Agricultural practices have changed dramatically since the time of hunters and gatherers, which initially were related to land use change and changes in management practices like irrigation and tillage. Several historical greenhouse gas (GHG) anomalies are thought to be associated with these shifts like,
for example, an increase in the methane concentration with the start of paddy rice farming in Asia about 5000 years ago. With an ever increasing population to feed, larger scale changes were needed to meet the demand for food. During the 20th century, agronomic research focused on creating high yielding
varieties, and agriculture intensified by mechanisation and the use of agrochemicals such as mineral fertilisers, herbicides and pesticides. The “Green Revolution” enabled, for example, cereal production in Asia to double between 1970 and 1975 with a concurrent land use change to agriculture of only 4%.
However, it generally encouraged the further expansion into previously uncultivated areas due to higher profits. Intensive agriculture relies on high external inputs, particularly of fertilisers, pesticides, herbicides, irrigation and fossil fuels, applying management strategies that are simple to maintain at a large scale. The environmental and social costs (pollution, loss of biodiversity and traditional knowledge) are high and may potentially undermine future capacity to maintain required levels of food production. It is currently estimated that there is still more land under extensive agriculture (17%) compared to intensive agriculture (10%), with an even greater share occupied by domestic livestock (40%). However, with an increasing demand for
food, this may change in favour of more and more intensively farmed land. Indeed, some have argued that since land suitable for conversion to agriculture is
dwindling, intensification on the agricultural land currently available will be the only way to feed the projected 9 billion people on the planet by the end of this century. In addition the increasing competition for access to the dwindling stocks of fossil fuels will increase the competitiveness of crops grown for bioenergy and will cause a financial incentive to increase the amount of land used for intensive arable purposes, and ultimately lead to higher prices for agricultural and forestry products and competition for land between energy and food production. Agriculture is a major contributor of GHGs to the atmosphere, but the emissions vary depending on the land use and the way that the land is managed. However, a quantified separation of intensive and extensive agriculture is difficult for a number of reasons, a) there are many complex interactions between different practices and effects, b) statistics on intensity of land use are rarely available (statistics are collected in a different form), and c) often, intensive and non-intensive farming practices are present on the same farm, making categorisation of farms as intensive / non-intensive very difficult. For this reason, this report focus on the individual practices known to influence GHG emissions to the atmosphere, and were possible it presents information at the aggregated systems level to examine the impacts of intensive vs. non-intensive agriculture.

By: J. Bellarby, B. Foereid, A. Hastings, P. Smith

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