Environmental Engineering Reference
In-Depth Information
Pesticide production
72
Farm machinery
158
Irrigation
369
Fertilizer production
410
Manure
413
Rice production
616
Biomass burning
672
Methane from cattle enteric
fermentation
1792
Nitrous oxide from soils
2128
Land conversion to
agriculture
5900
Figure 3.4
Global emissions of greenhouse gases from different agricultural sources expressed in million
tonne of carbon dioxide equivalent.
Adapted from Bellarby et al., 2008.
Pesticides can drift during application or volatilize from the target area and contaminate the
surrounding air, soil, water, and unintended vegetation. The deposit of pesticides in surface
water bodies created by runoff from fields or from drift during application affects the life of
fish and other aquatic organisms. Several pesticides can be carried though the soil and
contaminate shallow groundwater used as drinking water in many parts of the world. In ter-
restrial ecosystems, useful organisms such as bees, which intervene in the pollination of crops,
and pest natural predators, are collateral victims of the application of insecticides resulting in
an unbalance of the ecosystem and lost of important natural services.
Greenhouse gases released from agriculture
Agricultural emissions of greenhouse gases—primarily carbon dioxide, nitrous oxide, and
methane—come from different sources including land conversion to agriculture, soil manage-
ment, animal husbandry, fossil fuel consumption, and biomass burning among others (Fig. 3.4).
Conversion of land to agriculture is the largest source of greenhouse gases emitted as
carbon dioxide. This trend is expected to continue, mainly in developing countries, as a
consequence of population and economic growth, whereas in developed countries, most of
the land with potential for agriculture has been already converted in the last few centuries.
Other sources of carbon dioxide emission are biomass burning, fertilizers and pesticides
production, energy used for irrigation, and the use of fossil fuels in farm machinery for
operations including tilling, seeding, spraying, and harvesting. In addition, tilling
contributes to the release of carbon contained in the ground as organic matter. The distur-
bance of the soil due to tilling exposes organic matter to the air and accelerates its
decomposition.
The main source of nitrous oxide emissions comes from nitrogen fertilization of soils
with industrial fertilizers, manure, or nitrogen-fixing crops. In anaerobic conditions,
nitrogen contained in the soil as nitrate (NO
3
−
) is converted by bacteria into molecular
