Soil–plant water relations: which statements about hygroscopic water, wilting point, field capacity deficit, and spatial variability are correct?
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AUnused pellicular water is termed hygroscopic water
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BPermanent wilting of plants occurs at the wilting point moisture content
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CWater needed to raise soil from current moisture to field capacity is soil moisture deficiency
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DMoisture deficiency varies spatially within a field or catchment
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EAll the above
Answer
Correct Answer: All the above
Explanation
Introduction / Context:Irrigation scheduling, drought assessment, and crop-water modelling require accurate terminology for soil water states. This question validates key definitions used by agronomists and hydrologists.
Given Data / Assumptions:
- Unsaturated soil with pellicular (adsorbed) water films on particles.
- Crop water stress relates to soil water availability.
Concept / Approach:Hygroscopic water: tightly adsorbed (pellicular) water not available to plants.Wilting point: moisture content at which plants cannot extract sufficient water and wilt permanently.Soil moisture deficiency: water depth required to bring soil back to field capacity from current state.Spatial variability: texture, structure, rooting depth, and microtopography cause differing deficits across a field.
Step-by-Step Solution:
1) Identify each term from soil physics.2) Map each option to the definitions above.3) Confirm all are correct statements.4) Choose the inclusive answer.Verification / Alternative check:Standard soil science texts and FAO irrigation guidelines use the same definitions, corroborating all statements.
Why Other Options Are Wrong:Choosing any single statement would ignore that all listed statements are valid, so the most comprehensive choice is correct.
Common Pitfalls:
- Confusing field capacity with saturation.
- Assuming uniform moisture deficit across heterogeneous soils.
- Believing hygroscopic water contributes meaningfully to transpiration.
Final Answer:All the above