What percentage of the root zone should be wetted to provide the benefits of irrigation?

• A. 75 %
• B. 25%
• C. 50%
• D. 85%

Answer: (C)

Keeping root-zone moisture around half of its available water is the practical target. The root zone has a certain amount of water plants can use, between the wilting point and field capacity. If you wait until it’s almost dry (very little available water left), plants stress; if you water too often or too much, you waste water and can create saturated, poorly aerated soil. By aiming to keep about 50% of the available water in the root zone, you provide enough moisture for plant uptake while leaving space for air and preventing leaching. In practice, you irrigate when soil moisture has fallen to roughly halfway between wilting point and field capacity, replenishing back toward full saturation.