A long-term assessment of the emergy use in an Argentinean agroecosystem

D.O. FERRARO; BENZI, PATRICIA

Toulouse

Conferencia; 19th biennial ISEM Conference - Ecological Modelling for Ecosystem Sustainability in the context of Global Change; 2013

ISEM

The emergy synthesis could be a useful environmental indicator as it quantified both the energy required directly and indirectly to create a product or service. Although, it could be used as a basic measure of real wealth on a long term, there are a few studies showing the time trend of emergy flows in managed systems. Here, we used emergy synthesis for identifying historical trends in both ecological and economical productivity and efficiency in an Argentinean agroecosystem. The study site was located in the northwestern of Córdoba province (32°45′S, 62°10′W), within the subhumid area of the Pampean region (Argentina). We used agronomic and environmental data, covering the time period form 1984 to 2010, from a long-term experimental site. We analyzed the historical emergy performance of corn, spring soybean and the wheat/summer soybean double crop (i.e. summer soybean crop sowed immediately after wheat harvest). The emergy synthesis classified the system inputs as local renewables, local non-renewables and purchased and the sum is total system emergy use. The different flows are primarily expresses in their own units (joules, grams, dollars) and then multiplied by their solar transformities to transform them into emergy units (seJ). Finally, a set of emergy-based indices and ratios were calculated to evaluate system sustainability. The three crops studied shared a common temporal pattern characterized by three identifiable phases. The first (1984-1994) was characterized by a significant improvement of emergy metabolism due to 1) the decreasing of purchased emergy inflow, 2) the increasing efficiency of the purchased inflow (i.e. EYR), 3) the increasing of the overall system efficiency (i.e. transformity), 4) a greater system renewability, and 5) the increasing in the emergy received for emergy delivered in the economic system. The second phase (1995-2001) showed a break in this positive trend due to a plateau in 1) the system transformity, 2) the economic trade balance, along with an increase in the emergy purchased (used at lower efficiency). Finally, during the third stage (2002-2010) the cropping systems reduced the deterioration rate exhibited in the former period by reducing the EYR negative annual rate. Emergy accounting revealed the environmental costs associated with two technological changes that occurred simultaneously. Firstly, the increasing of purchased emergy was linked to higher emergy costs due to transgenic crops introduction by 1995. Oppositely, the adoption of zero tillage would mitigate the GMO environmental costs due to lower environmental pressure on soil condition and thereby increasing the return of emergy invested. The changes detected in the historical analysis would largely replicate the regional pattern in terms of technology adoption, and the results would allow extending the findings to other ecosystems in the Pampas region with similar characteristics.