August, 2024 What's so good about O.M.? Everything by Ginger Easton-Smith

WHAT’S SO GOOD ABOUT O.M.? EVERYTHING!

First off, what is O.M.? Well, it stands for organic matter. Definitions vary, depending on the

setting where it is being used, but a good general one is, organic matter is material that is, or was,

living and can decompose or is decomposed. It can come from plant materials, insects and other

similar creatures, and animals. In my world, it refers to soil OM.

Soil OM includes all the organic substances in or on the soil. With the numerous types of soils,

the percentage of it varies greatly but is in the range of one to six percent by weight. OM is

sometimes described as having three parts: living organisms such as plant roots, insects, fungi,

and earthworms; recently deceased living organisms including what I just mentioned as well as

things like recently fallen leaves; and the well-decayed and stable mixture of materials called

humus. So, basically it is just a bunch of rotting stuff on top of and in the soil! But it is good.

Why is it good? It helps plants of any kind grow and be healthy. Since OM is primarily

decomposed plant material, it contains the nutrients that plants need! There are not enormous

quantities of them, but the variety is there, and can be a constant source of nutrients.

OM also improves soil structure making it better for plant growth; it increases infiltration of

water into the soil and reduces erosion. In addition, the humus portion of it adsorbs and holds

nutrients in a form that is available to plants (some mineral parts of soil bind nutrients in a way

that plants cannot take them up). Amazingly, soil OM holds 10 to 1,000 times more water and

nutrients than the same amount of soil minerals, a game changer in our sandy soils. OM also

benefits high-clay soils by improving drainage due to improved soil structure and improving

fertility.

It may be surprising to learn that soil organisms—defined as those that live all or part of their

lives in soil—include a wide variety of critters, most of which are microscopic. There are very

tiny one-celled bacteria, algae, fungi, protozoa, nematodes, and miniature arthropods (mini-

insects, pill bugs, spiders, and millipedes), as well as the not so tiny earthworms, larger insects

and spiders, and small vertebrates like moles, gophers, mice, and snakes. The variety of soil

organisms is so huge it is estimated that they represent about 25% of the world’s total species,

which is astounding!

These diverse types and sizes of creatures feed on what is in the soil including each other, plant

debris, and manure from all the different critters. Their activity recycles plant nutrients and

mixes organic matter into the soil. Substances produced by plant roots, fungi and earthworms

help stick exceedingly small soil particles together which improves and stabilizes the soil

structure. Plant roots, fungal structures, earthworms, and other burrowing organisms form

channels in the soil that both aerate it and allow water to move deeper into the soil.

Surface OM, which could be natural leaf litter or applied organic mulch, also provides great soil

benefits. It protects the soil from erosion by wind and heavy rainfall, and from sun which speeds

up decomposition and can kill many microorganisms if the soil gets hot enough. It also makes

the soil surface less prone to crusting, thereby increasing water infiltration, and decreasing

runoff.

OM also has an impact on both ground and surface water quality (it is all related!) since a higher

percentage of water infiltrating the soil and increased soil microbial activity make the soil a

better and more effective filter.

It feeds and builds itself too – more OM supports more soil organisms, which builds OM, which

increases soil microbial activity, which helps plants grow, etc. Perhaps soil organisms like fungi

and bacteria do not sound like a good thing, but most of them do not attack plants; where there

are many diverse types, they keep each other in check, resulting in fewer problems with diseases,

nematodes, and insects. Research has shown that when diversity and populations of soil

organisms and organic matter increase, so does plants health and vitality, including improved

drought tolerance.

So, now you see why I say that everything about organic matter is good.