This question tests whether we know the layout of the infiltration profile that forms when water moves into soil during irrigation. Let us check each option by picturing where the water enters and how far it has travelled.
- Transmission Zone - Wetting Zone - Transition Zone - Saturation Zone: This puts the transmission zone at the top and the saturation zone at the bottom, which is backwards, water enters from the top, so the saturation zone has to be uppermost.
- Saturation Zone - Transition Zone - Transmission Zone - Wetting Zone: This matches the real order. The soil is saturated right at the surface where the water enters, then water content eases off through the transition zone, stays fairly steady through the long transmission zone, and finally drops sharply at the wetting zone and wetting front at the bottom.
- Transmission Zone - Transition Zone - Saturation Zone - Wetting Zone: Here the saturation zone is placed in the middle of the profile, but it always sits at the top, right under the ponded or applied water.
- Wetting Zone - Transmission Zone - Transition Zone - Saturation Zone: This is the complete reverse of the true order, with the wetting front placed at the surface instead of at the bottom.
The correct listing, from the surface downward, is Saturation Zone, Transition Zone, Transmission Zone, Wetting Zone.
Let's summarize:
- The saturation zone always sits just below the surface where infiltration starts.
- The transmission zone is the longest lasting zone since it just carries water down as infiltration continues.
- The wetting zone and its wetting front mark the deepest, driest edge of the wetted profile.
So option 2 gives the correct top to bottom sequence.