<p style="text-align: justify;">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.</p>
<p style="text-align: justify;">Dr Mike Beare of Plant &amp; 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.</p>
<p style="text-align: justify;">&ldquo;Developing soil management practices that lead to increases in soil C stocks depends on identifying soils that have the capacity to store more C.</p>
<p style="text-align: justify;">&ldquo;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.&rdquo;</p>
<p style="text-align: justify;">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).</p>
<p style="text-align: justify;">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&rsquo;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.</p>
<p style="text-align: justify;">&ldquo;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,&rdquo; says Dr Beare.</p>
<p style="text-align: justify;">&ldquo;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.&rdquo;</p>
<p style="text-align: justify;">Building on knowledge gained in the NZAGRC programme, Dr Beare says: &ldquo;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.</p>
<p style="text-align: justify;">&ldquo;There are some important practical implications of this research for increasing soil C storage in New Zealand&rsquo;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.</p>
<p style="text-align: justify;">&ldquo;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.&rdquo;</p>