5.1.2—Soil composition
- Syllabus
- First assessment 2026
- Objective
- 5.1.2
- Level
- SL
Build Soil from Four Components
Soil combines mineral particles, organic matter, pore water and pore air; it is not solid rock or solids only.
Rock fragments provide structure; humus stores carbon and nutrients; pore water transports dissolved substances; pore air supplies gases to roots and microbes. Their proportions control function.
A compacted soil may contain the same minerals but less pore air and water movement, restricting roots.
A complete account of soil composition includes mineral particles, organic matter, pore water and pore air; texture alone describes only part of the system.
Pore space is part of the system even though it is not a solid ingredient.