When the carbon balance changes

Arable fields

In contrast to forest soils, arable soils generally contain lower levels of soil organic matter, and their carbon dynamics are therefore strongly influenced by land management. Intensive tillage mixes soil layers and increases aeration, which can accelerate microbial decomposition. Removing crop residues after harvest reduces the organic material returned to the soil, while simplified crop rotations limit the diversity and timing of organic inputs.

From an arable-management perspective, the diversity and continuity of plant inputs matter most. Cropping systems that include cover crops, diverse and longer rotations, or perennial phases supply more diverse organic inputs. Monocultures with long periods of bare soil provide fewer carbon inputs and often increase erosion risk. Soil compaction from heavy machinery may further affect structure and how organic matter is stabilized or lost.

Environmental conditions interact with these management choices. Warmer temperatures generally increase microbial activity and decomposition, while drought or heavy rainfall can affect plant growth and erosion. In recent decades, climate change and land-use change have increased the frequency or intensity of many disturbances, affecting soil carbon balances in both forests and agricultural landscapes. Together, these examples show that soil carbon levels are dynamic — responding to natural processes and to land-management decisions.

Optional: Curious about climate-smart arable soil management? See Bolinder et al. (2020).