Water logging is a condition in soil where the pore spaces in the root zone become saturated with water. This happens when water is supplied more than the soil's capacity to drain it away. When the soil is waterlogged, the roots of crops do not get enough air (oxygen) because the air spaces are filled with water. This lack of oxygen is harmful to most crop roots and can lead to poor growth, reduced yield, and eventually, crop death.

Understanding Water Table and Water Logging

The water table is the upper level of the underground surface in which the ground is saturated with water. Its depth below the ground surface can vary depending on rainfall, irrigation, and drainage conditions.

Water logging is directly related to the depth of the water table. When the water table is close to the surface, specifically reaching or rising into the root zone of the plants, it creates waterlogged conditions.

• A deep water table (several meters below the ground level, like 3.0 m, 4.0 m, or 4.5 m) generally indicates good drainage and is unlikely to cause water logging in the upper soil layers where most crop roots are located.
• A high water table, meaning it is close to the ground surface, poses a risk of water logging.
• The most critical situation for water logging occurs when the water table rises to the level of the root zone. This is because it directly impacts the environment where plant roots need to respire (take in oxygen).

Why Water Logging Occurs Up to the Root Zone

Plant roots require oxygen for respiration, which is essential for energy production and nutrient uptake. In a healthy soil, there is a balance between water and air in the pore spaces. When the water table rises and saturates the soil in the root zone, it pushes the air out, creating anaerobic (oxygen-deficient) conditions. Most crops cannot tolerate such conditions for extended periods.

Therefore, water logging specifically happens when the water table is high enough to fill the pore spaces in the soil layer where plant roots grow, which is the root zone of the crops.

Considering the options provided:

• Options 2, 3, and 4 describe a water table that is several meters below the ground level (G.L.), which is generally considered deep and not a cause of water logging in the root zone for most common crops.
• Option 1 states the water table is "up to root zone of crops". This directly corresponds to the condition where the soil in the root zone is saturated with water, leading to water logging.

Revision Table: Water Logging

Additional Information: Managing Water Logging

To prevent or manage water logging, drainage is crucial. Drainage systems help lower the water table and remove excess water from the soil. There are two main types of drainage:

• Surface Drainage: Removing excess water from the soil surface through channels or land shaping. This helps prevent water accumulation on top of the soil.
• Subsurface Drainage: Removing excess water from below the soil surface, typically using buried pipes (tile drains) or drainage wells. This helps lower the water table.

Other measures include managing irrigation to avoid applying more water than needed and selecting crop varieties that are more tolerant to wet conditions if drainage is difficult.