Indicators for Energy Balance

One important aspect in evaluating agricultural systems, which has been regrettably overlooked with only a few exceptions (e.g. CLM 1996; Gomez et al. 1996; Uhlin 1999b; EISA 2000; Hülsbergen et al. 2001; Hülsbergen et al. 2002; Tzilivakis et al. 2005) is that related to energy input, since energy intensity is a measure of the environmental effects associated with the production of crops (consumption of fossil fuel and other resources, emission of carbon dioxide and other combustion gases) (Hülsbergen et al. 2001).

An indicator based on energy ratio or energy productivity (namely, the output/ input ratio) is not always meaningful, first because the energy in output, namely in agricultural products, may have a negligible interest as explained by Pimentel (1980), like in the case of ornamentals, and second because an extremely high energy ratio can easily be achieved at the expenses of production whenever a very low input, even close to zero, is adopted; in this sort of budget, the input of solar energy is generally not considered, nor is that of human labour. The same consideration applies to energy intensity, defined by Biermann et al. (1999) as the ratio of energy input to that contained in the product and by-product, expressed in units of Grain Equivalent (GE); production in terms of GE parallels to some extent dry matter production (Biermann et al. 1999).

Energy gain, namely the difference between output and input, is a more significant indicator: to illustrate this point, consider two examples referring to a low-input and a high-input farming system (A and B system, respectively). In system A, an energy input of 2 GJ (GigaJoules)/ha gives origin to an output of 12 GJ (about 0.8 t dry matter); in system B, an input of 20 GJ produces an output of 60 GJ (about 3.5 t dry matter). Clearly, the low-input system A has a better (higher) energy ratio, namely, 12/2 versus 60/20, than system B; a better (lower) energy intensity than high-input system B, namely, 2/0.8 versus 20/3.5, but such better performance in terms of energy ratio and energy intensity masks the poorer productivity, as revealed by energy gain, 10 GJ in system A and 40 GJ in system B. If agriculture must feed evermore people without expanding the arable area, namely without further loss of forests, biodiversity, wildlife and recreational areas, increasing the unit output is of paramount importance.

Biermann et al. (1999) comment this point writing maximizing energy gains ranks first, also from the angle of energetic use of renewable resources. The energy intensity is particularly suited for rating product-related impacts on the environment (resources and energy consumptions, CO2 emission) and for deriving optimal fertilizer and production intensity levels. Their long-term research, comparing effects of fertilization with only mineral N, only organic N and combined mineral plus organic N, shows that the best results in terms of both energy intensity and energy gain were obtained when a combination of organic and mineral nitrogen was applied.

An analysis of energy indicators for Swedish agriculture (Uhlin 1999a) evidenced that, contrary to what many maintain, intensive systems are more energy productive than low-input, self-sufficient systems: compared to 1956, outputs in 1993 had a 40% increase as opposed to an input increase of only 14%, with a parallel enhance ment in energy gain. Considering the solar energy productivity of plant production, namely the gross biomass in plant production divided by total solar energy, a 75% increase can be appreciated passing from 1956 partly traditional agricultural systems to 1993 specialized, mechanized and fully fertilizer-based systems.

Illuminating indications can be obtained if the 'emergy' analysis is applied, since it can supply guidelines for the improvement of the 'Best Management Practices' (Cavalett et al. 2006) and for logically linking environmental and economic evaluations (Hau and Bakshi 2008). In the words of the latter authors, in fact emergy analysis provides a bridge that connects economic and ecological systems. Since emergy can be quantified for any system, their economic and ecological aspects can be compared on an objective basis that is independent of their monetary perception thus permitting to eliminate the highly subjective factors afflicting present economic researches related to environmental factors. They explain: Through the last two decades, economists have developed techniques to assign monetary values to ecological products and services. However, this assignment typically relies on consensus of boards of experts, often with tenuous physical and biological foundations, and generally scaled to some market-derived values that may be, for example, highly skewed by advertising. In contrast, emergy analysis is meant to be independent of human valuation, but based on the principles of thermodynamics, system theory, systems ecology and, ultimately contribution to survival.

Synthesis of Section 3.1 - Conventional, high input agricultural systems are not sustainable, but sustainability is difficult to define and reach. System approaches are required to flexibly combine solutions best fitting any specific condition, in order to satisfy the three pillars of sustainability. To evaluate solutions in turn indicators are required. Since energy input is a highly significant indicator of pollution, it deserves special attention. Emergy analysis is an excellent indicator, permitting to simultaneously evaluate economic and environmental aspects.

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