This column was published in the Waikato Times on July 14
Could New Zealand agriculture be part of the solution to climate change? We know all too well that it is part of the problem – and that’s not an accusation, by the way, just a recognition. But problems are there to be tackled, and what is called carbon farming looks like one way in which agriculture can substantially contribute to climate change mitigation and at the same time improve the soils on which it depends.
The concept is simple. It is to increase the carbon content of soils, so that a greater proportion of the atmospheric carbon dioxide absorbed by plants remains stored in the soil. Globally, there is huge potential for enhanced carbon storage through management changes and soil restoration. Widely employed it could lead to a significant lowering of atmospheric carbon dioxide levels. The benefit for the soil is that a high carbon level greatly improves its structure, aeration, porosity, water holding capacity and nutrient holding capacity, all of which enable better growing.
Hamilton soil scientist Robin Janson, of Ecosynergy Research, works on biochemical indicators, measuring soil microbial activity. High activity tends to correlate well with high soil carbon levels. He is helping set up a New Zealand carbon farming association to get the message out that increasing soil carbon can be a practical consequence of good agricultural practice. He explained that by world standards many NZ soils already have exceptionally high levels of carbon, which, depending on agrotechniques, can increase or decrease. Indeed some think that the soils are at maximum capacity and in a steady state whereby the carbon taken in through photosynthesis and the carbon released back into the atmosphere balance at an optimum level. He agrees this may well be the case when considering standard soil tests, where only the top ten centimetres are measured. Under high fertiliser and/or tillage, increases below ten centimetres are rarely seen. Dr Janson says there is ample scientific and field based evidence supporting the building of higher levels of carbon at these depths.
How is this achieved? Through a variety of management practices, which may vary depending on the purposes for which the land is being farmed and the way soils respond. The range of possibilities is wide, and the few mentioned here should not be thought of as complete. Full ground cover is important to prevent soil being blown or washed away and to improve the conditions for those microbes and small animals that engender soil health. For pastoral farming this means avoiding overgrazing, pugging, and heavy chemical fertilisation. Light rather than heavy grazing is also important to enable plant roots to go deeper into the soil where they help create more carbon. Where crops are being planted, no-till methods are preferred (the majority of Canada’s crops are managed under no till today). Farmers abandon ploughing and plant seeds by dropping them into ruts which barely disturb the soil. Disturbing the soil releases soil carbon. The more stable forms of soil carbon tend to build up more when least disturbed.
The message is that careful and knowledgeable management aimed at substantially increasing the carbon content of soil can and does succeed. Innovative farmers have already proven this to be so. Some are already looking at the prospect of trading carbon as the substantial build-up in their soils is certificated – a welcome supplement to farm income.
Carbon farming is a win win approach, another reminder that there are ways still open to us of restoring the balances which enabled human civilisation to develop on Earth. Sustainability can be for real if we make the changes good science points us to.