Advanced technologies for the creation of forest cultures in the southern regions with arid climate

The article analyzes the of the drip irrigation and biologically active substances fertilization use effectiveness in forestry in arid regions; the main advantages and disadvantages of drip irrigation for protective afforestation in dry steppe and semi-desert are indicated, the conclusion about the possibility of its use in the creation of forest crops with economic feasibility, the availability of infrastructure (a water source with water suitable for irrigation, power lines) is made. The use of drip irrigation is advisable when planting plantations of particular value (forest seed plantations, walnut groves, orchards, landscaping plantings in recreational areas, etc.). However, for an unambiguous answer, it is necessary to lay experimental crops in different soil and hydrological conditions, with different types and mixing schemes, woody and shrub species composition, to develop irrigation and watering norms, to test the latest biological preparations that improve the processes of root formation, growth, and resistance to diseases and environmental stressors.


Introduction
Currently, one of the most promising irrigation methods used in southern regions with arid climates is drip irrigation. Drip irrigation is widely used in forest nurseries when growing planting material for oneand two-year-old seedlings (squat elm, robinia false acacia, narrow-leaved loch, common pine and Crimean pine, petiolate oak, leafless juzgun, Tatar honeysuckle, golden currant, shrubby amorpha, leather scumpia).
Drip irrigation has a number of significant advantages over sprinkling and subsurface irrigation, which are shown to the same extent, both in agriculture and in forestry.
Irrigation by sprinkling, in which water is sprayed in the form of drops over the surface of the soil and plants, is one of the most common types of irrigation, but leads to a number of negative consequences (soil erosion and deterioration of its structure). In addition, with this method of watering, moisture is not consumed rationally. A significant amount evaporates from the surface before reaching the root zone of woody plants. In the case of intra-soil irrigation, water enters directly into the growth zone of the plants root systems through a specially created pipeline system. This method of irrigation is very effective in terms of water and fertilizer consumption. However, the construction and maintenance of subsurface irrigation systems on large areas of reclaimed land requires significant costs. Therefore, it is currently little used.

Materials and methods
The southern part of the Volgograd region, the Republic of Kalmykia, occupies the extreme south-east of the European part of Russia with unstable atmospheric moisture (annual precipitation of 170-350 mm/year). At the same time, the evaporation rate from the soil surface exceeds 3-3.5 times. In zonal terms, this region belongs to the soil dry-steppe and semi-desert subzone. The soil cover is complex, with the participation of solonetz and salt marshes of different degrees of salinity, depending on the development of macro-and microrelief. The climate is sharply continental, summers are hot, very dry, winters are snowless, but the main precipitation falls in the winter. In the summer, droughts are regular, accompanied by dry winds, which often lead to dust storms. These circumstances create quite complex forest growing conditions and cause a low percentage of forest cover (0.2-3.4%) in the arid south of Russia.
The purpose of the research is to examine the effectiveness of non-traditional technological methods and operations used for growing seedlings in forestry of the Republic of Kalmykia, the southern districts of the Volgograd region based on the analysis of modern domestic and foreign literature and our own research. Also, the purpose is to evaluate the experience of other subjects and countries with similar conditions of forest growth in the use of irrigation, mineral fertilizers, growth stimulators with the help of a drip irrigation system when creating forest crops; to identify the main advantages and disadvantages of drip irrigation, specific and critical for protective afforestation in the dry steppe and semi-desert. Based on the findings, develop recommendations for the inclusion of drip irrigation individual elements (irrigation regime, irrigation and irrigation rate) as the main technology for creating forest stands in regions with arid climates.

Results and discussion
The advantages of drip irrigation include the following features: -water is supplied directly to the plant root growth zone, creating a humidification cone that ensures their growth, which is relevant in conditions of a shortage of water suitable for irrigation; -when creating perennial plantings in areas with complex terrain, light granulometric composition of soils, sloping areas with large slopes, i.e. on such lands where the use of traditional irrigation methods is impossible or extremely difficult.
The peculiarity of this resource-saving type of woody plants irrigation is a completely new approach to solving the issue of water supply to plants, as well as rationing water distribution, setting technical parameters of the irrigation network and other technological solutions.
Mode of irrigation under drip method of irrigation is different from sprinkler and furrow irrigation. This technology involves depending on the phase of plant growth and water-physical properties of the soil instead of water supply regulations prior to 1700 m 3 /ha, application of fractional irrigation rates at short intervals (even daily water flow low rate of from 4 to 12 l/h (200-300 m 3 /ha). Also, through the drip system, it is possible to supply fertilizers, growth regulators, ameliorants and pesticides directly to the root zone, depending on the needs of the plants. The distribution of water in this type of irrigation in the soil occurs in a capillary way in the horizontal and vertical directions with a small gravitational influence. The water saturation level of the humidification circuit is determined by the resulting gradient of the total water tension. Near the emitter, its level is less, and in the peripheral zone of the moistened area is more.
The resulting gradient of water tension is influenced by the temperature of the soil, air and the elasticity of water vapor, and a moisture contour is formed. Its effective area and volume inside the soil (root layer) is brought to the necessary parameters due to the technique and technology of irrigation. At the same time, there is a creation of equivalent conditions for the spread of plant roots. This movement of water has a very favorable effect on the air regime of the soil. The air from the soil pores in the volume of the humidification circuit is almost not displaced by water, which creates favorable conditions for root respiration and their growth. The risk of root rot is also reduced. At the same time, large pores in the soil remain dry, forming a moisture level that exceeds the lowest moisture capacity of the soil, Drip irrigation creates, first of all, favorable conditions that allow the roots of plants to consume the necessary amount of oxygen during the entire growth period. At the same time, there is no oxygen starvation during irrigation, as with surface irrigation methods. Woody plants easily adapt to drip irrigation both after rain-fed growing conditions and after furrow irrigation. At the same time, there was no inhibition in growth [1].
With drip irrigation, it is technologically simple to feed food elements into the root layer of the soil. In this respect, it contributes to the maintenance of soil fertility and conditions for the active life of the soil microflora, which ensures the health of the soil. With this method of irrigation, the greatest effect of ensuring the plant nutrition regime is noted. The supply of fertilizers in water-soluble form directly to the root zone in the required quantities together with water creates the required level of nutrients supply. This allows the root system to absorb nutrients quickly and efficiently. The root system in the humidification circuits is very dense and developed, which undoubtedly has a positive effect on the woody plants seedlings growth and development.
By reducing the amount of fertilizers and adjusting the frequency of their application, it is possible to maintain a uniform level of nutrients and control their flow into the soil, depending on the changing (by phase of development) needs of plants throughout the growth period. Thus, the drip irrigation system should be considered not only as the method of moistening the soil, but also as an effective way to apply mineral fertilizers where it is required and at the right time.
The efficiency of drip irrigation in the cultivation of woody plants is expressed in [2]: -in the high survival rate of plantlets and seedlings at the planting site in the first year of cultivation and a low percentage of mortality in subsequent years (mortality is not associated, as the rule, with a lack of moisture); with this method of irrigation, evaporation and unproductive water consumption by weeds takes 2.0-2.5 times less moisture; -in a high coefficient of irrigation water use (in the absence of excessive runoff), even on complex terrain and sandy soils; in reducing the influence of negative environmental factors while creating favorable conditions for soil moistening during the entire period of seasonal plant development; -in a low coefficient of irrigation water loss in conditions of its shortage; -in the automation of irrigation with minimal human involvement to ensure the operation of the irrigation system.
It should be noted that drip irrigation allows woody plants in difficult forest conditions to fully realize their biologically inherent potential. With this method of irrigation, even in the absence of precipitation and available groundwater root systems, it is possible to provide seedlings with a quick start of growth (Table 1).
The main part of the increase (up to 80%) falls on May and Junethe most favourable months for the hydrothermal regime. Despite regular watering in the hot and dry period, woody plants on the experimental site practically did not grow, which is due to their biological characteristics. Watering at this time is only necessary to maintain the plantings in a viable state.
Despite the numerous advantages presented, drip irrigation has a number of disadvantages: -lack of a source with water suitable for watering plants (high mineralization, high content of calcium, iron, hydrogen sulphide); -high initial cost of all the drip system elements (development of a well or installation of a tankreservoir, installation and purchase of a pumping station, sand-gravel and mesh filters, main pipeline, distribution pipelines with drip lines, other components and related parts); -no electricity source to power the pumping station; -the possibility of deposition in the emitters of drip tubes of dirt and carbonates oxides, clogging the discharge holes; -the need to use irrigation water of a high degree of purification; -training and maintenance of highly qualified service personnel; -carrying out care in the rows of plants with the help of frequent and regular manual labor; -the need for periodic repairs and updates of drip lines (pipes are damaged by workers during weeding, as well as by mice and birds). Obviously, the main disadvantages of drip irrigation are the availability of a suitable reservoir and the economic costs associated with the purchase, a drip irrigation system installation and maintenance.
One of the best sources of water is a natural (river, lake) or artificial (water channel, reservoir, pond, well) reservoir with weakly mineralized water. You can also use a well as a source of irrigation water, but it is undesirable to use ground water for watering plants directly due to the difference in soil temperature and water raised from the depths. Therefore, to eliminate these shortcomings, it is recommended to use special filters and capacitive tanks, and in particularly hot times to carry out watering at night. If there is free access to tap water, which is usually subjected to chlorination, it can also be used after pre-filtering and settling.
The schematic diagram of the drip irrigation system used in agriculture and forestry consists of: -a central node (with a possible digital control unit); systems of subordinate pipelines (main and distribution ones); -connecting units and parts; -gate valves, valves, cranes (with the possibility of both manual and remote control); -drip lines of various designs.
The systems use irrigation pipes made of low-density polyethylene pipes with the diameter of 20 or 25 mm, to which droppers made of polymer materials are attached. To do this, connectors and plugs (fittings) made of ABS plastic are used. Drip lines of irrigation pipelines are installed along the rows of plants. Their length is limited to the length of 100 m. The shorter the drip tapes, the more evenly the water is poured out of the emitters. With the large length of droppers, their efficiency is reduced due to the uneven distribution of water pressure inside.
The main pipelines of the "Liflet" design with a diameter of 110 mm are used, which are made of a flexible pipe PVC-U of SDR 17 with maximum operating pressure (MOP) 1. dissolved nutrients in the amount of 2-5 l/hour (depending on the design of the system). A typical drip irrigation system includes: -gravel filter 5"; -mesh filter 5"; -fertilizer unit 5"; -Venturi injector 1"; -pressure regulator 4"; -pipe PVC-U of SDR 17 with MOP 1.25-1.6 with the diameter of 110 mm; -pipe PE 100 with the diameter of 63 mm; -start connectors and connection fittings; -drip irrigation tube; -valve ball 4"; -fittings made of PVC.
Pipes and connecting parts made of various polymer materials of both domestic and imported production, including polyethylene pipes, can be used for laying outdoor water supply networks. Drip irrigation in the humidification circuit maintains soil moisture at 70-85% of the total moisture capacity.
As mentioned earlier, in traditional forestry, drip irrigation is used exclusively for growing the planting material of forest crops. In our opinion, if there is a free source with water suitable for irrigation, it is possible to create forest stands from especially valuable species. These could be plantings laid along large irrigation channels (for example, fruit trees), massive and wide-band plantings along the banks of reservoirs, rivers, dammed gullies, which serve to expand the biodiversity of landscapes and protect local flora and fauna that attract migratory birds for temporary deployment during their spring or autumn migrations. Also, the use of drip irrigation would be economically feasible when creating protective green zones (rings) around the perimeter of settlements or livestock complexes, farms, sheepfold (farmprotected forest plantations), located near the city water supply, wells and other sources of fresh water.
Green spaces perform important environmental protection and stabilizing functions, improve the microclimate, sanitary and hygienic situation, protect the population from snow and sand drifts, cold winds, dust storms, have fire and recreational value. In the presence of fertile unsalted areas, forest plantations, orchards, vineyards, and walnut groves can act as green areas.
Regardless of the function and species composition of the stand, the main event in the creation of such a plantation should be a careful selection of forest-suitable areas with full compliance with technological techniques for preparing the soil and further agrotechnical and forestry care [3]. Microand macro-depressions, where surface runoff is concentrated, the bottoms of gullies, hollows, the lower parts of slopes with relatively light and sifted surface sediments, accessible fresh and slightly mineralized ground water, and areas with light sandy loam soils, have increased forest suitability. In the absence of such measures, it is necessary to carry out a number of consecutive moisture-storing and moisture-saving measures [4].
In the modern scientific literature, there is little information about the use of drip irrigation in forest crops. However, the positive experience of creating a protective green belt around the capital of the Republic of Kazakhstan Nur-Sultan (Astana) and recreational landings of Turkmenistan was not without the use of this technology [5,6,7]. It should be noted that the successful result of growing green spaces was affected by the integrated approach. It consisted in the study of land plots and the assessment of the degree of forest suitability, the selection of the adapted range of wood species and mixing schemes, the use of moisture-saving technologies (inter-room "stores" of moisture, drainage trenches) and regular maintenance of the soil, which was accompanied by appropriate funding for forest planting and constant scientific support. Among the methods that are not typical for forestry, we should note the use of irrigation (both drip and sprinkling one) at the early stage of plant life, the introduction of growth stimulators and fertilizers, the use of enlarged planting material and seedlings with a closed root system, which did not always lead to success [8,9,10,11,12].
Thus, it can be concluded that the quality of protective afforestation in regions with arid climates directly depends on the state of forestry and socio-economic development of the region (the country as IOP Conf. Series: Earth and Environmental Science 843 (2021) 012056 IOP Publishing doi:10.1088/1755-1315/843/1/012056 6 a whole), strict compliance in practice with the developed and proven low-cost technological techniques for creating and growing sustainable long-lasting plantings and increasing their reclamation efficiency.
In the conditions of the Volgograd region, there is a positive experience of using drip irrigation for growing protective plantings on light chestnut soils (Table 2). Plantings were developed in 2010-2015 on industrial land for the purpose of reclamation of unproductive land. At the same time, the seedlings were planted in rows with drip lines. Irrigation was carried out in the dry period without applying fertilizers and growth regulators with clean filtered water. In the experiments, it was noted that after the installation of a drip irrigation system at the experimental sites in the Volgograd region, the rows of planted shrubs were naturally seeded with individual tree species: white and black poplar, squat elm and false-acacia robinia. These species formed a good-quality selfseeding, successfully taking root in the irrigated area.

Conclusion
In our opinion, the use of drip irrigation in the cultivation of forest crops in the arid conditions of the Republic of Kalmykia, the south of the Volgograd region is possible, but it should be economically justified and biologically feasible from the point of view of the continued existence of the stand without additional irrigation, i.e. in conditions of extremely stressful water regime. It should be valuable by breed composition (rare, red-book, nut-bearing, selectively improved) and/or functional purpose of forest stands created at settlements, livestock points, reservoirs, along the banks of natural watercourses. When using drip irrigation, it is possible to lay forest stands by sowing seeds of tree and shrub species in a permanent place, taking into account the type and scheme of the projected mixing. This would make it possible to avoid injury to the root system of the seedling during transplanting and would ensure the maximum percentage of preservation of forest crops. Regular rich watering, especially with the use of growth stimulators, complex fertilizers, will provoke increased growth and powerful development of both the underground and aboveground parts of the plant, so that the transition of young trees to a state of horizontal closeness will occur 1.5-3 times earlier than traditional cultivation of forest crops.
But after the transfer of crops to a forested area and the termination of irrigation, plants adapted to a certain water regime and accumulated a powerful biomass will experience an acute lack of moisture and mineral starvation, which will lead to a sharp slowdown in development, up to the mass death of crops. To prevent such a scenario, it is recommended to dose the amount and frequency of irrigation from the very beginning of drip irrigation, use fertilizers and growth regulators moderately and if absolutely necessary, and gradually reduce the intensity of irrigation after the plants reach the design parameters, using it only on acutely arid days.
The proposals presented above are of a recommendatory nature and need to be thoroughly tested over many years to develop optimal modes of application of drip irrigation, mineral fertilizers and biologically active substances.
To obtain reliable unambiguous results, it is necessary to organize pilot plantings of test crops from the main types of trees and shrubs used in afforestation in Republic of Kalmykia, the Volgograd region, the Stavropol Territory, etc. (elm, robinia, ash, oak, pine, juzgun, tamarisk) with the use of drip