Annona Species Monograph.pdf - Crops for the Future

Chapter 10. Agronomy
are not greater than 16% (Nunes, 1997). The use of sprinkler irrigation also
has certain restrictions, especially regarding its use during the period of
pollination and fruit set, since it can impede visits of pollinator insects and
provoke the abscission of small fruits. Market prices of the irrigation system,
costs of installation and maintenance, and financial resources are some of the
economic aspects to be considered. Finally, the quality of the labour which
will operate the irrigation system is the most important human aspect
involved (Silva et al., 1996).
The cost of buying and installing the irrigation system is generally the first
critical aspect influencing any decision; therefore the cheapest irrigation
system is often chosen. However, the price is not necessarily related to the
efficiency. For example, the gravity flow of surface water through furrows
and flood irrigation are the cheapest systems; however, water distribution is
seldom uniform, leading to poor efficiency in the orchard as a whole (Santos,
1997). In Spain, flood irrigation is used only in orchards situated in riverbottoms
(Farré et al., 1999). In north-eastern Brazil, furrow and flood
systems are considered old-fashioned, and have been substituted by drip and
micro-sprinkler irrigation.
In many areas, water has become very expensive; thus it is necessary to
minimize costs by not over-irrigating. Drip and micro-sprinkler irrigation
systems decrease costs and increase the efficiency of water use and
management (Nunes, 1997), as well as improving fertilizer use and
management, resulting in higher yields and better fruit quality. These
localized irrigation systems are, nowadays, the commonest methods used on
annona trees in north-eastern Brazil. A good irrigation scheme must be
designed before orchard establishment. Bucks and Davis (1986) outlined a
typical scheme for establishment of a drip irrigation system in the field (Fig.
10-12).
The shape and size of the 'wetted bulb' or area of soil moistened by the
system, which will be filled with tree roots, depends on the type and size of
emitter, the volume of water applied, and the structure and texture of the soil
(Santos, 1997).
A drip irrigation system should be used in areas where water is very limited,
e.g., in arid zones (Rungsimanop et al., 1987; Singh 1992). This system has
several advantages, such as decreasing the loss of water through evaporation,
reducing weed infestation and the negative effects of increased salt
concentration (Silva et al., 1996). An enormous disadvantage however, is the
need for filters, which are sometimes obligatory because of poor water
112