Understanding Soil Terms Part 2

Now that we’ve covered the… non-optimal terms, lets start on some of the most confusing words.

HUMUS TERMS: Humus is a term which gets thrown around without much consideration to whether or not it is being used appropriately. Garden centers are full of bold claims of the humate or humus concentrations within a product. This is likely a result of the etiology of the term humus (Latin for of or from the ground,) and non monolithic character being described by the term. To understand this, one must understand, in very broad strokes, natural soil formation (pedology AKA soil genesis). Soil begins its formation from mineral layers being broken down due to the actions of weatherization, plant roots activity, and decaying plant matter. These young soils are then shaped and diversified by regional conditions and initial factors such as parent material (non organic mineral layers), organic life, topography, time, and climate. As these macro factors form the young soils into somewhat unique surface and substrates materials, microbiological factors kick into high gear to break down the organic material and reform it into new chemical bonds that plants and other organism can use as nutrients. It is during this last phase, natural composting completes, and what generally is considered humus is formed. SO… back to humus..

HUMUS: “Simply” the black organic (carbon containing) material left over from composting containing no recognizable cellular structures or organizations equitable with plant or animal bodies. This material does not rapidly decompose, contributes texture to the soil matrix, and  provides a slow and very stable organic content. When one looks at the various organic building blocks of soil, be those alkanes, amino acids, carbohydrates etc, a chemical formula and resulting structure can be generated, not so with humus. So it’s very existence is ambiguous which makes the public’s use of the term equally so, at least in terms of agronomic processes. What is not debatable is the soil building, soil cleansing, water retention, and positive influence on nutrient availability to our plants by humus. In terms of humus on a broad scale, we should all understand that this is a material responsible for significant carbon sequestration and carbon cycling whose benefit to our living earth is essential and is a primary mineral storage in healthy soils! For more information in digestible terms search out the Ted Talk “Humus – The Essential Ingredient” by Graeme Sait

HUMIC and FULVIC ACIDS: Much has been made of the quality of Humic Acids as a selling point for a healthy soil but such simplicity negates much of what makes humic acids and the potential variations of humic acids in a product unique and either wonderful for your garden or just a waste of money. Again the ambiguity is related to the nature of humic acid. From the point of view of general chemistry an acid is a molecule that donates hydrogen ions (H+) when interacting with other molecules and usually when discussing an acid, sulfuric acid for example, we are discussing a very precise molecule (H2SO4). However when discussing humic acid we touch on a class of molecules made up of a numerous acids containing carbonic acids (aka phenol groups -C6H5OH) and carboxylic acids (carboxyl -COOH). Since humic acids contain numerous aromatic rings with carboxylic substituents it has the properties that allow it to form structures containing ions critical for plant health in forms available to plants and soil microbes such as the magnesium, calcium, and iron ions. Humic acids (and Fulvic acids, which are humic acids that are lighter molecules containing greater amount of oxygen) are critical parts of healthy soils, as is humus, one just need be wise to the use of such terms as selling points for high prices amendments when simple composting at home is a sure way to build and promote these substances for free!

To be continued…..