Irrigation field management

from Wikipedia, the free encyclopedia
Characteristic top view with pivot irrigation

Irrigated field management (rarely: irrigated agriculture ) describes the cultivation of the cultivated soil and agricultural production with methods of artificial irrigation . Irrigation is the supply of a cultivated land with water. Irrigation serves to compensate for or supplement the rainfall that is lacking for crop production and to open up agricultural cultivation regions beyond the limits of rain- fed agriculture .

history

Very early on, people discovered that plant growth depends on water. 5000 years ago in ancient Egypt and the Orient the first irrigation techniques were developed for growing plants when there was a lack of water. The scarce supply was made up by the addition, lifting and storage of water. This required joint and coordinated work, which was an essential prerequisite for the emergence of earlier high cultures .

Tasks and importance of irrigation

Irrigated areas worldwide in% of the agricultural area - according to Siebert 2002

Irrigation is mostly operated in arid regions so that the abundance of sunshine in these areas can be better exploited, as well as in regions with very water-requiring plants such as B. Rice. It is also used during seasonal dry periods and to increase production on old cultivated areas. The fertilizers and nutrients carried along during irrigation promote plant growth and lead to an increase in yield while at the same time improving quality. With a secure water supply, plants respond better to fertilization and yields are multiplied. In contrast, increases in yields in rain-fed agriculture , in semi-arid areas, can hardly be achieved.

In 2003 approx. 273 million hectares worldwide, that is 20% of the agricultural arable land, were irrigated. The contribution of irrigated land to global food production was around 40%. This means that irrigated land is far more productive than non-irrigated land.

Irrigated farmland is unevenly distributed across the continents. Almost two thirds of the world's irrigated area is in just a few countries: India, China, Pakistan, the USA, and the Central Asian states of the former USSR. Almost 68% of the world's irrigated area is in Asia, 9% in Europe, 17% in North and South America, 5% in Africa and 1% in Oceania.

Irrigated land on the continents
region Arable land (in 1,000 ha) Irrigated arable land (in 1,000 ha) Share of the irrigated area in the total arable area
Africa 177.251 12,538 7%
Asia 495.039 192,962 39%
Europe 291.102 24,406 8th %
North and Central America 259,589 31,395 12%
South America 96,142 10,326 11%
Australia and Oceania 49,987 2,539 5%
world 1,369,110 274.166 20%

Irrigation is still often seen as the engine of overall rural development. The rural population has easier access to the local education and health infrastructure through dense settlement in irrigated areas than in the case of scattered settlements in rain-fed areas. Irrigation has a significant impact on migration by creating jobs in rural areas.

During periods of drought, in which production in rain-fed agriculture is almost completely lost, a relatively secure income can be achieved through irrigation farming. As a result, greater flexibility and better adaptation to the market are possible.

The income gap between urban and rural areas is narrowing, even if a new gap usually arises at the same time between the more prosperous irrigated and the poorer rain-fed areas.

The advantages of irrigation field management, but also the political and economic motives of its protagonists, mean that more and more arable land is artificially irrigated worldwide. Further reasons for an expansion of irrigation field management are given as their importance for rural regional development, the reduction of rural exodus and a higher national level of self-sufficiency with food.

The water is applied to the agricultural land to be irrigated using the following methods:

  • to water
  • Damming of horizontal surfaces or flooding.
  • Irrigation over inclined surfaces (superficial runoff).
  • Sprinkling or irrigation , i.e. spraying water over the areas to be irrigated. This method is widely used in modern agriculture of humid areas as well as on golf courses .
  • In the case of underfloor irrigation, underground water enrichment takes place in particular with the help of pipes laid in the ground, which are either porous or provided with slots.
  • In the case of drip irrigation , outlets are attached to above-ground hoses at regular intervals, which release only small, exact amounts of water (drop by drop), largely independent of the pressure in the pipeline . Developed in dry countries for water-saving use, this process is increasingly being used in Central Europe in viticulture (e.g. in the Wachau ) but also in home gardens and parks. In addition to the exact application of the water while avoiding evaporation losses, an advantage of the process is that the leaves are not wetted and thus fungal diseases of the plants are not further promoted.
  • There are also special methods such as watering with dew that can be used under extreme conditions.

The various methods that have now been developed are presented in more detail in the article Irrigation .

Calculation of requirements

In order to save water, the needs of the plant must be calculated precisely. To do this, it must be known how much water is available to the plant through natural precipitation.

Not all of the water that is supplied through rainfall or irrigation is also available to the plant. Some of the water is evaporated through the surrounding soil. Evaporation from the ground is known as evaporation . The plant itself also evaporates water, which is referred to as transpiration . The sum of evaporation and transpiration is what is known as evapotranspiration , which must be taken into account when calculating requirements. In addition to evapotranspiration, water also evaporates via interception (direct evaporation from the vegetation surface).

With capillary irrigation with fiberglass wicks and / or mats, the water requirement does not need to be calculated precisely because these aids work with differential humidity (fine control with wick quantity and / or wick suction height).

Irrigation farming problems

Socio-economic problems

Agriculture is the largest consumer of water in the world. Approx. 70% of the world's freshwater is used for agriculture . In the dry regions of Asia and Africa, it sometimes uses up to 90% of the fresh water. In Europe, however, the percentage mark is only 35%.

Since only 1.73% of the water on earth is usable freshwater (1.679% groundwater and 0.033% surface water ) and this 1.73% is regionally very unevenly distributed, there are major conflicts of use between agriculture, households and industry. The water consumption of metropolises increases with increasing size and in many countries the abstraction of groundwater exceeds the renewal.

In arid areas, the social and economic effects of irrigated agriculture are clearly visible.

The urgently needed amounts of water are obtained through complex large-scale projects such as dams and sewer systems. In China, Turkey and other countries, gigantic dam projects and their social and ecological effects result in regional and domestic political conflicts, but also conflicts with neighboring countries. Large river diversion projects fuel economic and foreign policy crises. Such large-scale construction projects destroy the habitats of the local population, cut off traditional pasture areas for nomadic tribes and make it difficult for them to access the cattle troughs. Social communities are being destroyed by the resettlement of people and cultural landscapes are irretrievably flooded.

The irrigation industry is often operated by state or private-sector monopolies , with smallholders having little influence on decisions and often being disadvantaged.

Ecological problems

Sprinkling wheat (Arizona): some of the water evaporates
Aerial view of a circular alfalfa field in the Kalahari

As the agricultural areas continue to expand, their influence on other usable areas increases. The reasons for the expansion often lie in the country itself, such as overpopulation. In this way, pastures are being pushed into increasingly drier areas and reduced in size.

Due to the construction of numerous dams in the upper and middle reaches of the rivers to irrigate arable land, the water flow of the rivers is reduced and former pasture areas in the river plains are largely drying up.

Technical water abstraction systems, which were introduced primarily through irrigation agriculture, create population concentrations. These are perhaps adapted to the water supply, but the natural vegetation (firewood) and the soils cannot cope with the high population density. Degradation occurs as a consequence.

When irrigated via dams and canals, more and more fertilizers are finding their way into the rivers and further into the oceans. This has a serious impact on the plankton community . The algae absorb the supplied nutrients and multiply explosively.

When the algae die off towards autumn and dead organic material sinks to the bottom, bacteria begin to decompose this form that can be used by other living beings. Oxygen is required for this conversion process. Due to the amount of organic material, the bacteria multiply strongly and the oxygen content of the water decreases. Fish have to emerge to gasp for air. The consequences for the creatures of the sea are dramatic.

Change in the water table

The main problems with irrigation, however, are the salinisation or waterlogging of the soil and the exhaustion of the groundwater supplies.

If the groundwater level rises due to the ingress of large amounts of water, the soil becomes wet. Most crops cannot thrive in soil that is saturated with water. The waterlogging is largely due to the year-round irrigation, whereby water losses on the transport routes (seepage in ditches) and the poor drainage possibilities of the heavy seasonal rainfall led to a rapid increase in the groundwater surface. As a result, the land becomes swampy and unusable for agricultural use.

If, on the other hand, the groundwater level sinks due to increasing underground irrigation or population concentrations around the irrigation areas, this has a serious impact on fauna and flora. The consequences are the devastation of areas that were once rich in vegetation and the loss of drinking water in traditional wells . The wells are mostly adapted to the groundwater resources, as they only use the water that seeps back into it. In addition, groundwater is an important key to development in arid regions, as it can be used independently of drought and is less contaminated by pathogens than surface water.

Soil degradation

Desertification

Desertification describes a process in which soil degradation (drying up) occurs. This subsequently leads to the spread or formation of deserts or desert-like conditions. The process of desertification can be observed primarily in arid, semi-arid and dry sub-humid areas. It arises from complex interactions between several human and natural factors.

In nature, desertification occurs due to natural fluctuations in precipitation. Drought periods can trigger or intensify desertification. For the most part, however, it is anthropogenic . Every human cultivation of the land results in a change in the natural ecosystem . In monocultures , individual components are excessively withdrawn from or added to the soil. The original equilibrium of the soil can no longer be restored because the interaction of the microorganisms is destroyed. Plant pests can also multiply strongly. By increasing the use of fertilizers and pesticides , attempts are made to compensate for crop losses, but this continues to pollute the soil.

It is estimated that over a billion people and more than 1/3 of the world's arable land are threatened by soil degradation .

In the humid climates, such as in the Central European west wind zone, there is no desertification. Deserts cannot develop in these climates, as the regenerative power of the natural flora is much greater than in the fringes of large deserts. Although the ecosystems in semi-arid areas are quite stable and adaptable, they prove to be very unstable under strong anthropogenic influence.

Desertification mostly occurs in regions where the population has increased significantly in recent decades. The population growth in most of the affected areas is between 2 and 3 percent. In arid regions , however, there are also areas with low population density due to possible water shortages . Due to the availability of water or technical water extraction systems, these areas are used permanently. The ecological balance is destroyed by the use of inadequate irrigation techniques and the natural regeneration capacity of the soil and vegetation is prevented.

The consequences essentially consist of losses in crop yields , loss of soil fertility , malnutrition , hunger , rural exodus and loss of the income to be generated.

Aral Sea : Drought and salinization of the soil due to the water requirements of irrigation farming

Desertification sets in motion a vicious circle . If the soil vegetation is destroyed, this leads to a greatly increased evaporation and the soil dries up. This lowers the groundwater level and the plants are no longer supplied with sufficient water and need more irrigation.

The most important cause of the desertification caused by the irrigation field management is the degradation of the soil by salt deposits.

Salinization

In the areas that irrigation has made safe (or seemingly safe) agricultural production sites, salinization is the main cause of desertification. The permanent irrigation results in an accumulation of water-soluble salts in the soil.

The salinization of the soil can also be caused by natural factors. In arid climates, groundwater salinization occurs due to the evaporation of capillary rising water when its minerals are left behind (be it before or after use by plants). The absorbed water also dissolves minerals from the depths of the ground during the ascent and brings them into the upper layers of the earth.

Slightly salted water can be used to sprinkle cotton

The proportion of large-scale artificial irrigation in salinization is far greater, which is often due to the use of incorrect or non-location-adapted irrigation techniques.

Since water is naturally limited in arid regions, irrigation management is particularly problematic in these areas. Since the potential evaporation is very high in the arid zones, even surface irrigation with low-salinity water can have immense effects.

Furthermore, salinisation can occur through evapotranspiration or through leaching of salts from gypsum minerals , which can be contained in the cultivation soil.

Consequences of salinization

The accumulation of salts in the soil impairs plant growth and leads to a decline in crop yields. At higher concentrations, irreversible soil degradation can occur, which often leads to the complete loss of agricultural land.

Damage to the crop occurs at around 0.3% salt content. Since even low-salt water has a salt content of 0.1%, salinization problems occur relatively quickly. Overall, for example, over 50% of the areas in the Central Asian countries are affected by salinization processes.

The salt and toxic dust left behind from fertilizers and pesticides, which are distributed annually in the regions by steppe storms after desertification, have serious health consequences for the population.

River branches

Rivers and reservoirs are being diverted to irrigate fields on the one hand and to replenish depleted groundwater on the other. With gigantic river diversion projects, irrigation can be operated on a large scale and food production increased.

Dams and canals were built in antiquity and before for irrigation purposes. However, they are in no way comparable with the purpose pursued today.

Problem using the example of the People's Republic of China

The People's Republic of China is well on the way to reducing hunger in the country. As a result of the great efforts made in recent years, the country is no longer among the country with the most malnourished people, but is in penultimate place ahead of India . In order to be able to increase food production further, irrigated agriculture is carried out on a large scale.

A 60 billion euro project that is currently underway is supposed to bring urgently needed water to Beijing, the country's granary. In the regions around the city, the groundwater level has dropped by around 60 meters in recent years and is falling by another 1.5 meters every year. As a result, the ground has sunk by up to three meters in many places.

In order to still be able to use the area for agricultural purposes, the Yangtze River 1000 kilometers away is being diverted north. An elaborate system of pumping stations and reservoirs will lead the water uphill. The planned water course will partly use existing canals such as the 1500 year old Kaiserkanal . This saves costs, but brings with it further problems. Natural waters seal themselves down with suspended matter . Channels, on the other hand, have to be sealed with layers of clay , which is a complex process. In the deserts and semi-deserts through which the river is supposed to flow, however, there are no suitable sealants . In addition, there is evaporation, through which another part of the precious water is lost.

The Yellow River is a dramatic example . The great river of East Asia has been drying up for decades. Numerous canals drain too much water that is used for irrigation farming. In hot summers it dries up completely on its lower reaches. Because little water evaporates over the river bed as a result, the climate in many regions around the river has changed significantly. Precipitation is decreasing, soils are degrading and need more artificial irrigation. That is why the Yellow River is to be donated from the Yangtze River. However, agricultural experts expect both rivers to dry out over the next few decades.

Further examples

Not only in China, but all over the world, such gigantic projects are planned without considering future consequences.

In the United States, for example, orange plantations and grain fields (where the grains grown are mainly used to feed animals) consume more groundwater than nature can regenerate . The major rivers of Alaska and Canada are designed to provide a way out of this problem. Their water seems to flow uselessly into the oceans. Indeed, every drop of water belongs to a global system. The diversion of flowing waters not only influences the climate of the respective region, but also has a significant influence on the global climate. The fresh water flowing into the seas and oceans is part of a complex interplay between temperature, salinity, stratification of the water and prevailing currents. The Gulf Stream, for example, is believed to be influenced by such factors.

In the 1930s, construction of an extensive canal irrigation network began in South Africa on the lower reaches of the Vaal . It was then called Vaalhart's Irrigation Scheme .

Future prospects

The irrigation industry will face a number of challenges over the next few decades. On the one hand, it must provide the largest share of the world's necessary food and fiber production in order to continue to meet the food and clothing needs of the growing world population and to make its essential contribution to poverty reduction and economic development. On the other hand, it will be confronted with the demand for a more economical, quality-improving use of the increasingly rare resource water.

In order to be able to continue to fulfill its tasks, irrigation will inevitably be expanded over the next few decades. However, arable land is still being lost to soil degradation.

The future of the conventional irrigation industry must be reconsidered in view of such social and ecological, i.e. socio-ecological, challenges . A sustainable irrigated agriculture and the economical use of water through more efficient irrigation methods and adapted crop rotations are necessary.

Approaches to improvement

The availability of water plays a major role in all areas of irrigated agriculture and is an important obstacle to its expansion. Of the estimated 1,384,120,000 km³ (1.386 billion cubic kilometers) of water on earth, only 48 million cubic kilometers (3.5%) are fresh water. Of these 3.5%, with 24.4 million cubic kilometers (1.77%), most of the fresh water is bound as ice to the poles , glaciers and permafrost and only 1.73% is fresh water available for irrigation agriculture. Of this, 23.4 million cubic kilometers are groundwater and 190,000 km³ are flowing waters and inland lakes .

The efficiency of the water used in irrigated agriculture averages 40 percent worldwide. Much of the water flows away unused. Since around 70 percent of the world's freshwater is used for agriculture, there is great savings potential in increasing the efficiency of irrigation technologies. With a ten percent improvement in irrigation efficiency in the Pakistani part of the Indus Basin, for example, two million hectares of arable land could be irrigated.

The extent to which irrigated agriculture is sustainable and therefore practicable in the long term depends on a number of factors. These are the nature of the soil, the climate - together with the water cycle of precipitation, surfaces and groundwater reservoirs, the cultivated plant species, etc. For sustainable irrigation, models created by experts are necessary that cover sufficiently large periods of time and with a sufficiently large spatial discretization consider the interaction of all these relevant factors and processes as far as possible. The possibility of deficit irrigation should also be considered.

Particularly where the water issue is precarious, regulations on water use must be made and institutions must be created to resolve and monitor water rights regulations. Improved training and advice for irrigation farmers and their participation in management decisions are also very important.

In addition to a complex monitoring system, financial support for the countries concerned and the provision of experts are necessary.

Problem solving desertification

Since the causes of desertification are largely anthropogenic, they can also be combated.

In combating desertification, the primary consideration must be to restore the regenerative capacity of the ecosystem instead of increasing agricultural production. The important thing is not to eliminate the consequences of desertification, but to act preventively and prevent it from occurring.

To combat desertification, a plan is required that takes into account all of the regional, political and social conditions in the affected areas, such as water availability, land use potential, climatic conditions, social and economic problems, cultural behavior patterns, population pressure, economic ties with other regions and others , recorded and taken into account to different degrees.

The simplest prevention against desertification is to convert and adapt the cultivated product to the soil conditions. Changes or rotation of the crop rotation and a shortening of the fallow periods would prevent unnecessary pollution and leaching of the soil, so that it uses up its nutrients less quickly.

Improved cultivation methods and proper tillage are also very important. For example, plowing in the direction of the slope increases the runoff of soil material. In the case of particularly steep terrain, terraces must be created so that the soil is not further removed on the already steep mountain.

The erosion effect of the wind can be counteracted by small earth walls or vegetative and agroforestry protective measures such as the planting of trees and strips of trees on arable land. Strips of trees also help maintain soil fertility. Due to their shadow effect, they help to minimize evaporation losses and counteract the aridification of the soil.

The plant cover can generally be regenerated in a relatively short time, provided that it is not completely destroyed.

The effect of soil breaking up can be counteracted by various soil preparation measures, such as adding sand to clayey soils.

Other measures include maintaining soil moisture and stopping soil degradation, setting an optimal groundwater level through well-coordinated irrigation and drainage, and replacing outdated irrigation systems with more modern ones.

It is necessary to solve the economic and political problems of the affected countries so that a long-term fight against desertification can be achieved. Often, however, the financial means and also not the technical knowledge to use better systems are not available. However, various measures often fail for social and religious reasons.

Problem solving salinization

There are technical possibilities for the regeneration of salinizing soils such as the removal of the uppermost soil layer, which is heavily enriched with salt, lowering the groundwater level or the leaching of the soil through various drainage measures, but most of these projects are often not feasible on a large scale for reasons of cost and bring many other problems with himself.

The lowering of the water table can lead to various socio-economic problems (see above). If there is underground or well water irrigation, this measure is ruled out. With drainage there is a risk of additional leaching of salts from gypsum stone, which can be contained in the cultivation soil.

Increased efficiency in the use of water

A large volume of it can be saved by recycling water.

The reuse of water that has already been used to increase efficiency has the disadvantage, due to evapotranspiration (evaporation of the water from the plant and soil, leaving behind its salts, which are in turn absorbed by the remaining water), that the salt concentration in the soil and in the draining water increases sharply. One way to reduce evapotranspiration is to use alternative irrigation methods, such as underground drip irrigation.

The desalination of the irrigation water as well as cleaning by sewage treatment plants and recycling are often ruled out for cost reasons. However, it would reduce the runoff of fertilizers into rivers.

Irrigation with low-salt water can prove very beneficial, such as B. a process used in the Indus, in which the water has a value of only 0.03% soluble salts, proved. However, salt accumulation in the soil cannot be completely avoided. With an annual irrigation volume of 300 mm on an uncultivated acreage of one hectare, 900 kg of salts still come together.

For greater resource efficiency, irrigation must be better adapted to seasonal climatic fluctuations and the different plant cultures and soils, just like an adaptation of the plant varieties to the existing soils and the salinity, possibly also by changing the crop rotation to crops that require little water or crops with shorter growing periods , must be done. The flooding of fields must be avoided and irrigation must be carried out at times with low potential evaporation (evenings).

Use of more modern systems

Due to the nature of the system, only individual irrigation applications in the order of magnitude of> 75 mm are possible with surface irrigation, B., watering at a height of 30 mm would be completely sufficient.

By improving irrigation management and using more modern irrigation technologies, such as drip irrigation , agricultural water productivity can be further increased and at the same time soil salinization can be counteracted.

When switching to drip irrigation systems in India, for example, an increase in overall productivity per liter of water used of between a remarkable 50 and 250% was achieved.

Change in yield and water consumption when changing from surface to drip irrigation
Crop Yield Water consumption Overall productivity
Bananas 52% −45% 173%
Cabbage 2% −60% 150%
cotton 25% to 27% −53% to −60% 169% to 255%
grapes 23% −48% 134%
potato 46% 0% 46%
Sugar cane 6% to 33% −30% to −65% 70% to 205%
sweet potato 39% −60% 243%
tomatoes 5% to 50% −27% to −39% 49% to 145%

Switching from surface irrigation methods such as flooding to drip irrigation is usually only possible if it involves irrigation of row crops with a relatively large distance and a high market value . Otherwise, the use of drip irrigation is not economically viable. There are also corresponding limitations for the use of irrigation. As with drip irrigation, this may require a. continuous water supply must be guaranteed. Rotational irrigation systems do not allow the use of irrigation or micro-irrigation methods.

One way to forego using groundwater for irrigation is the desalination of seawater and reuse of service water (pretreated wastewater, which is, however, enriched with nutrients). Since these processes are very complex and use a lot of energy, they are not widely used.

Establishing a water price

The introduction of a price system can bring about efficient water use. In many places, the use of water for agriculture is currently free of charge. When enough free water is available, all other operating options are unfavorable to farmers.

The provision of water is often associated with high costs, which are often covered by public funds. These costs arise, for example, from the construction of reservoirs , canals etc. However, the provision of water also entails costs for the environment and society that cannot be expressed in figures, such as the loss of biodiversity , ongoing destruction of fertile soil and others.

An introduction or increase of water prices would inevitably have lost income in this i. A. The result is an already weak economic sector, but could encourage more efficient use of water and thus counteract the widespread waste of water.

In addition, money can be saved for further dams, which could be invested in the desalination, drainage and sewage treatment plants. For many farmers, a change on their own is out of the question because many lack the necessary funds.

The perspective of “virtual or production water ” could be used to enforce pricing in international trade.

Water harvesting method

The introduction of " water harvesting " systems has proven its worth on slopes . This is a collection and return of the rainwater runoff, but also of drainage water . The water that collects in the rubble heaps of the mountain slopes is partly channeled through large artificially created shafts ( qanates ) and led with a slight gradient over long distances to the fields, sometimes more than 40 km away. Under certain circumstances five times more water can be brought into the ground than rain.

In Iran z. B. more than three million hectares of arable land is artificially irrigated and a large part of the population is supplied with drinking water.

Avoidance of evaporation and seepage losses

Surface irrigation through semi-open channels

The replacement of open and easily contaminated supply and distribution channels with half-shell lines or closed pipes prevents the evaporation or seepage of water. In the case of longer water transport routes, the resulting loss can be up to half of the water introduced.

Relief improvement

Through relief improvement , i.e. H. Leveling and leveling the soil surface in the case of unfavorable micro-relief, the water distribution on the irrigation area is improved when using various surface irrigation methods, and the amount of water required is reduced. With the same water volume, both the yield is increased and the soil erosion due to soil wetting is reduced.

Relief improvements cannot be implemented in all cases. As a rule, they are only possible if the soil is sufficiently deep and the extent of the required soil movements is limited.

See also

literature

  • Achtnich W. (1980): Irrigation farming. Agrotechnical basics of irrigation management. Ulmer, Stuttgart
  • Breckle, S. et al. a. (2003): Ecological optimization of water use in irrigation methods with salty water (in arid areas). Bielefeld Ecological Contributions, Vol. 16
  • Federal Ministry for Economic Cooperation and Development (2001): Water Answers to the Global Crisis: Bonn BMZ
  • German Association for Water Management and Cultivation DVWK (Ed.) (1993): Ecologically Sound Resources Management in Irrigation. DVWK Bulletin No. 19
  • Maydell H. (1985): Agroforestry in the tropics and subtropics. Update u. Orientation d. Research activities in d. Federal Republic of Germany; Report of DSE / ATSAF expert discussion, May 29 - 31, 1984 in Feldafing. DSE report
  • Pearce, F. (2007): When the rivers dry up. Kunstmann, Munich
  • Rehm, S. (1986): Fundamentals of Plant Production in the Tropics and Subtropics. Ulmer, Stuttgart
  • Fritz Scheffer / Paul Schachtschabel: Textbook of soil science
  • Withers, B. / Vipond, S. / Lecher, K. (1978): Irrigation. Parey, Hamburg

Web links

Individual evidence

  1. The water we eat - Irrigated agriculture, a heavy burden -. In: eea.europa.eu. Retrieved August 27, 2015 .
  2. ^ Ernst Klett Verlag - Textbook Online - Haack World Atlas Online - School books, teaching materials and learning materials. In: .klett.de. Retrieved August 27, 2015 .
  3. Irrigated Agriculture - Lexicon of Geosciences. In: Spektrum.de. Retrieved August 27, 2015 .
  4. E. Giese et al. a. (1998): Environmental degradation in the arid regions of Central Asia .
  5. PM Magazin Umwelt & Technik (02/2005): How the water is dug off the rivers ( Memento from November 13, 2010 in the Internet Archive ).
  6. to Pearce, When the rivers dry up.
  7. PM Magazin Umwelt & Technik (02/2005): How the water is dug off the rivers ( Memento from November 13, 2010 in the Internet Archive ).
  8. PM Magazin Umwelt & Technik (02/2005): How the water is dug off the rivers ( Memento from November 13, 2010 in the Internet Archive ).