National soil carbon monitoring

Producing a nationwide baseline soil carbon measurement 

This study will improve New Zealand’s ability to report greenhouse gas emissions and removals under international climate change agreements and satisfy a growing desire by primary industry organisations and individual farmers to know how New Zealand’s soil carbon stocks might be changing.

Manaaki Whenua – Landcare Research has received  funding from The New Zealand Agricultural Greenhouse Gas Research Centre  (NZAGRC) and the Ministry for Primary Industries (MPI) to commence the first  phase of a new nationwide baseline soil carbon measurement study.

This study will  improve New Zealand’s ability to report greenhouse gas emissions and removals  under international climate change agreements and satisfy a growing desire by  primary industry organisations and individual farmers to know how New Zealand’s  soil carbon stocks might be changing.

Under the United Nations Framework  Convention on Climate Change and the Paris Agreement, New Zealand is obliged to  report annually its national man made (anthropogenic) greenhouse gas emissions  and removals. Currently, national-scale  changes in soil carbon are estimated using a statistical model that predicts changes  in soil carbon for changes between broad land-use classes (e.g. pasture to cropping).  This is a well-established approach, but assumes that  soil carbon is at steady state if the land-use class doesn’t change (even if  management practices within the land use change), and that changes in a land-use  class result in changes in soil carbon over a period of twenty years to a new  steady state.

There is  currently limited data from direct measurements of soil carbon change through  time in New Zealand with which to test these assumptions. The evidence  available indicates that soil carbon is largely constant in flat and rolling  pastoral land, except for organic/peaty soils where soil carbon is declining.  There is some evidence that hill country pastoral soils gained carbon between  about 1980 and 2010, but it is not clear how widespread these  gains were, and whether they have continued since 2010. The information available is also largely based on historical soil survey sampling sites which were not explicitly selected to be  representative of all agricultural land in New Zealand.

A new approach

The study is designed to directly measure changes in soil carbon through time using a statistically  designed framework to ensure unbiased, representative monitoring across all  agricultural land in New Zealand, grouped into the five broad land-use classes:

• Cropland
• Horticulture
• Dairy pasture
• Flat-rolling drystock pasture
• Hill-country drystock pasture

The overall plan is to monitor changes in soil carbon at a total of 500 sites (about 100 within each land class) across New Zealand (Figure 1) and is designed to detect a change of about 2 tonnes of carbon per hectare over 12 years, within each of the five land use classes.