The goals of this study were to: (a) develop a robust, model-based life-cycle GHG emissions comparison of organic and conventional farming methods for a relatively large selection of crop products;
(b) use the best available production data for these crops from specific agricultural regions in the United States, including information on management practices; and (c) account for the effects of soil carbon sequestration in relevant farming systems taking into account the climate zone, moisture regime and soil type for the geographical regions.
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. In addition to analyzing steady-state scenarios in which the soil organic carbon stocks are at equilibrium, this study models a hypothetical scenario of converting each conventional farming system to a corresponding organic system and examines the impact of soil carbon sequestration during the transition. 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.
This study compares the environmental impacts of 12 distinct crop products that are grown in the agricultural regions of California using both conventional and organic methods. Using publicly available agricultural production data for these crops, it applies standards-based LCA techniques to compare the cradle-to-farm gate GHG emissions per kg of each crop product grown using each production method. In addition to analyzing baseline steady-state scenarios in which the SOC stock is at equilibrium in both the conventional and organic systems, this study models a hypothetical scenario of converting each conventional farming system to a corresponding organic system and examines the impact of soil carbon sequestration during the transition. In order to accomplish this last part, the study establishes the climate zone, moisture regime, soil type, land use, and management practices for each of the conventional and organic farming systems.
Of the 12 crop products, steady-state organic production has lower GHG emissions in only five cases. Steady-state conventional production has the lower emissions in the other seven cases. Average emissions for steady-state organic production are higher by 10.6% (excluding walnuts as an outlier). The reasons for this vary, including: lower yields and higher on-farm energy use in organic farming, the production and delivery of large quantities of compost or manure to organic farms, and the fact that emissions from the manufacture of synthetic fertilizers and pesticides used in conventional farming are not large enough to offset the additional emissions in organic farming.
Transitional organic production fares better than steady-state organic production. It generates lower GHG emissions than steady-state conventional production in seven cases, and 17.7% lower emissions on average (excluding walnuts). It also generates lower emissions than steady-state organic production in all but one case where they generate equal emissions. Soil carbon sequestration drives the emissions for transitional organic production lower by an average of 23.2% compared to steady-state organic production. The results demonstrate, within the limitations of the data and the modeling, that converting additional cropland to organic production over the next few decades may offer significant GHG reduction opportunities by way of increasing the SOC stocks during the transition. If those higher levels of carbon stocks can be maintained in the soil over the long term (as assumed in this study), then converting to organic production may indeed prove to be an important tool in the mitigation of climate change. The results also suggest the possibility that some non-organic farming systems may be able to improve their environmental performance by adopting practices to increase soil carbon stocks without entirely switching to organic methods.
Venkat K (2012). Comparison of Twelve Organic and Conventional Farming Systems: A Life Cycle Greenhouse Gas Emissions Perspective, Journal of Sustainable Agriculture 10.1080/10440046.2012.672378
NB: This study, like the MEXALCA study also finds treenuts to have very high GWP values, which I found surprising.
You can download the paper here (subscription access only). Alternatively you might want to contact the author, Kumar Venkat, who’s an FCRN mailing list member via the FCRN user pages (you’ll need to log in to do so).