Annona Species Monograph.pdf - Crops for the Future

Chapter 10. Agronomy
root systems. James (1988) comments that there are several types of microsprinkler
emitters that are differentiated based on their water distribution
patterns (Fig. 10-13). Annona growers in Brazil prefer the single microsprinklers
with 300° of water distribution, or two micro-sprinklers with 180°
each, so that they don't moisten the tree trunks and encourage infectious
fungal or bacterial diseases. When selecting a micro-sprinkler system
additional parameters must be considered, such as the emitter outlet and its
sprinkling radius, as well as the intensity of water application through the
radius (Santos, 1997). In general, micro-sprinklers have fewer problems of
obstruction in the emitters than drip irrigation (Santos, 1997).
Farré et al. (1999) conducted a study to compare the drip, micro-sprinkler
and spray irrigation systems with respect to the area moistened under the
canopy and the planting density. They concluded that with 313 cherimoya
trees/ha (spacing of 8 x 4 m) 1,800-2,000 drippers/ha (6 drippers/tree) were
frequently used. With the advent of low-density spray irrigation below the
canopy, larger areas have been irrigated in Spain with better results. An
irrigation schedule of 24 to 25 litres/tree and 6 drippers of 4 litres/h results in
20% of the area moistened to more than 25 cm depth, while one microsprinkler
of 25 litres/h wets 12 m², resulting in approximately 40% of
moistened area. Unfortunately the study did not investigate the variation in
the parameters with different soil types, which is very important in
understanding the formation of the wetted bulb.
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