Chemical sequestration involves the conversion of carbon dioxide to inorganic car­bonates, and the use of carbon dioxide in the production of urea and plastics.

Agricultural practices

Agriculture uses a very large area of land and because of this size it is responsible for the emission of large quantities of greenhouse gases. Agriculture has been regarded as responsible for 25% of carbon dioxide, 50% of methane and 70% of the nitrous oxide released (Hutchinson et al., 2007). The World Resources Institute (2006) gives the values of 27% carbon dioxide, 53% methane and 75% nitrous oxide. The green­house gas emissions from agricultural sources are given in Table 3.9. These emissions arise from the following:

• Fossil fuel use in cultivation, harvesting, etc.

• Nitrogen fertilizer use.

• Rice production.

• Deforestation.

• Livestock (enteric fermentation).

• Manure.

Mitigation of greenhouse gases, sometimes known as stabilization, may require meth­ods that are expensive, therefore low-cost options have been investigated. Agriculture offers a number of low-cost technologies that include:

• Altering land use.

• Changing cultivation methods.

• Better management of livestock.

• Altering crop mix and fertilization methods.

• Expanding the production of biofuels.

An example of the changes that can be made to carbon dioxide sequestration is shown in Table 3.10. A number of agricultural methods have been shown to increase the retention of carbon in soils for Canadian Prairies (Hutchinson et al., 2007). Another example of changes in agricultural methods that reduce greenhouse gas emis­sions is the anaerobic treatment of slurry and liquid manure. Rather than placing liquid manure on the land or retaining it in lagoons where methane and nitrous oxide are produced, it can be anaerobically digested. Slurry or liquid manure anaerobically digested produces a mixture of methane (CH4) and carbon dioxide (CO2) which can be use as a gaseous fuel (Clemens et al., 2006).