What is Irrigation?

Irrigation is artificial watering of land to sustain plant growth. Irrigation is where rainfall does not provide enough ground moisture. In dry areas, irrigation must be maintained from the time a crop is planted. In areas of irregular rainfall, irrigation is used during dry spells to ensure harvests and to increase crop yields. Irrigation often produces over twice the yield of nonirrigated fields. Irrigation, however, can waterlog soil, or increase a soil's salinity (salt level) to the point where crops are damaged or destroyed. This problem is now jeopardizing about one-third of the world's irrigated land. In many cases irrigation is correlated with drainage to avoid soil salinity, leaching, and waterlogging. Irrigation may also involve preliminary clearing, smoothing, and grading of land.

Methods include check-flooding, in which water flows over strips or checks of land between levees, or ridges or the furrow method, in which water runs between crop or tree rows, penetrating laterally to the roots. Also, water has been diverted from waterways to fields by ditching.

Problems With irrigation

The chief problem caused by continuous irrigation is that of salt accumulating in the upper layers of the soil and stunting or preventing plant growth and rendering the soil unfit for crop production. Nearly all irrigation water, whatever its source, contains some salt, which percolates down to the water table and makes it increasingly brackish. Where drainage is bad and the water table approaches root level, the concentrated salt makes plant growth impossible. Good drainage systems, therefore, which keep the water table well below the root level and allow water to flush salts through the topsoil, are now understood to be a crucial aspect of a successful irrigation system.

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