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An overview of the energy data of agricultural operations in the united states

However, the potential for UA to impact energy demand beyond production is substantial e. In addition, figure 1 excludes wastewater and food waste treatment; therefore, a complete consideration of energy use associated with the expansion of UA will require an examination of not only food production but also energy inputs across the entire food system, including waste handling and treatment.

Changes in energy use relative to the status quo must also investigate the food—energy—water nexus to validate the environmental case for scaling up UA and avoid any unintended shift of impacts from one resource system i.

Energy benefits of urban agriculture Proponents suggest a number of energy-related benefits are realized through the reintroduction of food production within cities Howe and Wheeler 1999Garnett 1997Smit and Nasr 1992Kulak et al 2013. Meanwhile, peri-urban agriculture can preserve higher-yielding prime agricultural land Krannich 2006Francis et al 2012which has the potential to provide less resource-intensive production.

Looking at more sophisticated integrated operations vertical farms, integrated greenhousesexploited waste streams CO2, heat, macronutrients could offset energy requirements that are required for providing these inputs in conventional operations Despommier 2013Zhang et al 2013. Interactions with other components of the urban food—energy—water nexus Urban agriculture has the an overview of the energy data of agricultural operations in the united states to affect energy-related components of the food—energy—water system within urban boundaries and beyond.

Suggestions of positive and negative impacts, both within and beyond the urban boundary, are presented in table 2. It is important to note that energy demand for services required in UA can differ from those provided through open-field agriculture. An exploration of literature that can provide greater insight on how these different UA approaches can influence energy needs follows.

Energy demand for UA water systems Energy demand in irrigation systems are a noteworthy component of scaled-up UA that must be considered in order to avoid inadvertently increasing demand relative to conventional open-field systems. Irrigation systems in an open-field agricultural setting are relatively low-energy when compared with potable urban water systems that could be used in UA; in one study open-field irrigation energy demand is estimated at 0.

However, in a UA system, potable water may be used for irrigation and generally requires substantially more energy for treatment, with the Electric Power Research Institute 2002 suggesting an estimate of 1. Meanwhile, Racoviceanu et al 2007 estimate energy demand at 2. Data on Massachusetts' 2007 energy demand for water treatment and distribution suggests an average value of 1.

This latter California report also suggests that when desalination options are employed in water treatment, an additional 9. The types of secondary energy used can also vary for different types of irrigation, influencing both cost, overall energy efficiency, and GHG emissions.

For example, Ontario, Canada's field crop irrigation is typically powered by diesel systems, while greenhouse irrigation is generally powered by electricity Carol 2010.

  1. Urban agriculture could play a role in attenuating this phenomenon, by increasing surface albedo and the cooling effect of plant evapotranspiration Ackerman et al 2014. This latter California report also suggests that when desalination options are employed in water treatment, an additional 9.
  2. Urban agriculture could play a role in attenuating this phenomenon, by increasing surface albedo and the cooling effect of plant evapotranspiration Ackerman et al 2014.
  3. Transportation and supply chain considerations While UA and other forms of localization are often intuitively thought to reduce life cycle energy demand, the reality is more complicated Webb et al 2013.
  4. Further, if stormwater can be diverted from treatment plants to UA in jurisdictions using combined sewer systems, energy demand, as well as pollutants to receiving bodies, could be reduced. A summary of the energy implications of production methods is provided in table 3.

For example, hydroponic 13 systems have been shown to have lower water demand than soil-based production, in addition to avoiding the need for a solid growing medium and the associated energy inputs of its provision Albaho et al 2008. Focusing on energy, Shiina et al 2011 study hydroponic urban 'plant factories' temperature controlled, artificial lighting and humidity controlled in Japan, and show that the energy intensity of the production resulted in estimated greenhouse emissions of 6.

Continuing to use GHG emissions as a proxy for energy demand, this compares with estimates of 0. Meanwhile, Goldstein et al 2016a compared cumulative energy demand of rooftop hydroponic greenhouse tomatoes and 'conventional' production and find the former to be roughly ten times as energy intensive, with important implications for carbon footprint.

However, switching energy source from the Massachusetts electricity grid to hydroelectric or solar PV makes rooftop hydroponic greenhouse production less carbon intensive than conventional production. These demonstrate that are potential for trade-offs when addressing environmental footprints through UA if focusing on a single performance metric i.

Though, as hydroponic growing systems can be used in controlled, protected, and open-field growing systems and with a wide selection of hydroponic technology options available, variation can be expected in the yields and energy demand of hydroponic operations; this introduces uncertainty in applying these figures to specific contexts, but underscores the need for careful consideration in designing for energy and water demand reduction.

As examples, wastewater treatment in California and Massachusetts is estimated to require, on average, 1. This has the potential to be reduced if conveyance and treatment requirements are avoided through application of wastewater in UA.

Further, if stormwater can be diverted from treatment plants to UA in jurisdictions using combined sewer systems, energy demand, as well as pollutants to receiving bodies, could be reduced. Finally, depending on how UA is managed, runoff from open field urban farms could result in increased nutrient loads being passed down to receiving bodies or downstream wastewater treatment plants Pataki et al 2011.

Packaging materials The use of packaging materials can also potentially be avoided in UA operations, in instances of production for personal consumption or within shorter distribution chains such as when food is sold directly by the producer Garnett 1999.

Still, the authors noted that modified atmosphere packaging using plastics have been shown to increase shelf life by two or three times, which may reduce waste and, consequently, GHGs associated with tomato production and disposal. This waste reduction could then offset the embodied energy needed for the packaging material that provides this added shelf life.

The use of packaging does not need to be an all or nothing proposition; employing some packaging for various meal components can result in a net energy savings relative to 'typical' packaging configurations when accounting for avoided waste and marginal energy requirements; semi-prepared meals examined by Hanssen et al 2017 were slightly more energy efficient when compared with those prepared from scratch. It is generally important to recognize the embodied energy of the food products and packaging materials being considered; higher embodied energy food products cheese, beef, bread more easily justifying the additional energy inputs associated with packaging than unprocessed fruits and vegetables Williams and Wikstrom 2011.

Similarly, the application of plastic films and containers may be more easily justified when compared with more energy-intensive materials such as steel, aluminum, or glass. Transportation and supply chain considerations While UA and other forms of localization are often intuitively thought to reduce life cycle energy demand, the reality is more complicated Webb et al 2013. Broad-scale localization of agriculture has the potential to increase transportation energy, as well as associated GHG emissions, relative to the conventional supply chain if definitions of local and implications for modified supply networks, including transport modes, are not carefully considered.

Considerations for reducing food system energy demand while scaling up urban agriculture

Indeed, a commonly cited reason to pursue UA is to reduce energy-related impacts associated with transportation. Numerous studies from the literature Coley et al 2009Edwards-Jones et al 2008Pirog et al 2001 have challenged the common assumption that 'localizing' food production results in reduced transport energy use and GHG emissions, and effects on distribution networks need to be evaluated on a case basis to justify such a claim.

For instance, transport-related impacts for cheese shipped 20 000 km from New Zealand to consumers in England by boat were dominated by road-freight and consumer automobile use, highlighting the limitations of singular focus on transport distance Basset-Mens et al 2007. The GHG implications of external energy inputs to support year-round urban food production and their ability to overwhelm gains achieved through reduced distribution distances must be considered in the context of upscaling of urban food production.

Urban heat island mitigation The predominance of dark low-albedo surfaces in cities results in the absorption of solar radiation and elevated temperatures in and around urban areas, raising the demand for cooling energy the urban heat island effect; Oke 1973. Urban agriculture could play a role in attenuating this phenomenon, by increasing surface albedo and the cooling effect of plant evapotranspiration Ackerman et al 2014.

Vegetation situated on buildings has been shown to reduce individual building cooling demands in Toronto, Canada, Madrid, Spain and La Rochelle, France Bass and Baskaran 2001Saiz et al 2006Jaffal et al 2012. The importance of this ancillary benefit of UA could become more important with the increasing frequency and severity of heat waves under likely climate change scenarios Jansson 2013.

Impact of type of production system Assuming UA may involve the use of protective structures or controlled environments, it is relevant to consider the energy demand associated with such structures. Generally speaking, open-field and protected agriculture e. In the French case, heated operations required six times more energy per unit of weight than the protected system Boulard et al 2011.

Goldstein et al 2016a found similar patterns of variation for tomatoes depending on production method, with resource requirements presented in table 2 modified here to present consistent units. Nevertheless, studies that directly compare controlled-environment growing with open-field agriculture for certain crop types present a mixed picture.

The additional energy demand in the greenhouse operations is dominated by the greenhouse structure, in spite of some savings realized through reduced cultivation-stage fertigation infrastructure, nursery plants and irrigation needs.

Their study did not include the embodied energy of the greenhouse structure. The greater yield coupled with lower labor, machinery, and irrigation energy provide a net energy saving relative to open fields, in spite of greater fertilizer, electricity, and pesticide inputs for these greenhouses. This study also excludes embodied energy of greenhouse infrastructure.

When taken together, these studies suggest that inputs required for UA will be operation, crop, and climate dependent, emphasizing the need for consideration of these elements when making comparisons and considering UA expansion.

  • Numerous studies from the literature Coley et al 2009 , Edwards-Jones et al 2008 , Pirog et al 2001 have challenged the common assumption that 'localizing' food production results in reduced transport energy use and GHG emissions, and effects on distribution networks need to be evaluated on a case basis to justify such a claim;
  • Though, as hydroponic growing systems can be used in controlled, protected, and open-field growing systems and with a wide selection of hydroponic technology options available, variation can be expected in the yields and energy demand of hydroponic operations; this introduces uncertainty in applying these figures to specific contexts, but underscores the need for careful consideration in designing for energy and water demand reduction.

With respect to soilless production systems, Albaho et al 2008 state that aeroponic 15 systems require an uninterrupted electrical supply but it is unclear as to whether this energy demand is offset by lower inputs and higher yields relative to conventional controlled-environment or hydroponic systems.

A summary of the energy implications of production methods is provided in table 3.