Increasing the quantity of carbon stored in agricultural soils has the potential to offset emissions of greenhouse gases to the atmosphere, while soil carbon losses would further add to those emissions.
However, realising this mitigation potential is technically challenging when soil carbon stocks are already high (as they are in New Zealand), potential changes in soil carbon are small and spatial variability is high.
The current NZAGRC programme has three distinct components:
(1) testing specific management practices that may increase the long term soil carbon store in field situations;
(2) developing and using models to predict how a range of management practices may influence long and short tem soil carbon storage; and
(3) identifying those factors that influence the stability of current or newly added soil carbon.
We have also supported international work to map on farm soil carbon and will participate in the international research programme CIRCASA.
Dr David Whitehead, Manaaki Whenua - Landcare Research (2010-present)
Professor Frank Kelliher, AgResearch (2010-2017)
Grassland soils have potential to offset GHG emissions
At least 60% of New Zealand's high-producing grasslands - those on less than 20-degree slopes - have some potential to sequester carbon and help in the fight to reduce greenhouse gas emissions in the atmosphere.
Dr Mike Beare of Plant & Food Research and an objective leader in the NZAGRC soil carbon (C) programme, says increasing the storage of C in soils is recognised as an opportunity to reduce carbon dioxide concentrations in the atmosphere and partially offset the effects of greenhouse gas emissions.
“Developing soil management practices that lead to increases in soil C stocks depends on identifying soils that have the capacity to store more C.
“In general, soils with a high clay content and a high mineral surface area have the greatest capacity to store C. Our recent research found that soils with a high mineral surface area are better able to protect new plant C inputs from decomposition, which helps to explain why these soils have a greater potential to stabilise C.”
Their findings, which have been prepared for publication in a scientific journal, are the result of research carried out as part of the soil carbon research programme funded by the New Zealand Agricultural Greenhouse Gas Research Centre (NZAGRC).
Previous research on soil C stabilisation focussed on the top 15cm of pasture soils where most of the inputs of C from plant roots and livestock (dung) occur. While this work indicated that many of New Zealand’s pasture topsoils are approaching the upper limit of their capacity to store organic C, this does not apply to the soils below 15cm which have considerably lower concentrations of C.
“This suggests that they may be able store much more C if we can develop management practices to expose them to greater C inputs. These management practices may include the sowing of pasture species with large deep-penetrating root systems that deposit more C deep in the soil profile,” says Dr Beare.
“Another option may be the one-time use of full inversion tillage during pasture renewal to bury topsoil C and bring low-C subsoil to the surface where it can be exposed to high inputs of C from the vigorous growth of new pasture.”
Building on knowledge gained in the NZAGRC programme, Dr Beare says: “The potential benefits and trade-offs of pasture renewal using full inversion tillage are being investigated by scientists from New Zealand, Ireland and Germany in a separate research programme supported by the Global Research Alliance for Agricultural Greenhouse Gases.
“There are some important practical implications of this research for increasing soil C storage in New Zealand’s pasture soils. First, the development of management practices to enhance soil C storage should target those soils that have a relatively-high mineral surface area.
“Second, they should focus on exposing low-C subsoils (15-30cm deep) to higher inputs of C from plants (or perhaps manure), particularly where the subsoil C concentrations are less than half that of the surface (0-15cm) soils.”
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