Understanding Soil Terms Part 1

Frequently I am asked to clarify what the difference, if any, there is between soil and compost. Far too often I find folks, including agronomist and other who should know better, interchanging the terms soil, compost, humus, mud, and dirt as though these are all a single homogeneous material. Without letting my inner soil nerd out (too much), I hope to enlighten those confused by these terms, as the differences between are significant.

DIRT: The strongest four letter word to someone dedicated to soil. Soil is a material which in nature is formed over thousands of years via biological, and to a lesser degree geological, processes. Soil is a rich ecosystem where plants, bacteria, arthropods, nematodes, protozoa, fungi, birds, and larger animals interact to form the soil food web. Soil teems with life! Every day I work in soil, I lovingly tend to environmental factors to select and promote specific communities of organism to achieve specific results. Dirt on the other hand is quasi sterile as dirt is soil that has lost its unique food web and whose microbiological life has been depleted and eradicated to the point where recovery without inoculations is untenable. Soil is full of life and life-giving. Dirt is what I wash off my hand and boots when my day is done. See the difference?

MUD: I had to search through almost every soil science and engineering book I have before finally finding a definition for Mud within a physical geology textbook. This definition relates to material morphology within the context of “mass wasting” events (e.g. geotechnical descriptions used to define types of materials involved in the movement of earth, from imperceptible creep to landslides,  and how this affects their nature and rate of movement).  The simplest definition is “Term loosely used for silt and clay, usually wet” As our materials use very little mineral content defined as silt and clay, mud, even when wet, just isn’t a physical term that meets our material specs.

To Be Continued…