Soil–water terminology in irrigation hydrology: choose the correct statements about pellicular water, field capacity, and available moisture.

Introduction / Context:
In irrigation and soil physics, precise terminology for water held in soils is essential for scheduling irrigation and estimating plant water availability. Terms such as pellicular water, field capacity, and available moisture describe how water is retained and used by crops.

Given Data / Assumptions:

• Soil contains gravitational, capillary (pellicular), and hygroscopic water.
• Field capacity is the soil water content after free drainage stops (capillary retention dominant).
• Available moisture is the fraction plants can withdraw between field capacity and permanent wilting point.

Concept / Approach:
Pellicular water, often synonymous with capillary water films, adheres to soil particles due to molecular forces. Its mobility is influenced by surface tension and capillary potential. After gravitational water drains, the remaining water (largely pellicular) defines field capacity. Plants extract a portion of this until the wilting point is reached.

Step-by-Step Solution:
(a) Definition aligns with soil physics: thin films on grain surfaces ⇒ correct.(b) Surface tension/capillarity govern movement and retention ⇒ correct.(c) Field capacity correlates to retained capillary (pellicular) water after gravity drainage ⇒ correct in practical agronomic usage.(d) Available moisture refers to extractable water between field capacity and wilting point ⇒ correct.

Verification / Alternative check:
Soil water characteristic curves and capillary theory support these relationships; irrigation texts use these operational definitions for scheduling.

Why Other Options Are Wrong:
All listed statements are consistent within standard agronomic conventions; hence the inclusive choice is appropriate.

Common Pitfalls:
Equating field capacity with a fixed moisture percentage irrespective of soil texture; ignoring that “pellicular” and “capillary” are often used interchangeably in this context.

Final Answer:
All the above.