Figure 3.4 indicates how between 1910 and 1970 the energy inputs to food produced in the USA


Figure 3.4

Figure 3.4 Energy input to food production from farmer to consumer in the USA: the number of calories put into the system to obtain one calorie of food. Probable values used for 1910 to 1937.

increased. Up to about 1920, the amount of energy used to produce and supply food to the consumer roughly equalled the amount of energy released when the food was eaten. By 1970 the amount of energy used to produce food had increased on average by eight times. So for every one unit of energy supplied to a person when eating food, eight times as much energy had gone into produc­ing that food. This is a significant increase in the energy required for food production.

Ratios between the energy content of food when eaten and the energy used to produce the food are referred to as energy ratios. In the United Kingdom detailed energy ratios have been calculated for a number of agricultural products. These took account of all the associated energy inputs up to the point where crops left the farm. In 1968 the average energy ratio for all foods in the United Kingdom was 0.2, which means that for every joule of energy provided by eating food, five joules were used to produce that food (Leach, 1976). Although less than the ratio of eight to one for food in the USA at that time, the trend of increasing energy inputs to food was similar.

When thinking about urban agriculture, we are assuming that during the initial stages of its integration into cities, fruit and vegetables will form the principal produce. This is on the basis that these crops provide the highest yields and value per area cultivated. In order to estimate what impact organic production might have on the embodied energy of crops we undertook a study of Leach’s figures for the embodied energy of farm crops (Leach 1976). Although the actual figures used by Leach relate to years between 1968 and 1972, the study gives an indication of potential energy savings. It should be noted that Leach’s figures include energy inputs up to the point at which a crop leaves the farm. They take no account of processing, packaging and dis­tribution to point of sale.

Figure 3.5 shows how the calculations were done and Figure 3.6 presents results for a range of crops.

These calculations take account of the possible reduction in yield due to the conversion from conventional agro-chemical-based production to organic farming. In this assessment we have used a worst case assumption – that organic farming yields are two thirds of those from conventional farming (Wright, 1994). This assumption leads to a relative reduction in benefits of organic production. However, some more recent estimates for yields from organic production are less pessimistic. Stanley refers to the Royal Agricultural Society for England, who state that, ‘Organic vegetables (yields) are comparable (with conventionally farmed) and potatoes 50 per cent less.’ (Stanley, 2002).

Figure 3.7 illustrates the situation usually presented for organic farmers. Yields per hectare may be lower than those for conventional farming, but the price paid per unit output is higher. The relationship between yield and price varies between one crop and another, and so in some instances organic production is more profitable than conventional pro­duction and in other cases less profitable (Lampkin and Padel, 1994). If organic yields for fruit and vegetables are similar to those from conventional production, as Stanley notes, then the economics of organic farming become far more attractive. In all of the above cases no allowance has been made for the added value provided by organic farming, for example, the promotion of biodiversity, reductions in greenhouse gas emissions and less leaching of fer­tilisers into groundwater.

Seasonal consumption

Earlier in the text, the consumption of local seasonal crops was referred to as an important element of urban agriculture. Not only do seasonal

Figure 3.5

0 2 4 6 8

Figure 3.5 Comparison of energy ratios for conventional and organic potato production of UK. Energy input and outputs measured in GJ per hectare per year.

Figure 3.6 Comparison of energy ratios for conventional and organic production of UK crops. An energy ratio is defined as the edible energy output of food divided by the energy input necessary to produce it.





Figure 3.8


crops reduce the need for the transnational ship­ment of foods, and hence reduce embodied energy due to transport, but also they have implications for how crops are grown locally.

One way of extending the season of crops is by using greenhouses. These provide a means of growing crops earlier and longer than would be possible in the open. Greenhouses using the sun’s energy to warm them provide an effective low energy solution to extending the growing season. But in Europe, for example, the pressures of agri­business demand ever-earlier crops and conse­quently many greenhouses are heated, so that yields are increased and the growing season is extended. A study undertaken in the Netherlands has indicated that on average vegetables produced in greenhouses require over 57 times as much non-renewable energy to produce compared to the same vegetables grown in open fields, see Figure 3.8 (Kol, Bieiot and Wilting, 1993).

The desire to consume the same fruit and veget­ables all the year round is one of the more important causes of large-scale greenhouse gas emissions associated with food production, resulting as it does in transport requirements and greenhouse heating.

In developed countries, marketing has effectively reduced seasonality to a folk memory. The argument goes that access to all varieties of fruit and veget­ables, all year round, provides unlimited choice, and thus the best of all worlds. There are of course merits to this argument, but it does not provide the only answer to a fulfilling culinary life. The obvious drawbacks are those related to international food transport. Within the issue of food transport, environmental matters only worsen as attempts are made to solve inherent problems with the system. We can illustrate this with the situation in England. Currently, many fruits are available in supermarkets that would not be available if grown outside locally. These fruits, when bought, tend to be unripe, because they have been picked early, refrigerated and transported to the supermarket. Experience shows that these fruit never achieve a natural ripeness and rot before they are ready to be eaten. On the other hand they look perfect and by now many consumers cannot compare the quality of these cheap fruits, to quality fresh produce.

One solution to the above problem generated within the food industry is to transport fruit and vegetables

Figure 3.7 Comparative yields and sale price for conven­tional and organic crops in the UK, as reported in 1994.

Figure 3.8 Comparative embodied energy for vegetables produced in open fields or in heated greenhouses, based on a Dutch study.

by air, so reducing the time between harvesting and consumption. As Angela Paxton points out in her chapter on food miles (see Chapter 5), this only worsens the environmental impact of the goods.

Updated: October 3, 2015 — 2:18 am