A national soil carbon monitoring system for agricultural land
A study to 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.