To provide irrigation benefits for most plants, what percent of the root zone should be wetted?

• A. 85 percent
• B. 75 percent
• C. 50 percent
• D. 25 percent

Answer: (C)

Wetting about half of the root zone during an irrigation event provides the right balance between supplying water and keeping soil air spaces available. When about 50% of the root zone is wetted, plants get enough moisture to meet their needs, while enough of the soil remains unsaturated to allow roots to respire and to avoid prolonged saturation that can lead to root decay and wasted water. If you wet a larger portion of the root zone, the soil stays too wet, wasting water and reducing oxygen for roots; if you wet too little, the plant may not receive enough water between irrigation events. So, around 50 percent is the practical target for most plants.