The Leaching Requirement During Irrigation

The Leaching Requirement During Irrigation

The leaching of soluble salts from the plant rooting zone is a pivotal concern when irrigating cropland. Irrigation water is used to maintain crop productivity, so drought conditions need not occur to induce irrigation measures. Irrigation simply provides supplemental precipitation that may not be achieved through natural processes, i.e. rainfall.

Basically, leaching is described as passing additional water through a medium to remove unwanted materials. This is usually achieved through two types of ponding. Additional water is pumped onto the soil surface and allowed to accumulate until surface ponding occurs. There are two mechanisms that perform this duty, continuous or intermittent ponding. Intermittent ponding, applying the excess water in intervals, is more favorable for milder climates where evaporation rates are low (NATO, 1994). Continuous ponding, applying all the water at once, may not be appropriate given geographical, climatic, or user-related constraints.

Salts accumulate in the soil profile over time, therefore, leaching may serve as a form of soil “reclamation”. Normally, leaching curves are developed to determine the amount of water that may be actually required to reduce the initial soil salinity by a certain percentage (NATO, 1994). Although rainfall and the present soil already have saline concentrations, additional salts are added to the soil via irrigation water. Moisture is then extracted by the processes of evaporation and transpiration, and the salts begin to precipitate. Now, the salt balance of the soil profile changes: excessive salt concentrations are introduced without having adequate outlets. If located it the plant’s root zone, ...

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