Soil Composition
Elementary School
Definition
The mixture of materials that make up soil, including weathered minerals, organic matter (humus), water, and air. The proportions of these materials affect how fertile a soil is and what can grow in it.
Worked examples
A sample of soil contains 45% weathered minerals, 25% air, 25% water, and 5% organic matter (humus).
These four components together determine the soil's texture, drainage, and fertility.
Sandy soil has large mineral particles with lots of air space but drains quickly and holds few nutrients.
The high mineral and air content but low organic matter makes sandy soil less fertile.
Clay soil has tiny mineral particles that pack tightly, holding water but draining poorly.
The small mineral size and tight packing trap water and leave little room for air.
Common mistakes
- Soil is just dirt — only crushed rock and minerals. → Soil is a mixture of minerals, organic matter, water, and air. Forgetting that living and once-living material (humus) is essential to fertile soil.
- All soil has the same composition everywhere. → Soil composition varies by location and affects what plants can grow. Different climates, parent rock, and ecosystems produce soils with very different proportions of the four components.
Where you'll use it next
You'll apply soil composition when studying ecosystems and food webs, agriculture and crop science, erosion and weathering processes, and later in environmental science and Earth systems courses.
See also
Reviewed by Pat Cheng, M.Ed. — StudyPug Curriculum Lead · Last updated June 6, 2026