additional amounts of irrigation do not increase them any further. The location of that
point is not easy to define and; thus, when water is not limited or is cheap, irrigation is
applied in excess to avoid the risk of a yield penalty. However, allocating a suboptimal amount of water can decrease yields to a greater extent than irrigation water is
saved (Fereres and Soriano 2007). A principle of the RDI technique is that plant
sensitivity to water stress is not constant during the growing cycle, and that intermittent water deficits during specific periods may actually improve water use efficiency
(WUE). Under an RDI strategy, irrigation is used to maintain plant water status
within certain limits of deficit during certain phases of the crop cycle, normally when
fruit growth is least sensitive to water reductions. The major disadvantage of RDI is
that it is required to maintain a plant’s water status within narrow limits, which is
difficult to achieve in practice (Costa et al. 2007).
An alternative strategy is PRD, which involves the exposure of roots to alternate
drying and wetting cycles, enabling plants to grow with reduced stomatal conductance but without showing signs of water stress. This technique is based on plant root
to shoot chemical signaling, a process that influences shoot physiology and can be
operated in drip- or furrow-irrigated crops. Theoretically, roots on the watered side of
the soil will maintain a favorable plant water status, while dehydration on the other
side will promote the synthesis of hormonal signals which will reach leaves via the
transpiration stream and further reduce stomatal conductance. This will decrease
water loss and vegetative growth, while leaving fruit yields affected only to a minor
extent – meaning that WUE can be increased (e.g., Spreer et al. 2007).
6.2 Irrigated Mango Production
Mango (Mangifera indica L.) is a commercially important tropical fruit and morphologically is a non-deliquescent drupe – a dicotyledonous fruit tree within the
Anacardiaceae family, and originates from the Indo-Burmese region. Mango is one
of the most important tropical fruit in Asia (Tharanathan et al. 2006), and has a long
history of cultivation in Thailand. However, it is only recently that its importance as
an export product has risen and that irrigation of this drought-tolerant tree has been
considered worthwhile. To understand the requirements of modern mango irrigation activities in Thailand, it is worthwhile considering the development of the
mango export industry.
Table 6.1 Air temperature (T a ), relative humidity (RH) and rainfall during the mango fruit
growing season (February to April) for the years 2010 and 2011, as compared to the previous
10 year average (1997–2007)
Mean T amax (
C) Mean T amin (
C) Mean T a (
C) Mean RH (%) Rainfall (mm)
1997–2007 35.0
18.3
26.6
62.4
89.0
2010
38.5
16.8
26.1
65.1
47.2
2011
35.3
18.6
25.4
70.3
200.4
6 Mango and Longan Production in Northern Thailand: The Role of Water Saving. . .
217
point is not easy to define and; thus, when water is not limited or is cheap, irrigation is
applied in excess to avoid the risk of a yield penalty. However, allocating a suboptimal amount of water can decrease yields to a greater extent than irrigation water is
saved (Fereres and Soriano 2007). A principle of the RDI technique is that plant
sensitivity to water stress is not constant during the growing cycle, and that intermittent water deficits during specific periods may actually improve water use efficiency
(WUE). Under an RDI strategy, irrigation is used to maintain plant water status
within certain limits of deficit during certain phases of the crop cycle, normally when
fruit growth is least sensitive to water reductions. The major disadvantage of RDI is
that it is required to maintain a plant’s water status within narrow limits, which is
difficult to achieve in practice (Costa et al. 2007).
An alternative strategy is PRD, which involves the exposure of roots to alternate
drying and wetting cycles, enabling plants to grow with reduced stomatal conductance but without showing signs of water stress. This technique is based on plant root
to shoot chemical signaling, a process that influences shoot physiology and can be
operated in drip- or furrow-irrigated crops. Theoretically, roots on the watered side of
the soil will maintain a favorable plant water status, while dehydration on the other
side will promote the synthesis of hormonal signals which will reach leaves via the
transpiration stream and further reduce stomatal conductance. This will decrease
water loss and vegetative growth, while leaving fruit yields affected only to a minor
extent – meaning that WUE can be increased (e.g., Spreer et al. 2007).
6.2 Irrigated Mango Production
Mango (Mangifera indica L.) is a commercially important tropical fruit and morphologically is a non-deliquescent drupe – a dicotyledonous fruit tree within the
Anacardiaceae family, and originates from the Indo-Burmese region. Mango is one
of the most important tropical fruit in Asia (Tharanathan et al. 2006), and has a long
history of cultivation in Thailand. However, it is only recently that its importance as
an export product has risen and that irrigation of this drought-tolerant tree has been
considered worthwhile. To understand the requirements of modern mango irrigation activities in Thailand, it is worthwhile considering the development of the
mango export industry.
Table 6.1 Air temperature (T a ), relative humidity (RH) and rainfall during the mango fruit
growing season (February to April) for the years 2010 and 2011, as compared to the previous
10 year average (1997–2007)
Mean T amax (
C) Mean T amin (
C) Mean T a (
C) Mean RH (%) Rainfall (mm)
1997–2007 35.0
18.3
26.6
62.4
89.0
2010
38.5
16.8
26.1
65.1
47.2
2011
35.3
18.6
25.4
70.3
200.4
6 Mango and Longan Production in Northern Thailand: The Role of Water Saving. . .
217