No-till farming climate benefits ‘may be overstated’

The role of no-till agriculture in mitigating climate change may be overstated, say scientists.

No-till and reduced tillage are methods of establishing crops with minimum soil disturbance, in contrast to conventional tillage involving ploughing or other cultivation practices.

The methods can deliver benefits in many, though not all, situations, including improved soil quality and retention of water in soil for use by crops. This has a clear advantage, especially in dry regions of the world.

No-till usually leads to an increase in the concentration of organic matter – measured as organic carbon – near the soil surface.

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This is often interpreted as an absolute accumulation or “locking up” of carbon in soil, termed carbon sequestration, leading to no-till being promoted as a form of climate change mitigation.

This claim was recently restated in the 2013 United Nations Environment Programme (UNEP) Emissions Gap Report.

However, an international group of scientists, led by Professor David Powlson, Lawes Trust senior fellow at Rothamsted Research, has released a report which concludes that the role of no-till agriculture in mitigating climate change may be exaggerated.

The review, published in the journal Nature Climate Change, found that there was sometimes a genuine, but small, net accumulation of organic carbon in soil under no-till compared to conventional tillage.

In addition, the soil sampling methods normally used tend to exaggerate the effect. Consequently, the climate change mitigation achievable from converting to no-till agriculture is likely to be overstated, the report states.

Prof Powlson said: “Overstating the climate change benefits of no-till is serious as it gives a falsely optimistic message of the potential to mitigate climate change through altered agricultural practices.

“If the climate change mitigation achievable through adopting no-till is far less than claimed, then there is even more pressure to decrease greenhouse gas emissions from other aspects of agriculture, and from other sectors of human activity.”

The authors concluded, however, that no-till has a role to play as one of the strategies contributing to global food security and the protection of soils, and therefore to climate change adaptation through building agricultural systems that are more resilient to climate and weather variability.

See the full report.