DR. Don Research Update
Life cycle analysis of a crop system, Part 2
Using LCA to compare organic to conventional winter wheat production

By Don Lotter

February 12, 2004: The last research update introduced the concept of life cycle assessment (LCA) and how it is being developed for crop production by a team of German scientists (View Part 1). In the first of their two papers the researchers develop the framework for doing a comprehensive LCA on a crop system. In the second paper, summarized here, they describe how the LCA was done on winter wheat, using data from the classic Broadbalk Experiment in Rothamsted, England.

Using LCA, the researchers examined the environmental impacts of the production of one ton of wheat at different levels of nitrogen fertilizers – 0, 48, 96, 144, 192, 240, and 288 kg/ha.

The agricultural operations that were included in the study were:

  • Phosphate, potassium, and Mg application
  • Soil preparation and tillage
  • Seedbed preparation and seed drilling
  • Ammonium nitrate application
  • Herbicide applications
  • Fungicide applications
  • Combine harvesting and bale pressing

The resources used in these operations were totaled for their cost in:

  • fossil fuel use
  • climate change
  • ecosystem degradation
  • acidification (acid rain etc.)
  • terrestrial eutrophication
  • aquatic eutrophication

Energy use was assessed for:

  • fertilizer production
  • transportation
  • farm machinery production, repair, and use
  • seed production
  • production of herbicides, fungicides, and pesticides
  • P and K fertilizer production
  • Non-energy related impacts were assessed for things like cadmium pollution from P fertilizer applications and eutrophication from N and P.

Each of these environmental impact areas is weighted so that a single score (EcoX) can be computed. This was done for each level of N fertilizer for producing one ton of wheat.

Since wheat yields at the different N rates took the classic diminishing returns curve, plateauing at between 96 and 144 kg/ha, the EcoX score was lowest (best) for these levels of N. This is because at the low N levels the crop operations were the same and the yields much lower, so the EcoX score was much higher. At the high end of the N rates, aquatic eutrophication caused the scores to skyrocket.

Energy use did not figure prominently due to the authors’ placing agricultural energy use in perspective to total societal energy use, which comes out to about 4%. This may or may not bode well for future LCA comparisons of organic vs. conventional cropping systems. Organic crop production generally takes significantly more tractor use for tillage and weed control, accounting for more fossil fuel use. However, the energy use in synthetic N fertilizer production for conventional agricultural generally outweighs tractor fuel use in organic systems.

The use of manures in organic farming takes a huge load off of the environment, as those manures would ordinarily need to be disposed of, at high cost. Any LCA should show this as a large difference between organic and conventional systems.

The other area that would show large differences is in the eutrophication category. Organic systems consistently show far less leaching of nitrates and phosphorus loading into waters. Since this area has a high priority in the authors’ LCA framework, organic systems would score well here.

The lower crop yields in organic systems however, will, bring the organic EcoX score down substantially. Recent research has shown however, that organic crop systems can yield 90% to 95% of conventional, so the EcoX score in this comparison will depend heavily on yield. The exception to this is in Europe where conventional grain production tends to outyield organic systems by 20-25%. It will be interesting to see how organic vs. conventional comparisons come out.

Brentrup, F. et al. 2004. Environmental impact assessment of agricultural production systems using the life cycle assessment methodology II. The application to N fertilizer use in winter wheat production systems. European Journal of Agronomy. 20, 265-279.

Don Lotter has a Ph.D. in agroecology and has worked in sustainable agricultural development in North America, Latin America, and Africa over the past 25 years. He can be contacted via his website www.donlotter.com

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