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.