Which amendment is recommended to improve structure and porosity in clay soils?

• A. Sand
• B. Gypsum
• C. Lime
• D. Organic matter

Answer: (D)

Organic matter is the amendment that most effectively improves structure and porosity in clay soils. It acts like a binder that helps clay particles form stable aggregates, creating a network of larger pores for better drainage and air movement while preserving smaller pores that hold plant-available water. As organic matter is added and broken down by soil life, these aggregates stay active, continually enhancing tilth, root penetration, and infiltration. Other options address different issues or are not generally effective for this purpose: sand can fill pore spaces and worsen compaction in clay soils; gypsum helps mainly when there is a sodic condition to improve permeability; lime changes soil pH and can promote some flocculation but does not produce the sustained pore structure that organic matter does.