Soil water forms in irrigation science: Which of the following statements is correct regarding water available to plants and forms of soil water?

Introduction / Context:
Plant-available water is governed by how moisture is stored in soils. Understanding gravity, hygroscopic, and capillary water helps in irrigation scheduling and field capacity concepts.

Given Data / Assumptions:

• We compare three forms of soil water and their relevance to plant uptake.
• Standard agronomy definitions are used.

Concept / Approach:
Gravity water drains rapidly through macropores after rainfall/irrigation and is not retained for uptake (it is not inherently “harmful,” it is simply transient). Hygroscopic water is held as thin films by adsorption with high suction and is generally unavailable to plants. Capillary water is held by surface tension in meso/micropores and constitutes the main fraction available to roots between field capacity and wilting point.

Step-by-Step Solution:
Identify which form plants actually use: capillary water.Recognize that hygroscopic is too tightly bound; gravity water usually drains.Select the statement that correctly reflects plant availability: option (c).

Verification / Alternative check:
Soil–water characteristic curves consistently show available water between field capacity and permanent wilting point—predominantly capillary-held moisture.

Why Other Options Are Wrong:

• (a) “Harmful” is inaccurate; gravity water mainly percolates beyond root zone.
• (b) Hygroscopic water is not generally plant-available.
• (d) All of the above is false due to (a) and (b).

Common Pitfalls:
Equating temporary waterlogging with gravity water being intrinsically harmful; conflating adsorption (hygroscopic) with capillarity.

Final Answer:
Capillary moisture held in soil pores by surface tension is utilized by plants