New review shows the role of no-till agriculture in mitigating climate change is "overstated"
According to a new review published in Nature, the role of no-till agriculture in mitigating climate change is "widely overstated".
In no-till with GM herbicide-tolerant crop systems, weeds are controlled not through ploughing but through herbicide applications.
The past couple of decades have seen a spate of claims that GMOs are going to save us from climate change, on the supposed grounds that herbicide-tolerant GMOs enable the adoption of no-till.
The soil in no-till systems is claimed to lock up or "sequester" carbon, in contrast with ploughed systems, in which carbon is released into the atmosphere as the climate-change-inducing gas carbon dioxide.
The new review found that there was sometimes a genuine, but small, net accumulation of organic carbon in soil under no-till compared to conventional tillage. But while there was extra organic carbon near the surface, at deeper levels there was less.
One of the authors, Prof David Powlson of Rothamsted Research in the UK, said, “Over-stating 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.”
Quite. Let's hope those consultants to the biotech industry, PG Economics, are paying attention.
Remember the billions of kg of carbon that they claim have been saved through the spread of no-till with GM herbicide-tolerant crops (weeds are controlled not through ploughing but through herbicide applications)?
In 2012 they claimed:
"Crop biotechnology has contributed to significantly reducing the release of greenhouse gas emissions from agricultural practices. This results from less fuel use and additional soil carbon storage from reduced tillage with GM crops. In 2010, this was equivalent to removing 19.4 billion kg of carbon dioxide from the atmosphere or equal to removing 8.6 million cars from the road for one year."
In 2014 they upped the figure again:
"The use of biotech crops has led to saving about 27 billion kg worth of carbon emissions that could have been released in the atmosphere if the technology did not exist, according to the 9th annual report by Graham Brookes of PG Economics, a UK-based company specializing in plant biotechnology.
"This is equivalent to taking 12 million cars emitting carbon dioxide and other greenhouse gases off the road, Brookes said."
Monsanto was also trying to claim carbon credits for no-till agriculture with Roundup applications.
In fact readers of GMO Myths and Truths will already know that the claimed carbon benefits of the "GM with no-till" farming model are illusory. The report explains:
"No-till fields do not sequester more carbon than ploughed fields when carbon sequestration at soil depths greater than 30 cm is taken into account. Studies claiming to find carbon sequestration benefits from no-till only measure carbon sequestration down to a depth of about 30 cm and so do not give an accurate picture."
The reference for this statement dates back to 2007 (Baker JM, Ochsner TE, Venterea RT, Griffis TJ. Tillage and soil carbon sequestration – What do we really know? Agric Ecosyst Environ. 2007;118:1–5).
And as Dr Doug Gurian-Sherman has pointed out, GM didn't much affect the adoption of no-till agriculture anyway.
With the publication of the new review, maybe PG Economics will finally catch on.
(Comment: Jonathan Matthews and Claire Robinson)
Limited potential of no-till agriculture for climate change mitigation
Farming Online, 31 July 2014
An international group of scientists, led by Professor David Powlson, Lawes Trust Senior Fellow at Rothamsted Research, have published a critical review in the journal Nature Climate Change which concludes that the role of no-till agriculture in mitigating climate change may be over-stated.
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. No-till 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 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. 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 UNEP Emissions Gap Report.
Organic Carbon overstated
The review found that there was sometimes a genuine, but small, net accumulation of organic carbon in soil under no-till compared to conventional tillage. But, much of the observed effects result from a redistribution of organic carbon with depth - extra organic carbon near the surface but less deeper in the soil. 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 over-stated.
The authors of the new paper conclude that no-till agriculture has a role to play as one of the strategies contributing to global food security and the protection of soils, and thus to climate change adaptation through building agricultural systems that are more resilient to climate and weather variability. In regions where no-till or reduced tillage is agriculturally appropriate it should be promoted on these grounds, but not on the basis of equivocal evidence for climate change mitigation. Climate change mitigation is a small, but useful, additional benefit, not the key policy driver for its adoption.
The review also states that those who promote no-till as a means of combatting climate change frequently refer to the potential amount of additional carbon that may be stored, or sequestered, in soil. However, in the UNEP report and elsewhere, the barriers to adoption of no-till tend to be ignored. The authors argue that there are numerous social, practical and infrastructural factors that can make its adoption difficult for farmers, especially small and resource-poor farmers in developing countries. These issues are being addressed by CIMMYT and others but progress in overcoming the barriers is often slow. Thus, even where there is a real potential for mitigating climate change, it is often difficult to achieve in practice.
More pressure to reduce emissions
Professor David Powlson of Rothamsted Research, which receives strategic funding from BBSRC, said “Over-stating 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.” He added “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”.