Cashew (Anacardium occidentale L.) is grown principally for its nutritious kernel, the
edible part of the nut1 (Figure 3.1). The hard shell surrounding the kernel is a source of
‘cashew shell nut oil’, which can be used in a number of polymer-based industrial
processes. The swollen pedicel (the stalk to a single flower), known as the ‘cashew
apple’, is another potentially valuable by-product, for example as a fresh fruit and
source of juice (especially in South America), since it is very high in vitamin C, and as a
basis for alcohol production.
Cashew is a native of South America with a likely centre of origin in the cerrados2 of
central Brazil, or possibly in the coastal zones of north-eastern Brazil, since this is
where there is the greatest diversity of the Anacardium species. Cashew was probably
introduced into Africa and India by the Portuguese in the sixteenth century. It is now
found throughout the tropics at latitudes between 27º N (Florida) and 28º S (southern
Africa) at altitudes below about 800 m. Cashew is a crop generally associated with
coastal regions (Nambiar, 1977; Martin et al., 1997; Bezerra et al., 2007; Nair, 2009;
all citing others).
Vietnam is currently (2010) the world’s largest producer of cashew with an annual
production of ‘nut-in-shell’ of 1.16 million t (from 340 000 ha), followed by India
(613 000 t; 923 000 ha) and Nigeria (594 000 t; 330 000 ha). Brazil is the largest
producer in South America (102 000 t; 750 000 ha). Cashew is also an important crop
in eastern Africa, for example in Mozambique and Tanzania. The total world production
is 3.59 million t from 4.0 million ha (FAOSTAT, 2012). Some of these data appear to be
totally unrealistic, including the world average yield of nearly one tonne per hectare,
and should be viewed with caution. The complexity of the farming systems within
which cashew may be an important component makes it difficult to collate reliable
statistics (Ascenso, 1986a)
The structure of the cashew industry in the principal producing countries has been
described by Hall et al. (2007). For example, in Vietnam, where the industry has
expanded rapidly in recent years (it now produces 32% of the world’s crop), the
majority of cashew growers are typically smallholders with 2-ha orchards. Similarly,
in Tanzania most households have fewer than 100 cashew trees (Martin et al., 1997).
By contrast, in Brazil, although small- and medium-size producers are in the majority
(in 1995/96 there were 195 000 farmers growing cashew trees), 32% of the crop is produced on large-scale land holdings (>100 ha) (Hall et al., 2007). In India, where
cashew is described as a ‘poor man’s crop but a rich man’s food’, the cashew industry
employs around one million people as labourers, mainly women, to process the raw
cashew (Nair, 2009).
The water relations of cashew have been the focus of only a limited amount of
research, undertaken mainly in Brazil and Australia. This is despite its importance
nationally and internationally. It is estimated that less than 1% of the planted area in
the world is irrigated, since cashew has the reputation of being a drought-tolerant crop.
Irrigation is, however, being encouraged in some regions, for example in north-eastern
Brazil (Bezerra et al., 2007). It should be noted that this refers to irrigation of ‘dwarf’
cultivars grown primarily for cashew apple production
Crop development of Cashew
The following topics are considered in this section: vegetative growth, flowering,
fruiting, plant density, roots and the partitioning of dry matter.
Vegetative growth
There are two types of cashew, known simply as ‘talls’ and ‘dwarfs’. Both are evergreen
trees. ‘Talls’ can grow to a height of more than 10 m and have a domed-shaped canopy
with a span of up to 20 m. ‘Dwarfs’ are generally small and low-spreading and require
pruning to keep the branches off the ground (Figures 3.2 and 3.3). Dwarf cultivars are
less common than ‘talls’, but they are of increasing commercial importance (Ascenso,
1986b; Bezerra et al., 2007). Until the 1980s, cashew was propagated by seed, but now
grafting of clones on to seedling rootstocks is the accepted method. Cashew comes into
production in about the third year after planting.
In its native habitat, the cashew tree has a period of rapid vegetative growth followed
by a quiescent stage and then a series of pre-floral vegetative flushes. Flowering and
fruit development and maturation follow. The major period of vegetative growth
coincides with the rainy season, and the flowering and fruiting phases with the dry
season (Grundon, 1999).
Under cultivation, the number and duration of each phase varies depending on local
conditions. As an example, the sequence of the crop development stages that occur in
Binh Phoc province in Vietnam, where there is a single rainy season, is summarised.
In the case of young cashew trees, vegetative growth occurs in a series of flushes
throughout the year. With mature trees, two to three periods of active shoot growth can
be identified. The first flush occurs in late April to May, after the harvest has ended, and
soon after the start of the rains. This is followed by a second flush in August or early
September. A so-called pre-flowering flush occurs in late October and November, at the
start of the dry season.
Summary: crop development
1. Vegetative growth occurs in two or three identifiable flushes each year.
2. Flowers form on the end of branches in the dry season: they can be male or
hermaphrodite.
Flowering continues over a two- to four-month period.
4. The development of the nut takes about two months from pollination.
5. Harvesting extends over 10–12 weeks, preferably when it is dry.
6. Wide tree spacing allows intercropping in the early years: close spacing requires
surplus trees to be thinned subsequently in order to minimise water stress.
7. The spreading root habit of cashew is critical in its successful adaptation to dry
conditions.
8. Roots can extend to depths >5 m: water extraction has been monitored down to 4 m.
9. Nut-in-shell and cashew apple together make up less than 10% of the above-ground
dry mass of the tree.
Research on gas exchange and the water relations of cashew is limited, but useful work
has been reported from Brazil and, surprisingly perhaps, Australia, where cashew is still
described as an ‘emerging crop’.
