Agriculture Reference
In-Depth Information
ranges of defi ciency and adequacy suggested. For plant growth and fruit
production, large amounts of nutrients are required. These nutrients come
from the soil and decaying plant material, and the remainder comes from
applied organic matter and fertilizer. The amount of nutrients removed by the
harvest of cv. 'Cavendish' fresh fruit with a yield of 50 t/ha/year includes 189
kg/ha nitrogen (N), 29 kg/ha P, 778 kg/ha K and 101 kg/ha calcium (Ca).
As a proportion of the total nutrients taken up by the banana plant, this is
equivalent to 49% of the N, 56% of the P, 54% of the K and 45% of the Ca.
These total amounts and proportions are about half of those for plantain
(Table 8.4). Most of the data have been derived from experimentation with
bananas produced for export, especially from varieties in the 'Cavendish'
subgroup. Cultivar and subgroup dif erences have been recorded, with the
optimum nutrient supply not being the same for all cultivars. Seasonal
infl uences on fertilization are much greater on bananas growing in
the subtropics, where temperature probably has the greatest infl uence.
Intercropping needs should also be considered.
The large N and K requirements are modifi ed by the local soil nutrient
concentrations. The rate of application depends on climate, soil type, variety,
management practices and yield. Since vegetative and reproductive stages of
development are found in one fi eld at the same time, and as the initial stages
of fruit infl orescence development are crucial for fi nal yield, a constant supply
of nutrients is essential for high yield. If the pseudostem is left standing
after bunch harvest, up to 40% of the nutrients (especially N, P and K) can
be removed by the following ratoon sucker (Fig. 8.6) and increase the bunch
weight of this next generation. Delaying fertilization can have a signifi cant
impact on yield, reducing it by 40-50% or more; a 3-month delay makes it
dii cult for the plants to recover.
Because of the extensive root system, fertilizer should be applied away
from the pseudostem, mostly on the side of the next ratoon. Solid fertilizer is
applied three to four times per year, more frequently if there is high rainfall,
for this a 60 cm semicircular strip of fertilizer 30 cm wide is broadcast 30-40
cm in front of the ratoon sucker. Fertilizer applied through irrigation water
(fertigation) is more ei cient and gives better control of application time and
rate to meet demands. Frequency of fertilizer application is increased when
fertigation is used monthly, weekly or continuously, especially if drip irrigation
is used. Foliar application is also used.
Numerous forms of fertilizers have been tested. If the dif erent forms
meet the management strategy and crop needs and do not lead to excessive
runof or leaching, most are suitable. The most common forms of nitrogen
are ammonium nitrate (NH 4 NO 3 ), ammonium sulfate (NH 4 ) 2 SO 4 and urea; it
should be applied three to six times per year. For phosphorus, simple or triple
superphosphate is usually applied once a year due to slow P mobility, at rates
of 40-60 kg of P 2 O 5 /ha/year, while, for potassium, potassium chloride (KCl),
potassium sulfate (K 2 SO 4 ) and potassium nitrate (KNO 3 ) are used, the sulfate
 
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