|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
- 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
- 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