Combining individual and collective management of animal manure to reduce environmental impacts on a territory scale

Combining life cycle analysis (LCA) and simulation modelling (SM) has been used to assess and improve a collective manure management plan set up in Brittany (north-western France) by a group of farmers to comply with current Nitrogen reduction regulations in agriculture. The plan studied aimed at organizing the spreading of slurry surpluses produced by 11 pig farms (representing 57.6 tons N/year) on crop land loaned by 22 crop farms located approximately 44 km away. LCA was used according to its normalized methodology to statically assess the potential environmental impacts based on 4 criteria: eutrophication, climate change, acidification and use of non-renewable energy. COMET, the dynamic systems model used in this study, has been implemented with the Vensim® software by coupling: logistics models, to simulate the transportation and spreading of manure, both at the individual (within farms) and collective (transfer plan) levels; biophysical models, mainly empirical, to simulate ammonia (NH3) and methane (CH4) emissions as the main criteria of the environmental evaluation with COMET. The approach encompassed four steps that alternated between the LCA and SM methodologies: (i) LCA was initially performed to assess the environmental impacts of two disposal scenarios, i.e. slurry biological treatment or transfer for application to remote crop farms. The analysis concluded the transfer scenario had the least environmental impact as, if properly implemented, it may save on the use of chemical fertilizers. (ii) SM using the COMET model simulated the logistics and agricultural feasibility of the transfer scenario to verify to what extent the collective management plan can be fully completed in due time on appropriate cropping systems. (iii) A second iteration of LCA was made to assess the environmental impacts of simulated variants of the transfer scenario, this time using simulation outputs instead of reference database information. These analyses showed important differences of impacts among the management options simulated. (iv) Finally, simulations with COMET were performed to examine the interaction between the individual level of management (manure spreading within animal farms) and the collective level (manure transfer plan to land loaners' crop farms). The variability of impacts between individual situations was very high, suggesting that farmer equipment should be adapted and collective rules made flexible to secure farm stock management. Beyond the results from the first three steps, this paper emphasises the more realistic outcomes achieved in the fourth and final step. This step allowed the variability of individual pig farm logistics and gas emissions to be analyzed, as well as simple techniques, that could be implemented by individual farmers to improve the whole system agricultural and environmental performance, to be checked. This paper concludes that benefits can be drawn from combining LCA and SM, as this makes possible to consider the diversity of actual farming situations and practices and, so, to design management rules balancing individual and collective needs. (Résumé d'auteur)