Agriculture Reference
In-Depth Information
be a costly operation, but once it is done, furrow and fl ood irrigation will be
cheap though very inei cient in water usage. Furrows are more suited to fl at
or almost fl at land where the slope is 0.5-1.0%. The furrows can be made to
follow the contour, with the same slope of 0.1-1.0%. Higher slopes can lead to
erosion, which will destroy the irrigation ditches and the furrows will become
excessively deep.
In furrow irrigation, water is conducted along the tree rows and around
the trees. For young plants, one furrow is often sui cient, later increased to
two furrows, one at each side of the trees, and this could be increased to four
furrows in older orchards. Furrows can also be dug around the trunk or have a
side furrow that directs water under the canopy. Furrows should be no longer
than 120-180 m in loamy soils and 60-80 m in very permeable soils. If a
furrow is excessively long, the time for the water to reach the end will allow
for excessive infi ltration at the start beyond the root zone and waste water and
fertilizers. Short furrows have the opposite ef ect of insui cient penetration
and faster onset of water stress.
In the basin system, around each canopy drip line a 25-30 cm mound of
soil is prepared to retain the water and allow fl ooding of the canopy area till
the soil becomes saturated. This system has 35-40% water-use ei ciency and
is used where water is abundant and cheap or free.
Furrow and basin irrigation are less ei cient in water usage because of
the excessive infi ltration at the start of the furrow and the loss of water in
transporting to the fi eld. Care is taken to ensure no fl ooding or excess irrigation
water comes in contact with the base of the trunk, as this can lead to serious
trunk diseases and even tree death.
Low-pressure irrigation
Drip and micro-sprinkler irrigation are low-volume, low-pressure systems (Fig.
4.5a, b). These systems can be used on steep and uneven land, and require no
land levelling. Pressure compensation built into emitters and sprinkler heads
means that all points receive similar amounts of water. Water is applied only
where needed to the plant roots, and these systems are the most ei cient for
reducing water wastage. The distribution of the water in pipes and hoses
results in very little evaporative loss, saving 30-40% of the water in relation to
conventional surface systems.
Drip irrigation consists of having hoses running along the tree rows (Fig.
4.5a), and these hoses will have several drippers, normally three or four under
the canopy drip line, with one or two hoses on each side of the trees along
the rows. In sandy soils, lateral movement of water is poor, so more drippers
will have to be used or the frequency of irrigation increased. Sometimes
micro-sprinklers are a better alternative in sandy soils. Normally with micro-
sprinklers (Fig. 4.5b), there will be one per tree to keep the soil under the
canopy moist. Some large banana companies use sprinklers that hang from
cables. Watering is more frequent and a lower volume applied each time, so
