Knowledge for better food systems

The role of no-till agriculture in climate change mitigation may be over-stated

This review, published in Nature Climate Change, 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 low soil disturbance as opposed to conventional tillage involving ploughing or other practices.

The benefits of no-till include improved soil quality and retention of water in soil for use by crops, something that presents an advantage in dry regions of the world. The review also states that promoters of no-till as a means of combatting climate change (among them the authors behind the Emissions Gap Report 2013 from UNEP) frequently refer to the potential amount of additional carbon that may be stored, or sequestered, in soil. 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. The research group find however that 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. Furthermore, the soil sampling methods normally used tend to exaggerate the effect. Therefore the authors conclude that the climate change mitigation achievable from converting to no-till agriculture is likely to be over-stated. Nevertheless, no till offers other advantages with relevance to food security: it can help protect and improve the quality of soils and contributes to the building of agricultural systems that are more resilient to climate and weather variability.

Abstract

The Emissions Gap Report 2013 from the United Nations Environment Programme restates the claim that changing to no-till practices in agriculture, as an alternative to conventional tillage, causes an accumulation of organic carbon in soil, thus mitigating climate change through carbon sequestration. But these claims ignore a large body of experimental evidence showing that the quantity of additional organic carbon in soil under no-till is relatively small: in large part apparent increases result from an altered depth distribution. The larger concentration near the surface in no-till is generally beneficial for soil properties that often, though not always, translate into improved crop growth. In many regions where no-till is practised it is common for soil to be cultivated conventionally every few years for a range of agronomic reasons, so any soil carbon benefit is then lost. We argue that no-till is beneficial for soil quality and adaptation of agriculture to climate change, but its role in mitigation is widely overstated.

Citation

David S. Powlson, Clare M. Stirling,  M. L. Jat, Bruno G. Gerard, Cheryl A. Palm,Pedro A. Sanchez & Kenneth G. Cassman, Limited potential of no-till agriculture for climate change mitigation, Nature Climate Change 4, 678–683, 2014, doi:10.1038/nclimate2292

The paper can be accessed here and an article discussing the paper can be read here.

Read more about no-till practices in agriculture in our research library here.  For an FCRN briefing paper on soil carbon sequestration based on a workshop we organised in 2010, see here.

You can read related research by browsing the following categories of our research library:
 

Add comment

Member input

Plain text

CAPTCHA
This question is for testing whether or not you are a human visitor and to prevent automated spam submissions.

Comments

Simon Ward's picture
Submitted by Simon Ward (not verified) on

It's never good to start with an apology. I do.  Unfortunately I do not have access to the full paper so my comments may be dealt with but I would appreciate any counter arguments to my suggestions. My interests are two fold:

1. Soil carbon depends on the rate of carbon addition less the rate of oxidation. A change of practice establishes a new equilibrium which is reached at progressively slower steps as it is approached. Rate of addition depends on crop and yield and in the UK at least, rate of addition is many times higher than 50 years ago. Rate of loss depends on temperature and moisture (both vary with soil type and location) as well as cultivation technique and conditions at the time of cultivation. Theory at least, would suggest that the impact would vary and could be large or small so any general statements require an enormous number of samples over many sites over many years. Is this correct and can we make general statements with confidence yet?

2. A key component in our temperate climate is water logging and nitrous oxide release from the nitrogen contained in the residues. Again depending on time of year and the factors above more residue added could result in more nitrous oxide release which may or may not result in more GHG release than gained through the carbon captured. I suspect nitrous oxide release is very dependent on time of year when the cultivation is carried out. Was the nitrous oxide release recorded? It is harder to measure but possibly more important. Theory would suggest nitrous oxide release would increase as the carbon equilibrium is reached and less carbon captured so the relationship might change. Was this found to be the case?

Geoff Beacon's picture
Submitted by Geoff Beacon (not verified) on

Thanks for this summary of the report.

One (unsurprising) point it makes is that tillage moves carbon down further in the soil and carbon counting should take account of this. Another good point is

Nevertheless, no till offers other advantages with relevance to food security: it can help protect and improve the quality of soils and contributes to the building of agricultural systems that are more resilient to climate and weather variability.

I found an interesting report a few years ago by the World Food Programme Malawi which distrusted the use of hybrid crops and fertilisers.

To get the money for inputs, people sell their crops and animals – the very items that they spent so much time, money and energy to raise! Each year the soil becomes more unhealthy, so each year the farmer tries to buy even more fertilizer and seed.

What I like about this report is that it gives guidance of how to create local, resilient food sources. The UNEP report just seems to be discussing another method of doing industrial grow-it-1000s-of-miles-away farming.

What we need is resilient, carbon-saving food production, which should also have the aim of increasing soil carbon. That means much of it should be local.

I would be interested in reseach that showed the best in class for food production rather than one, which investigated different attachments to the tractors - but where is the budget for that?

Links:

Food: Scientists vs amateurs.

World Food Programme Malawi, Low Input Food and Nutrition.

Simon Ward's picture
Submitted by Simon Ward (not verified) on

My worry is the "it can help protect and improve the quality of soils and contribute to the building of agricultural systems...". By implication this means that the opposite may be true and this is where the research is needed. Direct drilling will usually (but not always) increase the use of herbicide and the adoption of GM herbicide resistance technology has done a lot to increase the practical implementation of direct drilling. In some climates conventional ploughing and other cultivation allows growers to plant earlier without damaging the soil to extend the season and thus increase yields (and soil carbon). On some weakly structured soils deeper cultivation increases the water flow reducing root disease and again increasing yields. Nitrous oxide (because of its GWP) can throw the debate as far as GHG. Sadly life is complicated. 

Region

Region: 

Australasia

This region of Oceania comprises Australia, New Zealand, the island of New Guinea, and neighbouring islands in the Pacific Ocean. Its ecozone forms a distinct region with a common geologic and evolutionary history which has resulted in a set of unique types of animals and plants. Due to the reverse seasonality with the US and Europe, much food produce is exported to these countries in the winter from Australia and New Zealand. Except for the lush rainforest of Queensland and the east, much of the Australia is arid and unsuitable for arable agriculture. The country is considered highly vulnerable to climate change and associated impacts including droughts and wildfires.

View articles relating to Australasia

Source

Doc Type