Carbon Flows & Residence Time
The continuous exchange between atmosphere, plants, and soil
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Section 2 of 5The Carbon Cycle in Soils
Soil carbon is not static—it is constantly cycling between the atmosphere, vegetation, and soil through photosynthesis, decomposition, and microbial respiration.
Carbon Inputs
- • Photosynthesis (120 Gt C/yr)
- • Root exudates & turnover
- • Crop residues, manure, compost
- • Microbial necromass
Transformations
- • Microbial decomposition
- • Humification (stabilization)
- • Aggregation with clay minerals
- • Physical protection in pores
Carbon Outputs
- • Soil respiration (60-80 Gt C/yr)
- • Erosion & leaching (DOC)
- • Harvest removal
- • Fire & combustion
Interactive Carbon Flow Animator
Watch carbon move between atmosphere, plants, and soil across different time scales
Residence Time: Why It Matters
Not all soil carbon is equal. Fresh plant residues decompose in weeks to months. Humus protected in clay aggregates can persist for centuries. Deep subsoil carbon may remain stable for millennia.
Climate benefit depends on residence time. Sequestering 1 ton of carbon in the active pool provides temporary benefit. Sequestering it in the passive pool via deep root systems, biochar, or mineral stabilization offers centuries of climate mitigation.