Agriculture Reference
In-Depth Information
surface into the soil by irrigation or rainfall. When irrigation facilities are not
available, the farmer should wait for a day when he is certain that there will
be rain and fertilize just before it rains. Fertilizer applied during the dry season
will not be available to the plants until it rains, unless an irrigation system
is available.
In many orchards, a wide and 10-15 cm deep furrow is made that follows
the drip line of the canopy, and the fertilizer is placed in that furrow and
buried to avoid losses. Four to six holes about 30-40 cm deep can be made in
the vicinity of the drip line in a square or a hexagon layout, and the fertilizers,
sometimes including manure, are buried.
Dilute application
Large banana companies used to fertilize every 2-3 months with nitrogen and
potassium, using 'cannons' or large sprinklers that covered a circle of about
a hectare. They fi rst irrigated with water containing no fertilizer until the soil
was wet, then injected the soluble fertilizer into the water until the calculated
amount had been applied to the fi eld and ended the process with plain water.
The last phase of irrigation without fertilizer ensured that the fertilizer had
been taken into the soil and that leaves and metallic structures in the fi eld
were washed, so that fertilizer residues, especially urea, did not burn the leaves
or corrode the metals. This approach applied a large amount fertilizer a few
times a year. When sprinklers, micro-sprinklers and drippers are used, smaller
amounts of fertilizer are applied with each irrigation. The advantage of using
smaller amounts at more regular intervals is that the fertilizer is placed near
the root zone and less fertilizer is lost because of leaching. Small, regular,
almost continuous application ensures that most of the fertilizer is used by the
plants, reduces plant nutrient stress and the application rate can be readily
adjusted to the stage of plant development. Nitrogen applications near harvest
time have to be reduced or eliminated to avoid delayed fruit maturation,
excessive fruit succulence and to achieve a better-fl avoured fruit. The
reduction in nutrient stress associated with almost continuous application of
fertilizer results in higher yields and allows growers to recover the investment
made in the irrigation infrastructure, in addition to signifi cant reduction in
fertilizer and water usage.
Foliar fertilization
Although the roots are the main organs that the plants use to absorb needed
nutrients, foliar applications can be made to correct certain defi ciencies. Foliar
fertilization is normally used to apply micronutrients and in exceptional cases
to supplement for a defi ciency of a major element, especially nitrogen in the
form of urea. Because of the large plant needs for major elements and the low
concentrations tolerated by the leaves, especially urea, it is almost impossible
to fi ll the needs through the leaves. Microelements are also normally taken up
by the roots, but in situations with low micronutrient availability or the root
 
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