Factors Affecting Soil Moisture Characteristic Curve
- Soil Texture
- Clayey soils retain more water at any suction level compared to sandy soils.
- Reasons:
- Higher specific surface area of clay.
- Negatively charged clay particles attract water.
- More micro-pores hold water tightly.
- Sandy soils have macro-pores, leading to lower suction & moisture retention.
- At high suction, clay holds water too tightly for plant uptake.
- Soil Structure
- Low suction range (0 to -1 bar): Water retention depends on structure (pore arrangement).
- Compacted soil:
- Lower saturation water content (reduced total pores).
- Higher water retention at high suction (more small pores hold water tightly).
- Aggregated soil:
- More macro-pores → better water retention at low suction.
- Less water retention at high suction (fewer small pores).
- Swelling & Shrinkage of Clay
- Swelling clays (e.g., Na⁺, Ca²⁺-rich) retain more water than non-swelling types (e.g., K⁺, H⁺).
- Cation order for swelling: Li⁺ > Na⁺ > Ca²⁺ > Ba²⁺ > H⁺ > K⁺.
- Exact impact on moisture curves not fully understood.
- Entrapped Air Bubbles
- Air trapped in pores reduces water storage capacity.
- Affects drainage and saturation levels.
- Sudden Drying/Wetting
- Rapid changes alter soil structure, affecting pore distribution & water retention.
- Can lead to cracking (in clay) or crusting (in silt/sand).
- Prolonged Saturation
- Long-term waterlogging degrades soil structure, reducing pore efficiency.
- Can increase anaerobic conditions, altering moisture retention properties.