17 June 2005 Soils Offer Chance to 'Farm the Atmosphere' For Carbon Credits

It's easy to understand the "surprise" of the Convenor of the Ministerial Group on Climate Change, Pete Hodgson, at the "$1 billion botch-up in the estimates" of greenhouse gas emissions, as reported in The Press of 17 June. "Surprise" must be an understatement!

As a result of the "botch-up" officials have now been asked to come up with drastic "new measures" to reduce New Zealand's carbon emissions. To use an old cliché, perhaps the answer is in the soil!

Many scientists believe that using the soil to store carbon from human and animal induced sources is the most cost-effective mitigating option for bridging us into the future.

The soil can buy us time as a buffer until alternative energy options are developed in the next 15 to 20 years in response to the drastic reductions in greenhouse gases required under the obligations of the Kyoto Protocol, for those who are signatories, or under the expectations of "responsible global citizenship" for those who are not.

Global estimates of soil's ability to sequester or "capture and hold" carbon are of the same order as that for forest trees and are between one-third to two thirds of the annual increase in atmospheric carbon dioxide levels.

Given this, our farmers and land users should be offered financial incentives to use practices which enhance carbon sequestration in soils as a direct means of reducing greenhouse gas emissions in the atmosphere and also as carbon credits to offset the carbon tax.

As a full signatory to the Kyoto Protocol, which came into force on 16 February 2005, New Zealand is required to stabilise its greenhouse gas emissions at the 1990 levels, over the commitment period of 2008-2012. The new carbon tax is designed as a part of our commitment to the Protocol. Agriculture, being the major contributor to the New Zealand economy, is also the main contributor to the New Zealand's greenhouse gas emissions. Unlike other countries, 55 per cent of our emissions are as methane and nitrous oxide from the agricultural sector. However, the new carbon tax specifically excludes agricultural emissions. This has important implications as the agricultural sector can be made to earn carbon credits and buffers if appropriate techniques are developed to mitigate greenhouse gas emissions.

One of these mitigations which has been studied extensively recently overseas is to use soils to enhance the storage of carbon known as "soil carbon sequestration". This is often hidden from our sight and few people are aware that the secret to reduce the greenhouse gas emissions may rest in the very soil beneath our feet. Soils contain about three times more carbon than that in the vegetation and twice that in the atmosphere. Direct sequestration of carbon occurs when plants photosynthesize atmospheric carbon dioxide into plant biomass carbon. This biomass carbon is subsequently sequestered in the soil when plant roots and residues are decomposed by soil micro-organisms and part of this is stored or buried in the soil as soil organic carbon or soil organic matter. Thus the carbon is fixed in the soil into medium and long-lived (15-100 or more years) carbon pools, depending on the soil type, climatic conditions and soil management practices.

A variety of techniques such as conservation tillage, erosion controls, incorporation of crop residues, composts and sewage sludge, establishing and improving pastures and forests, growing cover crops, planting of trees in agricultural land (agroforestry) and hedges, and the growing of biofuel crops are considered to be some of the effective methods. Appropriate practices differ between soil, climate and plant or crop requirements. Integrated combinations of practices are found to be more effective than a single practice. A site specific approach should be adopted in selecting the appropriate practices to meet local needs including environmental and social implications by considering all inputs and benefits associated in implementing each input.

By adopting these techniques farmers can literally "farm the atmosphere" or engage in "carbon farming" and earn carbon credits. This means farmers who store carbon in their soils will be rewarded with credits that they can save or sell to the industry. Industries will need these credits to continue emitting greenhouse gasses. This biospheric sink of carbon in soils is included in Article 3.4 of the Protocol under land use and land management changes relating to improved management of agricultural soils (Marraketch Accords). Many countries overseas are developing methods to determine an inventory of the land to assess the present soil carbon levels and the present rates of carbon sequestration under different land use and management practices.

For example, in the United States it has been estimated that the total carbon sequestration and fossil fuel offset potential of U.S. cropland is 154 million metric tons of carbon per year, equivalent to 133 per cent of the total emissions of greenhouse gases by agricultural activities in the U.S. Similar estimates for New Zealand are not available at present. However, our research at Lincoln University has shown that in the early phases of pasture establishment in the long-term irrigated pasture trials at Winchmore, Canterbury, significant accumulation of soil organic carbon occurred for at least 15 to 16 years before it reached a steady state.

In addition, enhancing soil carbon storage also brings in a number of "co-benefits". This is often regarded as a 'win-win' strategy. Increasing soil carbon directly increases soil organic matter which in turn enhances agricultural and forest production, reduces soil erosion and improves soil quality, air quality, water quality, crop health and vigour and biodiversity. These co-benefits are the key elements of not only sustainable agriculture but also environmental quality.

Kuan M Goh is the Professor of Soil Science at Lincoln University, a specialist in soil organic matter research, an author of over 280 scientific papers including chapters in 17 books. He has been invited by the joint FAO/IAEA (Food and Agriculture Organisation of the United Nations/International Atomic Energy Agency) in Vienna, Austria to write several chapters in a book to be published in 2005 entitled "Carbon Isotope Tracers in lnvestigating Soil Carbon Sequestration and Stabilisation in Agro-ecosystems-Guidelines".

Professor Kuan Goh, Professor of Soil Science, Lincoln University, Canterbury, New Zealand