Text B Applying Irrigation Water to Crops

Proper application of irrigation water requires considerable skill. A farmer must know when to irrigate different crops and how much water to use. In general, plants need irrigation only after they have used up most of the moisture in the soil. But a farmer also must consider other factors before irrigating. These include the amount of water available for irrigation, the type of crop, the distance of the water table from the surface, and the ability of the soil to hold water.

There are four general methods of applying irrigation water: (1) surface irrigation, (2) sprinkler irrigation, (3) trickle irrigation, and (4) subirrigation.

Surface irrigation is considered to be the most common method of irrigation. In surface irrigation, the farmer runs water over the surface of the field. There are two chief types of surface irrigation, flood irrigation and furrow irrigation.

Flood irrigation covers the entire surface of a field with water, which soaks into the soil. Small soil walls called dikes or levees hold the water on the field. On many farms, the dikes divide the field into sections. The farmer floods each section individually.

Flood irrigation works best on level or gently rolling terrain where water is plentiful. The soil should be deep and able to hold a large amount of water. This method is generally used on crops of alfalfa and rice, wheat, and other grains. Rice grown in paddies (fields enclosed by dikes) is flooded continuously. Other crops are flooded for only a few hours at a time.

Furrow irrigation. Most crops that are planted in rows, such as corn, cotton, and potatoes, are irrigated by water from narrow ditches called furrows. In this method, rows of furrows are dug across a field. The farmer plants seeds in the ridges between the furrows. As water enters the furrows, it seeps into the ridges. Furrow irrigation is used on many soils and terrains.

Sprinkler irrigation provides water through pipes that lie on or are mounted above the ground. This method became popular with the development of inexpensive plastic and aluminum pipe in the 1940s.In sprinkler irrigation, a pump forces water through a pipe to nozzles called sprinkler heads. The sprinkler heads distribute water to the crops in a spray or mist, in most cases, the farmer can move the pipe to irrigate the entire field. Self-propelled sprinkling systems have an engine and wheels built into the sprinkler unit. These systems move across a farm under their own power.

Sprinkler irrigation can be used on most crops and soils and on level or rolling terrain. It provides an efficient way to irrigate farms with a small water supply. Sprinkling systems may require large amounts of energy, and so their use is limited to areas with ample energy supplies. But some systems use low-pressure sprinkler heads, which require much less energy.

Trickle irrigation, also called drip irrigation, furnishes water through plastic tubes that lie on or under the ground. The tubes have small openings called emitters at points corresponding to the location of the plants. As water flows through the tubes, it trickles out of the emitters into the soil. Only the soil directly around the plants receives moisture. As a result, trickle irrigation wastes little water.

Trickle irrigation can be used on all crops, soils, and terrains. Its efficient use of water makes it ideal for areas with small water supplies. But the high cost of installing and maintaining trickle irrigation makes it impractical for most farming. The method generally is used only for high-value crops, such as fruits and vegetables.

Subirrigation applies water from beneath the roots of plants. The water comes from ditches or underground pipes, and the surface of the ground remains dry. Subirrigation requires a watertight layer of soil or rock below the plant roots. Water collects above this layer and moistens the roots.

 

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