The correct option for the question regarding which properties of soil determine its water-holding capacity is B. I and IV only (Texture and Structure). Detailed Explanation 1. Understanding Water-Holding Capacity: Water-holding capacity refers to the ability of soil to retain water for use by plants. This is crucial for agricultural productivity, as it affects how much water is available to crops between rainfall or irrigation events. 2. Key Properties of Soil: - Texture (I): Soil texture is determined by the relative proportions of sand, silt, and clay particles in the soil. - Why it Matters: - Clay particles are very small and can hold water tightly, while sand particles are larger and do not hold water well. - Soils with a higher clay content generally have a greater water-holding capacity because they can retain more moisture due to their small particle size and high surface area. - Conversely, sandy soils drain quickly and have lower water-holding capacity.

• Structure (IV): Soil structure refers to the arrangement of soil particles and the spaces (pores) between them.
• Why it Matters:
  • Well-structured soils have good aggregation, which creates larger pores that can hold water while also allowing for drainage and aeration.
  • Poorly structured soils may have compacted layers that restrict water movement and reduce the soil's ability to hold water effectively.

3. Why Other Options Are Incorrect: - pH (II): - While soil pH can influence nutrient availability and microbial activity, it does not directly affect the soil's physical ability to hold water. Therefore, it is not a determining factor for water-holding capacity.

• Colour (III):
• Soil color can provide some information about organic matter content and mineral composition, but it does not influence the physical properties that determine water retention. Thus, it is not relevant to water-holding capacity.

Summary of Key Points

• Correct Answer: B. I and IV only (Texture and Structure).
• Texture: Affects water retention; clay holds more water than sand.
• Structure: Influences pore space and water movement; well-structured soils retain water better.
• pH and Colour: Do not directly affect water-holding capacity.

Revision Summary

• Water-holding capacity is crucial for plant growth and is influenced by soil texture and structure.
• Clay-rich soils retain more water than sandy soils due to particle size.
• Well-structured soils allow for better water retention and drainage.
• pH and color do not determine water-holding capacity.