Irrigation and agriculture

Agriculture: Agriculture the artificial cultivation (growing or rearing) of plants or animals. Agriculture that grows crops is known as arable agriculture, agriculture that involves rearing animals is known as pastoral agriculture.

Agricultural land: This simply refers to land that is suitable for farming. The amount of agricultural land can be increased through irrigation and use of fertilisers. However, the amount of agricultural land may also decrease because of land degradation and desertification.

Aquaculture: Aquaculture is the artificial farming of aquatic plants and animals. Aquaculture may take place in freshwater or seawater.

Primary sector: Agriculture and and aquaculture are both in the primary sector of the economy. The primary sector extracts or harvests resources from the surface of the earth.

Irrigation: This means artificially watering the land. There are three main types of irrigation; gravity flow, sprinklers and drip systems.

Land degradation: Land that is overused or misused can become degraded. This basically means that the quality of land has been reduced and it is less productive. For more information about land degradation go to: Soil and change.

Desertification: Very simply, this is the process of land turning into desert. This can happen because of natural factors like rising temperatures and drought, or human factors like overgrazing and deforestation.

Eutrophication: This is the processing of artificially adding nitrates and phosphates (through fertilsers and sewage) to wetland areas e.g. rivers and lakes. The added nitrates and phosphates causing excessive growth of algaes. The algae growth can reduce the oxygen content of the water as well as reducing the amount of sunlight that it receives. The nitrates and phosphates often come from agro-chemical run-off, but can also come from domestic sewage and industrial waste.

Fertilisers: Fertilisers are substances that artificially supply the soil with nutrients. Fertilisers can increase the productivity of agricultural land, but can also cause eutrophication of nearby wetlands.

Salinisation: This is the increase in the salt content of water. Salinisation can happen because of evaporation or unsustainable water extraction. If the water become to salinated it becomes less fertile.

Saltwater intrusion: When saltwater enters aquifers make the freshwater salty and therefore unfit for human consumption or use in agriculture.

GROWING DEMAND FOR AGRICULTURAL PRODUCTS

DECREASING SUPPLY OF AGRICULTURAL PRODUCTS OR LAND

The world's population is growing. The current population is about 7 billion, but it is expected to peak at nearer to 10 billion. Because fossil fuels are finite, alternative forms of energy are being looked at. One form of renewable energy being used are biofuels. Biofuels are made out of biological matter and therefore are increasing the demand for agricultural products. Economic development. As more of the world's population is removed from poverty, their calorific intake increases. This increase in food consumption, is increasing the demand for agricultural products. Pastoral farming. As the world population increase, the demand for meat also increases. Most farm animals are omnivores or herbivores so need agricultural products like corn to eat.

Urbanisation. As the world develops, urbanisation increases tends to happen increasing the size of urban areas. As urban areas grow they eat into greenfield sites in rural areas, reducing the amount of agricultural land. Land degradation and desertification. Land that is overcultivated or overgrazed can become degraded (less fertile). AS farmers try to react to demand by growing more intensively, more land is being degraded. In extreme circumstances, the land may turn to desert (desertification). Rising sea levels. Some of the earth's most fertile agricultural areas are floodplains and deltas. As world sea levels (eustatic changes) increase much of this fertile land is lost. Conversion to biofuels. Although not strictly reducing the amount of agricultural products (biofuels are agricultural products), this does decrease the supply of agricultural products available for human consumption. Biofuels are often favoured by farmers, because they demand a higher price. Hazards. Natural hazards like tropical storms, volcanoes and tsunamis can reduce the amount of agricultural land available for cultivation. Disease. There is an increasing amount of intensive monoculture (growing of one crop) taking place. Monoculture always runs the risk of been impacted by the outbreak of diseases or pests that attack the particular crop e.g. wheat leaf rust fungus.

World food prices: With growing demand and reducing supply, world food prices are at a high. It is usually the poor that are most impacted by rising food prices, because they spend a greater percentage of their income on food. World Food Prices at Fresh High - BBC article

Biofuels debate: Although biofuels are considered to be a renewable form of energy, they are causing deforestation in countries like Indonesia and Brazil and global increases in food prices. Brazil rejects biofuels criticism - The Guardian

Desertification: China is seeing desertification on its northern border with the Gobi desert. With its growing population and rapid economic development, it is likely to be hit very hard by falling agricultural production. China official warns of 300 year desertification fight - BBC article

Hazards: The recent tsunami in Japan, will have effected Japan's agricultural production. This will not only put pressure on already high food prices, but has led to rationing in Japan. Sendai residents queue for food and fuel - BBC article

The amount of agricultural land can be increased by:

Irrigation: By irrigation areas of land, areas that were previously too arid to support agriculture can be used for agricultural production e.g. a long the banks of the River Nile in Egypt.

Drainage: Areas of wetlands can be drained, or that they can be used to grow agricultural products. The East of England used to be largely covered in fens. The fens have now been drained and it is England's most productive agricultural area.

Land reclamation: With land on the earth running out, more land is being reclaimed. This can be done by reclaiming land through drainage (above) or infilling coastal areas. Although this increases the amount of available land, the land can have a high water table with a high salt content. However, it does mean coastal reclaimed land can be used for urban growth, leaving more greenfield sites for agricultural production.

Deforestation: By removing trees, this can increase the amount of agricultural land. However, areas that have been deforested tend to degrade very quickly. By removing trees you are removing the grounds source of humus and reducing its stability (tree root network). With the trees removed the ground becomes very vulnerable to wind and water erosion.

Greenfield Protection: By protecting areas of greenfield from urban growth, you are not increasing the amount of agricultural land, but you are at least protecting what you already have.

Fertilsers: Land that lacks nutrients can be brought into production by increasing the fertility of soil. This can be done by adding nutrients to the soil. It might also be possible to use previously unsuitable farm land by growing GM crops.

Terracing: Terracing tends to happen on volcanic mountains, because the soil is so fertile. Terracing is simply cutting multiple layers into the mountainside to create small areas of agricultural land.

Irrigation

Irrigation has taken place for nearly 6000 years and is simply the process of adding water to the land. Water to be irrigated can be take from rivers, surfaces stores (natural and artificial) and groundwater stores (aquifers). Below is a summary of three main types of irrigation, as well at the impacts of irrigation and a case study of irrigation in Libya.

TYPES OF IRRIGATION	ADVANTAGES	DISADVANTAGES
GRAVITY FLOW:This type of irrigation is normally done through the use of drainage ditches and canals. It is called gravity flow, because water is transported under gravity. Gravity flow systems normally flood the whole field. Gravity flow is normally used when flooding rice paddies are adding water to cotton fields (both very thirsty crops).	The technology is relatively simple and can be developed anywhere. The technology is inexpensive and just involves a lot of manpower. Effective for areas that need saturating i.e. rice paddies. A lot of excess water will infiltrate, recharging soil moisture and groundwater stores.	Fields can become watterlogged (saturated). It creates temporary and artificial surface stores which increase evaporation. Also water is evaporated from the irrigation channels. The watterlogging of fields and the flow of water can cause the fertile topsoil to be eroded. Areas of land with no crops may be watered, therefore wasting the water. Gravity flow can be hard to stop completely, it can only be redirected to other areas.
SPRINKLERS: This type of system normally operates from a central pivot and sprays water over a field. Water is normally pumped through pipes and hoses to the area that is being irrigated (sprayed).	Sprinklers can be turned on and off when necessary, so they respond directly to demand. Sprinklers can normally be directed only to water areas of vegetation so there is less wastage.	Water spraying through the atmosphere can be evaporated. You need a central source of water that can be turned on or off. If the water pressure is low, the sprinklers will not work. They are expensive to install and may need electricity to pump water.
DRIP SYSTEMS: These are the most precise form of irrigation and add water directly to the stem or trunk of a plant. Water is transported through hoses and pipes and simply drips out of holes in the hose/pipe.	These are the most efficient forms of irrigation. The supply of water can be turned on and off to react to demand. Only the crops that need water receive water. There is less water lost through evaporation.	They can be very expensive to install, especially over large areas. They are not suitable for irrigated some crops, like rice. Again they need a supply of water that can be turned on and off and may need an electricity supply to pump water

POSITIVE IMPACTS OF IRRIGATION

NEGATIVE IMPACTS OF IRRIGATION

Irrigation increases the amount of agricultural land, by making arid areas more productive. Irrigation may increase the number of harvests and the size of the yields. Irrigation can reduce malnutrition and reduce countries dependency on food imports. It can also provide a valuable source of foreign currency as agricultural exports can be sold. By increasing the supply of agricultural products, the price of food can be reduced on the global market. Irrigation can actually increase the water table of the area, because of infiltration. However, it must be remembered that extra water can not be created, so by raising the water table in one area, you must be reducing the amount of water in another area. Irrigation can increase precipitation. With the increased availability of water, evapotranspiration rates increase. This increases the humidity of the atmosphere and increases the chance of precipitation

Irrigation can reduce the earth's albedo (the reflectivity). This is because sandy surfaces have a higher albedo than dark green surfaces. If you reduce the earth's albedo then more incoming radiation is absorbed by the surface of the earth, furthering global warming. Obviously this change in albedo has to be offset by the increased amount of photosynthesis and also the increase in shaded areas. If groundwater is used unsustainably, irrigation can cause the water table to fall. In Texas, US, the water table has fallen by up to 50 metres. Irrigation has been blamed for creating tornadoes in Texas. Tornadoes are circulating columns of air in contact with the ground and cumulonimbus cloud. To develop they need a high moisture content in the atmosphere Irrigation often leads to an increase in salinisation. This can because of increased evaporation from surface stores (reservoirs) and irrigation channels or water being drawn to the surface and evaporating. Because irrigation increases the amount of agricultural land, it is also blamed for the increase in the amount of fertilisers used. This in turn can lead to eutrophication of wetlands.

Libya - Irrigation case study

Libya is located in north Africa. It has land borders with Egypt, Tunisia, Algeria, Sudan, Chad and Niger and a sea border with the Mediterranean Sea. Its capital city is Tripoli, located on the north west coast. Libya's settlements and population are concentrated along the northern Mediterranean coast. This is because much of Libya is covered by the Sahara Desert and to arid to support large population densities. To overcome the arid nature of the country, Libya has undertaken the largest irrigation project in the world (The Great Manmade River). While searching for oil in southern Libya in 1953, huge underground aquifers of freshwater were discovered. The water was held in sandstone aquifers. The project to use this water to irrigate the desert was conceived in the 1960's and work began in 1984. The aquifers being mined were filled during the last ice age and even though they are not being recharged, it is estimated that they could last 1,000 years. 1,300 wells over 500 metres deep, extract the groundwater. Over 6,500,000 m3 of water are extracted daily. The extracted water is transported to the coast via 4,000km of underground pipes (4 metres in diameter). The pipes are underground to reduce evaporation in the desert. The first water reached the capital Tripoli in 1996. The total cost of the project is estimated at about $25 billion. As well as providing fresh drinking water to the coastal cities of Libya, the water is also going to be used to irrigate the desert to increase agricultural production and provide water to industry. Libya is a net importer of foods, so by increasing the amount of irrigated land, this should reduce their dependence on other countries. Libya's thirst for fossil water - BBC article

The Aral Sea - Irrigation and Salinisation Case Study

Nearly all water, including precipitation, contains small amounts of salt. If the concentration of water increases because of evaporation, then the salt content of water increases. This process is called salanisation.

The Aral sea is an inland lake on the border of Kazakhstan and Uzbekistan. The Aral Sea used to be the fourth largest inland lake in the world, with a surface area of 68,000km2. The sea is fed by two rivers, the Amu Darya and the Syr Darya. Since the 1960's the sea has been shrinking because the two rivers have been diverted to irrigate the desert. The USSR decided to irrigate the desert because they wanted to increase their production of melons, rice, wheat and cotton. Rice and cotton both need extremely high amounts of water to grow. Because the irrigation canals were built quickly and poorly maintained, it has been estimated that up to 75% of water gets lost through evaporation or leakage. Even today, only 12% of Uzbekistan's irrigation canals are lined to stop leakage. Between 1960 and 1988 the surface of the Aral Sea shrank by nearly 60% and its volume by up to 80%. By 1998 its surface area was only 26, 687km2 making it the eighth largest lake. At the same time the salinity of the lake changed from 10 g/L (grams per litre) to about 45 g/L. In 2004 the Aral Sea was only 17,160km2 or 25% of its original size. By 2007 it was only 10% of its original size and its salinity had increased to 100 /L (normal seawater is only about 35 g/L). The rapidly increasing salinity has largely killed the sea's ecosystem. Huge salt plains have appeared as more water is evaporated. The salt on the plains is often whipped up in storms, killing crops and also cooling winters and warming summers. The fishing industry has collapsed and residents health worsened due to inhalation of salt, a lack of clean water and food shortages.

Aral Sea Recovery? - National Geographic article

Dam Project Aims to Save Aral Sea - BBC article

Dianchi Lake (Kunming, China) - Eutrophication Case Study

Eutrophication: This is the processing of artificially adding nitrates and phosphates (through fertilsers and sewage) to wetland areas e.g. rivers and lakes. The added nitrates and phosphates cause excessive growth of algaes. The algae growth can reduce the oxygen content of the water as well as reducing the amount of sunlight that it receives. The nitrates and phosphates often come from agro-chemical run-off, but can also come from domestic sewage and industrial waste.

Lake Dianchi is suffering from extreme eutrophication or is hyper-eutrophied. The lake has vast areas that are covered by dense algal blooms like green dye and fish-breeding has been almost totally abandoned because there is no oxygen for them to breath. Almost all native water plants and many fish species have been killed. Snails die from lack of oxygen in the bottom water. In addition due to the poor water quality it is very difficult to supply water for domestic use that meets legal standards. Dianchi Lake has suffered from eutrophication because of domestic sewage (urbanisation and population growth), industrial waste and reclamation of wetlands around the lake to farm, leading to agro-chemical run-off. Kunming has a population of over 1.2 million residents. Its first sewage treatment works opened in 1993, but only 10% of domestic waste gets treated.

Yunnan unveils plans to clean Dianchi lake

China launched battle against lake pollution

China invests more in pollution control at Dianchi Lake

For a case study about eutrophication in Lake Biwa, Japan go to: Water and change.

How to manage eutrophication:

• Reduce the use of fertilisers and detergents
• Don't use fertilisers when rain is forecast and there is likely to be surface run-off
• Don't apply fertliserrs on saturated ground when there is likely to be more surface run-off
• Revert to organic farming
• Regulate agricultural, domestic and industrial emissions
• Clean-up and restore polluted wetlands
• Try and apply fertlisers using drip techniques rather than sprinklers or aerial spraying
• If aerial spraying don't spray while conditions are windy
• Employ crop-rotation and allowing fallow periods to let ground recover naturally.

Agro-chemical run-off: Agro-chemicals are any chemicals used by farmers. Most commonly this means fertilisers and pesticides. As we already know fertliser run-ff can cause eutrophication. However, run-off pesticides or nay chemical can pollute groundwater and surface water, changing ecosystems, killing animals and polluting drinking water.

Hinkley - Groundwater Pollution Case Study

Although not caused by agriculture, the groundwater contamination is an interesting case study, because it was made famous in the film Erin Brockovich. The town of Hinkley, in the Mojave Desert of California in the US. Its groundwater has been contaminated with hexavalent chromium. The cause of the contamination was blamed on Pacific Gas and Electric. The film Erin Brockovich is based on Erin Brockovich campaign to get compensation for the contamination.

Pacific Gas and Electric have a compressor station in Hinkley. They need to compress gas every 350km as they transport gas through their pipe network. Hexvalent chromium was used to stop compressing machinery from rusting. While not in use the hexavalent chromium was stored in unlined ponds, allowing it to infiltrate into the local groundwater supply. Pacific Gas and Electric knew of the pollution, but informed local residents that was no concern because chromium was actually put in multivitamins. However, hexavalent chromium can actually cause problems with the lining of the nose and throat, irritation of the lungs, damage to the kidneys and liver, cause stomach upsets and even accelerate cancer. After Pacific Gas and Electric lost a number of individual lawsuits, in 1996 they agreed to pay damages of $333million to more than 600 residents and clean-up the contamination.

In 2010 tests have shown that some contamination may have reached lower aquifers.

Toxic Waste Clean-up costs taxpayers 12.7 million - Guardian article

Erin Brockovich town in second battle over polution - The Guardian

Acid Rain

Although acids rain does not appear on the specification in Freshwater, it is still a manmade environmental problem that can pollute surface and groundwater. Acid rain was first discovered in Manchester, UK in 1852, but it was not properly studied until the 1960's. Acid rain can take two forms, wet deposition and dry deposition. Wet deposition is when pollutants mix with rain water and fall to the ground as acidic precipitation. Dry deposition is when pollutants and particulates fall to the ground without mixing with rain water.

Sulphur dioxide and nitrous oxides are the two main chemicals that react with water to make acid rain. The chemicals are commonly released from power stations, factories and transport (cars, planes, etc.). Acid rain can damage buildings, vegetation and surface water. Any change in the pH of water can change ecosystems and kill plants and animals. Once surface water is polluted, water can then infiltrate and pollute groundwater.

Third of China hit by acid rain - BBC article

UK sites in acid rain recovery - BBC article

Other key ideas:

Contour ploughing: This is a simple technique of ploughing with the contours, instead of against the contours. This reduces surface run-off and therefore the need to irrigate as much.

Terraces: Terraces are common in mountainous areas. Like contour ploughing they reduce surface run-off and therefore the need to irrigate as much. The problems with both contour ploughing and terraces you can create temporary surface stores, therefore losing water to evaporation.

Crop rotation: Crop rotation simply means varying the crops that you grow in a field. By doing this you vary the nutrients being taken from the soil and returned to the soil. By doing this you reduce the amount of fertilisers that need to be used and therefore hopefully reduce the chances of eutrophication.

Organic farming: Organic farming is farming that minimises the use of fertilisers or pesticides. By reducing the use of fertilisers and pesticides you are going to reduce eutrophication and groundwater contamination.

GM (Genetically Modified) crops: To some GM crops are a saviour, to others they are a biological disaster. Agree or disagree with the use of GM crops they might reduce the amount of irrigation needed and reduce the amount of fertiliser used. This can be done by making crops more drought resistant, more disease resistant and simply grow quicker and bigger.

Fallow: Fallow means not growing anything and allowing the soil to rest. If you allow the soil to rest it gives the soil chance to regain its fertility and again hopefully reduce the needs for fertilisers and therefore eutrophication.