Agriculture Reference
In-Depth Information
9.11.2
Irrigation Methods Around the World
The Philippines
In the Philippines it is common for rice farmers to place rocks across a stream
upstream from their rice paddies to impound water, which is then directed
through a series of open canals to the paddies. No expensive infrastructure is
involved once the canals are dug. Paddies are flooded with water covering the
whole area to a uniform desired depth. Thus no water distribution system in
the field is needed. Water from the river may pass through several paddies
owned by several different farmers between the initial water takeoff and the
water finally exiting into the ocean. The consequence is that many rivers have
little water in them by the time they reach the ocean.
This system has a secondary benefit in that it can handle large rainfall events
without causing flooding.
In spite of irrigation, soils in the Philippines generally do not have salt
buildup problems because of the high rainfall. However, in northern Luzon
there is a distinct dry season, and as a consequence there are concerns related
to salt buildup from irrigation in this part of the country.
Ecuador
All types of irrigation practiced in the Philippines and the United States are used
in Ecuador, although not to the extent used in the United States.
The United States
Much irrigation in the United States is done by overhead sprinkler irrigation,
shown in Figure 9.18, via pipes carried over the field on large wheels. Initially,
these irrigation systems sprayed water into the air to spread it out over the
area to be irrigated. Spraying water in this fashion is a wasteful irrigation
method because it maximizes evaporation of water, resulting in less water
available to plants, and it encourages salt buildup in the soil. Often this type
of irrigation is called center pivot because the pipe and wheels move in a circle
around the field leaving a circular field of green in an otherwise brown
environment. Today, these irrigation systems have hoses, which drop the
water down closer to the soil surface before spraying, thus improving water
use efficiency.
Other types of irrigation such as spray (shown in Fig. 9.19), which has much
higher evaporation than other systems, and furrow and drip, which can also
have mulch to further conserve water, is shown in Fig. 9.20, are also common.
In furrow irrigation ditches are dug across a field and crops are planted on the
ridges in between. The crops are irrigated by periodically filling the ditches
with water from a main irrigation ditch. In drip irrigation small plastic tubing
is run down the row of crops and there is a small “leak” at each plant such that
each plant has a source of water. This is the most water-efficient irrigation
method and is even more efficient when combined with any type of mulch.
These methods require large amounts of water and expensive equipment to
implement. Because of this, they are not applicable to many parts of the world
and are not available to most of the world's farmers.
