Water and soil

caurtesy :Water and soil

Specific terms

To understand how much water is held in soil, the following terms are important:

• field capacity—the amount of water held in the soil after it has been fully wetted and free drainage has stopped. Water applied above this limit will make the soil saturated but water will drain quickly or be lost as runoff.
• permanent wilting point—the soil moisture condition at which the plant could not obtain water and has wilted and died. The crop cannot be revived by an irrigation or rainfall event.
• plant available water capacity (PAWC)—the amount of water between field capacity and permanent wilting point that is available to a plant. This requires careful management and depends on soil texture, structure and organic matter in the soil.
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• Waterlogging

  When the soil is at or near field capacity, micropores in the soil are full of water and the macropores allow for the movement of oxygen.

  When a soil is above field capacity, the macropores fill with water and the soil is depleted of oxygen. When this happens, plant roots cannot get oxygen from the soil and microbial activity slows. Over a prolonged period, plants eventually die.

  Also, without oxygen in the soil, nitrogen breaks down and is lost as gas in a process called denitrification. This can cause a decline in soil fertility.

• #water and soil.
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