Agriculture Reference
In-Depth Information
equivalent joules required per unit input. These are called unit emergy
values (UEV) and given in seJ/unit, e.g., seJ/g or seJ/J. Emergy used by
a system is divided into different categories [23] and in the following we
describe how they are applied in this study.
Local renewable resources (R).
The term “R” includes fl ows of sun,
rain, wind and geothermal heat and is the freely available energy fl ows
that an agricultural system captures and transforms into societal useful
products. We include the effect of rainfall as evapotranspiration. To avoid
double counting only the largest fl ow of sun, rain and wind is included.
Local non-renewable recourses (N).
This includes all stocks of energy
and materials within the system boundaries that are subject to depletion. In
agricultural systems, this is typically soil carbon and soil nutrients. In this
study we assume that these stocks are maintained.
Feedback from the economy (F)
consists of purchased materials (M)
and purchased labor and services (L&S) [23]. M includes all materials
and assets such as machinery and buildings. Assets are worn down over a
number of years and the emergy use takes into account the actual age and
expected lifetime of each asset. The materials come with a service or indi-
rect labor component. This represents the emergy used to support the labor
needed in the bigger economy to make the products and services available
for the studied system. It is refl ected in the price of purchased goods.
Labor and service (L&S).
In this study, the L&S component is ac-
counted for based on monetary expenses calculated from the sales price
of the vegetables. This approach rests on the assumption that all money
going into the system is used to pay labor and services (including the ser-
vices provided in return for government taxes or insurances). This revenue
is multiplied with the emergy money ratio, designated em£-ratio (seJ/£),
which is the total emergy used by the UK society divided by the gross do-
mestic product (GDP). Thus the em£-ratio is the average emergy used per
£ of economic activity. To avoid counting the service component twice,
UEVs assigned to purchased materials (M) are without the L&S compo-
nent.
Total emergy use (U).
The sum of all inputs is designated “U”. We use
three emergy indicators to reveal the characteristics of the food supply
system: (1) Emergy Yield Ratio (U/F), a measure of how much the system
takes advantage of local resources (in this study only R) for each invest-
