Measuring soil carbon

We report carbon stock changes in soils as part of tracking New Zealand’s greenhouse gas emissions from land use. This page explains the role of soil organic carbon and how it is monitored.

Role of soil carbon

Soil is an important reservoir of carbon. Soil organic carbon is the measurable component of soil organic matter, which is made up of micro-organisms and decomposing plant and animal material.

A change in land use can cause the soil carbon stock to increase or decrease depending on the balance of carbon inputs and outputs. When a land-use change decreases the soil carbon stock, carbon dioxide, a greenhouse gas, is emitted to the atmosphere. When a land-use change increases the soil carbon stock, carbon is removed from the atmosphere.

Mineral soils: monitoring carbon stock changes

The Soil Carbon Monitoring System is a statistical model designed for estimating soil organic carbon stocks in New Zealand’s mineral soils. It follows methodology recommended by the Intergovernmental Panel on Climate Change (IPCC).

The model combines actual soil carbon data (samples collected from New Zealand soils under different land uses) with national spatial datasets of soil type, climate, land use and topography. The Ministry for the Environment uses it to:

  • derive estimates of soil organic carbon stocks for all land uses
  • estimate changes in soil organic carbon following changes in land use.

Organic soils: measuring carbon stock changes

Organic soils are generally drained peatlands used for agriculture. These occupy a relatively small area of New Zealand, but the carbon emissions from drained organic soils are disproportionately large.

The Ministry for the Environment uses IPCC default methodology to calculate carbon stock change in organic soils and work is underway to refine this approach based on the 2013 Wetlands Supplement.

Find out more

Guidance the Ministry for the Environment uses when measuring soil carbon.

Soil data are available to central and local government agencies, research institutes, universities and other organisations, see Forest, soil and LiDAR data.