vary depending on the underlying rocks and the planned type of economic use. For example, when using techno-soils for perennial leguminous grasses, perennial plantations and leguminous crops, it can be reduced or replaced by a local application of the humus layer. For vegetable crop rotations, on the contrary, it can be increased.
The thickness of the created humus horizon strongly affects crop yields. For example, in the conditions of the Kursk Magnetic Anomaly, the maximum crop yield of cultivated crops was obtained when the humus layer with the thickness of 60 and 80 cm was applied to the rocks, and the maximum increase in every additional 20 cm is accounted for by the thickness of 40 cm.
Table. Crop yields depending on the thickness of the applied layer of black earth and bedrock (by A.M. Burykin, average for 4 years, 1986), t/ha
With the same thickness of applied black earth, grain yield on loam is significantly higher than on chalk. Alfalfa, barley and millet are more responsive to the increased thickness of the applied layer, while winter rye and sainfoin are less responsive.
According to the Dnepropetrovsk Agricultural Institute, cereal yields on recultivated plots with a layer of black earth of 30-50 cm are close to the yields on old ploughed lands. Increasing the thickness of the layer applied up to 80-90 cm increases the yield of winter wheat by 2 times, while 10-20 cm reduces the yield to 10-30% of the yield obtained on the old arable lands.
One of the important methods of recultivation is the use of ameliorative crop rotations, in which a large proportion falls on soil-improving crops such as lupine, melilot, alfalfa, sainfoin. For example, in the conditions of the Kursk Magnetic Anomaly a crop rotation is used for development of arable lands: the 1st-3rd years – lucerne with plowing, the 4th – winter crops, the 5th – row crops, the 6th – cereals with undersowing of perennial grasses. In process of development and improvement of state of cultivation of recultivated lands intensive type crops are introduced into crop rotation.
To increase the fertility of recultivated lands, green fertilizers in combination with increased doses of mineral and organic fertilizers, rotary tillage tools, such as rotary plows, milling machines, combined aggregates, allowing to create a deep homogeneous soil layer are used. For example, in the Nikopol manganese basin the use of N90P90 with a thickness of the bulk black earth layer of 30-40 cm allowed to get a crop of winter wheat, as well as on the old-soil lands.
In PA “Phosphates”, Moscow region, on arable land created by applying a layer of glauconite sand on the surface of the dumps, the application of nitrogen fertilizers allowed to obtain a yield by 30-50% higher than on zonal soils.
The method of direct improvement of the state of cultivation
Application of the full mineral fertilizer N60P60K60 on techno-soils of the Kursk Magnetic Anomaly allowed to increase barley yield by 1,3 t/ha, or 186%; application of N90P90K90 under millet increased it by 1,2 t/ha, or 276%.
Table. Yield of spring wheat on different species depending on method of cultivation (by A.M. Burykin, average for 2 years, 1986), t/ha
According to the results of field experiments, bacterial fertilizers show high efficiency. For example, inoculation of legume grass seeds with rhizotorfin increased hay yield of clover by 0.63 t/ha, sainfoin by 2.43 t/ha, and alfalfa by 2.48 t/ha. Protein content of the fodder increased by 0,5-1,3%, and the collection of protein from 1 ha was 1 000, 1 901 and 1 526 kg, respectively (Stifeev A.I.).
There is an experience in land reclamation for creation of irrigated pastures. For this purpose, grass mixtures of blue alfalfa, hedgehog and meadow bluegrass are used. Yield of green mass for two mowing in the first year of use is 18.0 t/ha. In the zone of sufficient moisture, the dry mass yield of the grass mixture of twigs and brushwood was 1.48 t/ha, which is higher than on undisturbed natural pastures.
Optimization of tillage, mulching with straw and ash, and irrigation have a favorable effect on the process of soil recovery.
Hayfields and pastures can be created on dumps without application of humus layer. According to A.I. Stifeyev’s researches it is possible to grow perennial leguminous grasses on overburden rocks of Kursk Magnetic Anomaly in the first 3-5 years which show high productivity with good fodder qualities. It is most rational to use dumps immediately after their backfilling and leveling for fodder grasses, since there is still little weed vegetation, and the loose state of rocks contributes to the germination of seeds and growth of grasses.
When using techno-mixtures and loess lithozems for hayfields and pastures, the following schemes of crop rotation are used:
- Year 1-3 – perennial grasses (with plowing), year 4 – winter rye, year 5 – millet with undersowing of perennial grasses, years 6-8 – perennial grasses;
- In years 1-2 – melilot with embedding of green mass; in year 3 – winter rye; in year 4 – millet with undersowing of perennial grasses; in years 5-7 – perennial grasses.
Tillage for grasses on overburden rocks in the first years of development includes harrowing, cultivation, milling, which provide high yields at 15-20% less cost than plowing.
According to A.I. Stifeyev’s data the grassing of loess lithozems and hydro-dumps allows to receive about 16 t/ha of green mass of melilot and more than 20 t/ha of lucerne.
Recultivated rock dumps and hydro dumps in the Magadan region in permafrost conditions give 15 t/ha of green mass of oats and peas, which is 10-20 times higher than the yield of wild grasses on natural fodder lands. At the same time favorable water and thermal regimes are provided on the recultivated lands, soil freezing is eliminated. In these conditions land recultivation can be more profitable than development of new lands.
Earthing method – covering low-productive lands with a fertile humus layer of soil of different thickness, which allows obtaining crop yields 2.5-3 times higher.
For example, on shale ash dumps formed from bulk material, they create cultural hayfields. The properties of ash dumps depend on the “age”, the density of the deposit and the chemical composition of ash.
The reaction of ash dumps is often strongly alkaline, with alkalinity increasing with depth. Thus, the pH of 0-5 cm layer is – 7,9-9,7, at a depth of 30 cm – 12,3-12,6. The chemical composition of oil shale ash contains 32-35% calcium oxide and 24-30% silicon oxide, sulfur, magnesium, iron and carbon compounds. Granulometric composition of oil shale ash is close to sand and coarse dust fraction, with density of 0,9-1,28 g/cm3.
The content of nutrients in ash is insufficient, and the ratio is not conducive to plant growth. Nitrogen compounds are practically absent, mobile forms of phosphorus are very small – 0,2-0,4 mg/100 g, but a lot of exchangeable potassium – 135-760 mg/100 g of soil.
Therefore, to create cultural meadow on ash dumps, peat or soil is used, which are applied in a layer of thickness of not less than 10 cm. With such a layer it is possible to carry out harrowing with light harrows and grass maintenance works. If the ash dump only needs to be grassed, it is enough to create a layer of humus 3-5 cm.
Mixtures of red fescue (Festuca rubra), bromegrass (Bromus inermis), hedgehog (Dactylis glomerata), meadow clover (Trifolium pratense) and creeping clover (Trifolium repens) are used for laying cultural meadow on ash dumps. The root system of cereal grasses is located in the upper layers of the soil, while that of legumes penetrates deeper. Legumes, binding atmospheric nitrogen, provide it to themselves and to cereal grasses.
For biological recultivation of disturbed lands, planting of woody and shrub vegetation, including economically valuable trees and shrubs (berry, nut-bearing, medicinal from among local and introduced species) on overburden rocks is used.
Forest plantations on the dumps improve the ecological condition of the territory, reduce the manifestation of erosion processes, accelerate the soil formation process and the formation of biocenoses.
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