Agriculture Reference
In-Depth Information
Fertilization
The
Annonas
have an indeterminate growth habit (axillary fl owering), and
applying nitrogen (N) in somewhat excessive amounts does not interfere
greatly with fl oral initiation, as is the case with plants having determinate
growth habit. However, excessive tree vigour is usually associated with reduced
fl owering and yields in many tree crops and the atemoyas are no exception
(George
et al.
,
1989).
In Australia, continued research and fi eld observations on atemoya
nutrition have led to greater refi nements in terms of quantity of fertilizer
and times of incremental applications during the annual growth and fruiting
cycles (Table 6.4). The use of foliar nutrient analysis has become a useful
management tool in determining atemoya fertilizer programmes (Sanewski,
1991). Sampling for foliar analysis consists of obtaining the most recently
matured leaf - the fourth or fi fth leaf below the growing point. Leaves are
selected from non-bearing shoots without a leaf fl ush during late summer
or early autumn (Table 6.5). After 10 years of age, the annual amounts of
N, phosphorus (P) and potassium (K) remain the same, as tree size is kept
relatively constant by annual pruning and by competition from adjacent trees.
The annual requirements of N and K are split into four increments (Table 6.4).
In the cool subtropical areas, greatest vegetative growth takes place during the
warmer months, from spring to autumn. Reduction in N during the winter
minimizes new vegetative growth in young trees that are vulnerable to cold
temperatures. This adjustment is not necessary in the warm tropics. P is given
once per year during the early-autumn application.
Table 6.4.
A guide to annual application of NPK for 'Pink's Mammoth' atemoya
trees of different ages using straight fertilizers (g/tree/year) and percentage
distribution of application of annual amounts (Sanewski, 1991).
Urea
(g/tree/year)
Superphosphate
(g/tree/year)
Potassium chloride
(g/tree/year)
Tree age (years)
2
400
500
360
4
860
550
930
6
1300
780
1170
8
1600
880
1500
10
1750
880
1650
Early
spring
Early
summer
Early
autumn
Late
autumn
Fertilizer
Urea
20%
30%
40%
10%
Superphosphate
100%
Potassium chloride
10%
30%
40%
20%
