Question

The upper portion of soil usually dark in colour and rich in organic material where most of the earth's biological soil activity occurs is called

Answer 1

The A horizon is the top layer of the soil horizons, often referred to as 'topsoil'. This layer has a layer of dark decomposed organic materials, which is called "humus".The technical definition of an A horizon may vary, but it is most commonly described in terms relative to deeper layers.

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