No-till agriculture – a climate smart solution?

Summary

No-tillage farming systems or no-till, as an aspect of conservation farming, are actively promoted by international research and development organizations to conserve soils and by this, ensure food security, biodiversity and water conservation. Instead of tilling before seeding, seeds are deposited directly into untilled soil by opening a narrow slot trench or band. Today, it is also seen as mitigation and adaptation option and thus being promoted as a measure to be supported under the United Nations Framework Convention on Climate Change (UNFCCC). There are even many voices advocating no-till to benefit from any future and existing carbon market. But: Is no-till the solution to reduce the hunger in the world and to mitigate climate change? It has been proven that no-till can signifi cantly reduce soil erosion and conserve water in the soils. This is regarded as a basis for higher and more stable crop yields – but science shows that this is not necessarily true. Discouragingly, there are numbers of examples of no yield benefits or even yield reductions under no-till in developing countries, especially in the first up to ten years. However, particularly the crop yields are crucial for the food security of small-scale farmers and not whether a method is more efficient or not. Although humus can be enriched under no-tillage, the sequestration of soil carbon, is result of the accumulated organic matter in the topsoil, is restricted to the upper 10 cm of the soil. Compared with ploughing, no carbon benefi t – or even a carbon defi cit – has been found at soil depths below 20 cm. This is why no-till makes little or no contribution to carbon sequestration and does not prove to reduce greenhouse gas emissions in croplands. The quantifi cation of carbon sequestration rates under no-till are highly doubtful. Anyhow, it is very likely that emission reductions generated from no-till projects in developing countries would serve to offset emissions from he industry and transport sector in developed countries. Those well quantifi ed emissions from developed countries would thus be offset by uncertain reductions from agriculture projects. The overall aim of the UNFCCC – to avoid dangerous climate change – would be jeopardized. Even if no-till became a promising mitigation option, other environmental problems would remain. No-till farming systems often come along with the industrialization of agriculture with high inputs of agrochemicals. On the one hand, small-scale farmers are not skilled in handling such chemicals. On the other hand there remains a risk that they apply cheap chemicals, which persist long-term in the environment. Efforts should therefore be strengthened on how to combine sustainable production systems such as organic agriculture with no-till practices. To summarize, there are too many open questions and uncertainties concerning the impact of no-till on crop yields and carbon sequestration, so that no-till could not be sold as the solution for hunger reduction and adequate option to mitigate climate change but as an important part of integrated strategies. Therefore, we recommend keeping no-till and reduced till out of the carbon market unless reliable carbon offset quantifi cation and monitoring can be undertaken at reasonable cost.