the introduction of improved micro-sprinkler systems on a communal level and, at the
same time, establish an irrigation extension service which can advise farmers on
water efficient irrigation techniques, including the option of using deficit irrigation
during extended drought periods (Schulze et al. under review).
6.3 Irrigated Longan Production
In contrast to mango, longan (Dimocarpus longan Lour.) is usually not exported
fresh, but mainly in a dried form. The main importing country for dried longan from
Thailand is China. The most important quality parameters – size and color –
develop best with on-season production during the dry season. As longan trees
are sensitive to drought, irrigation is essential.
6.3.1 General Management
Longan is a subtropical fruit tree indigenous to Southeast Asia. Together with
lychee (Litchi chinensis Sonn.), it is the most popular member of the Sapindaceae
family, which has over 2,000 species and 150 genera (Menzel and Simpson 1991).
Thailand is currently the biggest longan producer in the world, with drained rice
fields and gently sloping fields in the foothills of the upper Ping River Basin in
northern Thailand being the main production areas. Naturally, longan trees grow up
to 20 m in height, but on Thai plantations, they are typically grown in a 10 Â 10 m
pattern, reaching 7–10 m in height. Previous research on new pruning techniques
recommended growing smaller trees (Manochai et al. 2008), but this advice has not
yet been widely followed in practice. Longan flowering can reliably be induced
through the application of potassium chlorate, and as a result, production is possible
all year round (Manochai et al. 2005). However, flower induction and management
is expensive and weather dependent (Ongprasert et al. 2010b), plus incomplete
degradability of potassium chlorate in the soil leads to a lower response rate, which
in turn results in ever increasing application rates (Ongprasert et al. 2010a).
Therefore, and because size and color develop best during the dry season, presently
about 80 % of longan fruit is produced during the ‘on-season’, which starts with
flowering in February and ends with the fruits being harvested in July. Longan trees
are particularly sensitive to drought during the flowering and early fruit development stages (Menzel and Waite 2005), so irrigation management is crucial in
growing regions which have a distinctly summer rainfall pattern (Diczbalis et al.
2010). As on-season flowering and fruit development coincides with the dry season
in Thailand, high fruit yields can only be obtained using irrigation. Irrigation water
requirements are calculated based on a climatic water balance: ET c. ¼ ET 0 · k c , and
using a crop coefficient (k c ) of 0.83, based on empirical data from Diczbalis (2002)
or 0.85, as determined by Spohrer et al. (2006), based on physiological
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W. Spreer et al.
same time, establish an irrigation extension service which can advise farmers on
water efficient irrigation techniques, including the option of using deficit irrigation
during extended drought periods (Schulze et al. under review).
6.3 Irrigated Longan Production
In contrast to mango, longan (Dimocarpus longan Lour.) is usually not exported
fresh, but mainly in a dried form. The main importing country for dried longan from
Thailand is China. The most important quality parameters – size and color –
develop best with on-season production during the dry season. As longan trees
are sensitive to drought, irrigation is essential.
6.3.1 General Management
Longan is a subtropical fruit tree indigenous to Southeast Asia. Together with
lychee (Litchi chinensis Sonn.), it is the most popular member of the Sapindaceae
family, which has over 2,000 species and 150 genera (Menzel and Simpson 1991).
Thailand is currently the biggest longan producer in the world, with drained rice
fields and gently sloping fields in the foothills of the upper Ping River Basin in
northern Thailand being the main production areas. Naturally, longan trees grow up
to 20 m in height, but on Thai plantations, they are typically grown in a 10 Â 10 m
pattern, reaching 7–10 m in height. Previous research on new pruning techniques
recommended growing smaller trees (Manochai et al. 2008), but this advice has not
yet been widely followed in practice. Longan flowering can reliably be induced
through the application of potassium chlorate, and as a result, production is possible
all year round (Manochai et al. 2005). However, flower induction and management
is expensive and weather dependent (Ongprasert et al. 2010b), plus incomplete
degradability of potassium chlorate in the soil leads to a lower response rate, which
in turn results in ever increasing application rates (Ongprasert et al. 2010a).
Therefore, and because size and color develop best during the dry season, presently
about 80 % of longan fruit is produced during the ‘on-season’, which starts with
flowering in February and ends with the fruits being harvested in July. Longan trees
are particularly sensitive to drought during the flowering and early fruit development stages (Menzel and Waite 2005), so irrigation management is crucial in
growing regions which have a distinctly summer rainfall pattern (Diczbalis et al.
2010). As on-season flowering and fruit development coincides with the dry season
in Thailand, high fruit yields can only be obtained using irrigation. Irrigation water
requirements are calculated based on a climatic water balance: ET c. ¼ ET 0 · k c , and
using a crop coefficient (k c ) of 0.83, based on empirical data from Diczbalis (2002)
or 0.85, as determined by Spohrer et al. (2006), based on physiological
222
W. Spreer et al.