Small changes in the amount of carbon stored in soils can have large impacts on the amount of carbon present in the atmosphere and hence help the effort to reduce global warming. New Zealand scientists, funded by MPI through the New Zealand Agricultural Greenhouse Gas Research Centre (NZAGRC), have been working on how management practices can be changed to increase the amount of carbon stored in New Zealand grasslands. A comprehensive review of eight years of work has recently been published in the prestigious international journal Agriculture, Ecosystems and Environment.
The review “Management practices to reduce losses or increase soil carbon stocks in temperate grazed grasslands: New Zealand as a case study” was commissioned by the NZAGRC and sets a benchmark on what we currently know about soil carbon management.
The review’s lead author, Manaaki Whenua – Landcare Research scientist Dr David Whitehead leads the NZAGRC’s
The review summarises eight years of scientific research and identifies a list of criteria that can be used to assess the impact of changes to farm management practices on soil carbon stocks.  
Key findings include:

new, more rapid, methods for estimating soil carbon stocks based on remote sensing show great promise
modelling studies suggest there is theoretical potential for some soils to hold more carbon but management and environmental factors mean this potential may never be realised in practice
confirmation that New Zealand’s grasslands soil carbon stocks are already high and that increasing them is challenging. Research should focus on reducing the rate of loss of carbon from soils in some situations
there is no evidence that addition of nitrogen and/or phosphorus fertilisers leads to increases in soil carbon stocks. However soil carbon may benefit if fertiliser applications are incorporated alongside changes made to the intensity and frequency of grazing
supplementary feeding can lead to small increases in soil carbon stocks but that must be balanced with possible negative impacts on soil carbon where the feed is grown
irrigation can increase carbon stocks where plant production has been severely constrained by lack of water but in more humid environments irrigation can have a negative effect

The report also identifies priorities for research to address knowledge gaps that currently prevent scientists from being more certain in their advice to farmers and policy makers.
NZAGRC Director Harry Clark says the review is an important step in deciding where future solutions might be found and where research should be targeted.
“As a substantive study into New Zealand soil carbon, this gives us a benchmark to work from. It also gives us a better understanding of what the next steps should be for the NZAGRC’s programme of work dedicated to soil carbon,” says Dr Clark.
 Dr Clark says New Zealand is also playing a full part in international research aimed at finding options to increase soil carbon stocks.
“For example new research is underway in New Zealand to evaluate full inversion tillage to depths greater than 0.5 m. The intention is that surface soil carbon will be buried and retained at lower depths and new surfaces with a high potential to absorb and retain carbon are exposed. 
This new research is funded via the New Zealand Government’s investment to support the objectives of the Global Research Alliance of agricultural greenhouse gases (GRA).
More broadly, the NZAGRC and New Zealand’s research investment is contributing to the “4 per 1000 Initiative” that sets a goal to increase carbon stocks across the world’s agricultural land by 4 parts per 1000 or 0.4% per year.
“Global soils contain two-to-three times more carbon than the atmosphere. If this carbon level was increased by 0.4% per year in the top 30-40 cm of soils, the annual increase in carbon dioxide in the atmosphere would be stopped,” says Dr Clark.
A second international research project that the NZAGRC is contributing to, with the aid of GRA funding, is CIRCASA (Cooperation of International Research Coordination on Soil Carbon Sequestrations in Agriculture).
CIRCASA takes stock of the current understanding of carbon sequestration, identifies stakeholders' knowledge needs and fosters the creation of new knowledge.
Its research recognises there are knowledge gaps in soil carbon such as permanence of sequestered organic carbon, long-term changes in agricultural systems and of agricultural practices in diverse climatic conditions, and the difficulty of detecting improvements.
“Continued international research on soil carbon, its storage potential and changes over time will translate into better guidance to farmers on what they can do to mitigate greenhouse gases.” says Dr Clark.

This article was first published in Agri-Gate - Latest news about MPI's Investment Programmes

 
More information





Agri-Gate: Soil carbon research moves forward




 
Paper: Management practices to reduce losses or increase soil carbon stocks in temperate grazed grasslands: New Zealand as a case study





Factsheet: Reducing New Zealand's agricultural emissions: Soil Carbon