Driving forces for energy use in agricultural production

In an overview of the national economies of industrialised countries, agriculture accounts for only a small percentage of total energy use. In Organisation for Economic Co-opera-tion and Development (OECD) countries, an estimated 3 to 5 per cent of total energy use can be ascribed to the agricultural sector (FAO, 2004). Methodological and system-bound-ary settings might mask the true picture, owing to the large quantity of agricultural-pro-duction inputs supplied by other sectors. Looking at energy balances for the EU-25, agri-culture accounts only for 2.27 per cent of total energy use (covering coal, crude oil, petro-leum products, gas, nuclear, hydro, geothermal, solar, waste, electricity, heat and others) (OECD/IEA, 2005).

Nevertheless, energy use in agricultural production has been dealt with at length in both recent and older contributions to the literature. From the final consumer’s point of view, «about two-thirds of the energy use arises during the production of food, before it reaches the consumer’s shopping basket» (Jungbluth et al., 2000). Energy-use analysis has been performed from different viewpoints and with a broad range of system-boundary settings. These range from comprehensive international analysis, to national or sectoral analysis⁷, to analysis at regional (Franzluebbers and Francis, 1995; Ryan and Tiffany, 1998) or local level (Moerschner, 2000, Spugnoli et al., 1993). Analysis is performed irrespective of location (Pervanchon et al., 2002), or with regard to a specific field plot (Moerschner, 2000). Furthermore, investigations are carried out both independently of a specific produc-tion activity (Diepenbrock et al., 1995; Heyland and Solansky, 1979) and with regard to it⁸. Comparisons are made between organic and conventional production systems (Dalgaard et al., 2001; Ramharter, 1999) or between production systems with different intensity levels (Mrini et al., 2002). The focal point of the study may be food production (Carlsson-Kanyama and Faist, 2000) or bioenergy crops (Hanegraaf et al., 1998, Kaltschmitt and Reinhardt, 1997). In a broad range of studies, a comprehensive assessment of production systems is performed using Life-Cycle Analysis methodology, and thus covering non-re new able-ener gy use as one of a number of parameters (Antón et al., 2005; Antón et al., 2003; Sanjuán et al., 2005; Russo and Mugnozza, 2005; Antón et al., 2005a; Velden and Janse, 2004; Oude Lansink and Silva, 2003; Nemecek et al., 2005). In addition, non-renewable-energy use in agricultural production is considered in models used to assess the sustainability of produc-tion systems (e.g. Hülsbergen, 2003).

Apart from the definition of a functional unit as given in Chapter 1.6, which may have a sectoral-, field-, animal- or product-specific focus, a number of other parameters domi-nate the energy use of agricultural production. The relevant literature data is often difficult to compare, owing firstly to their individual scope (direct/indirect energy use), and secondly to the energy coefficients used in the calculation process at several levels of energy use (such as lower and upper heating value with or without the provision of the energy source,

7 Such as Pimentel (1980);

Stanhill (1984); Fluck (1992);

Outlaw et al. (2005); Conforti and Giampietro (1997);

Schnepf (2004); Robinson and Mollan (1982); Karkacier and Gokalp (2005); Ozkan et al.

(2004).

8 See Tzilivakis et al. (2005);

Pluimers et al. (2000); Basset-Mens and van der Werf (2005); Velden (1998).

etc.) covered by the different coefficients. Nevertheless, a brief overview is given below.

In plant production, mineral-fertiliser application is one of the most important energy sources used in agricultural production systems. Diesel fuel is another important input fac-tor in energetic terms. National-level analysis such as Outlaw et al. (2005) corroborates this, stating that over 55 per cent of the total energy used on US farms stems from diesel and fertiliser. As regards fertilisers, in 2002, 89 per cent were nitrogen-based, 4 per cent were phosphate-based, and the remaining 7 per cent were potash-based. Pesticides contribute another 18 per cent of the total indirect energy (Outlaw et al., 2005). In terms of indirect energy sources, only pesticide and fertiliser input are considered, whilst machinery and buil-dings are missing in the above-mentioned study. The statement that «nearly one-third of all the energy used in agriculture is for nitrogen fertiliser» (Fluck, 1992) underscores the importance of mineral fertilisers. Direct-energy use accounts for another third of total energy use (Fluck, 1992). The remaining share encompasses machinery, buildings, pesticides, seed and other inputs. This rough distribution of total energy use is also shown in Robinson and Mollan (1982).

Looking at the activity level and taking soft wheat as an example, the overall agricultu-ral picture is displayed. Depending on the system settings, mineagricultu-ral fertiliser accounts for up to 50 per cent of total energy use (Diepenbrock et al., 1995), followed by direct-energy sources. Other indirect sources such as machinery, buildings, plant protection and seeds follow. The role of fertiliser acquires even greater importance when we look at specific ana-lysis for experimental weed-management trials, where soft wheat accounts for up to 80 per cent of total energy use for fertilisers (Clements et al., 1995).

A shift to the process analysis of a plant-production activity shows the driving forces for energy use more precisely, with the analysis usually being carried out in specific condi-tions and within precise, region-specific system-boundary settings. Nevertheless, it can be shown that direct-energy use is largely driven by region-specific production conditions such as soil quality, which determines diesel-fuel and machinery requirements for soil prepara-tion. In many cases, soil preparation and harvesting represent the lion’s share of diesel-fuel consumption (Dalgaard et al., 2001; Tzilivakis et al., 2005; Ramharter, 1999; Moerschner, 2000). Comprehensive data on direct-energy use by agricultural machinery is provided by Rinaldi et al. (2005). Comprehensive machinery-use quantification is a rather complex task, and a number of different approaches are used in current analysis. Kalk and Hülsbergen (1996) developed a methodology similar to economic depreciation, using machinery weight, labour demand and repair coefficients to distribute the machinery weight over time and production activities.

As with machinery, it is no easy task to include building energy use in energy-use ana-lysis. Usually, owing to a lack of data, alternative approaches are chosen to consider the energy use. Depreciation according to practices for machinery is described in Kalk and Hülsbergen (1996). Literature data concerning the overall role of buildings in activity-spe-cific energy use varies sharply depending on the analysis in question (see Basset-Mens and van der Werf, 2005 or Diepenbrock et al., 1995). On a sectoral basis for the UK, buildings account for 4 per cent of total energy use (Robinson and Mollan, 1982).

In animal production, provision of feedstuffs is by far the most important driver for energy use. The provision of young animals accounts for the second-highest share in the overall balance of animal-production activities. Both are strongly linked to regional/national production patterns, and differ in their absolute value and share. Basset-Mens and van der Werf (2005) calculate that between 74 and 96 per cent of total energy use is required for crop and feed production, depending on the production system. Dalgaard et al. (2001) state a norm value of 2.5 GJ/livestock unit as farm-building and inventory requirements.

A number of activities require specialised production equipment usually linked directly and/or indirectly to high additional energy use. These include greenhouses for under-glass production, particularly if heated. Irrigation or grain drying can also be mentioned in this connection.

Many studies have dealt with these items, evaluating driving forces and inter-regional differences. Due to climatic conditions, energy use varies over a wide range. Whereas Medi-terranean greenhouses use very little energy (Antón et al., 2005a), the Netherlands requires large amounts of direct energy for heating and lighting⁹, which results in fuel consumption that is up to 17 times higher in Dutch tomato, sweet pepper and cucumber production than in Spain (Velden and Janse, 2004). It is not just in direct-energy terms, however, that differences can be described between regions: the energy use of buildings differs depen-ding on the system employed. The environmental-impact analysis of greenhouse types using LCA methodology shows the highest impact to be from a vaulted roof structure in zinc-plated steel with glass covering, whereas the lowest impact results from a pitched roof structure in wood with plastic film covering, a system widely used in the Mediterranean (Russo and Mugnozza, 2005). Once such energy-use data has been provided, the associa-ted CO₂ emissions can be determined, permitting horizontal comparisons between diffe-rent production activities (see Hanegraaf et al., 1998; Nemecek and Baumgartner, 2006) or vertical comparisons of individual technological alternatives. For comparisons, however, efficiency instruments are a commonly used tool, as shown in Oude Lansink and Silva (2003), where specialist vegetable-growing companies in the Netherlands are compared both in terms of the energy and CO₂ technical efficiency of their heating technologies, as well as economic preferability.

Irrigation is another region- and activity-specific production-system element linked to potentially high direct and indirect energy use. About 25 mio ha of agricultural land is irri-gated in Europe (Derbala, 2003), with 35 per cent using surface irrigation systems, 61 per cent using sprinkler systems and 4 per cent using localised systems. Energy use differs not only according to system, but also according to water source (either surface or reservoir water), and the amount of water used (Derbala, 2003; Jacobsen, 2006; Lal, 2004). In the USA, total direct and indirect energy use for irrigation is estimated at 21 per cent of the total energy used in farm production (Lockeretz, 1977), with electricity and natural gas being the leading energy sources. In the EU, recent analyses show that 65 per cent of all irrigation-pump energy is delivered by electricity, and the rest by diesel pumps (Rouxel, 2007).

Grain drying is a further production system which is linked to high direct and low indi-rect energy use. Grain drying is one of the few post-harvest processes considered in this study. The system boundary is set such that the primary agricultural good is available in a marketable form, which for most grains usually means a moisture content of 14 per cent (Nemecek et al., 2003; Sauer, 1992). Consequently, the energy use necessary for delivering the target moisture content is included in the study. The initial moisture content is a para-meter determined to a large extent by regional or even local harvest-weather conditions, and is rather difficult to predict (Atzema, 1994; Ryniecki et al., 1993).

In conclusion, it is important to highlight the differences occurring in international and inter-regional comparisons of agricultural-energy use such as those of Conforti and Giam-pietro (1997), where the output/input energy ratio of agriculture in 75 countries was com-pared by a cluster analysis, or in Nemecek and Baumgartner (2006), where, among other parameters, energy use of feed components such as oilseed rape, wheat, barley and peas was compared across four EU countries with their respective study regions.

9 Approximately 4 per cent of the Netherlands’ greenhouse gas emissions are caused by the Dutch glasshouse industry (Oude Lansink and Silva, 2003).

2.3 Agricultural-energy use in the context of greenhouse-gas