Agriculture Reference
In-Depth Information
homes more comfortable. In irrigated areas electric pumps are used to pump water from
deep wells or reservoirs. In India approximately 20 percent of the nation's electricity is
used for farm irrigation.
8
The cost of electricity is significant, even when the govern-
ment subsidizes agricultural users.
In the United States we take electricity for granted. It is rare to lose electric
power for more than a few minutes. In developing countries electricity is highly
valued because it is often difficult to get a reliable connection. During the hot
season in India (April and May) the grid is overloaded because of added fans and
air conditioners. The power stations respond by rationing electricity, cutting
service to areas for 5 to 6 hours each day. Many other national systems use hydro-
electric generators that must go on reduced schedules in dry seasons when irrigation
is most needed. Keeping medicines and vaccines for livestock is a problem without
reliable
refrigeration.
Provision
of
a
reliable
electrical
supply
is
essential
for
modern farming.
10.15
WATER: IRRIGATION
Irrigated lands are often the most productive. It has been estimated that the practice
of irrigation results in a 100 to 400 percent increase in crop yields.
9
An estimated
15 percent of the cultivated land in the world is irrigated. This relatively small area pro-
duces 35 to 40 percent
10
of the world's food! The proper use of irrigation greatly
decreases risks of crop failure from drought, increasing food security in a country.
Many national plans for increasing food production include expansion of irrigated areas.
Irrigation is not a new technology. It was practiced by Egyptians as early as
5000
BC
. Most societies have used irrigation to improve crop yields or to prevent
losses from drought.
The quality of irrigation water depends largely on its source. Water taken from
lakes or rivers will vary depending on the conditions in the watershed. A watershed,
or catchment area, is all of the land area contributing water to a river or lake. If the
land is forested with little human activity, the water is likely to be of good quality
for irrigation. If the land is cultivated farmland, there is a chance of irrigation water
carrying eroded soil with nutrients, chemicals, and diseases from the watershed. If
the watershed is an urban area, there will be runoff from yards, streets, and industries
carrying pollutants detrimental to growing plants.
Water taken from wells may seem to be pure and ideal for irrigation. In most cases,
well water is biologically pure. A serious problem for irrigation is the accumulation of
salts such as sodium, calcium, magnesium, and potassium. These come from rocks and
soils as part of the natural breakdown process of weathering and soil formation. Other
toxic elements such as boron or arsenic may also be present. When the concentration of
salts in irrigation water is high, use of this water may result in their accumulation in
the soil eventually causing a dramatic reduction in yields. The field shown in
Figure 10.21 has a serious salt accumulation on the tops of the ridges between
furrows. It is estimated that half of the irrigated fields in the world suffer from some
degree of salt accumulation.
