Contributions to LCA Methodology for Agricultural Systems. Site-dependency and soil degradation impact assessment

Resumo

Life Cycle Analysis (LCA) is a meted for the environmental assessment of industrial systems. This thesis studies the applicability of LCA to agricultural systems, and suggests solutions for some of the weaknesses detected in the method. Based on a study of apple production in New Zealand, the factors mainly determining the results of agricultural LCA are analysed. It has been shown that the type of agricultural technology (e.g.: organic or integrated fruit production) decides some types of environmental impact (human toxicity, energy consumption), however it is not enough to predict them. Indeed, the results of the thesis show the high relevancy of the characteristics of the site of production on the results of the environmental analysis of agriculture, and therefore to importance of obtaining data on these characteristics for a credible study. Especially, the physical conditions of the site (soil type and weather), and producers technique (i.e.: how the producer applies the technology type, through the degree of mechanisation, amount of fertilisers used, composition of pesticides, irrigation technique) are the main elements of these site characteristics. For instance, energy consumption for field operations show differences of up to 50% between apple orchards of the same technology (organic or integrated), due to variations in farmers practices. In the case of the physical site conditions, the differences in soil types generate variations of up to one order of magnitude in the emissions of pesticides to groundwater, for the same substance applied in the same amount. Impacts from pesticides are shaped by to farmers practices as well, and the selection of different active ingredients produces great variations in the effect on human toxicity in the different apple orchards. Finally, the application of LCA to apple production in New Zealand has suggested several options for environmental improvement, and has allowed a quantified prediction of the environmental improvement derived from their application. Besides, the thesis suggests a new method for the analysis of impacts on soil quality in agricultural LCA, using Soil Organic Matter (SOM) as an indicator. The method suggests the use of existing mathematic models for the prediction of SOM level evolution as affected by agricultural practices, and its application is illustrated with an example. This new method is representative and applicable enough to include the life support functions of land in LCA, and is especially recommended for the inclusion of the impacts on soil quality in agricultural LCA. Indeed, the application of this method allows for more relevancy and credibility in comparative LCA of agricultural systems that treat soil quality in a different way, such as organic and Conventional / integrated agriculture. In addition, the application of the SOM indicator through the use of mathematic models increases the sensitivity of the calculation of other impact categories such as global warming (thanks to the prediction of carbon emissions / sequestration by soil) and eutrophication and acidification (thanks to the modelling of the nitrogen cycle).