REGULATED DEFICIT IRRIGATION FOR MICRO-IRRIGATED CITRUS (CITRUS RETICULATA VAR. BLANCO) TREE - Management, Performance, and Applications of Micro Irrigation Systems - page 241

TABLE 4 mol m -2 s -1 ), stomatal conductance (g s , mmol m -2 s -1 ),

transpiration rate (T r , mmol m -2 s -1 ), and leaf water use efficiency (LWUE) of 'Kinnow'
mandarin under regulated deficit irrigation (RDI) and full irrigation (FI) during 2010 and 2011.

Photosynthesis rate (P n , μ

Leaf physiological parameters
2010 2011 Mean
P n g s T r LWUE P n g s T r LWUE P n g s T r LWUE
RDI 0 3.03 c 29.13 c 1.73 c 1.75 c 3.61 c 28.48 c 1.51 c 2.39 c 3.32 c 28.8 °C 1.62 c 2.05 c
RDI 50 3.59 b 31.01 b 1.82 b 1.97 a 4.16 b 30.47 b 1.57 b 2.64 a 3.88 b 30.74 b 1.70 b 2.28 a
FI 3.88 a 37.78 a 2.08 a 1.86 b 4.37 a 37.37 a 1.74 a 2.51 b 4.13 a 37.60 a 1.91 a 2.16 b
Data in one column followed by different letter are significantly different at P <0.05, as per separation by Duncan's
multiple range test.
RDI 0 = No irrigation at early fruit growth period (EFGP); RDI 50 = Irrigation at 50% crop evapotranspiration at EFGP.

Treat-
ments

19.3.5 LEAF PHYSIOLOGICAL PARAMETERS
The P n , g s and T r of leaves during EFGP was significantly influenced by irrigation
treatments (Table 4). The values for P n , g s and T r varied in the range 3.03-3.88 mol

m -2 s -1 , 29.13-37.78 mmol m -2 s -1 and 1.75-1.86 mmol m -2 s -1 , respectively, in 2010,
whereas in 2011, these values were 3.61-4.37

μ

μ mol m -2 s -1 , 28.48-37.37 μ mol m -2

s -1 and 2.39-2.51 mol m -2 s -1 . The higher values of P n in 2011 were probably due

to lower temperature in this period, which favored the better photosynthesis rate of
mandarin plants in comparison to that in 2010 [4]. However, the P n started to decrease
when air temperature became more than 35 °C, probably due to the partial damage of
photosynthetic system with high temperature in this cultivar, as found in other citrus
cultivars [23, 30].
The higher values of P n with fully irrigated trees indicated the negative effect of
soil water defi cit on P n of citrus trees. The greatest reduction in P n value was between
RDI 50 and RDI 0 (14.5%) than that in between FI and RDI 50 (6.0%). The higher reduc-
tion of P n in between RDI 50 and no irrigation treatments indicated the existence of
threshold limit of irrigation applied at 50% ET c , resulting in optimum P n of mandarin
plants under this treatment. In other way, it can be expressed that the mandarin plants
could sustain their photosynthesis rate with 50% reduction of water supply, which is
called as the photosynthetic acclimatization nature of citrus [31]. The g s and T r values
followed the same trend of P n in different irrigation treatments. However, the high-
est reduction percentage in g s (18.2%) and T r (11.0%) was observed between FI and
RDI 50 comparison with that between irrigation at RDI 50 and RDI 0 (g s , 6.3%; T r , 4.7%),
refl ecting the existence of critical soil water regime in relation to transpirational water
loss with irrigation at 50% ETc. The maximum reduction in g s and T r at higher irriga-
tion level (50% ETc) compared to P n (at no irrigation) refl ects the less sensitivity of
the trees to soil water defi cit in irrigation at 50% ETc to produce higher water use
effi ciency in leaf level. Moreover, the reduction of g s was higher than that of T r under
RDI compared to FI. The lower reduction of T r could be probably due to the contribu-
tion of residual or mesophyll conductance (movement of water through intercellular

μ