Micro-irrigation

Micro-irrigation

Drip irrigation

Drip irrigation is carried out by water well purified by special filters and supplied to a field through flexible polyethylene pipelines by means of special fittings, i.e. trickles. Due to low discharge (0.9…9.1 l/s), water slowly, drop by drop comes to the soil moistening only its rooting zone and leaving the spaces between rows dry.

At present, this irrigation method is in most common use in protected agriculture (under coverage). Dissolved nutrients enter the soil together with water due to the presence of a fertilizer-mixing tank, which makes this method still more efficient. Drip irrigation has given a good account of itself in the process of cultivation of vegetable and fruit crops on open and protected ground.

Among the principal advantages of drip irrigation are:

considerable saving of irrigation water as compared to traditional methods, particularly with sprinkling irrigation, viz. by 50…80% and over;
sharp diminution of water losses to filtration and evaporation;
absence of surface flow, water erosion, and water transfer and losses to atmosphere taken place in sprinkling irrigation;
reduction of weed vegetation and consequently of unproductive water consumption in the spaces between the rows of plants;
optimal and sustainable moistening of root zones in the context of plant growth and development periods;
possibility of local low-dosed application of fertilizers along with irrigation water;
reduction of the frequency of inter-row cultivation due to lower development of weed vegetation;
possibility of compaction of crop seeding down;
absence of groundwater rise and risk of repeated salinization;
possibility to use saline and particularly sea water;
possibility to be used on immature soils with shallow bedding of sand and shingle, where leveling operations are not required;
diminution of energy consumption for provision of water pressure in pipelines in comparison with sprinkling irrigation; and
increase in the productivity of tomatoes, fruit crops and citrus fruit crops up to 25…50%.

However, along with the mentioned advantages drip irrigation has some drawbacks:

high original cost;
risk of fouling and clogging of pipelines and trickles by depositions of ferric oxide and insoluble carbonates and, consequently, need of installation of special water purification filters; and
necessity of rearrangement of the system in the case of crop rotation on the field.

Drip irrigation system consists of the following principal parts: pumping unit (motor and pump); filter manifold; water receiving and accumulator tank; water flow and pressure control device; fertilizers mixing tank; injector for jetting of fertilizer liquid; supply pipeline made from polyethylene or PVC pipes; distribution pipeline; flexible trickling/dripper/emitter lines made of polyethylene with addition of carbon soot for prevention of development of aquatic vegetation in the pipes; water outlet pipes-trickles.

Water supply to the system is adjusted manually or automatically. Water is supplied to the system by using centrifugal pumps. Valves and pressure gauges are mounted to control water discharge and pressure. Maintenance of low pressure in the system allows using trickles of larger diameters and cheaper pipes and materials.

To avoid clogging of trickles and holes in microporous pipes the system is equipped by 1…2 screen filters, which should have no less than 30 holes per 1 cm² of length. The cost of filters amounts to 10% of all the capital investment. For algae control, copper vitriol is added to water at a rate of 1 mg/l. The diameter of drip lines comes usually to 12…19 mm and up to 25 mm.

Drip lines are laid on the ground surface in shallow (6…10 cm) furrows or just along the rows of plants. The interval between the drip lines depends upon row-spacing width: for vegetables, it is 0.8…0.9 m; for orchards and vineyards, from 2.5…3.0 to 6 m. At piggyback pipelay, the supply pipeline is laid not on surface but in the soil, and the drip lines are taken out to surface. For perennial plantations, drip lines are laid for several seasons.

The diameter of trickle holes usually does not exceed 2 mm. Water discharge from every trickle ranges from 0.9 to 10 l/h. The trickles may have various designs. Water from the trickles passes through twist riflings made at the points of connection of the capsules to a branch pipe. Adjusting the screwdriving tightness of the capsule in the branch pipe, one can control the water discharge.

Micropipes with an inner diameter 0.5…2.0 mm are used instead of capsules. In this case, water discharge is controlled by adjusting the pipe length and diameter. The interval between trickles or pipes depends of their discharge. At a trickle discharge of 3.8 l/h, the interval is 1 m, the length of the drip line is 40 m, and the diameter is 12 mm. At a discharge of 10 l/h and the same intervals and length of the drip line, diameter is taken equal to 16 mm.

When watering fruit crops, every crop is served by several trickles with a discharge of 1.0…7.6 l/h. With installed drip irrigation systems for close-sown (0.9 m) crops 10,700 m of plastic pipes will be used per 1 ha; for wide-row crops (3.0 m), 3000 m will be used.

To apply fertilizers together with irrigation water, they usually use tanks of a volume of 50…100 l. Injection of fertilizer liquid into the supply pipeline is carried out by means of an injector. Fertilizer liquid is supplied by using a special pumping device NRA (in Russian: НРА) in proportion to pressure or discharge in network. Required pressure for operation of injector is about 0.25 MPa.

Subsurface irrigation

Subsurface irrigation through pipes-humidifiers laid at a depth of 0.4…0.6 m is a convenient and promising method of influence on plants at open/unprotected ground and particularly protected (conservatory, greenhouses) cultivation. With subsurface irrigation, the root zone is moistened by regulating groundwater table.

Advantages of subsurface irrigation are as follows:

mechanization of agricultural works and high utilization factor of the irrigated area;
retention of the structure of topsoils and keeping them in loose condition;
possibility of overcrowding of crops with a glance of optimal feeding area and orientation of crop rows proceeding from optimal light conditions and, consequently, maximum use of solar energy;
diminution of water application rates and more efficient use of irrigation water;
possibility of bilateral control of water regime on drained soils;
combination of irrigation and simultaneous application of soluble nutrients directly in the root zone;
possibility of combination of moistening and simultaneous soil warming by thermal and warm waters discharged from thermal power plants; and
possibility of automation and, consequently, reduction of labour costs at irrigation.

When organizing subsurface irrigation, especially on large areas, following drawbacks too should be taken into consideration:

possibility of use only on soils with good capillary conductivity, notably on loam soils or light soils provided that there is water confining stratum (aquiclude) at a shallow depth;
non-applicability on saline soils with shallow bedding of mineralized groundwater and with high (50%) content of carbonates that cause ground subsidence;
necessity of supply of pure water given the risk of silting of pipelines-humidifiers; and
high need for pipes and, as a rule, great lump-sum capital investment to construction and equipping of the system.

Subsurface irrigation rests upon soil absorption capacity. The higher the capillary conductivity of soil, the higher the absorption capacity of it. It depends not only upon the texture and alternation of some soil layers, but also upon soil water detention. With soil humidity approaching field moisture capacity (FMC), the absorption capacity approaches zero; in absolutely dry soil, it reaches the maximum value.

Subject to the soil texture, absorption capacity may vary as follows: on heavy soils in dry condition, it comes to 40…50 cm, and under humidity of 55% of FMC it will come to 4…5 cm; on light soils, it will come to 15…20 cm and 1…2 cm, respectively.

Irrigation system with subsurface irrigation can be of semi-closed or closed types. In the semi-closed system, canals are made open, while pipes-humidifiers are made closed. In this case, the pipes-humidifiers’ heads are laid at a given level at some height from the sprinkler bottom so that to generate a required pressure to engage as many as possible pipes-humidifiers simultaneously to the irrigation process. In closed system, the entire supply and regulation network is composed of buried pipelines. The closed system is the most perfect. It allows raising the land-use intensity (LUI), completely automating the irrigation process, applying fertilizers, and flushing the system. At subsurface irrigation, the supply and distribution pipelines composed of standard asbestos-cement pipes are laid at a depth no less than 50…60 cm from the ground surface. Pipes-humidifiers are laid at a depth 45…50 cm and at an interval generally equal to 1.25…1.5 m but no more than 2.0 m. The pipes-humidifiers can be made from clay (tile) or perforated made of polyethylene or PVC. Water inflows from the pipes to soil through clay pipe joints of 1.0…1.5 mm or through the perforation holes.

The length of the pipes-humidifiers is taken within a range of 150…250 m, i.e. 200 m at the average. The pipes-humidifiers are flushed out to prevent their silting. According to their operation manner, they distinguish free-flow and pressurized water systems. In free-flow water system, water flows through its pipes by gravity. To prevent silting of the pipes-humidifiers, they are laid towards the field disposal collecting pipe with a gradient no less than 0.004…0.005; then the water velocity in the pipes will be no less than 0.7…0.8 m/s.

In pressurized system, soil is watered under pressure. At intermittent water supply, pressurized systems are more efficient than free-flow systems. They allow increasing the interval between the pipes-humidifiers up to 2…3 m, shortening water application timeframe and rates; they dissolve and wash away water-soluble salts from the plant rootage zone; perform regular flushing out of buried humidifiers.

In pressurized system, pipes-humidifiers are laid at adverse slope to the pipeline which serves not only as a sprinkler but also as a collection manifold.

At subsurface irrigation, the pipes of closed irrigation network area installed by using special machines, i.e. ditch-and-trench excavators and drain-pipe layers. Prefabricated polyethylene pipes with a diameter of 40, 50 and 70 mm are used for the installation of pipes-humidifiers; they are laid in soil by machines DPBN-1.8 (in Russian: ДПБН-1,8); for installation of clay pipes – by machines D-659А (in Russian: Д-659А).

Subsurface irrigation is also used for watering vegetable crops on protected soil. Here tubular subsoil-humidifying network would be most acceptable, which will be well coupled with heating of hothouses. The air in hothouses is warmed by hot-water radiators, and to provide a required soil temperature during cold seasons, the water fed to the system is heated by the mixers mounted at the points of water delivery to the distribution pipelines. Air-steam mixture and steam are used to heat the soil. As far as the plant root system is not developed enough, high water temperature will not be dangerous; but as soon as the root system develops enough, it will be necessary to make sure the temperature does not exceed 45° C.

The method of subsurface irrigation by pumps has been worked out; it is based on mechanized water supply to a specified depth simultaneously with soil loosening. At that, water is supplied to the aggregate through a flexible hose under pressure, and then is brought into the soil through working members (hollow feet). The pressure in the hose is produced by a mobile pumping installation situated at a water source. During water application, the flexible hose is wound around the reel specially fixed on a tractor and which revolves synchronously with the speed of the aggregate (when moving towards the middle of the pass/run), then gets unreeled (when moving from the middle towards the end of the pass/run). The length of the hose is 150 m, diameter is 89 mm, the depth of water supply into the soil is 25…35 cm. Irrigation network for water supply consists of subsurface irrigation pipelines with hydrants; pressure at hydrants is 0.6…0.7 MPa.

The aggregate is driven by one tractor driver: within one shift he can irrigate 5…8 ha. For water application by means of the aggregate, there is no need to level irrigated field. When using the aggregate for subsurface irrigation by wastewater, the pump unit is to be equipped with a sanitary pump.

Tubular systems of subsurface irrigation are used for raising and regulation of fresh groundwater table in a humid region by means of bilateral water control on waterlogged soils.

Soil moistening by regulating fresh groundwater table, which is called subirrigation in foreign countries, will be practicable in an arid zone if there is solid aquiclude over the whole irrigated area and in the absence of injurious salts in the soil and water (such conditions are in floodplains of glacier-fed rivers). Under such conditions, water is fed to subsoil humidifiers with a relatively sparse layout (in 10…100 m) and under shallow fresh groundwater table and aquiclude.

Source: www.skyrage.ru

Local impulse irrigation

The bottom line of local impulse irrigation is that water is supplied through special water outlets directly to the rhizosphere of plants. This prevents heavy water consumption and damage of leaves. Therefore, the system of local impulse irrigation has great advantages over other types of irrigation.

To arrange local impulse irrigation, suffice it to have a set of a water tank, dive culvert with collector and pipeline network. There is no need to purchase additional electrical equipment, pumps, filters, as well as permanent human factor. Properly installed system operates automatically.

This type of irrigation enables applying fertilizers and mineral substances directly to the roots of vegetable crops in water-dissolved form. The system provides high uniformity of their distribution as well as allows exact dosing required quantity of helpful microelements. Such combined irrigation system minimizes consumption of fertilizers at maximum effectiveness of their application.

With local impulse irrigation, maintaining only the rootage zone in wet condition, while the row-spacings remain dry, which ensures reduction of the quantity of weeds. Owing to regular irrigation, soil temperature is always higher than that at usual irrigation, which allows getting early harvest.

The system of local impulse irrigation is simple, practical, and efficient. To use this set, there is no need of special knowledge and grounding, power supply, etc. Use of automatic irrigation has a lot of advantages:

freedom from daily hard, monotonous work
saving of water of up to 60-70%, of mineral fertilizers of up to 40-50%
reduction of risk of the development of fungus diseases of plants
elimination of risk of sunscald
optimum ratio of water and oxygen in soil
even distribution of water and nutrient solution
minimum input of fertilizers
effective side-dressing directly to the rootage zone
absence of exceed moisture
possibility of watering by warm water.

The most important advantage of these irrigation systems is considerable diminution of daily working hours. Full automation of the soil moistening process allows spending more time on other works or on rest.

Simplicity of the estimation and adjustment of the water supply scheme makes it understandable even for a beginner horticulturist. Properly installed system operates without a failure performing continuous automatic irrigation regardless of any ambient conditions. Water supply is carried out without pressure saving from occurrence of mud or splashing.

Use of local impulse irrigation facilitates shortening of the crop growth time and rise of crop yield due to competent management of plant water balance and improvement of the fertilizer accessibility process.

Even application of water with higher salt content will not lead to settling of salts on plant surfaces. Due to optimization of assimilation and evaporation processes, vegetables ripen synchronously and more quickly.

Source: vodaleich

Mist irrigation

Mist and fogging irrigation methods are designed for regulation of microclimate over the field. Application of them is most effective and advisable on the areas with complex relief, steep slopes, with water resources shortage, and high climate aridity. Disperse sprayers make drops of less than 0.5…1 mm in diameter, and mist-forming plants create a cloud of atomized water mist with drops of 300…500 micron in diameter. Dispersion over the field of 100…400 l/ha lowers the air temperature by 6…12 °C at hot hours and raises its humidity.

Use of mist and fogging irrigation combined with common sprinkling irrigation allows improving the air-ground interface microclimate, crop nutrition regime, setting optimum temperature and water regime of crops, saving irrigation water, and increasing of cropping capacity. In addition, technical facilities can be used to control crop diseases and pests, application of trace and major mineral elements.

Practicability of the use of mist and fogging irrigation is subject to natural and climate conditions (climate, relief, water availability, quality of irrigation water) and economic conditions (cropping pattern and characteristics, their physiological requirements, cultivation conditions, availability of resources).

To select properly the mist and fogging irrigation regime, it is necessary to possess data not of only the number of days of critical temperatures and air humidity, but also of the duration of these periods within a day. For example, the duration of this period for potato within a day in June comes to about 6…7 hours. Maintenance of daytime air temperature within the range of physiologically optimum values is essential for increase of cropping productivity under hot climate conditions. Use of mist and fogging irrigation yields good results in controlling hot dry winds on raind-fed and irrigated lands in the steppe zone and in protecting crops against frosts.

Frost protection of crops by means of mist and fogging irrigation is based on the rise of the temperature of air-ground interface or crops, which can be achieved in the result of water transition from one state to another. Atomized water mist freezes up immediately on the surface of crops or in the atmosphere. At that, the temperature of inversion layer of air rises.

Source: skyrage.ru