Annona Species Monograph.pdf - Crops for the Future

Chapter 10. Agronomy
(Grossberger, 1999). Similarly, in soursop, pollination should be practiced in
the morning, preferably around 9 am and approximately 19 h after the
collection of the pollen donor flowers (Pinto and Ramos, 1999). The donor
flowers should be collected from the terminal portion of the branch, since
these flowers generally present low fruit set themselves (Torres and Sánchez,
1992; Pinto and Ramos, 1999).
Hand pollination is considered to be time-consuming and costly (Nakasone
and Paull, 1998). Attempts have been made to substitute hand pollination by
growth regulators to enhance fruit set. Experiments carried out by Yang
(1988, cited by Nakasone and Paull, 1998) indicated that fruits grow very
slowly and with less fruit drop when indole-acetic acid (IAA) and
naphthalene acetic acid (NAA) are applied, while gibberellic acid (GA)
promotes adequate fruit set and growth rate. Saavedra (1979) found that the
application of either NAA or GA can stimulate some production of seedless
fruits weighing 200-300 g, but only GA significantly enhanced fruit set and
stimulated growth of seedless fruit. However, GA can also induce severe
cracks in fruit rinds before harvest. Therefore, hand pollination is still the
most effective strategy to increase production and quality of fruit.
Fruit thinning is necessary to regulate crop load and to maintain fruit size,
especially for high yielding annona cultivars (George et al., 1987). The
thinning operation involves the removal of misshapen fruit and thinning of
fruit clusters, both of which improve the quality of the remaining fruit for
market.
10.3.5 Nutrition and fertilization
Planting and Juvenile Phases
The establishment of a fertilization programme should be based on the
nutrient uptake by the target species (Mengel and Kirkby, 1987; Torres and
Sánchez, 1992; Hermoso and Farré, 1997). In establishing orchards, the
preliminary fertilization (especially of phosphorous) and soil pH correction
of the field should be based on soil analysis. Sufficient sub-samples, for
instance 25 per hectare for phosphate and potassium, should be collected in
order to obtain a representative sample (Mengel and Kirkby, 1987). Soil subsamples
should be taken from the 0-40 cm soil layer, by walking a zig-zag in
the area, a mixture of these sub-samples should then be prepared and a 200-
300 g composite soil sample sent off for nutrient analysis (Pinto and Silva,
1996; Bonaventure, 1999).
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