The Problems with a Large-Scale Shift to Organic Farming

Questionable Assumptions in the Case for Organic

A new study, led by the Research Institute of Organic Agriculture, gives the impression that a large-scale shift to organic farming would largely bring environmental benefits. And indeed, that’s how the paper has been covered. But if we look under the hood, the findings are dependent on several pretty questionable assumptions about diets and production systems that, together, make the paper’s conclusions hard to take too seriously.

The authors conclude that converting 100% of world food production to organic would nearly eliminate nitrogen pollution and pesticide use, and marginally reduce greenhouse gas emissions, at the cost of more land use and deforestation.

But the progress the authors describe in the paper is only feasible by assuming massive changes in how much meat people eat, how much food is wasted, and how efficiently farms operate – an ambitious if not unattainable scenario. Their findings also rest on several flawed and unrealistic assumptions about how productive organic farms can be with limited nitrogen. Under more realistic assumptions, scaling up organic agriculture looks far less appealing, leading to large environmental harms, with limited benefits.

Converting all food production to organic, according to the study, would increase the amount of land needed for agriculture by 33%, and deforestation up to 15%, but would reduce greenhouse gas emissions up to 7% compared to a scenario following current agricultural trends. This is an unacceptable environmental tradeoff and so the authors note that scaling up organic would only be desirable and feasible if food waste and meat production were cut. Cutting food waste by 50%, for instance, would also cut the amount of extra land needed.

These reductions may or may not be realistic. Meat demand is increasing as global population and incomes grow. Although many studies highlight the environmental benefits of reducing meat consumption, there is no clear path to doing so. And although cutting food waste is possible, a certain level of waste is inevitable. Regardless, these system changes do not depend on converting more land to organic. In fact, if cuts in meat and waste are possible, they would be even more beneficial when combined with conventional rather than organic farming.

Environmental consequences

The study finds that scaling up organic farming would cut nitrogen pollution, greenhouse gas emissions, and pesticide use, but a careful and critical reading shows otherwise. To come to these conclusions, the authors make three questionable assumptions: that organic farming could maintain high crop yields even when crops do not receive enough nitrogen, that organic farming could use nitrogen at least twice as efficiently as conventional farming, and that organic farms do not apply pesticides.

Organic farming prohibits the use of synthetic fertilizers, the primary source of nitrogen for crops worldwide.1 With less of this essential nutrient available, organic production tends to produce less food per plot of land – about 20-25% less on average, according to recent estimates.2,3 It therefore requires more land to grow the same amount of food as non-organic methods.4 The study incorporates this gap in yields into its estimates, but misses the mark when considering other ways that yields may be lower.

Assumption 1: Constant yields under insufficient nitrogen

The study’s estimates of additional land use from organic farming are likely underestimates, as other researchers such as weed scientist Chris Preston have noted. In modeling a scaling up of organic farming, the authors assume that farmers plant a legume crop every five years (using 20% of their land). They note that this might not provide enough nitrogen for crops to grow if more than 60% of the agriculture converted to organic. This suggests that organic farming at this scale would have an even higher yield gap and may not be able to meet global food demand. To grow enough food organically, even more land would need to be used to grow legumes and fix nitrogen. Before the advent of synthetic fertilizer, for instance, farmers would typically set aside 25-50% of their land to fix nitrogen5 – more than the 20% assumed in the study – and yields were still far lower than they are today. However, the study did not account for this, simply noting instead that organic agriculture would have “critically low N[itrogen] levels” and may require more nitrogen.

Additionally, the study overestimates the amount of nitrogen available to crops from legumes. The authors estimate that planting a legume crop every five years would provide enough nitrogen. However, they mistakenly assume that all of the nitrogen in crop residues (the part of the plant remaining after harvest) is taken up by subsequent crops.6 A wide variety of other types of studies find that only a fraction of this nitrogen is actually taken up – usually less than 30%.7 With at least 70% less nitrogen available, land use would need to be even larger to provide enough nitrogen and yields to meet food demand.

This additional need for land would require converting new land, such as tropical forests and grasslands, to cropland, resulting in significantly more deforestation, habitat loss, and greenhouse gas emissions than the researchers project. This would be a major setback not only for global conservation efforts, but also for climate mitigation.8 The study’s finding that converting to organic farming could reduce greenhouse gas emissions depends both on how much nitrogen fertilizer is used as well as on how much forests, which are rich carbon sinks, are converted to farmland. Therefore, the additional land use would likely mean that scaling up organic agriculture, particularly to 80 or 100%, would result in more emissions than conventional, not less.

Assumption 2: Improved nitrogen efficiency for organic, but not conventional

The study’s authors also grossly underestimate the difference in nitrogen use and pollution under conventional and organic farming. In comparing the two, they assume that organic farming could maintain production while using nitrogen 60-80% more efficiently, citing a paper by Nathan Mueller and colleagues. This is an unrealistic assumption – Mueller told me he would never use the results from the paper they cited to support their claims. Other studies have found that per unit of food production, organic farming often results in more nitrogen-related pollution due to the use of manure.9

More importantly, the authors don’t make the same assumption about improved efficiency for conventional farming, such that what they present as a comparison between organic and conventional is in fact far from apples to apples. If they did and farmers around the world were able to maintain yields while using nitrogen more efficiently, they could use far less synthetic fertilizer. Such a situation appears to be technically feasible; farmers in China and the American Midwest, for example, could use less fertilizer, while farmers in less productive regions could increase production by using more fertilizer.10 This decreased fertilizer use would generate substantially less greenhouse gas emissions (as well as nitrogen pollution) than the authors estimate in their study. Taking both this and the additional land use into account strongly suggests that meeting future food demand with organic farming would contribute more to climate change than conventional farming, not less.11

Assumption 3: Zero pesticide use under organic

The study also assumes that scaling up organic farming would eliminate pesticide use. This is a common misconception that many consumers hold. Organic farming prohibits the use of synthetic pesticides (with a few exceptions) but allows the use of various naturally derived pesticides. Some of these, such as copper sulfate, pose large ecological and human health risks.12 There is no simple or widely agreed-upon way to compare the environmental performance of these organic pesticides with conventional ones.13 However, it's clear that organic pesticides can be environmentally harmful, sometimes as much or more so than synthetic ones.14 For instance, pesticide use on a sample of organic vineyards in northern Spain was found to have a larger environmental impact than that on similar conventional vineyards.15

New Directions

There are pros and cons to organic farming. Many practices common in organic farming, such as cover cropping and planting diverse rotations, are beneficial. But organic’s restriction on synthetic fertilizer use (and to some extent on other inputs) limits its yields and increases its environmental impacts. Scaling it up around the globe and eliminating synthetic fertilizer use would further threaten forests, their rich biodiversity, and the climate.

Rather than focusing on organic production, we ought to promote any production method that minimizes land use and farming’s other environmental impacts while providing enough healthy food for everyone. In most, if not all cases, this will involve at least some use of synthetic fertilizer. In an upcoming essay, I take a hard-nosed look at how much extra land organic production requires and whether changes in production (rather than in food demand) that the authors here did not consider could allow a 100% conversion to organic farming.

1. Lassaletta, L., Billen, G., Garnier, J., Bouwman, L., Velazquez, E., Mueller, N. D., & Gerber, J. S. (2016). Nitrogen use in the global food system: past trends and future trajectories of agronomic performance, pollution, trade, and dietary demand. Environmental Research Letters, 11(9), 095007.

2. Ponisio, L. C. et al. (2014). Diversification practices reduce organic to conventional yield gap. Proc. R. Soc. Lond. B Biol. Sci. 282, 20141396.

3. Seufert, V., Ramankutty, N. & Foley, J. A. (2012). Comparing the yields of organic and conventional agriculture. Nature 485, 229–232.

4. It is important to note too that these estimates are misleading. The 20-25% “yield gap” specifically measures yields for a harvest of a single crop, e.g., corn. However, organic production may have fewer harvests per year on average or may be nutrient-limited outside of field experiments and therefore have lower yields than is often reported.

5. Crews, T. E., & Peoples, M. B. (2004). Legume versus fertilizer sources of nitrogen: Ecological tradeoffs and human needs. Agriculture, Ecosystems & Environment, 102(3), 279–297.

6. This is documented in the authors’ code: "04SetNewParameterValues_V2.gms":
*Z) FACTORS FOR FERTILIZER SUPPLY CALCULATIONS: ResiduesApplicationFactor(FAO_Countries,Crops,"Crop",Sys,"CurrentSituation")=1; 0.5; ResiduesNutrientUseEfficiencyFactor(FAO_Countries,Crops,"Crop",Nutrients,Sys,"CurrentSituation") = 1.

7. Peoples, M. B., Brockwell, J., Herridge, D. F., Rochester, I. J., Alves, B. J. R., Urquiaga, S., … Jensen, E. S. (2009). The contributions of nitrogen-fixing crop legumes to the productivity of agricultural systems. Symbiosis, 48(1–3), 1–17.

8. The researchers estimate that a reduction in greenhouse gas emissions from synthetic fertilizer manufacturing and application would offset emissions from deforestation, but note that emissions could easily be higher.

9. Clark, M., & Tilman, D. (2017). Comparative analysis of environmental impacts of agricultural production systems, agricultural input efficiency, and food choice. Environmental Research Letters, 12(6), 64016.

10. Mueller, N. D., West, P. C., Gerber, J. S., MacDonald, G. K., Polasky, S., & Foley, J. A. (2014). A tradeoff frontier for global nitrogen use and cereal production. Environmental Research Letters, 9(5), 054002.

11. The authors do not clearly decompose emissions from deforestation and fertilizers. But based on the author’s statement that 100% conversion to organic would reduce GHG emissions 3-7% including deforestation, and 8-14% excluding deforestation (mostly from eliminating emissions from fertilizer production), I assume that improving conventional nitrogen efficiency (by assuming 50% reduction in synthetic fertilizers) would result in a 4-7% reduction in GHG while avoiding deforestation. Therefore net GHG emissions under the two scenarios are similar when using the authors’ land-use projections. Given that these are underestimated, emissions under organic would likely be greater.

12. As the study’s authors note.

13. Kniss, A. R., & Coburn, C. W. (2015). Quantitative evaluation of the environmental impact quotient (EIQ) for comparing herbicides. PloS One, 10(6), e0131200.

14. Bahlai, C. A., Xue, Y., McCreary, C. M., Schaafsma, A. W., & Hallett, R. H. (2010). Choosing organic pesticides over synthetic pesticides may not effectively mitigate environmental risk in soybeans. PloS One, 5(6), e11250.

15. Arandia, A., & Aldanondo-Ochoa, A. (2011). Pollution shadow prices in conventional and organic farming: An application in a Mediterranean context. Spanish Journal of Agricultural Research, 9(2), 363-376.