Agriculture Reference
In-Depth Information
IRRIGATION
In some parts of the tropics with abundant rainfall, such as the Atlantic
coast of Costa Rica, which receives ~4000 mm/year, irrigation is not
necessary, even for bananas; drainage is the main concern, to remove the
excess rainwater. In tropical areas with high rainfall, most have a dry season
of a couple of months, when irrigation is needed. Installation of irrigation
will depend on an economic analysis of the situation as to whether artifi cial
irrigation will improve fruit size, production and quality. The analysis should
take into consideration the species, trees' growth phase, temperature, wind
and relative humidity during the dry months. If the dry season occurs during
the cool season, when little wind occurs or high relative humidity is present,
irrigation needs are less than if the dry season is hot and windy and the
relative humidity is low. A problem arises in abnormal years with a longer
than usual dry period, when productivity can fall signifi cantly. Two or three
dry months under the tropical heat can have detrimental ef ects on yields of
some species not adapted to long dry spells and it can be wise to irrigate during
the dry season.
Many fruit crops that originated in the monsoon areas need a dry period
to restrict tree growth, mature the foliage and induce fl owering. The mango
is an example of a tree that evolved in a monsoon environment and fl owers
better if subjected to cool weather and dry soils. In many places, mango is
grown with only rainfall, though yield may be reduced. Some fruit trees are
subjected to a water stress even when irrigation is available, with irrigation
resulting in heavier and more uniform fl owering. A number of tropical species,
such as many
Spondias,
have evolved mechanisms to withstand the dry season
by shedding their leaves to minimize water loss.
Tropical fruit trees should be irrigated or receive adequate rainfall in order
to yield their maximum. Most modern orchards install an irrigation system
even if the rainfall is adequate to keep the plants growing; irrigation under
these circumstances will provide extra water in case of mild stress or when the
rainfall pattern changes.
Irrigation systems
The irrigation system installed will depend on many factors: amount and cost
of water, availability of money, steepness of the land, and the technical level of
the farmer. Several systems are used in tropical fruit orchards.
Surface irrigation
Surface irrigation includes furrow and basin irrigation, with furrow
irrigation being the most popular. The land needs to be fairly level or to have
been levelled during preparation (Avilan
et al.
, 1989). Land levelling can
