When the abstract includes the word “metaanalysis” that is your first clue that reading the actual paper will be an exercise in trying to keep your eyes open. But as a dedicated columnist, I felt it was my duty to plow through two recent papers that both had that word, front and center, in their abstracts. More importantly, both papers evaluated the impact of organic food. The first, a study by statisticians and medical doctors from Stanford, evaluated the potential human health impacts of eating organically grown produce and meat in comparison to conventionally grown and raised produce and meat (Smith-Spangler et al., 2012). The second evaluated differences in soil carbon sequestration for organically managed versus conventionally managed soils (Gattinger et al., 2012). Both were published in highly prestigious journals and both were subject to peer review.
Before I get to the results, let me first describe what a metaanalysis is. When doing research, it must include enough replication to be certain the results are a consequence of the treatment rather than natural variability. The power of the results grows as the sample size grows: the larger the study, the more certain the researcher can be of their results. A metaanalysis takes data from all studies that meet their established criteria (usually for sufficient replication, sample size, data quality) and analyzes it all together so the results will be as good as all the available data out there.

Organic Food Study

The study on organic food evaluated the nutrients in the food, health of people who eat it, pesticide residues in the food and the people that eat it, and contaminants in the food including bacteria, E. coli and antibiotic resistant bacteria. The differences based on organically grown versus conventionally grown for these criteria were limited. Organically grown foodstuffs have higher phosphorus and higher phenols. There are more w-3 fatty acids in organic milk and chicken (good things).
Conventionally grown has about a 30 percent higher risk of pesticide contamination than organically grown (note that 7% of organically grown had pesticide residues). In general, bacteria were similar in both, although if one study was removed from the data set, there was a higher incidence of E. coli in organically grown produce than conventional. Conventionally grown chickens and pigs had higher risk for antibiotic resistant bacteria than organically raised animals. The authors noted a dearth of studies on long-term health differences, but from the few studies that exist, no health differences were noted based on whether what is consumed is organically certified. The big, over arching conclusion was that there is not a really big difference between organically grown and conventionally grown for any of the factors evaluated. Results of this study were widely reported and hotly debated.

Soil Carbon Study

The second study looked at differences in soil carbon as a result of organic farming, again using results from all available data. Almost all of the data sets included were from North America, Europe and Australia/New Zealand. A few were from Asia and none from Africa. Across all continents, growing organically resulted in much greater soil carbon storage than growing conventionally, about 3.5 +/- 1 ton per hectare. This translated to an annual increase of about 0.4 tons/hectare/year.
The authors noted that some people object to the use of composts and manures derived from feedstocks or animals off the farm to be included in these calculations. The concern is that large inputs of external organic matter are the soil carbon equivalent of paying a ringer to take your SATs. Based on that they also looked at whether organic farming practices with minimal external inputs — the equivalent of one livestock unit of manure per hectare. They still came up with significant increases in soil organic matter, 2.2 +/- 1.7 tons per hectare but annual sequestration rates for organic farms were no longer appreciably different from conventionally managed farms.
The authors then estimated the impact this increase in soil C storage would have on annual CO2 emissions if adopted on a large scale to Europe and the U.S. These areas provided the most data analyzed by the authors and so also provided an increased level of confidence in the results. By applying organic practices, including compost and manure addition, we would meet 13 percent of the needed CO2 reduction to 1990 levels required to be on course for 2030. This estimate doesn’t consider additional benefits such as reduced use of synthetic fertilizers and the emissions associated with their manufacture.

Going Further

As a scientist I am happy to accept the results of both studies as valid. As a person who dreams of sustainably grown food, I can express my frustrations. My frustrations are not with the studies themselves but with the constraints that govern both organic certification and carbon accounting. Let’s start with the organic certification. The USDA National Organic Program rules were a fabulous first step. Provisioning of organically grown meats and vegetables has grown into a multibillion dollar business, and as the second study shows, also leading to increased carbon storage in soils. But the rule is not perfect and I would argue it is time for guidelines for sustainable systems. Adhering to organic certification is an expensive and sometimes prohibitively rigid process, something that is not always practical for smaller farms, local growers, and many municipal residuals.
While the organic versus conventional food metaanalysis showed little difference between the two, other studies have shown that locally grown has better flavor and that availability of locally grown increases the proportion of fresh fruits and vegetables in people’s diets. A sustainable standard, or even better guidelines, would allow a wider range of growers, including the back yard variety, to take lessons from organic certification and apply them. Ideally, guidelines would also allow more flexibility so that sustainable soil resources— including a broader range of urban derived soil amendments — would be accessible. Increased demand for these residuals might be sufficient impetus for more communities to stop talking about green energy from burning wet stuff and start producing products suitable for land application.
Which brings us to the next level of frustration. As the authors of the soil carbon paper pointed out, a portion of the carbon accountants do not approve of external inputs. They want carbon inputs to be limited to on farm sources: the cow, the six chickens and the pig. That is fine for the Old MacDonald version of a farm. However, as I wrote a long time ago (see “New MacDonald,” October 2007), our understanding of the ‘farm’ needs to expand to recognize that the traditional means of cycling organics on farms should be expanded. Farms produce for large urban populations. Working to recognize that organic urban residuals fit into this New MacDonald vision, as a substitute for those six chickens, provides for a much more sustainable system. One that should not only satisfy accountants, but help satisfy soils.
In short, believe the results of these two papers. Even if you can’t keep your eyes open while you try to read them. But put the results into a broader context: one that will help us to not only eat healthy, but maintain a healthier planet.
Sally Brown — Research Associate Professor at the University of Washington in Seattle — authors this regular column. Email Dr. Brown at slb@u.washington.edu.

References

Gattinger et al. 2012. Enhanced top soil carbon stocks under organic farming. Proceedings National Academy of Sciences www.pnas.org/cgi/doi/10.1073/pnas.1209429109
Smith-Spangler et al. 2012. Are Organic Foods Safer or Healthier Than Conventional Alternatives. Ann. Intern. Med., 157:348-366.