Soil carbon is a valuable resource, but all soil carbon is not created equal
Posted by admin on 6th February 2020

Human society is literally built on soil. It feeds the world and produces vital fuel and fiber. But most people rarely give soil a second thought.

Recently, though, soil has been getting some well-deserved attention from environmental organizations, policymakers and industry leaders. It has been covered in news articles, argued over in policy debates and has even received an international day of recognition.

Why all this attention? Because the world urgently needs ways to keep carbon out of the atmosphere, and to build food security for a rapidly growing global population. Soil can do both.

However, current efforts to promote carbon storage in soil miss a key point: Not all soil carbon is the same. As scientists focusing on soil ecology and sustainability, we believe that managing soil carbon effectively requires taking its differences into account.

How carbon cycles into and out of soil.
Jocelyn Lavallee, CC BY-ND

Soil carbon is amazingly complex

Building up soil carbon can help cut greenhouse gas concentrations in the air. It also improves soil quality in many ways: It gives soil structure, stores water and nutrients that plants need and feeds vital soil organisms.

But carbon in soil doesn’t exist on its own. It is combined with oxygen, hydrogen, nitrogen and other elements, in compounds that scientists collectively call soil organic matter. This material is amazingly complex stuff, made of thousands of different chemical compounds that remain from the decomposition and transformation of plants, animals and microorganisms.

Adding to this complexity, carbon can be found in different physical states within soil. It can be dissolved in water, present as larger chunks or “particulates,” enveloped by soil particles or bonded to minerals. These various forms all behave differently, and ultimately have very different impacts on plant growth, soil structure and carbon sequestration.

The challenge is how to conceptually divide up all of these different forms without getting completely lost in the muck. The soil science community – yes, we are out there! – has been studying this question for decades. As we discuss in a recent study, one key distinction can provide an underlying framework for soil carbon management: particulate organic matter versus mineral-associated organic matter.