REGULATED DEFICIT IRRIGATION FOR MICRO-IRRIGATED CITRUS (CITRUS RETICULATA VAR. BLANCO) TREE - Management, Performance, and Applications of Micro Irrigation Systems - page 236

of means was obtained using Duncan multiple range test (DMRT), according to the
methods described by Gomez and Gomez [11].

19.3 RESULTS AND DISCUSSION
19.3.1. SOIL WATER VARIATION
The mean fortnightly volumetric water contents ( v) observed at different soil depths

(0.2, 0.4, 0.6 and 1.0 m) in early fruit growth period (EFGP) during 2010 and 2011 are
presented in Figs. 1a and 1b. The

θ

v decreased progressively from the day after onset
of stress (DAOS) to end of stress period (60 DAOS) in both the years of experiment,
except at 0.2 m depth at 30 DAOS in 2010 and at 0.2 m and 0.4 m depths at 45 DAOS
in 2011. The increase in

θ

v at 30 DAOS in 2010 and 45 DAOS in 2011 attributed to
rain (8.8 mm and 33 mm in respective years) during EFGP. The fortnightly estimated
soil water depletion (SWD) was found maximum with RDI 0 (4.4-12.4% in 2010 and
3.4-9.0% in 2011), followed by RDI 50 (2.0-3.7% in 2010 and 1.0-2.4% in 2011) at
different soil depths. The higher SWD was estimated in 2010 than 2011, in spite of
higher rainfall in 2011 at EFGP. This was due to higher evaporative demand of the
plants in 2010 (mean daily pan evaporation, 10.01 mm) compared to that in 2011
(mean daily pan evaporation, 6.95 mm) in this period. However, the SWD at top 0.4 m
soil between 2 observations in a week was observed to be higher with FI than that with
other treatments, reflecting the higher evapotranspiration of the trees under increased
soil water regime in this treatment (Figs. 1a and 1b).

θ

19.3.2 VARIATION IN AVAILABLE SOIL NUTRIENTS

The v value increased with depth under each treatment. However, the maximum

SWD was found at 0.4 m soil depth, followed by 0.2 m depth, indicating the existence
of the most active roots of mandarin trees at 0.2-0.4 m depth. The earlier findings
showed a shallow active root zone of 0.15 m for drip-irrigated 'Nagpur' mandarin
budded on Rangpur lime grown in vertisol of central India [2, 19]. This difference in
rooting is due to the variation of citrus cultivars and root stock used in varied pedo-
climatic conditions.
However, the active root depth observed in 'Kinnow' mandarin in our research is
strongly supported by the earlier observation of Bhambota et al. [3], which showed
that the active root zone of Jatti Khatti, the citrus cultivar used as a rootstock for Kin-
now mandarin, exists within the top 0.4 m soil. The SWD value at 0.6 m depth under
RDI 0 was signifi cantly increased compared with that under RDI 50 and FI. This hap-
pened due to the higher root activity, which was probably caused due to extension of
roots in 0.6 m soil under water stress condition in RDI 0 treatment.

θ