Agriculture Reference
In-Depth Information
Dry conditions, preferably accompanied by cool temperatures during the pre-
fl owering period, promote fl owering, while cool, wet conditions reduce fl owering
in both crops. When mango fl ower buds begin to emerge, some soil moisture is
needed, preferably from irrigation rather than from rainfall. Light rain during
mango fl owering leads to severe anthracnose (
Colletotrichum
spp.), which can
destroy most of the infl orescences. Too much rain during litchi anthesis also
reduces fl ower opening and/or the insect activities needed for pollination.
Total rainfall is frequently less important than its distribution throughout
the year. In Loma Bonita and Acayucan, Mexico, two large pineapple-
producing areas, mean rainfall over a 5-year period was 1600 mm and 1500
mm, respectively. These approximate the upper limits of the optimal range for
pineapple; however, periods of serious drought are encountered, as 89 and
82%, respectively, of the rainfall occurs from June to November. In a tropical
rainforest, 85% of a 1 mm shower may be intercepted by plants, but only 12%
of a 20 mm rainfall, indicating that fall intensity, duration and frequency are
signifi cant factors. The interception by plants is signifi cantly infl uenced by
species; pineapple with its upright leaves funnels water to the centre. Plant
density similarly af ects rainfall interception.
Orchards located on fl at lowland areas can experience fl ooding during the
rainy season, particularly if drainage is poor. This is important for avocado,
papaya, litchi and pineapple, for which waterlogging causes severe root-rot
problems. Mango is slightly fl ood-tolerant, as indicated by reductions in leaf
gas exchange, vegetative growth and variations in tree mortality. Mangosteen,
by contrast, grows well under conditions of fl ooding and high water table.
A high water table may prevent mangosteen trees from experiencing the
moisture stress needed to induce fl owering.
Water defi cit, and therefore irrigation demand, is determined by
evaluating rainfall, evaporation and soil water storage. The two most common
approaches are the water balance (rainfall, evapotranspiration, water
storage, change in the root range, surface runof ) and actual soil moisture
measurement. The crop needs, along with the soil type, determine frequency
of irrigation; this determination should be made on at least a weekly basis for
fruit crops. The use of drip (trickle) and micro-sprinkler irrigation enables a
grower to match the needs of the crop to irrigation needs at dif erent stages of
growth and development, avoiding the need to rely on rainfall. These irrigation
methods allow precise placement of the water, reduce surface evaporation and
seepage, and increase water-use ei ciency. Other irrigation methods used are
basin, furrow, overhead sprinklers and cannons.
Strong winds, frost and hail
In the equatorial zone, strong winds are associated with localized thunder-
storms (diameter <25 km) having greater intensity than those in the middle
and upper latitudes and lasting from 1 to 2 h. Most occur outside the 0-10°
