Soil Science Fundamentals and Soil Genesis
Core concepts
Master the five soil-forming factors (climate, organisms, relief, parent material, time) and how they drive the processes of addition, loss, translocation, and transformation. Know the master horizons (O, A, E, B, C, R) and transitional/combination designations (AB, EB, Bt, Bw, Bhs), plus subordinate symbols (t, w, h, s, g, k, p, r). Understand soil texture classes and the texture triangle, structure types and grades, bulk density, porosity, and the difference between gravimetric and volumetric water content. Know cation exchange capacity, base saturation, pH buffering, and how clay mineralogy (1:1 versus 2:1) governs shrink-swell behavior and nutrient retention.
Traps in questions
Distinguish eluviation (removal, E horizon) from illuviation (accumulation, B horizon). Do not confuse soil texture (particle-size distribution, immutable) with soil structure (aggregation, manageable). Remember that a "g" (gley) subscript signals saturation and reducing conditions, not salinity. Bulk density rises with compaction while porosity falls; a question that says density increased and asks about porosity is testing that inverse link. Watch for questions equating high clay content with high permeability-swelling clays can be nearly impermeable.
Worked example
A profile shows a light-colored leached layer above a clay-enriched subsoil with clay films. Identify the horizons: the leached layer is an E horizon (eluviation), and the clay-enriched subsoil is a Bt (argillic) horizon. Rule of thumb: light color above plus clay skins below equals translocation, not mere deposition.
Rule of thumb
When diagnosing a horizon, ask which of the four processes (addition, loss, translocation, transformation) best explains the observed feature, then assign the symbol.