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Using a Life Cycle Assessment approach to develop an indicator of the impact of agriculture on soil quality (ACVSol)

Using a Life Cycle Assessment approach to develop an indicator of the impact of agriculture on soil quality (ACVSol)

Summary
Soils are an essential resource in both managed and natural systems, and maintaining soil quality is critical to the sustainable development of human activities, in particular agriculture. The difficulty in representing impacts on soil quality remains an unresolved problem in LCA because of soil’s spatial and temporal variability and the complex interactions among soil properties. It is crucial to consider soil quality in the environmental assessment of products, especially those with a majority of their life cycle in biological processes (such as agriculture and forestry). The objective of this study was to establish a framework for quantifying indicator(s) of impact on soil quality in a life cycle perspective, valid for all soil and climate conditions and considering both on-site and off-site agricultural soils. The method developed answers needs identified by Garrigues et al. (2012) for LCA indicators of impacts on soil quality. The case study focused on the soil-quality impacts of producing pig feed in Bretagne, France. The indicator categories considered were water erosion, soil organic matter (SOM) and compaction. Erosion and SOM impacts already exist in LCA approaches, but compaction impacts have yet to be estimated in detail in LCA.
The LCI and LCIA are based on simulation modeling, using models simple enough for use by non-experts, general enough to parameterize with available data at a global scale and already validated: RUSLE2 for water erosion (Renard and Ferreira, 1993), RothC for SOM (Coleman and Jenkinson, 2008) and COMPSOIL for compaction (O’Sullivan et al., 1999). Most of the input data necessary for establishing the LCI are common to the three midpoint indicators. Rules and recommendations for estimating or finding data are given to standardize the method. Guidelines are also specified to account for crop-based ingredients from multiple sites in products such as animal feeds. One difficulty lies in allocating soil-quality impacts of crop rotations to individual crops. Overall impact values result from the combination of soil, climate, and management characteristics for each crop in the feed. The erosion indicator represents a loss of soil, while the SOM indicator represents an increase or decrease in the stock of soil carbon stock. The compaction indicator represents a loss of soil porosity and distinguishes topsoil from subsoil compaction because the former is more easily reversible.
This method was tested with a case study of the production of a representative pig feed in Bretagne, France, containing 9 ingredients (e.g., maize, wheat, soybean meal, molasses) produced in 3 countries (France, Brazil, Pakistan). The method estimated that production of the ingredients in each tonne of pig feed led to an erosion of 166 kg of soil, a net loss of 41 kg of soil C, and a loss of pore space due to compaction of 27.3 m3. These global-scale impacts can be broken down into impact by country, crop, ingredient, and production stage. The framework allows for incremental improvement of the method through the inclusion of new soil-quality impacts. Improvement efforts will focus first on developing robust impact indicators for individual soil processes before considering whether to aggregate them into a single indicator. Nonetheless, a variety of aggregation approaches can be explored.

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Contact
INRA Rennes (Michael Corson)

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