Dr Tim Jenkins explores the ways that organic farming practices, including resilient agro-ecosystems, can help prevent and adapt to the major challenge of our times: climate change.
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The world faces unprecedented challenges to our way of life. Not the least of these is climate change. Resilient agro-ecosystems offer solutions to help reduce the impact of agriculture on the climate and to help a farm cope with the changes that have already started.
Capturing and storing carbon
Photosynthesis in plants fixes carbon dioxide into an organic form thus reducing atmospheric carbon dioxide. But organic carbon returns as atmospheric carbon dioxide (or methane) when plant material is eaten or decomposed. This is an important natural cycle; the soil microorganisms need the organic carbon as a nutrient source and bring multiple benefits as they break down the plant material. Mineral elements and nitrogen are released, feeding plants and more microbial growth.
Carbon storage on farm can be increased by:
- changing the way in which pasture and crops are managed,
- reducing the amount of deep cultivation, and
- including woody plants in the farm design.
Change in management
There is no plant better for building up the organic matter, soil fertility and structure of the topsoil than grasses. And by changing the grazing management of grasses, avoiding overgrazing, and increasing intervals between grazing, root systems can go deeper and have more time to build up soil organic carbon.
By including deep-rooted plants such as chicory and lucerne in the pasture mix, the deeper soil structure will improve, and even more carbon will be stored. Implementing such changes in management can store more and more carbon until a new equilibrium is reached of carbon in and carbon out.
Cultivation is the enemy of building up soil carbon. Deep cultivation stimulates fast decomposition of organic matter that might otherwise have been destined for long-term humus development.
Mycorrhizal fungi networks are broken, and soil structure can suffer further affecting soil biological activity. Try to minimize the amount and depth of cultivation and allow soil carbon to grow.
The total amount of carbon stored is even greater with the inclusion of woody plants in the system. This includes the standing shoot biomass of shelterbelts, tree crops and vines. Often even more biomass is created underground. This has tended to be underestimated in the past with studies usually more focused on the top 30 or maybe 50 cm of soil, whereas much of the stored carbon from woody perennials is stored below 50 cm and may even go down to a few metres.
Of course, some non-woody plants are also perennials such as most pasture grasses. In a mixed cropping situation, having more years of pasture between each cropping cycle will allow more carbon build-up in the soil. Some microorganisms can also leave a perennial legacy including the mycorrhizal fungi, with long-lasting and soil-structure-improving glomalin produced by the arbuscular mycorrhizae.
Many studies have shown that organic practices can reduce the carbon impact of farming. Perhaps the single most important aspect for this is the avoidance of synthetic nitrogen fertilisers. These fertilisers have a super high energy requirement to break the nitrogen-nitrogen bond in atmospheric nitrogen.
In organics, biology catalyses this bond breakage in legume nodules and other bacterial systems. We call this biological nitrogen fixation. We design our systems around legumes in pasture, cover crops and legume cash crops themselves, or we bring in organic matter that contains nitrogen from previous biological nitrogen fixation. And we include practices that improve the natural availability of nitrogen to plants, such as building up organic matter and improving soil biological activity.
As we build up soil organic matter or use organic mulches, we also reap another benefit: improved efficiency of water use. The organic matter holds water better from drainage and yet makes this water available to soil microbes and crop roots. This reduces the requirement for water, which also saves on energy use for pumping and makes our systems more resilient to the already present stresses of climate change.
Dr Tim Jenkins is a microbiologist and agricultural scientist currently based in Europe.