Assessing sustainability of a low-input single-farm vegetable box-scheme using emergy and LCA methodology.

Sustainable development implies necessarily making use of renewable resources to a larger extent. Thus a sustainability assessment has to identify hotspots for reducing use of non-renewable resources and potentials for substitution of these with renewable resources. LCA as well as emergy assessment provide tools for such analyses. Emergy is defined as the total solar exergy directly or indirectly required to make a given product or service and is measured in solar equivalent joules (seJ).
The two methodologies are to a large extent based on the same type of inventory of energy and material flows, but are based on different theories of values and system boundaries. LCA draws system boundaries around the studied system as supported by human dominated processes (resource extraction, refining, transportation etc.), whereas emergy accounting in addition considers processes occurring in natural systems and, thereby, also includes all direct and indirect flows of freely available resources such as sun, rain and wind. Another difference is that emergy accounting typically includes labor in order to take into account the indirect resources from society, e.g. infrastructure, needed to support the system. However, the emergy method lacks some of the standardization and robustness of LCA. In this study we apply both methods to the same case study.
The case considered is an organic stockless vegetable farm of 7 ha in UK which distributes its products in weekly boxes to 250 local consumers. The farm has systematically and successfully worked on reducing external inputs. The system provides over 70 varieties of seasonal vegetables as well as biodiversity conservation and other ecosystem services. As a main goal of the study was to locate opportunities for sustainability improvements for the food production, we chose the yearly production of the whole farm as the functional unit. Analyzing a single product brings the risk that improvements for one product are achieved at the expense of other products.
Contrary to expectation, emergy flow from the local renewable sources sun, rain and wind makes up only 16% (1.6% if including emergy support from labor) of the total emergy input to the system. The local non-renewable source ground water makes up 6%. Emergy flow of goods from society makes up the rest with fuel (28%), electricity (18%), woodchip compost (13%), potable water (8%) and machinery (6%) being the most important. Hotspots for minimizing resource use are fuels and electricity. Substitution of these would require the use of renewable energy. However, an increase in inputs from society may imply a lower net-yield to society from the farm and would thus be less desirable. The LCA data are currently being analysed and these results as well as the comparison between LCA and emergy analysis will be presented at the conference.
In conclusion, from a biophysical perspective, agricultural systems’ primary societal function is to convert local renewable flows of sun, rain and wind into food, fodder and fiber by investing a minimum of products and services from the society. Thus it is desirable to maximize farms’ use of local resources relative to imported resources. The emergy assessment’s unified measure of local and imported and renewable and nonrenewable resources adds an extra insight that can potentially lead to other suggested actions for improving sustainability.