Source: Pivot Irrigation System

Agricultural Uses
 
Devon Disrude disruddj@uwec.edu
 
Part of Water is Life, a class website on water privatization and commodification, produced by students of Geography 378 (International Environmental Problems & Policy) at the University of Wisconsin-Eau Claire, USA, Spring 2004.

     

    The use of water for agriculture has changed the production of crops dramatically in the 20th century. Agricultural use of water accounts for nearly 70% of the water used throughout the world, and the majority of this water is used for irrigation. During the 1970s, the construction of irrigation systems dramatically increased. Its rate of growth began to decrease in both developed and developing countries in the 1980s. An increase in irrigation development guarantees an increase in crop production in many countries. Irrigation allows the land that does not recieve enough precipitation annually to become land that can be used for productive agriculture.

    On the negative side, irrigation of land causes salinization of the land that is being irrigated, mostly in arid and semi-arid regions. Irrigation of cropland can increase the possibility fertilizers and pesticides will infiltrate into the groundwater or runoff into nearby streams. Along with the irrigation of crops, the farmers that have livestock must provide clean water for the livestock to drink. With a growing world population, expected to increase by 2 billion people by the year 2030, agriculture needs to find a way to use less water or to use the water more efficiently.

    Irrigation of Cropland

    Source: Ditch Irrigation

     

    There are several different systems that are used for irrigation purposes, including ditch irrigation, terracing, overhead irrigation, center pivot irrigation, lateral move irrigation, and drip or trickle irrigation. Irrigation of cropland has greatly increased production of food, but has also had some drawbacks due to the amount of water that is being drawn from aquifers. Some of the problems with irrigation are competition for surface water rights, depletion of underground aquifers, ground subsidence, and buildup of toxic salts on soil surfaces in regions of high evaporation rates, called salinization. These problems can be increased or be more detrimental during periods of drought. Irrigation has been increasing between 1960 and 1995, as the graph below depicts.

    Source: Increase in water for irrigation

     

    There are also many farms that are being heavily irrigated due to their location within an arid or semi-arid region of the world.

    Source: Annual Average Precipitation

    Source: Arable Land in World

    Groundwater Contamination

    Groundwater contamination occurs when the pesticides, livestock waste and fertilizers infiltrate through the soil and eventually reach the groundwater, which is called leaching. The problem with feritlizers is that they contain nitrates, which are very soluble in water and are very hard to remove, or cannot be removed from the water once they are in it. Leaching is more of a problem in regions that contain sandy soils. The sandy soils are very permeable, allowing the water and the nitrates, which are dissolved within the water to pass through the soil relatively fast before being absorbed by the plants. Infiltration can be a large problem for contaminating groundwater especially in regions with sandy soils.

    Conclusion

    Irrigation of cropland has become widely used practice throughout the world and has greatly increased the productivity of farmland. It has made it possible to farm in regions that would not be farmable without irrigation. But, with nearly 70% of the total water use throughout the world coming from irrigation for cropland, the need for newer and more efficient practices is becoming more important. Another problem with irrigated cropland is the possibility of groundwater contamination and the stricter restrictions that are going to have to be implemented on the amount of fertilizers and pesticides used to reduce the risk of the contamination.

    Sources

    For more information:

    Freshwater: http://freshwater.unep.net/index.cfm?issue=water_irrig

    Science Daily : http://www.sciencedaily.com/encyclopedia/irrigation#Ditch%20(Furrow)%20irrigation

    Food and Agriculture of the United Nations: http://www.fao.org/english/newsroom/focus/2003/water.htm

    Nitrate in the Groundwater: http://www.valleywater.org/Water/Water_Quality/Protecting_your_water/Nitrate_in_groundwater.shtm#1

    Water for Agriculture: http://www.iwmi.cgiar.org/agriculture/

    Clean Water Action Plan: http://cleanwater.gov/action/c1a.html

    Agriculture: http://www3.iptv.org/exploremore/water/uses/use_agriculture.cfm

    Water for Agriculture: http://webworld.unesco.org/water/ihp/publications/waterway/webpc/pag19.html