The B Horizon
2. Defining the Undefinable (Almost!)
Okay, let's get down to brass tacks. What exactly is the definition of the B horizon? In simple terms, it's a subsurface layer of soil that's characterized by the accumulation of materials that have been transported from the layers above. This accumulation process is known as illuviation. Fancy word, right? Just means stuff moving into the B horizon.
Think of it like a collector's shelf in your basement. All sorts of things eventually make their way there from the rest of the house: old books, forgotten toys, maybe even a rogue sock or two. The B horizon is similar; it's where clay, iron, aluminum, and organic matter tend to gather, giving it distinct properties.
However, defining the B horizon isn't always a walk in the park. Soil is complex, and the boundaries between layers can be blurry. Sometimes, it takes a trained eye and some careful analysis to determine where the A horizon ends and the B horizon begins. It can be a bit like trying to decide when a sunset turns into twilight; there's a gradual transition.
So, the official, slightly-more-technical definition includes that its a mineral horizon that formed below an O, A, or E horizon and is dominated by obliteration of all or much of the original rock structure and shows one or more of the following: (1) an illuvial concentration of clay, iron, aluminum, humus, carbonate, gypsum, or silica, alone or in combination; (2) evidence of removal of carbonates; (3) coatings of sesquioxides that give conspicuously darker, stronger, or redder color than overlying and underlying horizons; or (4) alteration so as to show a blocky or prismatic structure.
