Agriculture Reference
In-Depth Information
19.2 MATERIAL AND METHODS
The field experiment was conducted in Indian Agricultural Research Institute, New
Delhi, India. The citrus plant used in the study was 'Kinnow' mandarin (
Citrus re-
ticulata
var. Blanco) budded on rough lemon (
Citrus jambhiri
Lush) rootstock. The
experiment was conducted in 2010 and 2011 with 10 year-old drip-irrigated plants.
The plant-to-plant spacing in a row and within the row was 4 m and 5 m, respectively.
The texture of experimental soil was sandy loam with bulk density 1.54 g cm
-3
.
The fi eld capacity (-0.033 MPa) and permanent wilting point (-1.50 MPa) of the soil
were 24.0% and 8.5% on volume basis, respectively. The soil had almost neutral pH
(7.2) with mild EC (0.15 dS m
-1
). The water level in the groundwater wells, situated
at 100 m distance from the experimental plot, was around 17.0 m deep. The climate of
the experimental site is characterized as semiarid subtropical, with hot and dry sum-
mers. The mean annual rainfall is 600 mm, out of which around 85% is received dur-
ing monsoon (June-September). The mean daily class-A pan evaporation rate varied
from 1.6 mm in January to as high as 10.7 mm in June.
Two DI regimes: no irrigation (RDI
0
) and 50% crop evapotranspiration (RDI
50
)
were applied at EFEP and their impact on crop performance was compared with that
under full irrigation (FI, 100% crop evapotranspiration). The duration of EFEP was
taken from mid-April to mid-June, as suggested [7] for 'Kinnow' mandarin in the
study region. Irrigation was applied through drip system from mid-January to June
and from October to December. Water supply was stopped during monsoon season
(July-September) due to adequate rainfall fulfi lling the crop water need during this
period. The experimental design was randomized complete block. Twelve trees in
three adjacent rows were taken as a replicated unit and two central trees of each plot
were considered as experimental plants. All the measurements were taken from these
experimental trees.
Irrigation was imposed every other day through six on-line 8 l.h
-1
pressure com-
pensated drip emitters per tree, fi tted on two 16 mm diameter lateral pipes (3 emitters
per lateral). The emitters were placed at 1.0 m away from tree stem. The water quantity
applied under full irrigation (FI, 100% ETc) was estimated based on 100% class-A pan
evaporation rate for 'Kinnow' mandarin plants grown in Delhi condition [13], using
Eq. (1).
ETc = Kp
×
Kc
×
Ep
(1)
where: ETc = Crop-evapotranspiration (mm/day); Kp = Pan coefficient (0.8), Kc =
Crop-coefficient (0.60-0.85) for bearing 'Kinnow' plant [13] and Ep = 2-days cumula-
tive pan evaporation (mm). The volume of water applied under FI was computed with
Eq. (2).
V
id
= [
π (D
2
/4) ´ (
ET
c
- R
e
)
]/
E
i
(2)
where: V
id
= Irrigation volume applied in each irrigation (liter tree
-1
), D = Mean tree
canopy spread diameter measured in N-S and E-W directions (m), ETc = Crop-evapo-
transpiration (mm), R
e
= Effective rainfall depth (mm), and E
i
= Irrigation efficiency
of drip system (90%). As per FAO-25, the effective rainfall was estimated as the sum-
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