Introduction

Energy is required in agriculture on a massive scale. In fact, agriculture would not be possible without the input of human power, animal power or mechanization. Vast amounts of energy are also consumed in the processing and distribution of food, with cooking, freezing and transportation representing a large part of energy use in bringing food from the field to the table.

This dependency in the agri-food system on energy was particularly well illustrated during the January 1998 ice storm that struck eastern Ontario and southern Quebec: some 5,000 milk producers left without electricity for up to a month were unable to milk their cows. Some animals stopped their lactation cycle and milk had to be dumped because dairy processing plants were also out of power. This section presents an overview of energy use in agriculture in the modern era, examining the various types of energy available to a look at the energy efficiency of the main types of agricultural production. In the last section, ways to save energy and renewable energy sources that could be used in agriculture are tackled.

First, however, it is important to define what efficiency is, since this term is used extensively in the following section. Efficiency can most usefully be defined as the ratio of output to input, that is to say the amount of food produced from the energy used in its production. Such a ratio can apply to innumerable combinations of output and input and each of these can be expressed in many different terms. Familiar examples of efficiency ratio are 'miles per gallon', 'words per minute', 'miles per hour', 'gallons per cow' and 'protein per ha'. (Spedding, 1996)

Finally, the unit used to defined energy, in the International System of Units (abbreviated SI) is the joule (J). Since 1 joule is very small, energy is often expressed in kilojoules (kJ) where 1 kJ = 1E3 J, in megajoules (MJ), where 1 MJ = 1E6 J and in gigajoules, where 1 GJ = 1E9 J.