Agriculture Reference
In-Depth Information
ECOLOGY
Soil
All species are capable of growing in a wide range of soil types, from sandy
soil to clay loams. Nevertheless, they dif er in their soil preferences. Higher
yields occur on well-drained sandy to sandy loam soils, except in the case of
A. glabra
,
which can succeed in shallow ponds. Drainage is essential to avoid
root-rot diseases; hence the interest in
A. glabra
as a rootstock, related to its
tolerance of wet soils. Cherimoyas and atemoyas prefer sandy or sandy loam
soils with uniform moisture but with a good drainage to avoid root rots, and
a dry period at the end of winter at the time of leaf fall will enhance fl owering
uniformity. Sweetsop is capable of growing in a wide range of soil types, but its
shallow root system does not allow for fl ooded or waterlogged soils. It will do
best if good drainage exists and if soil pH is around 5.8-6.6.
Rainfall
In cherimoya and atemoya, rainfall and high humidity during the peak
fl owering season greatly enhance fruit production by preventing desiccation
of stigmas, prolonging their receptive period and increasing fruit set and early
fruit growth. Similar conditions are also ideal for other
Annonas
. The sweetsop
is probably the most drought-tolerant species and it grows and produces poorly
where rains are frequent. For example, sweetsop does much better in northern
Malaysia, where dry periods occur, than in the southern part, which has year-
round high moisture. For cherimoya and atemoya, a dry period at the coldest
time of the year enhances leaf fall and fl owering at the end of spring and early
summer. This dry period is not required for sweetsop.
Temperature
Temperature is the limiting factor, with frost killing young trees, especially
sweetsop, but older trees showing some tolerance. Cherimoya (7-18°C
mean minimum) is more tolerant to low temperatures (Fig. 6.3), followed
by atemoya (10-20°C mean minimum). Cherimoya can initiate vegetative
growth at ~7°C, while atemoya starts at ~10°C. Except for cherimoya, the
annonas do not require chilling periods and do well under lowland conditions
(George and Nissen, 1987b). Cherimoya is susceptible to high temperatures,
with a growing temperature range of 21-30°C (George and Nissen, 1986b).
Both cherimoya and atemoya are semi-deciduous, and growth declines at
