Humic acid: how humus benefits soil

This information is drawn from Eco Farming Daily written by Michael Martin Meléndrez, because the Wikipedia entry is too pompously erudite to be useful.

Hummus is the Middle Eastern dip made from chickpeas.

Humus is a general term that describes a group of distinctly different humic substances that include:

* Fulvic acid, a yellow to yellow-brown humic substance that is soluble in water .

* Humic acid, a dark-brown humic substance that is soluble in water at higher pH and is of greater molecular weight than fulvic acid. It can remain for centuries in undisturbed soil.

* Humin, a black humic substance that is not soluble in water and with high molecular weight and is never found in base-extracted liquid humic acid products.

While soil organic matter is material that is decomposing at various rates.

So then, humic acid is not the same thing as compost, organic material that is decaying that's used to adjust clay or sandy soil and that worms and plants use for nutrition. Although compost can be the source of humic acid. Essentially, compost is fertilizer in organic form so it's important to know the nutrient analysis of the compost you're using.

Humus is powerful. A small amount gets huge measurable results. As little as 40 pound per acre increases farm yields dramatically.

What does it do?

The electronegativity of humic acid transports nutrients from the soil to the plant by holding onto ionized nutrients and preventing them from leaching away. Humic acids are attracted to the depletion zone of plant roots. When the humic acids arrive in the depletion zone at the roots they bring water and nutrients that plants need.

Here comes some scientific stuff about fungus and its symbiotic relationship with plant roots. Hold onto your hat.

The depletion zone is the area around roots where they draw (deplete) nutrients. The zone can become depleted if there is a lack of humic acid or mycorrhizal fungus. (See what I mean? Science!) Mycorrhizae have hyphae-micro-tubes that can extend much further into the soil than the host plant can reach and gather mineral nutrition that benefits the plant from beyond the depletion zone. Humus is critical for plant nutrient availability if there aren't healthy mycorrhizal  relationships in the soil.

And there won't be mycorrhizal relationships with roots if you are relying chemical fertilizers.

This is why living soil smells alive.

The roots have a negative charge that attract and absorb positive ions around them. Humic acids hold cations (positive ions) such that they can be absorbed by a plant's root improving micronutrient transfer to the plant's circulation system.

This works because humic acids pick up positive ions and are then attracted to the root depletion zone and to the hyphae micro-tubes of mycorrhizae.

Since the roots negative charge is stronger than the humic acid biomolecules' negative charge the micronutrients are taken up by the plant's roots and absorbed by the plant's circulation system.

The plant will also take up some of the lighter molecular-weight humic acids as well. Essentially, the humic substances are chelating (bonding a metal ion with chemical compound) such cations (ion with positive charge) as magnesium, calcium and iron. Through chelation humic substances increase the availability of cations to plants.

Science! Right there.

How do you build humic acid levels?

You buy it and dump it on. Duh.

Compost and decomposing organic matter are not an efficient way to build soil humus levels because it decomposes and leaves its minerals behind and releases carbon into the atmosphere as CO2. While humic substances are stable long-lasting biomolecules, depending on their molecular weight up to 1,200 years.

Humus is a product of soil chemistry dependent upon a source of its precursor chemicals, amino acids.

Amino acids are the building blocks of protein. The best source of amino acids are produced by the Glomus species of mycorrhizae (fungi). These are associated with any natural grasses in undisturbed sites. It's why the tall grass prairies of the Midwest exemplify this soil-building process better than any ecotone (transition between biomes where two communities meet and integrate) because grasses use a Glomus-mycorrhizal relationship. That's why there is so much humus-rich topsoil in the tall grass prairies. Glomus makes a soil protein called glomalin rich in amino acids that combined with humus create a huge carbon sequestering banking.

Compost or other soil amendments of organic matter are not a reliable way of increasing soil humic substances. Trying to add adequate amounts of humic acid by application of compost would require such a huge amount that it would lead to overdosing the site with nutrients. The better the quality of the compost then the more concentrated the nutrients and the less you should use.

Per the Journal of Chemical Education:

Humic acids are remarkable brown to black products of soil chemistry that are essential for healthy and productive soils. They are functionalized molecules that can act as photosensitizers, retain water, bind to clays, act as plant growth stimulants, and scavage toxic pollutants. No synthetic material can match humic acid's physical and chemical versatility.