Agriculture Reference
In-Depth Information
water table is usually high in peat soils and other alluvial soils along streams
and canals, drainage is required. A major constraint is the tendency for trees
to lodge in these soils, especially for heavy bearers, because of poor anchorage
and limited root growth once fruiting commences. Cultivation of papaya on
sandy soils requires the incorporation of large amounts of organic matter
and heavy fertilization (8 kg/plant/year) coupled with irrigation. Boron
defi ciency and nematode infestations are two major problems encountered
on sandy soils. On acid-sulfate soils, which are compact, acidic, contain toxic
concentrations of certain micronutrients and prone to fl ooding, papayas have
a relatively short economic life. This short lifespan is due to a poorly developed
root system and extreme susceptibility to root and collar rot diseases under
poor drainage conditions. Similarly, heavy clay soils should be avoided due to
the poor drainage.
Climate
Rainfall
Papayas grow well and produce substantial yields without supplementary
irrigation if there is a minimum monthly precipitation of approximately
100 mm. Since most tropical areas have monsoon-type climates with
well-defi ned wet and dry seasons, successful production depends upon the
availability of supplemental irrigation during the dry period.
A minimum relative humidity of 66% has been reported for papaya's
optimum growth. Stomatal opening is controlled by humidity and, as relative
leaf water content is not af ected by drought stress, stomatal closure maintains
leaf water status, allowing rapid return of gas exchange fl ux and growth upon
rewatering (Marler, 1994; Clemente and Marler, 1996). Drought frequently
leads to the rapid shedding of new fl owers and older leaves, and poor fruit
set. Five days of fl ooding leads to abscission of fully developed leaves which
is preceded by chlorosis. Flooding frequently leads to plant death, due to root
rots, while recovery from non-lethal fl ooding is slow, due possibly to the low
root growth rate of fruiting trees.
Papaya has been ranked from extremely sensitive to moderately tolerant to
salt stress. Germination and early seedling growth are the most sensitive stages
to salt stress. It is probably moderately salt sensitive at other growth stages.
Temperature
Optimum temperature for growth is between 21 and 33°C; if the temperature
falls below 12-14°C for several hours at night, growth and production are
severely af ected (Lange, 1961). Dioecious cultivars are better suited to low
temperatures (<20°C), as female trees do not exhibit stamen carpellody shown
by the more temperature-sensitive bisexual (hermaphroditic) cultivars (Fig.
11.1). Hermaphroditic cultivars (Solo type) grown at minimum temperature
