Terminology: how better language can lead to better soil

You’ve heard of OM, but have you heard of GOM, POM, or MAOM? This is a PSA for acronyms that could change how we talk about soil and amendments.

Better vocabulary could empower soil stewards

WORDS! Words are tricky. They can be a source of clarity or confusion. Sometimes they’re limiting, sometimes they’re incredibly useful to communicate an idea. 

When it comes to the rhizosphere - a place where so much is unknown and new discoveries are being made all the time - language that represents the life and functions of soil is practically non-existent in some cases.

There’s one area of soil work that’s demystified enough to be ripe for new words, and that is the area of “compost”.

We (soil stewards and laypeople alike) tend to use this one word to refer to everything from…

1. the food scraps stored in a countertop bin

2. an actively decomposing heap of organic waste outside

3. to the “end-product” of that decomposition process (regardless of its physical, chemical, or biological qualities)

Here’s an actual sentence using the word compost in all its ill-defined meaning:

“I took my compost out to the compost to make compost!”

That’s like calling flour & eggs, batter, and the resulting baked good all “cake”. 

“I put cake together to make cake and then baked it into a cake!”

Even worse, it’d be like if we goofed on the recipe and the resulting baked good didn’t rise or taste good, and yet we still called it a cake and served it to people. 🙈

When I speak with my colleagues in soil health, we’ve found it essential to use new language to differentiate “compost” materials from one another in conversation. Today, I’m going to take you through our terms! 

Feel free to adopt this language, and please don’t give me credit for these ideas (just for sharing them 😉); I’ll note credit where it’s due.

Useful terms that differentiate types of organic matter

GOM: Ground Up Organic Matter

Pronounced like “gawm” | Coined by Leighton Morrison

POM: Particulate Organic Matter

Pronounced like “pawm” | Lavalle et al. 2020

MAOM: Mineral-Associated Organic Matter

 I pronounce this one like “mow-um” | Lavalle et al. 2020

POM and MAOM differ in how they form as well as how they function and persist in the soil 

The terms POM and MAOM came from the need to start differentiating types of soil organic matter (SOM), especially in relation to the global conversation of carbon sequestration and soil fertility (it’s all the rage!)

I’ve found this vocabulary to ALSO be useful in conversations about compost - a substrate that can facilitate similar activities happening in soil, resulting in the creation of POM and MAOM. 

POM is introduced to the rootzone from the “fragmentation” and partial decomposition of litter at the soil surface. POM as a substance is more readily available compared to MAOM, but the nutrients contained within it are harder for microbes to access as they’re insoluble. 

Basically, microbes have to spend more energy to tap into the nutrients contained in POM, but they do it anyway because it’s largely available to them where MAOM is harder to come by (not necessarily because there is less MAOM, but because it’s not ‘out in the open’ like POM)

Furthermore, the quality of the nutrients contained in POM varies quite a bit and is largely dependent on the characteristics of the plant litter from which it originated - important insight for compost making and mulch decisions.

MAOM can be created in many ways, but the most common pathway is when “low molecular weight compounds” adsorb to a mineral like silt or clay. Low molecular weight compounds leach directly from plant litter or are generated through the “microbial turnover pathway” i.e. where microbes transform OM by doing microbe things (like exuding enzymes, metabolizing, etc.) 

Nutrients in MAOM are soluble, making them easy for microbes and plants to consume, but they are not as readily available as POM since they’re often nestled away in some obscure tiny home (mineral) in the valley of a remote mountain range (aggregate).

GOM is a term more specific to the composting process

The two terms alone, POM and MAOM, don’t account for all the forms of organic matter that we find in the composting process. Which is why my friend and colleague, Leighton Morrison, started using the shorthand “GOM” in reference to ground-up organic matter.

Ground-up organic matter essentially becomes the “litter” that, if managed properly, can generate POM and MAOM. 

As discussed in a previous post (Compost: a loosey goosey term), GOM tends to be what most industrial compost producers make and sell. From a microbial perspective it contains mostly bacteria, and though it may contain a lot of nutrient potential, without a greater diversity of microorganisms, those nutrients go largely untapped. 

Soil life is essential to the transformation of OM

You may be thinking, well if I add GOM to the soil surface, isn’t that kind of like adding litter that will generate POM and MAOM? 

Not necessarily, and here’s why:

If POM is defined as “partially decomposed” organic matter, we must consider how GOM on the soil surface is going to decompose. Who is going to do the decomposing??

Bacteria alone is not enough to transform OM across all its forms in a meaningful way - in a way that actually promotes plant health in the season (or even years) that we’re stewarding a piece of land. 

To “partially decompose” OM or to transform it into a “low molecular weight compound” that can become “minerally associated”, we need shredders like macro and microarthropods, we need exuders, weavers, and connectors like fungi, we need predators that consume other organisms and release waste, we need a diversity of organisms going about their business generating the ever-mysterious *stuff* that makes up humus - we need the whole soil food web.

The fact is, most soils in our modern world, especially those that we cultivate, do not have a functional microbiome. Which is why GOM is more than a disappointment, it’s a shameful missed opportunity.

Our soils need inoculants - that is, “compost” that has a vibrant community of microorganisms that are already transforming GOM into POM and MAOM before we even introduce it to soil. That’s what will stimulate the rhizosphere so that it can once again become a popular stop in the carbon cycle.

Thank you so much for reading! 

Be sexy, and go make some soil. 🤎

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References:

Buckeridge, K. M., Creamer, C., & Whitaker, J. (2022). Deconstructing the microbial necromass continuum to inform soil carbon sequestration. Functional Ecology, 36, 1396– 1410. https://doi.org/10.1111/1365-2435.14014  

Lavallee, JM, Soong, JL, Cotrufo, MF. Conceptualizing soil organic matter into particulate and mineral-associated forms to address global change in the 21st century. Glob Change Biol. 2020; 26: 261– 273. https://doi.org/10.1111/gcb.14859

Morrison, Leighton. Kingdom Aquaponics LLC. www.kingdomaquaponicsllc.com