Do organics have a lower carbon footprint?

There is not a strong correlation between organic food production methods and lower carbon footprints. Our analysis shows that some organic crop products grown in California -- including alfalfa, broccoli, some apples, some wine and raisin grapes, blueberries, and walnuts -- generate somewhat higher cradle-to-farmgate GHG emissions than comparable conventional products grown in the same region. We've also seen that other organics -- such as strawberries and some wine grapes -- have lower emissions.

What are the key reasons for this? Organics require many of the same inputs as conventional production -- such as irrigation, fuel, electricity and transportation -- and sometimes they use more of one or the other of these inputs depending on the geographical location and management practices. They do save the emissions generated from the production of synthetic fertilizers and pesticides, but their on-farm energy use from fossil sources -- including gasoline, diesel and electricity -- is comparable to conventional production and sometimes higher. Organics have slightly lower nitrous oxide emissions from nitrogen applied to the soil, but in the same order of magnitude as conventionals based on the IPCC model. It is likely that much of the compost/manure used in organic production is sourced locally (for example, from within a 200 mile radius), but local delivery of these materials typically does not use the most efficient transport (single-unit trucks as opposed to the semi-trailers used for long-haul transport) and transporting large volumes of these inputs adds further to the emissions. In some cases, there is an additional impact from the periodic planting of cover crops. Finally, some organic systems have a significantly lower yield than conventional systems and may also have less optimal economies of scale.

What about carbon sequestered and/or released from the soil? When land use and management practices have been unchanged for many years, it is widely accepted that the soil carbon content approaches a spatially-averaged stable equilibrium value specific to the local conditions. Unless the management practices have changed recently (for example, within the IPCC default transition period of 20 years between equilibrium values) on a given cropland, the soil carbon content must be considered to be unchanged on average. In such an equilibrium state, any new carbon added to the soil through organic amendments is balanced by the carbon dioxide released through oxidation of soil organic matter -- although these are biological processes and therefore not instantaneous. So, organics generally do not get credit for building soil carbon except in the transition years following a switch from conventional to organic production. The results cited here are all based on the assumption that the agricultural systems are in steady state and the soil carbon is at equilibrium.

What about meat production? Any differences in the emissions generated to produce organic and conventional feedstuffs (hay, grain, etc.) will be reflected in the overall carbon footprints of conventional and organic meats. But meat production is impacted significantly by processes that are independent of feed production: manure management and enteric fermentation (the latter for ruminant animals). So, two meat production systems that use similar management practices and similar feed recipes -- except for some minor differences in how and where the feedstuffs are produced -- will likely not show much difference in their carbon footprints.

What about meat and milk from grass-fed animals? I bring this up because some organic systems include a fairly significant grass-fed component. Ruminants that get most of their feed from forage and hay produce significantly more methane from enteric fermentation than animals that are mostly grain-fed. For a given amount of dry matter or gross energy consumed, the methane emissions can vary by a factor of 2-4 depending on the types of feed consumed. Plus, manure dropped on an open pasture generates more direct nitrous oxide compared to many managed systems. On the positive side, grass-fed animals do not consume grains produced and transported using fossil-fuel based inputs. On balance, grass-fed animal products from ruminants are likely to have higher carbon footprints compared to products from conventionally housed/fed animals (this is without considering any gains in soil carbon).

A recent article in Time magazine claims that grass-fed animals have lower net emissions – even with the higher methane emissions – because grazing animals help the soil sequester carbon by working manure and decaying organic matter into the soil. The article does not cite any literature sources. While there may well be a benefit during a transition period, it is unlikely that the soil carbon can accumulate indefinitely without reaching equilibrium.

See my next post for part 2 of this discussion.

Kumar Venkat

Comments

[Kumar Venkat]

These comments are from Peter Spendelow (President, Northwest VEG; Natural Resources Specialist, Oregon DEQ):

This is very interesting and helpful.

Two comments:

First, are you aware of the great work by Nathan Pelletier and Peter Tyedmers on organic vs. conventional agriculture for growing corn, soy, canola, and wheat in Eastern Canada? They presented it a couple of years ago at a life cycle analysis conference here in Portland, and found that for all four crops, greenhouse gas production was significantly less for organics. The difference was almost entirely due to the energy/greenhouse gas impacts of using synthetic fertilizer. Organic vs. conventional was otherwise similar. Here is a link to a paper:
http://www.springerlink.com/content/1k376251x727ju03/

Second comment regarding the Time article you mentioned. The reporter talked to Nathan Pelletier for hours and Nathan explained the complexities of modeling carbon storage in soils, and that grass-fed animals tended to have higher, not lower emissions. Although the reporter did quote Pelletier in her article, she appears to have ignored the science as Pelletier explained it, and instead just given the conclusions of the grass-fed beef growers and enthusiasts. It was a very poor, misleading article that Time published.

[Kumar Venkat]

Peter, thanks for your comments. I have seen that excellent paper by Pelletier, et al. My understanding is that they have done scenario modeling based on hypothetical organic models constructed using data from multiple literature sources – which is a very useful thing to do. In our case, we have simply analyzed each product system based on specific production data derived from regional cost & return studies and enterprise budgets – which are typically developed based on surveys of local farms. We’ve generally not made any major assumptions about the inputs or farming methods. As a result, there are several possible differences between their analysis and ours that are worth noting:

• They assume all organic nitrogen inputs to be derived from the cultivation of intercrops or cover crops. The production data we’ve used show that nitrogen inputs often come in other forms such as compost and other organic forms (at least for the crops that we’ve analyzed). These inputs are typically purchased, transported and applied in large quantities. We do assume that they will be sourced locally (from within a 200 mile radius), resulting in some additional impact from local transport as I explained in my original post.
• They assume on-farm fuel inputs to be similar for organic and conventional production. We find significant variation in total on-farm energy inputs – including fuels and electricity – and also a much bigger contribution to the overall GHG emissions.
• They estimate that organic yields are 90-100% of conventional yields for the crops in their study. We find a much larger variation (and reduction) in the organic yields, which in turn impacts the GHG emissions attributed to each kg of product from an acre of land.
• There seem to be some differences in the field-level direct and indirect nitrous oxide emission calculations, but I am not entirely clear about how they do it. We use the current IPCC guidelines for this and calculate these emissions based on the actual amount of synthetic or organic nitrogen applied per acre in each product system.
• They assume that organic systems do not use pesticides. We see heavy use of sulfur in many cases as a fungicide, which does contribute to the overall emissions.
• As a result of all the factors that I mentioned in my original post, we find that synthetic nitrogen fertilizer production is not the dominant contributor to the total emissions (it often contributes less than 10%).

I do want to reiterate my earlier point that we are not seeing a strong correlation between organic production and lower carbon footprints. There are certainly some organics that do better than conventionals, and the reverse is true as well in other cases. We still have work remaining in further validating our results, and then I’ll be able to share more of the results.

[Peter Spendelow]

Thanks for the detailed reply. It was very informative.

With the paper from Pelletier et al., what I knew of it came from their presentation in Portland, as I have not had access to the actual paper except for the executive summary. However, I do remember them making a point about using intercrops and cover crops extensively in eastern Canada and that farmers there do not have access to large amounts of manure the way our organic producers do in Oregon.

I certainly have a lot to learn on this subject. It seems that exactly how things are modeled, how greenhouse gasses are allocated across co-products, and what other assumptions have been made can greatly affect the results. I obviously need to find out more about the standards used for making these assumptions. One thing that particularly interests me is how manure is included in the modeling. To me, the fact that manure from non-organic cows can be used in organic fields makes it that organic crops still depend heavily on synthetic fertilizers, only that those fertilizers are cycled through corn and forage and then concentrated through a cow gut before coming to an organic farm. Does this get modeled as a "free" nitrogen source to the farm other than the energy to move and apply the manure, or should one allocate some of energy used in making the fertilizer (that is used to produce cattle feed) to the organic crop, because that is where the fertilizer eventually ended up via an indirect path. I'm particularly interested in this from the standpoint of looking into what are called "stock-free" agricultural techniques, which rely almost exclusively on cover crops and intercropping for preserving/restoring soil fertility, without the use of manures, blood meal, fish wastes, or other animal products.

[irrigation systems]

the blog is very informative. it gives good knowledge about the organic plants and tells about the truths regarding organic vegetation.

[Michael]

Hi Kumar,

Can you please cite the study(ies) on which you rely for the conclusion that the net methane production from grass-fed beef is higher than that for grain-fed? I've had a hard time finding numbers on this, aside from this limited study:

http://jas.fass.org/cgi/content/abstract/77/6/1392

And is this methane alone, or total GHG carbon-equivalents on LCA?

Thanks!

[Kumar Venkat]

Methane production for grass-fed beef is higher (by a factor of 2-4) compared to grain-fed. There are a number of studies that support this. The IPCC Guidelines for GHG Inventories (vol. 4, chap. 10) provide emission factors based on the research literature(as of a few years ago): http://www.ipcc-nggip.iges.or.jp/public/2006gl/pdf/4_Volume4/V4_10_Ch10_Livestock.pdf .

The higher methane production can potentially swamp out any advantage that grass-fed beef may have from the avoided production of grains. Our internal LCAs confirm this. Also see this recent published LCA: Pelletier, et al, Comparative life cycle environmental impacts of three beef production strategies
in the Upper Midwestern United States, Agricultural Systems (2010).

Kumar