Comparing Environmental Impacts of Organic and Conventional Agriculture

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DOES ORGANIC FARMING REDUCE ENVIRONMENTAL IMPACTS? --A Meta-analysis of European Research Tuomisto (2012)


Organic farming practices have been promoted as, inter alia, reducing the environmental impacts of agriculture. This meta-analysis systematically analyses published studies that compare environmental impacts of organic and conventional farming in Europe.
The results show that organic farming practices generally have positive impacts on the environment per unit of area, but not necessarily per product unit.
Organic farms tend to have higher soil organic matter content and lower nutrient losses (nitrogen leaching, nitrous oxide emissions and ammonia emissions) per unit of field area. However, ammonia emissions, nitrogen leaching and nitrous oxide emissions per product unit were higher from organic systems.
Organic systems had lower energy requirements, but higher land use, eutrophication potential and acidification potential per product unit. The variation within the results across different studies was wide due to differences in the systems compared and research methods used.
The only impacts that were found to differ significantly between the systems were soil organic matter content, nitrogen leaching, nitrous oxide emissions per unit of field area, energy use and land use. Most of the studies that compared biodiversity in organic and conventional farming demonstrated lower environmental impacts from organic farming. The key challenges in conventional farming are to improve soil quality (by versatile crop rotations and additions of organic material), recycle nutrients and enhance and protect biodiversity. In organic farming, the main challenges are to improve the nutrient management and increase yields. In order to reduce the environmental impacts of farming in Europe, research efforts and policies should be targeted to developing farming systems that produce high yields with low negative environmental impacts drawing on techniques from both organic and conventional systems.


Methodology/Principal Findings

We report the results of a study examining the environmental impact of several new synthetic and certified organic insecticides under consideration as reduced-risk insecticides for soybean aphid (Aphis glycines) control, using established and novel methodologies to directly quantify pesticide impact in terms of biocontrol services. We found that in addition to reduced efficacy against aphids compared to novel synthetic insecticides, organic approved insecticides had a similar or even greater negative impact on several natural enemy species in lab studies, were more detrimental to biological control organisms in field experiments, and had higher Environmental Impact Quotients at field use rates.
These data bring into caution the widely held assumption that organic pesticides are more environmentally benign than synthetic ones. All pesticides must be evaluated using an empirically-based risk assessment, because generalizations based on chemical origin do not hold true in all cases.


It is commonly presumed that organic agriculture causes only minimal environmental pollution. In this study, we measured the quality of percolating water in the vadose zone, underlying both organic and conventional intensive greenhouses. Our study was conducted in newly established farms where the subsurface underlying the greenhouses has been monitored continuously from their establishment.
Surprisingly, intensive organic agriculture relying on solid organic matter, such as composted manure that is implemented in the soil prior to planting as the sole fertilizer, resulted in significant down-leaching of nitrate through the vadose zone to the groundwater. On the other hand, similar intensive agriculture that implemented liquid fertilizer through drip irrigation, as commonly practiced in conventional agriculture, resulted in much lower rates of pollution of the vadose zone and groundwater. It has been shown that accurate fertilization methods that distribute the fertilizers through the irrigation system, according to plant demand, during the growing season dramatically reduce the potential for groundwater contamination from both organic and conventional greenhouses.


Mitigation of greenhouse gas emissions in European conventional and organic dairy farming A. Weiskea, , , A. Vabitschb, J.E. Olesenc, K. Scheldec, J. Michela, R. Friedrichb, M. Kaltschmitta 2005

On average for all European dairy regions, the emissions from organic production systems were approximately 1.6 kg CO2-eq. kg−1 milk and thus 10% higher compared to the conventional model farms (1.4 kg CO2-eq. kg−1 milk).
When calculating the emissions on the basis of milk production, organic farms tended to have higher emissions than conventional farms at similar farm N surplus and N efficiency
The relationship was strongly significant for both organic and conventional farms, but with slightly higher GHG emissions from organic farms at similar farm N efficiency. This may partly be due to the higher estimated CH4 emissions from enteric fermentation due to a higher proportion of forage crops in the diet.

Greenhouse gas mitigation by agricultural intensification Jennifer A. Burneya,b,1, Steven J. Davisc, and David B. Lobella,b 2010

Intensive agriculture is preferable to less input agriculture. This has saved 161 GTC carbon so far since 1961 - 2005. soils continue to act as carbon stores but would become carbon sources if ploughed.

Comparison of Twelve Organic and Conventional Farming Systems: A Life Cycle Greenhouse Gas Emissions Perspective Kumar Venkat Journal of Sustainable Agriculture 36(6) · July 2012

Given the growing importance of organic food production, there is a pressing need to understand the relative environmental impacts of organic and conventional farming methods. This study applies standards-based life cycle assessment to compare the cradle-to-farm gate greenhouse gas emissions of 12 crop products grown in California using both organic and conventional methods.
The results show that steady-state organic production has higher emissions per kg than conventional production in seven out of the 12 cases (10.6% higher overall, excluding one outlier). Transitional organic production performs better, generating lower emissions than conventional production in seven cases (17.7% lower overall) and 22.3% lower emissions than steady-state organic. The results demonstrate that converting additional cropland to organic production may offer significant GHG reduction opportunities over the next few decades by way of increasing the soil organic carbon stocks during the transition. Non-organic systems could also improve their environmental performance by adopting management practices to increase soil organic carbon stocks.

Evaluation of conventional and organic agricultural 0production in relation to primary energy inputs and certain pollution gas emissions Federal Ministry for Food, Agriculture and Forestry (BML), Murphy, D. P. L.;, Roever, M., and Heinemeyer, O.

A form of farming with reduced use of mineral N-fertiliser by integration of crop and animal production combined the use of the local concentrate feed-stuffs production is advantageous with regard to primary energy consumption and greenhouse gas emissions. Such a system can be conventional or organic.

Monitoring GHG from manure stores on organic and conventional dairy farms R.W. Sneath, , F. Beline, M.A. Hilhorst, P. Peu 2005

Organic farming methods are claimed to be more environmentally friendly than conventional methods and the EU MIDAIR project had an overall aim to compare emissions from organic dairy farming with conventional methods of milk production. Manure stores are the second largest source of methane emissions (after enteric fermentation) on European dairy farming.
Large uncertainties in the measurement methods meant that even in the case of the uncovered stores differences between the two farming systems could not be said to be significantly different.

Methane and nitrous oxide emissions from organic and conventional rice cropping systems in Southeast China Yanmei Qin, Shuwei Liu, Yanqin Guo, Qiaohui Liu, Jianwen Zou

The results of this study suggest that organic cropping system might not be an effective option for mitigating the combined climatic impacts from CH4 and N2O in paddy rice production.

Comparing intensive, extensified and organic grassland farming in southern Germany by process life cycle assessment Guido Haas, , Frank Wetterich, Ulrich Köpke 2001

Analysing the impact categories biodiversity, landscape image and animal husbandry, organic farms had clear advantages in the indicators number of grassland species, grazing cattle, layout of farmstead and herd management, but indices in these categories showed a wide range and are partly independent of the farming system.
Lower CO2- and N2O-emissions of the organic farms are compensated by a higher emission of CH4 per unit of produced milk because of lower milk performance.

Life cycle assessment of conventional and organic milk production in the Netherlands 2008 M.A. Thomassena, , , K.J. van Calkerb, M.C.J. Smitsc, G.L. Iepemad, I.J.M. de Boera

In this paper, two Dutch milk production systems, i.e. a conventional and an organic, were compared on their integral environmental impact and hotspots were identified in the conventional and organic milk production chains.
Results showed better environmental performance concerning energy use and eutrophication potential per kilogram of milk for organic farms than for conventional farms. Furthermore, higher on-farm acidification potential and global warming potential per kilogram organic milk implies that higher ammonia, methane, and nitrous oxide emissions occur on farm per kilogram organic milk than for conventional milk. Total acidification potential and global warming potential per kilogram milk did not differ between the selected conventional and organic farms. In addition, results showed lower land use per kilogram conventional milk compared with organic milk.

Environmental impact assessment of conventional and organic milk production. Imke J.M de Boer 2003

Organic milk production inherently increases methane emission and, therefore, can reduce global warming potential only by reducing emission of carbon dioxide and nitrous oxide considerably.

Emissions of nitrous oxide from arable organic and conventional cropping systems on two soil types Ngonidzashe Chirindaa, c, , , Mette S. Carterb, Kristian R. Albertb, Per Ambusb, Jørgen E. Olesena, John R. Porterc, Søren O. Petersena 2006

Nitrous oxide emissions were similar or higher from conventional than from organic rotations except in Austria, where the input of N in manure was much higher from the organic rotation than from the conventional rotation

Fluxes of nitrous oxide and methane, and nitrogen leaching from organically and conventionally cultivated sandy soil in western Finland E. Syväsalo, K. Regina, , E. Turtola, R. Lemola, M. Esala 2006

Nitrogen leaching and gaseous N2O losses were slightly larger from organic grass than from conventionally cultivated grass, and the difference was even more obvious when the losses were calculated per yield.

The crop yield gap between organic and conventional agriculture Tomek de Ponti , Bert Rijk , Martin K. van Ittersum 2012

The crop yield gap between organic and conventional agriculture. We analyzed 362 published organic–conventional comparative crop yields. The organic yield gap is 20%, but differs somewhat between crops and regions. We found a weak indication of an increasing yield gap as conventional yields increase. We hypothesize that when upscaling to farm/regional levels the yield gap will be larger. In that context, research is needed at farm and regional level and on nutrient availability.

Comparing the yields of organic and conventional agriculture Verena Seufert, Navin Ramankutty & Jonathan A. Foley 2012

The average organic-to-conventional yield ratio from our meta-analysis is 0.75 (with a 95% confidence interval of 0.71 to 0.79); that is, overall, organic yields are 25% lower than conventional. This is just the overall average, however: as the figure below shows, there is considerable variability amongst different crops.

Environmental impact of meat meal fertilizer vs. chemical fertilizer Resources, Conservation and Recycling, 55(11), pp.1078–1086. Spångberg, J. et al., 2011

One of the challenges for organic farms without access to manure is to find sustainable sources of plant nutrients, since only natural, renewable and regenerative resources may be used

Food production vs. biodiversity: Comparing organic and conventional agriculture Gabriel, D. et al., 2013. . Journal of Applied Ecology, 50(2), pp.355–364.

When controlling for yield, diversity of bumblebees, butterflies, hoverflies and epigeal arthropods did not differ between farming systems, indicating that observed differences in biodiversity between organic and conventional fields are explained by lower yields in organic fields and not by different management practices per se.
Given these results and the yield vs. biodiversity relationships observed in our study, it is likely that the greatest gains in biodiversity per unit crop yield would occur in mixed and low-productivity landscapes. This result conflicts with the existing consensus that maximal biodiversity gain will occur by promoting organic farms in homogeneous, intensive landscapes

The crop yield gap between organic and conventional agriculture. De Ponti, T., Rijk, B. & Van Ittersum, M.K., Agricultural Systems, 108, pp.1–9. 2012.

Feeding the world with organic agriculture may require more land than with conventional agriculture and hence the area of natural and semi-natural ecosystems may be lower, whereas the quality of biodiversity on and around agricultural land may be higher.

Organic food: buying more safety or just peace of mind? A critical review of the literature. Critical reviews in food science and nutrition, 46(1), pp.23–56. Magkos, F., Arvaniti, F. & Zampelas, A., 2006.

Of relevance, a recent study reported that soups prepared from organically cultivated vegetables (purchased directly from retail sale) had almost six times as much salicylic acid (median, 117 ng/g; range, 8–1040 ng/g) than conventional soups (me-dian, 20 ng/g; range, 0–248 ng/g)
Thus, the selection of pest-resistant varieties in organic farming could also mean that these plants have higher levels of natural toxins, or levels of greater potency.

previous attempts to increase disease resistance in potato, celery and parsnip varieties by use of wild type plants and resistance breeding programs, led to increased natural toxin concentrations and the withdrawal of these foods from retail sale (Ames and Gold, 1989; McGregor, 1998; Fenwick et al., 1990).

Nevertheless, it was recently reported that sulfur had to be applied in amounts 40% higher than a corresponding synthetic fungicide,

Environmental Impact of Different Agricultural Management Practices: Conventional vs. Organic Agriculture. Gomiero, T., Pimentel, D. & Paoletti, M.G., 2011. Critical Reviews in Plant Sciences, 30(1-2), pp.95–124.

The paper then outlines energy use in different agricultural settings: organic agriculture has higher energy efficiency (input/output) but, on average, exhibits lower yields and hence reduced productivity.
Possible drawbacks from organic fertilization have been re-ported by some authors (e.g., Tilman et al., 2002; Sieling and Kage, 2006; Kirchmann et al., 2007;Wu and Sardo, 2010): the

‘slow release’ of nutrients from organic compost or green ma-nures can be difficult to control and harness and may fail to match crop demand, resulting in N losses through leaching and volatilization. Moreover, in organic systems, competition with weeds can greatly reduce N intake efficiency

In addition,Wu and Sardo (2010) suggest that mulching with polyethy-lene sheets (permitted in organic farming) is more polluting than spraying glyphosate, and that flame weeders (permitted in organic farming) are more costly and energy demanding than glyphosate and much less efficient in the control of perennial weeds.

Approaches to assess the environmental impact of organic farming with particular regard to Denmark Hansen, B., Alrøe, H.F. & Kristensen, E.S., 2001. . Agriculture, Ecosystems and Environment, 83(1-2), pp.11–26.

Mechanical weed control is frequently used in organic farming, and tillage has been shown to cause high mortality amongst the eggs and young of skylarks.

Facing food insecurity in Africa: Why, after 30 years of work in organic agriculture, I am promoting the use of synthetic fertilizers and herbicides in small-scale staple crop production Lotter, D., 2014.. Agriculture and Human Values, (Pretty 1997), pp.111–118.

Herbicide-mediated zero tillage CA via backpack sprayer can sub-stantially increase conventional maize yields while at the same time nearly eliminating erosion and increasing rain-water capture up to fivefold. In my view the specter ofmassive soil loss via erosion and nutrient loss via tillage in Africa in the next dec-ades vastly overshadows the possible health effects of expo-sure to the chemical.

Effects of organic-farming-compatible insecticides on four aphid natural enemy species. Jansen, J.P., Defrance, T. & Warnier, A.M., 2010. Pest Management Science, 66(6), pp.650–656.

The results indicated the potentially high toxicity of natural pyrethrins for beneficial arthropods. Although this toxicity needs to be confirmed in field conditions, the toxicity levels obtained in the laboratory were similar to or higher than those of several synthetic insecticides known to be toxic in the field

Natural products in crop protection. Dayan, F.E., Cantrell, C.L. & Duke, S.O., 2009. Bioorganic and Medicinal Chemistry,

Weed management under organic agriculture practices is very problematic. While most methods rely on soil cul-tivation, hand hoeing, biocontrol, organic mulches, and ironically plastic (synthetic) ground cover, and the use of some natural prod-ucts is permitted

A meta-analysis of the differences in environmental impacts between organic and conventional farming Mondelaers, K., Aertsens, J. & Huylenbroeck, G. Van, 2009. British Food Journal, 111(10), pp.1098–1119.

This loss of ecosystem service is large in comparison to the benefit of a reduction in emission of nutrients and pesticides.
From the paper's meta‐analysis it can conclude that soils in organic farming systems have on average a higher content of organic matter. It can also conclude that organic farming contributes positively to agro‐biodiversity (breeds used by the farmers) and natural biodiversity (wild life). Concerning the impact of the organic farming system on nitrate and phosphorous leaching and greenhouse gas emissions the result of the analysis is not that straightforward. When expressed per production area organic farming scores better than conventional farming for these items. However, given the lower land use efficiency of organic farming in developed countries, this positive effect expressed per unit product is less pronounced or not present at all.