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Review
, 365 (1554), 2991-3006

Energy and the Food System

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Review

Energy and the Food System

Jeremy Woods et al. Philos Trans R Soc Lond B Biol Sci.

Abstract

Modern agriculture is heavily dependent on fossil resources. Both direct energy use for crop management and indirect energy use for fertilizers, pesticides and machinery production have contributed to the major increases in food production seen since the 1960s. However, the relationship between energy inputs and yields is not linear. Low-energy inputs can lead to lower yields and perversely to higher energy demands per tonne of harvested product. At the other extreme, increasing energy inputs can lead to ever-smaller yield gains. Although fossil fuels remain the dominant source of energy for agriculture, the mix of fuels used differs owing to the different fertilization and cultivation requirements of individual crops. Nitrogen fertilizer production uses large amounts of natural gas and some coal, and can account for more than 50 per cent of total energy use in commercial agriculture. Oil accounts for between 30 and 75 per cent of energy inputs of UK agriculture, depending on the cropping system. While agriculture remains dependent on fossil sources of energy, food prices will couple to fossil energy prices and food production will remain a significant contributor to anthropogenic greenhouse gas emissions. Technological developments, changes in crop management, and renewable energy will all play important roles in increasing the energy efficiency of agriculture and reducing its reliance of fossil resources.

Figures

Figure 1.
Figure 1.
Primary energy use in agriculture, 1970–1995. Source: IPCC (2001). Light blue line, total fertilizers per ha cropland; brown line, cereal yield; purple line, total area equipped for irrigation; green line, tractors per ha; dark blue line, agricultural labour per ha cropland.
Figure 2.
Figure 2.
Global trends in the intensification of crop production (index 1961–2002/2005). Source: updated from Hazel & Woods (2008) based on FAOSTAT 2010. Dark blue line, industralized countries; pink line, economic in transition; green line, developing countries in Asia–Pacific; sky blue line, Africa; yellow line, Latin America; cyan line, Middle East.
Figure 3.
Figure 3.
Solar energy collection in harvested component of crops and fossil fuel energy requirements of Canadian (Ontario) crop production, in Giga-Joules (GJ) per hectare. Source: Samson et al. (2005). Grey bars, energy content of crop per hectare less fossil-fuel energy consumption; black bars, fossil energy consumption per hectare production.
Figure 4.
Figure 4.
Breakdown of energy used in major domestic crop production. Source: Williams et al. (2009). Green bars, fertilizer manufacture; red bars, pesticide manufacture; blue bars, post harvest; purple bars, machinery manufacture; black bars, field diesel.
Figure 5.
Figure 5.
Distribution of energy carriers used in field crop production. Source: Williams et al. (2009). Green bars, renewable %; red bars, nuclear %; grey bars, coal %; blue bars, natural gas %; black bars, crude oil %.
Figure 6.
Figure 6.
Effects of changing N supply on bread wheat using the Cranfield model. PE, Primary Energy; GWP, Global Warming Potential. Source: Williams et al. (2006). Black line, PE; red long dashed line, GWP; green long dashed line, land use.
Figure 7.
Figure 7.
Trends in global oil, gas and coal spot-market prices; 1961–2009 (US$ per GJ). Source: BP (2009); IEA (2009). Dark blue with diamonds, oil (Dubai): $ GJ−1; pink with squares, gas (EU): $ GJ−1; yellow with triangle, coal (EU): $ GJ−1.
Figure 8.
Figure 8.
Projected oil and gas price ranges to 2030; US$ per GJ. Source: US EIA (2009). Dark blue line, reference case ($130 per bbl oil); red line, high price ($200 per bbl oil); green line, low price ($50 per bbl oil); dashed violet line, gas: 2008 US$ GJ.
Figure 9.
Figure 9.
Energy consumed for 1 Kg wheat production in Maragheh region of Iran. Source: Tabatabaeefar et al. (2009). T1, mold board plough + roller + drill; T2, chisel + roller + drill; T3, cyclo-tiller + drill; T4, sweep + roller + drill; T5, no-till + drill.
Figure 10.
Figure 10.
Energy inputs into the main fertilizer building blocks; European average technology. Source: Jenssen & Kongshaug (2003).
Figure 11.
Figure 11.
Historic development in energy requirements in N-fixation for nitrogen fertilizer. Source: Konshaug (1998).
Figure 12.
Figure 12.
Percentage of world agricultural land that can be regarded as being under agro-forestry systems to varying intensities. Source: after Zomer et al. (2009). Dark green bars, >10%; green bars, >20%; light green bars >30%.

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