T max
Maximum temperature
T min
Minimum temperature
USD
US dollar
WUE Water use efficiency
6.1 Introduction
The irrigation of tropical fruit trees is important in the northern part of Thailand as
most fruit grow during the dry season, when the cloudless skies provide high levels
of radiation and the dry environment slows the growth of pests and fungi. Under
these conditions, premium fruit can only be produced under an intensive water and
nutrient management regime. In this chapter, our focus will be on the production of
mango and longan fruit.
In recent years, water availability has become increasingly problematic in
Thailand due to climate change, with increasing average annual temperatures
occurring along with more frequent weather abnormalities (Jintrawet 2011).
Farmers in northern Thailand are confronted with periodic droughts, such as in
2010 when the water stored in reservoirs was not enough to irrigate mangos up to
the harvest, or with early and abundant rainfall, as in 2011, which led to flooding
across the country. Table 6.1 shows that during the mango season in 2010, the
average maximum temperature was more than three degrees higher than the longterm average, while rainfall was about half the average, yet in 2011 rainfall was
more than twice the long-term average. At the time of writing this chapter, farmers
are reporting that abnormal rainfall in January 2012 may be about to destroy a good
part of the fruit set.
As water is becoming a scarce resource, so deficit irrigation strategies have been
developed to use water more efficiently. Deficit irrigation (DI) strategies deliberately allow crops to sustain some degree of water deficit and sometimes, some yield
reduction, through a significant reduction in water requirements. To date, two
methods of DI have been used to save water within the fruit production sector:
(1) Regulated deficit irrigation (RDI) in which – in accordance with the phenological stage of the plant – a certain percentage of potential crop evapotranspiration
(ET C .) is replaced by irrigation applied over the entire root-zone, and (2) Partial
root-zone drying (PRD), in which at each irrigation event only one side of the tree
row is watered, with the other side left to dry-out to a predetermined level before
being irrigated again.
DI is primarily an economic approach towards optimizing water allocation. Small
irrigation amounts increase crop evapotranspiration (ET) more or less linearly, up to a
point where the relationship becomes curvilinear because part of the water applied is
not used in ET and is lost. At a certain point, yields reach their maximum value and
216
W. Spreer et al.
Maximum temperature
T min
Minimum temperature
USD
US dollar
WUE Water use efficiency
6.1 Introduction
The irrigation of tropical fruit trees is important in the northern part of Thailand as
most fruit grow during the dry season, when the cloudless skies provide high levels
of radiation and the dry environment slows the growth of pests and fungi. Under
these conditions, premium fruit can only be produced under an intensive water and
nutrient management regime. In this chapter, our focus will be on the production of
mango and longan fruit.
In recent years, water availability has become increasingly problematic in
Thailand due to climate change, with increasing average annual temperatures
occurring along with more frequent weather abnormalities (Jintrawet 2011).
Farmers in northern Thailand are confronted with periodic droughts, such as in
2010 when the water stored in reservoirs was not enough to irrigate mangos up to
the harvest, or with early and abundant rainfall, as in 2011, which led to flooding
across the country. Table 6.1 shows that during the mango season in 2010, the
average maximum temperature was more than three degrees higher than the longterm average, while rainfall was about half the average, yet in 2011 rainfall was
more than twice the long-term average. At the time of writing this chapter, farmers
are reporting that abnormal rainfall in January 2012 may be about to destroy a good
part of the fruit set.
As water is becoming a scarce resource, so deficit irrigation strategies have been
developed to use water more efficiently. Deficit irrigation (DI) strategies deliberately allow crops to sustain some degree of water deficit and sometimes, some yield
reduction, through a significant reduction in water requirements. To date, two
methods of DI have been used to save water within the fruit production sector:
(1) Regulated deficit irrigation (RDI) in which – in accordance with the phenological stage of the plant – a certain percentage of potential crop evapotranspiration
(ET C .) is replaced by irrigation applied over the entire root-zone, and (2) Partial
root-zone drying (PRD), in which at each irrigation event only one side of the tree
row is watered, with the other side left to dry-out to a predetermined level before
being irrigated again.
DI is primarily an economic approach towards optimizing water allocation. Small
irrigation amounts increase crop evapotranspiration (ET) more or less linearly, up to a
point where the relationship becomes curvilinear because part of the water applied is
not used in ET and is lost. At a certain point, yields reach their maximum value and
216
W. Spreer et al.