Irrigation (on a smaller scale also casting period) is the supply of arable land with water to the growth promoting plant and missing rain to replace. It is mainly in arid regions between the tropics that water is used to take advantage of the abundance of sunshine and high temperatures. But even in humid regions, plants that are very watery - such as rice - or to bridge seasonal dry periods are irrigated.
Some very ancient agricultural techniques are used for irrigation . In many early advanced cultures , such as in Egypt , Mesopotamia , India , China , East Africa or in pre-Columbian America , the intensive use of irrigation techniques increased agricultural production so significantly that a noticeable increase in population was possible. It is sometimes argued that the considerable work to be done to set up the irrigation systems provided a major impetus for the formation of organized social structures.
Today we generally differentiate between three forms of irrigation:
- 1) Moisturizing irrigation is intended as a supplement to natural rainfall and provides the plants with the amount of water they need for optimal growth or fruit production. Moisturizing irrigation can be roughly divided into two sub-categories:
- a) Humidification through "uncontrolled" water supply (also wet field cultivation), and
- b) Humidification with controlled water supply, often referred to as artificial irrigation.
- Irrigation with uncontrolled water supply includes, for example, natural flood irrigation, rainwater irrigation or the use of natural wetlands. All these irrigation methods have in common that they make use of natural conditions and therefore also depend heavily on natural developments such as temperature and precipitation distribution. In contrast to processes with a controlled water supply, which strive for the greatest possible independence from natural fluctuations.
- 2) Fertilizing irrigation supplies the soil with plant nutrients along with the water.
- 3) The soil-cleaning irrigation ( drainage ) removes soluble substances that are harmful to plants and salts that have accumulated from previous irrigation.
The water required for irrigation is usually taken from naturally occurring surface water (watercourses, lakes, ponds) or from the groundwater (wells). In addition, water reservoirs ( reservoirs , basins, water tanks ) also play an important role in the provision of water. In the arid regions, cisterns and underground basins are predominantly used to collect rainwater .
Most of the irrigation methods used today are the result of thousands of years of practice and technical development.
Many surface irrigation methods have been practiced for thousands of years. Most of them are still of great importance today because they can be operated inexpensively and without complex technical systems.
Various damming and trickle processes are part of surface irrigation. The following procedures can be applied to a wide variety of relief situations. A common problem with all surface irrigation methods is the high rates of evaporation and seepage.
In damming processes, furrows or leveled or insulated areas are placed under water. Damming methods are among the most frequently used methods of irrigation management worldwide.
In the case of pool dams, 20 to 40 cm high pool dams are laid out horizontally and can be adjusted to a slight gradient. They are combined into blocks by supply and drainage channels, which are watered one after the other, starting with the highest basin. The cultivation area is supplied with water from one side of the block, and on the other narrow side of the basin the water is drained back along the dams.
The reservoir is suitable for fields with a slight gradient (<0.1%) and low to moderate water conductivity (<1 cm / h). If the gradient exceeds 0.1%, terraces must be created in order to continue to be able to practice irrigation by means of basins. On slopes with a gradient of up to 2.5%, irrigation basins are created as contour basins (terraces), with the dams following the contour lines.
If the saturated water conductivity exceeds 1 cm / h, the use of pool irrigation does not make sense, as high seepage losses occur. The main problem with basin irrigation is not the infiltration rates, but rather high evaporation losses, as there is an open water surface during the entire vegetation period. Thus, the water use efficiency in the case of pool irrigation is very low, around 40 to 50%. The basins themselves are a hindrance when working on the cultivation area.
Grains such as rice, numerous types of vegetables and other forage crops are mostly irrigated in arid areas by pool damming.
Overflowing is similar to pool irrigation, but the watered area is larger. Overflow is characterized by the fact that water no longer flows during seepage, but covers a large area of an insulated, flat area of 1 to 20 hectares. The water level is about 15 to 30 cm and therefore requires that a relatively large amount of water is applied at the same time.
When damming furrows, the entire cultivation area is not filled with water, but rather individual furrows between the plants placed in a row. This has the advantage that the free water surface becomes smaller and thus less water evaporates.
Furrow accumulation works with 20 to 30 cm deep trenches at a distance of 0.6 to 1 meter, which are created with a gradient of 0.2% to 0.5%. An inflow of water quickly fills the furrows. The water spreads evenly and evenly. The water comes to a standstill. Through additional grooves, the water can almost directly reach the roots. Less water is required than with other damming methods.
When choosing the furrow spacing, the water conductivity of the soil is an important criterion.
The method is mainly used in arid areas for row crops of fruit and vegetables.
With the trickle method, the water flows through furrows and slightly sloping surfaces.
In contrast to the damming process, basins or furrows are not permanently flooded with irrigation. Rather, the water is run along a slope over the irrigation area. Therefore, only areas with a gradient of more than 0.1% are suitable for irrigation. Repeated trickling over increases the workload, but evaporation and infiltration losses are reduced, as the water does not stand permanently on the surface. With repeated sprinkling, an almost exact water dosage can be achieved. In order to be able to use irrigation systems effectively, the saturated water conductivity of the soil must be low to moderate. Furthermore, on the side where the water is fed in, there must be a strip without a slope so that the water can first spread over the width of the field before it flows off along the slope.
With strip irrigation, also known as slope irrigation or wild flooding, the water is diverted from streams or rivers, often when the flood rises, and trickles unregulated from supply trenches over the ground. The irrigated strip of land shows a slight slope, depending on the permeability of the soil, and is usually 10 to 20 m wide and 150 to 400 m long. The irrigation area must not have any hollows, bumps, transverse gutters or longitudinal furrows so that regular irrigation can be guaranteed. The work and operating costs of the method are low, but the water is often distributed unevenly despite the effort. The consequences are under- or over-irrigation, waste of water and erosion . The process is mostly used in arid areas.
Furrow trickle / groove trickle
After pool irrigation, furrow trickling is the most common surface irrigation method. It is mostly used in crops that are grown in rows, such as. B. potatoes, tomatoes, corn, sugar cane and others.
The furrows have a U or V shape, are 15 to 20 cm wide and approx. 25 to 30 cm deep. With predominantly long rows of plants, they can also be flatter and up to a meter wide. The gradient can be between 0.5 and 2%. The water is in constant motion in the furrows. It is fed into the furrows from permanently installed supply and distribution lines. It must be ensured that the furrow is filled to its full length quickly enough to enable constant soil moistening. Any remaining water ends up in drainage channels. The amount of water, furrow slope and furrow length determine the uniformity of the distribution.
Irrigation covers the processes in which irrigation is carried out using stationary or mobile spray systems. The irrigation is mainly carried out in humid climatic areas.
Water is pumped through pipes to the systems in the field. Depending on the type of construction, a distinction is made between: Irrigation with fixed, partially fixed and mobile or fully mobile complete systems. It is possible to distinguish even more precisely between individual irrigation, circular irrigation, roller irrigation or rolling (self-propelled) irrigation.
The irrigation makes few demands on the surface quality of the cultivation area. Accordingly, uneven and sloping terrain can also be irrigated, so that under certain circumstances time-consuming leveling work as well as the construction of ditches or dams are not necessary.
Multi-purpose irrigation can also be carried out via the systems. Irrigation systems are used for frost protection and to apply fertilizers and pesticides.
The (multi-purpose) irrigation can be largely automated . Smaller water inflows per area and more precise metering lead to low infiltration and controlled moisture depth. This reduces the risk of salinization through overwatering and capillary suction.
Since the water is not fed directly into the soil during irrigation, but rather rains over the existing structure, high evaporation and interception losses result in a relatively low water use efficiency of 65 to 75%. Furthermore, there is an uneven distribution of water in the wind and on the edges of the fields. In addition to the high system costs, spare parts stores, high energy requirements and high operating, maintenance and renewal costs make large investments necessary. A certain degree of training of the operating personnel is also required for the maintenance and repair of the irrigation systems.
The irrigation methods were initially developed for additional irrigation in humid climates. Today 50 to 90% of the irrigation area in these regions is irrigated.
Because of its many advantages, the method is spreading more and more in semi-arid areas and is in third place there after basin and furrow irrigation.
Irrigation by means of stationary systems
In the case of the stationary systems, both the pumping station and the supply and sprinkler lines are permanently installed. The supply pipes are often laid underground, which is why the process is only suitable for permanent crops such as fruit, since laying the pipes is very costly.
Irrigation by means of partially fixed systems
In the semi-stationary systems, the pumping station and supply lines are permanently installed, but the sprinkler lines can be moved flexibly in the existing structure. This also includes processes such as circular irrigation or systems in which a sprinkler cart is pulled through the forest on ropes or a sprinkler sledge on a water hose.
Irrigation by means of fully mobile systems
In these systems, the pumping station and supply lines can also be used flexibly.
The underfloor irrigation method is used for flat to moderate relief. The plants are watered by the capillary rise of the groundwater. This may require water enrichment below the soil surface. This can be done by raising the groundwater level or with the help of underground pipes that are either porous or provided with slots.
The advantage of this method is that the underground irrigation prevents evaporation of the water. No land is lost through underground distribution systems and the amount of work involved in irrigation is comparatively low.
Since the water does not seep away from above, but rises from below, evaporation losses can be avoided, but not the salinisation of the topsoil. Salt accumulation in the soil often makes drainage necessary, as the rising water releases salts from the deeper layers of the earth and transports them to the surface.
Underground irrigation is not suitable for crops with shallow roots. High construction costs for the underground lines represent a further disadvantage.
Underground irrigation by raising the groundwater level
The groundwater level is artificially raised and kept high via trenches so that water can rise from the subsoil into the root space using capillary action.
Underground irrigation through pipes
The installation of a pipe system enables nutrients to be fed in and the water to be metered more precisely than when the groundwater is raised. The pipes must be well protected against silting up and lie deep enough so that soil cultivation (e.g. raking) is not hindered. In addition, there is less water loss through evaporation .
Ebb and flow irrigation
A special form of underfloor irrigation is ebb and flow irrigation in a plant tub . To do this, a substrate (bale) is flooded at intervals and the water level is lowered again. This type of irrigation is especially in hydroponics and hydroponic use. See also lifter (device) # ebb and flow system .
With micro-irrigation methods, only a small part of the soil is watered. In contrast to sprinklers / sprinklers, only a very small amount of water is applied. The advantage is that you can irrigate uneven surfaces with it.
Drip irrigation is the most economical of all irrigation methods, as only small amounts of water are applied. The water is fed directly to the root area of the plant through hoses or pipes laid above or below ground and through the so-called drippers installed on the plants. Small amounts of water are continuously released from the drippers, exactly according to the needs of the plant. Due to the targeted moistening of the narrow area around the plant or the root space, no water can seep into the rest of the soil or evaporate.
You can also mix fertilizers and pesticides with the water. The targeted irrigation and fertilization can also be automated. This in turn leads to less labor and more precise control of the irrigation. A major advantage of the process is the low energy and operating costs.
The leaching of soil minerals, soil nutrients, pollution of the soil by pesticides and salinisation are greatly reduced. The controlled distribution of water and fertilizer prevents weed growth.
The irrigation efficiency with drip irrigation is very high and is around 80 to 95% active efficiency. Thus, drip irrigation is the method with the highest water use efficiency and the fewest harmful side effects.
As far as the disadvantages are concerned, high demands are made on the cleanliness of the water used in order to avoid clogging of the small drip openings. This is usually possible by cleaning the filter. Because of the low operating pressure of the irrigation hoses, the surface must be as horizontal as possible. Added to this are the need for trained personnel and high system costs, especially for crops with narrow row spacing.
The drip irrigation method was particularly developed in Israel and should mainly serve for irrigation in the arid areas. Today it is also increasingly found in temperate zones. Due to its disadvantages, drip irrigation is mainly used for profitable and perennial crops such as vines, olive or fruit trees and hops.
Above-ground drip irrigation
The above-ground drip irrigation system is always divided into three areas: control unit, drip line and drip. The amount of water is controlled manually or automatically using a tensiometer . With above-ground drip irrigation, the drip lines are on the ground surface. The drippers can be very different, a long-travel channel or attachable drippers are often used.
Underground drip irrigation
With underground drip irrigation, the water is led directly to the root area of the plant. The drip lines are not on the ground, but are laid underground. This makes installation more complex and the lines cannot be moved so flexibly if necessary.
Capillary irrigation is an ecologically and economically sensible plant irrigation for hobby gardeners, gardeners and sales companies for potted plants. It does not require pressurized water or electricity. It uses the capillaries of preferably glass fiber wicks and / or mats as well as the difference in moisture in water to suck in water from deeper water sources, containers, gutters or pipes and bring it into the root area of the plants. The optimal substrate moisture can be set by adjusting the amount of wick and suction height.
Special methods of irrigation (rainwater, dew)
In addition, there are special methods such as irrigation with run-off rainwater and with dew, such as those that were further developed by Michael Evenari, for example with the flash water irrigation in the Negev desert, based on traditional cultivation methods . Various methods were developed to supply fields with runoff water. Each of them is adapted to particular terrain, climatic conditions and crops:
- The terrace system was used in ancient times. Several stone terrace walls were erected horizontally over a wadi . When it rains, the water fills a terrace field to a predetermined height. The excess water reaches the fields below via an overflow. The fields have an area between 0.1 and 2 hectares, while the watershed producing the runoff is 10 to 100 times larger.
- The Limnian system catches the runoff in a field about 0.5 hectare. This is created in an alluvial plain, a shallow depression or the wadi of a tributary and walled on from several sides. Although the walls are sometimes made of earth, they are much stronger than those of the »micro-catchments«.
- Micro-catchments are small areas that only feed a single tree or a few crops. A larger pit is created at the deepest point of each unit to collect the drainage water for the plant. Micro-catchments measure less than 0.1 hectare and are laid out in relatively flat terrain on which the water does not run off in certain paths. They are often created in series.
- The hill canal system is the further development of terrace construction. Narrow channels made of earth and stones guide the water that runs down from the hills onto the fields. In this way, little water is lost through seepage or accumulation in the depressions of the watershed. The ducts run diagonally along the hills and sometimes also collect the water from neighboring hills, which otherwise would not contribute to the supply of the fields.
- The drainage system is used to drain water from a large wadi onto the terraced fields of adjacent plains. For this purpose, a dam is being built in the wadi, which damms the water and diverts it into a channel, which in turn forwards it to the fields. Although the size of the fields corresponds to that of other terrace systems, the collecting areas are considerably larger. This explains the high flow of erosion, which makes it impossible to terracing the wadi itself.
Choice and limitations of irrigation methods
|Comparison of the procedures from a technical perspective|
|Surface irrigation||Artificial sprinkling||Micro irrigation|
|Installation costs in USD (1996)||400-700||600 - 1200||700-1500|
|Workload||high to low (depending on the system)||medium to low||low|
|Water efficiency||40% - 50%||60% - 70%||80% - 90%|
|Suitable soils||Almost flat land, not too sandy or rocky||Flat to moderately sloping land, not too loamy||Steep to flat land, any soil structure such as stony / gravel soils|
A complicated irrigation system consisting of dams and canals traditionally forms the backbone for the water supply and drainage. By choosing water-saving irrigation technology, the effort for the irrigation system is reduced.
The selection of the right irrigation method depends on factors such as the nature of the soil, the water supply, the vegetation to be irrigated (water requirement), the topography , the available technical means and budget, as well as the available workforce and their technical skills. Modern information and control technologies as well as learning models (e.g. artificial neural networks ) are increasingly coming into play.
In arid areas, the horizontal damming of rivers is often the prerequisite for permanent irrigation. Simpler surface irrigation methods such as furrow irrigation are particularly suitable for crops planted in rows. These include cotton, potatoes, tomatoes, and others.
In the case of flat terrain, in addition to pool irrigation, underground and drip irrigation are also possible. In the case of steep slopes, an elaborate route must either be carried out or methods such as sprinkling and sprinkling must be used. However, these methods require a greater use of technology and cause corresponding costs. A moderate hillside location tends to favor strip irrigation.
The type of soil is another important decision factor. The use of strip and furrow dust irrigation methods is uneconomical in light sandy and loamy soils due to their high water permeability. Trickle methods produce good results on such floors. If there is not enough water available, irrigation with damming and trickling methods is difficult to implement.
There are also differences between the individual procedures in terms of workload and technical training level of the operating personnel. Surface irrigation methods are very manual labor. There is hardly any possibility of mechanizing the systems, let alone automating them. That is why the employees do not need any special technical training. For the operation and maintenance of underground, drip irrigation and sprinkling systems, however, extensive technical knowledge and skills are required.
However, surface irrigation methods are by no means fundamentally unprofitable. With modern handling and the use of new developments, these methods can be quite interesting, especially in view of the increasingly expensive fuels for operating large systems.
|Comparison of the procedures from an economic perspective|
|Surface irrigation||Underfloor irrigation||Sprinkling||Drip irrigation|
|Water use efficiency||40% - 50%||60% - 70%||80% - 90%|
|Risk of salinization||low||high||high||low|
|Risk of silting up||medium||low||high||medium|
|Installation costs||low||low to medium||high||high|
|Suitable soils||heavy floors, no slope||Conductive topsoil on impermeable subsurface, no slope||all floors, no to slight slope||all floors, every slope|
|Possible crops||Backwater-tolerant species, e.g. B. Rice||All||All||mainly permanent crops, e.g. B. wine, olives, fruit but also vegetable growing|
Requirements for irrigation water and drainage
Irrigation must ensure that enough fresh water is drawn over the floor area . In arid areas in particular, where precipitation is lower than evaporation, the soil must be irrigated beyond the needs of the plants in order to avoid salinization and this water must be drained away again ( leaching ). In the case of soils that retain water and tend to become wet, it may therefore be necessary to drain the soil in order to avoid waterlogging , in which the water flows off again via underground pipe systems. The amount of excess irrigation required for this depends on the salinity of the water and the type of plant to be irrigated. In this context, the Na + content is of particular importance, which, in addition to the negative impact on the plants, leads to damage to the grain structure of the soil.
The quality of the irrigation water must, on the one hand, meet the requirements of the plants to be irrigated and, on the other hand, meet minimum hygienic standards. International guidelines on this were published by the FAO of the UN in Rome.
A seawater desalination for irrigation is often considered unprofitable. Nevertheless, most of the desalinated water from seas or aquifers is used for irrigation in agriculture. In the USA in particular, large amounts of water are desalinated for irrigation. In some areas of Europe, especially in Andalusia , desalinated seawater is used for growing vegetables. In individual cases, such as tomatoes, research has shown that irrigation with water that is mixed to a small extent with seawater can be beneficial. However, here too, care must be taken not to over-saline the soil.
To provide water and to compensate for the dry and wet seasons, the water in dry areas is sometimes kept in reservoirs ( dams ) before it is distributed over long distances. This happens through irrigation systems such as ditches up to sprinkling systems and trickle systems.
In many parts of Europe too, the amount of water available is a limiting factor in the development of agriculture. This can sometimes lead to conflicts between countries and regions.
Agricultural requirements and resulting problems
The agricultural requirements of irrigation farming and the problems resulting from it are dealt with in the article Irrigation farming .
- Meadow irrigation
- Deficit irrigation
- Virtual water
- Artesian well
- New Valley Project
- Hydraulic ram
- Water art
- Deichel / Teuchel
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