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Irrigation (in agriculture) is the replacement or supplementation of rainfall with water from another source in order to grow crops. In contrast, agriculture that relies only on direct rainfall is sometimes referred to as dryland farming.
The water source for irrigation may be a nearby or distant body of liquid or frozen water such as a river, spring, lake, aquifer, well, or snowpack . Depending on the distance of the source and the seasonality of rainfall, the water may be channelled directly to the agricultural fields or stored in reservoirs or cistern s for later use. In addition, the "harvesting" of local rain that falls on the roofs of buildings or on nearby unfarmed hills and its use to supplement the rain that falls directly on farmed fields also involves irrigation.
Various types of irrigation techniques differ in how the water obtained from the source is distributed within the field. In general, the goal is to supply the entire field uniformly with water, so that each plant has the amount of water it needs, neither too much nor too little.
The plants are grown in somewhat raised beds or listed rows, and the water is distributed throughout the field via canals, unlined ditches, or furrows, between the rows or beds. Depending on economic and physical factors such as the size of the field, the types of technology available, and the cost of manpower, the ditches can be dug with hand tools, turned with a plow pulled by an animal or tractor, or precisely fashioned using laser-guided instruments. Water can be transported to the furrows via rigid gated plasticThe term plastics covers a range of synthetic or semi-synthetic organic condensation or polymerization products that can be molded or extruded into objects or films or fibers. Their name is derived from the fact that in their semi-liquid state they are ma or aluminum pipeThe word pipe can refer to: a tubular man-made channel, generally round in cross section, for transporting or guiding a fluid substance. See plumbing and pipeline transport an exhaust pipe, for channelling waste fumes from an engine or stove certain music, layflat plastic with holes punched at each furrow, concreteIn general, a concept is considered concrete if it is not abstract: it must be both particular and an individual, and hence occupy both space and time. To say that a physical object is concrete is to say, approximately, that it is a particular individual or plastic lined ditches, or unlined ditches. Where ditches are used, siphon tubes are generally used to move water from the main ditch to the furrow. When pipes are used, water flow can be controlled by turning it on or off at the local source or by using automatic or manually controlled gates to shunt it from one set of ditches to another. Unless the field is small or very level, parts of it may suffer from water-logging while other parts may be too dry. Depending on heatCommonly, heat is estrus, a period of increased sexual drive in female mammals. For the National Basketball Association team, see Miami Heat. For the movie, see Heat (movie). Heat (abbreviated Q also called heat change is the transfer of thermal energy be, windFor the 1928 film, see The Wind. Wind in the most general sense, is the movement of air. It occurs at all scales, from local breezes generated by heating of land surfaces and lasting tens of minutes to global winds resulting from solar heating of the plan, and soilSoil is the layer of minerals and organic matter, in thickness from centimetres to a metre or more, on the land surface. Its main components are mineral matter, organic matter, moisture, and air. Soils differ in the ratio of these components. Modern soil permeabilityPermeability has several meanings: # In electromagnetism, permeability is the degree of magnetisation of a material in response to a magnetic field. In geology, permeability is a measure of the ability of a material to transmit fluids through it., much water may be lost before it can benefit the plants. Automatic valves, also known as surge valves , can increase the efficiency of furrow irrigation because they alternately wet the furrows and allow the soil infiltration rate to slow prior to using the furrow for actual irrigation.
Once common in the U.S., many ditch irrigation systems have been replaced because of high labor costs and increasing demands on water resources. Furrow irrigation also has a tendency to raise the water table in some areas and cause soil salination, requiring drainage. These types of systems are still common in other parts of the world.