Key Idea: Topic 5.1 explains what soil is, how it forms, what controls its properties, how soil affects ecosystem productivity (NPP), and why soil degradation is a major sustainability issue.
🧱 Soil formation + composition
Soil is effectively non-renewable on human timescales (forms extremely slowly).
🧪 Soil properties + horizons
🌱 Soil + productivity (NPP)
For 5–7 marks, write cause → effect chains (e.g., humus ↑ → CEC ↑ → nutrients held ↑ → plant uptake ↑ → NPP ↑).