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Sprinkling irrigation

Sprinkling irrigation is an agricultural irrigation method at which water is splashed in the form raindrops over the soil surface and plants.

In comparison with surface irrigation, sprinkling irrigation has a number of advantages: it improves the conditions for plants to grow, because it increases moisture content of not only soil, but also of surface air, lowering their temperature, reducing losses to evaporation from the soil surface. At sprinkling irrigation, dust is washed away from plants, which improves their respiration, carbon assimilation, development and accumulation of the organic matter. After sprinkling irrigation the soil structure deteriorates to a lesser degree, and post-irrigation cultivation can be started earlier, thereby more moisture remains in the soil. Sprinkling irrigation allows applying fertilizers together with irrigation water. Sprinkling irrigation can be carried out at any time of day or night and supply any water application rate beginning from the lowest (30 m3/ha). It allows maintaining the soil moisture content optimal for plants on lands of compound topography and on plots of shallow/thin soils available on highly permeable rock materials (sand, shingle), on which surface irrigation requires large scope of leveling works or it is related with considerable seepage losses. At sprinkling irrigation usually, there is no need for small canals and furrows; therefore, the ground area is used more fully and agricultural machines operate with higher performance. Sometimes, this irrigation method is less economically sound than surface irrigation, for example when watering at a higher water application rate (more than 700 m3/ha) and many water application operations.

Sprinkling irrigation is used for vegetative, refreshing (crop cooling), fertilizer-application, warming, and provocative irrigation for weed control, etc. It is widely used for cultivation of vegetable, industrial, forrage, grain, and fruit-and-berry crops, especially in an unstable wetting zone. Sprinkling irrigation in the context of water supply to soil in autumn will give the highest efficiency. In arid years, sprinkling irrigation provokes a large rise of harvest in non-chernozem zones and even in the north (for example, near to the Yakutsk city in Russia). Water application rate at sprinkling irrigation is usually a little lower than that at surface irrigation. Water application rate ranges from 30 to 600 (under favorable conditions up to 800) m3/ha; at vegetative irrigation, such a water application rate is supposed to provide moistening of soil root zone. Sprinkling irrigation should be performed in such a manner that water uniformly distributes over the field without forming pools and sink flows. Flow formation time depends on the water and physical properties of soil, size of raindrops, rain intensity (rain layer in mm per time unit), and character of water entry, i.e. whether continuous or alternating (at intervals of 1-8 min and more). Good-quality irrigation can be ensured when raindrop diameter does not exceed 1.5-2 mm and rain intensity is less than the actual soil permeability. Depending on concrete conditions, these values are usually determined by practical consideration.

Water sources for sprinkling irrigation can represented by rivers, ponds, canals, and other water bodies and watercourses. Conducting (canals, stationary pipelines) and distribution (surface, subsurface, and combined) networks supply water to a water application site and distribute it over the site, delivering it to sprinkling machines and sprinklers. Mapping and calculation of the conducting and distribution network at sprinkling irrigation have the following peculiarities: the shape of the water application site should be almost rectangular, its width is multiple of the range of the sprinkling machine, and the length should be no less than 400-600 m; temporary irrigation ditches and pipelines are arranged parallel to one another, and the interval between them is double the length of machines splashboard or the sprinkling radius (with a glance of the overlapped area).

Source: Great Soviet Encyclopedia

In comparison with other irrigation methods, sprinkling irrigation has a number of advantages, which boil down to the following:

  • mechanization of labor process and, consequently, full combination of water application with technologies of other agricultural works implemented in the farm;
  • possibility of getting of good and even as well as full sprouts, establishment and development of plants at the initial period on all types of soil;
  • possibility of overcrowding of crops with keeping optimal area of nutrition and arrangement of plant rows taking orientation to the establishment of optimum lighting regime and, consequently, maximum use of solar radiation heat energy;
  • applicability on compound reliefs and high slopes as well as on sandy and immature soils without or with minimum leveling works;
  • conduction of frequent water application at low rates in order not only to moisture the soil but also to improve the microclimate of the surface air (refreshing/crop cooling watering) and consequently to provide favorable conditions for physiological process and crop bulking at minimal water consumption;
  • due to enrichment with oxygen, carbonic acid gas and gaseous nitrogen, raindrops provide soil and plants with additional alimentation;
  • accurate dosing of irrigation water according to plant growth and development periods and land reclamation condition;
  • possibility to irrigate crops with simultaneous application of fertilizers at side-dressing and weed and pest-killer chemicals (pesticides) at pest and disease control as well as at defoliation of plants prior to harvesting;
  • due to integrated effect upon soil, plant, and consequently due to target-specific change of water and nutritive regimes it is easier to form and control yield;
  • due to more economical consumption of irrigation water, the water use efficiency rises by 25-30%.

However, despite having many advantages sprinkling irrigation has also the following drawbacks which should be taken into consideration when organizing crop irrigation especially on large areas:

  • high rain intensity, non-uniformity of soil moistening at watering and during windy weather and relatively low rain quality, which at higher water application rates, 600 m3/ha and over, leads to damage of soil structure and to its compaction, formation of pools and occurrence of surface flow and, as a result, to water erosion at high slopes;
  • dependence of rain distribution and uniformity of soil moistening on wind speed and direction, which under relief depressions leads to water stagnation, nonuniform development of plants and their lodging;
  • in the regions exposed to strong winds, long-range sprinkling machines stand idle, viz. reduction of their working time efficiency or substitution of circular sprinkling for fan-shaped one;
  • low water application rates, 300-400 m3/ha (gross), and, consequently, shallow depth of soil wetting in dry steppe and all the more so in the arid zone, especially on alkaline and residual soils, bring to excessively large number of water application operations. This makes water application process more costly, causes unproductive water losses to evaporation to increase, and often causes development of diseases of vegetables, cucurbitaceous, and grape.

However, in spite of this sprinkling irrigation is a promising irrigation method, especially with more perfect types of sprinkling systems and devices.

Sprinkling types

According to time framework and nature of water supply and, hence, of soil moistening and biological effect upon field crops, vegetables, tea, and fruit crops, three types of sprinkling irrigation are discerned as follows: regular, impulse, mist.

At regular sprinkling irrigation, water is supplied to fields in the form of rain at considerable intervals, i.e. 6-12 days, to make the microclimate of the surface air (high temperature, low relative humidity) milder and create optimal deposit of moisture in the active soil layer (0.5-0.6 m).

At impulse sprinkling irrigation, water is supplied to the crop every day within the time limit of the highest temperature, i.e. from 1 to 34 p.m., in order to reduce the shortage of air moisture.

Impulse sprinkling machines operate by separated cycles, and each cycle consists of periods-pauses, viz. water accumulation in a cauldron, generation of maximum pressure, and shot or water ejection to the atmosphere.

At mist sprinkling irrigation, water is supplied, like with impulse sprinkling irrigation, every day for 4-5 hours (from 1 to 45 p.m.) at the period of high temperatures and low relative humidity to irrigate vegetables and tea plantations. Powerful machines withdraw water from canals and pipelines and under high pressure eject it into the air. Depending on the wind force and direction, raindrops in form of fog distribute over an area of 200-300 m and more.

Stationary sprinkler irrigation

Stationary sprinkling is an irrigation method at which only sprinkling machines are mobile, while the other components of the sprinkling system (pumping and power equipment, main and distribution pipelines) have stationary operation.

At sprinkling irrigation, the irrigation system includes a water source, pumping station with a motor, water carrier network of canals, hydraulic facilities, sprinkling machines and plants. According to its operating principle, sprinkling systems are broken down as follows: stationary, semi-stationary, and mobile.

In stationary systems, all the components (i.e. pumping stations, every pipeline, sprinkling machines) are installed fixed. In such the systems, it is reasonable to widely implement automatic machinery, set up free-fall irrigation guns in special wells from where these guns go up under water pressure for watering and go back down when the water application operation is over. Short-range, medium-range and long-range sprinkling machines and plants are installed in automated stationary systems. The most favorable conditions can be provided in such systems for control of soil regimes depending on their moisture by using tensiometers.

In stationary systems, the pumping station, water carrier network, and hydraulic facilities have fixed location (i.e. not mobile). The pipelines are laid under the surface; only hydrants (taps) from subsurface pipelines come out to the surface; sprinkling machines and plants are connected to these hydrants (taps).

In stationary systems, all the components, except for sprinklers, are not mobile. Such systems are used in greenhouses and hothouses, for irrigation of mountain slopes and highly profitable crops.

When cultivating vegetables and perennial citrus plantations on small-area plots of 25-50 ha, stationary systems are composed of pipes laid overhead at a height of 2.5 m with short-range or medium-range sprinklers fixed on them. For the greenhouse facility they use stationary sprinkling automatic systems which consist of distribution pipelines with sprinklers with a range of no more than 2.5 m.

Semi-mobile sprinkler irrigation

Semi-stationary sprinkling irrigation is a water application method at which the pumping and power equipment, main and distribution pipelines have permanent (fixed) position, while the field pipelines are mobile along with sprinklers.

In semi-stationary sprinkling systems, the pumping stations, on-farm distributors and delivery ditches, group irrigation ditches (or pipelines) are made permanent; irrigation ditches and transporting pipelines are made temporary; and sprinklers are made self-moving and portable. At present, these particular systems are the most widely used. Mobile sprinkling plants and machines are of the following types: DDN-70, DDN-100, DTsA-100() (in Russian: -70, -100, -100(), respectively), Fregat, Voljanka, Dnepr, Kuban.

In semi-stationary irrigation systems, the pumping station and main pipeline have permanent position, while the distribution pipelines and sprinkling machines and plants connected to them move over an irrigated area.

Semi-stationary sprinkling systems are the most widespread. In these systems, pumping stations and transmission pipelines are generally stationary, while sprinkling machines and plants, sprinkler pipelines are mobile.

In semi-stationary sprinkling systems, the pumping stations, on-farm distributors and delivery ditches, group irrigation ditches (or pipelines) are made permanent; irrigation ditches and transporting pipelines are made temporary; and sprinklers are made self-moving and portable. At present, these particular systems are the most widely used. Mobile sprinkling plants and machines are of the following types: DDN-70, DDN-100, DDA-100, DDA-100 (in Russian -70, -100, -100, -100, respectively), Fregat, Voljanka, etc.

Sprinkling irrigation by mobile machines

Sprinkling irrigation by using mobile machines is an irrigation method at which all the elements of the sprinkler irrigation system are mobile.

In mobile sprinkler irrigation systems, distribution and transmission pipelines are composed of quick-disconnecting metal pipelines. At present, mobile sprinkler irrigation systems are usually arranged on small-area plots (irrigated vegetable plots, cultivated irrigated pastures, etc.), which do not require high water discharges. Currently, the most typical mobile system is the system of irrigation of cultivated perennial pastures of areas from 150 to 300 ha.

Mobile irrigation systems are used for water application to small-area plots located near to water sources. Their irrigation network consists of quick-disconnecting pipelines and a mobile pumping station.

In mobile sprinkler irrigation systems, all the elements travel in the course of the water application process. For example, when water application on one position is over, the pumping station and pipelines are removed to another position, where it supplies water to portable or transportable sprinkling plants or machines.

Mobile sprinkling machines of PDM-2500, PDM-3000 (in Russian -2500, -3000 respectively) types are used for artificial irrigation of agricultural lands, including hayfields, pastures, (clean-)tilled crops, vegetables, etc.

Sprinkling irrigation network

Components of this sprinkling irrigation system are as follows: irrigation water source; stationary and mobile pumping installations; permanent networks of canals and pipelines; temporary networks of canals or network of quick-disconnecting transmission pipelines; stationary and mobile sprinkling machines and plants with system of sprinklers.

The irrigation network of the sprinkler irrigation system can be of open, closed and combined types.

Open network is composed of permanent or temporary canals or flumes.

Closed network is composed of pipelines (steel, cast-iron, reinforced concrete, asbestos-cement, plastic).

Combined network combines open conducting canals and distributing pipe network, to which water is supplied by means of pumping stations.

Piped (closed) network consists of: main (or head) pipeline that delivers water from a water intake facility to an irrigated area; distributing pipelines of different order; irrigation pipelines with hydrants. It may be of stationary, mobile or semi-stationary types.

The stationary network is the most complete: it allows creating automated irrigation systems with usage of highly productive sprinkling equipment.

The mobile network is made from quick-disconnecting pipelines laid on the field surface, which requires much labor effort.

The semi-stationary network combines stationary (generally main and distributing) pipelines and detachable irrigation pipelines.

In comparison with open network, piped network has the following advantages: high efficiency, because of low water losses from it; high use ratio of irrigated lands; trouble-free mechanization of field works; possible to be used on compound land topography. Its principal drawbacks are as follows: a large number of pipes are required; considerable capital and operating costs.

The irrigation network scheme on fields should be linked to the operation schedule of specific sprinkling machines, configuration of irrigated areas, topography, etc. The irrigation network is to make provision for water delivery to sprinkling machines according to a corresponding irrigation schedule.

The diameters of irrigation network pipes, pressures required to supply required flow rates are to be specified by hydraulic computations. At that, the design flow rates must conform to the flow rate of the sprinkling machines.

Selected bibliography