Energy, nutrient and economic cross indicators of cropping systems in northern Italy

Agro-ecological indicators are useful tools to provide synthetic representations of agricultural systems. Simple indicators
can be combined to calculate cross indicators, for example efficiencies, calculated as a ratio between two
simple indicators. In sustainability studies, efficiency is frequently calculated in energy terms (energy output / energy
input); however, other “output” and “input” terms can be used. In this study, we evaluated how the ranking
of systems changes when different metrics of agricultural production (economic gross margin vs. energy output) and
resource use (nutrients inputs and surpluses, fossil energy inputs, economic costs) are used. The calculations were
carried out for a study area in northern Italy (Sud Milano Agricultural Park), characterised by intensively cultivated
arable cropping systems (cereals and forage crops).
Crop types were ranked differently when metrics changed. In general, maize (a highly productive crop) had good
performances when evaluated using the output / input energy ratio, while rice was good when we used the ratios
based on gross margin. When energy or monetary outputs were divided by N surplus, all crop types had very similar
median values, suggesting a common energetic and economic efficiency of N use. Overall, different cross indicators
may provide a different representation of the system studied. This means that it is not possible to provide a
unique synthetic evaluation of sustainability, which instead depends on the indicator(s) chosen.We conclude that it
is very important to clarify the objective of sustainability studies and to select accordingly the most adequate indicators.