Question

top most horizon is more important than all other horizons . give reason?

Answer 1

An A horizon is a mineral horizon. This horizon always forms at the surface and is what many people refer to as topsoil.  Natural events, such as flooding, volcanic eruptions, landslides, and dust deposition can bury an A horizon so that it is no longer found at the surface.  A buried A horizon is a clear indication that soil and landscape processes have changed some time in the past.  Compared to other mineral horizons (E, B, or C) in the soil profile, they are rich in organic matter, giving them a darker color.  The A horizon, over time, is also a zone of loss – clays and easily dissolved compounds being leached out – and A horizons are typically more coarse (less clay) compared to underlying horizons (with the exception of an E horizon). Additions and losses are the dominant processes of A horizons.