Agriculture Reference
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mation of soil water content enhancement in root zone of the trees (mm) due to rainfall
and potential evapotranspiration (mm) for the rainfall day [5].
The mean monthly water applied under different treatments in various months dif-
fered in two years of observation. This was attributed to change in evaporation rate,
rainfall and canopy diameter of the plants. Under different treatments, same quantity
of irrigation water was applied at different growth stages of the crop except EFEP. Ir-
rigation at 50% ETc was supplied at PFP to create desirable water stress for fl owering
in citrus. The water supply in each irrigation treatment was regulated by adjusting the
operating hours with the help of lateral valves provided at the inlet end of lateral pipes.
The fertilizer (354 g N as both urea and urea-phosphate, 160 g P
2
O
5
as urea-phos-
phate and 345 g K
2
O as muriate of potash per plant) was applied 4 times (January,
March, June and October) in a year through drip irrigation system, as recommended
for bearing 'Kinnow' plants in Delhi region [13]. Ground fl oor of the experimental or-
chard was kept weed free, and uniform plant protection measures against insect pests
and diseases were adopted for all plants in the experimental block.
Soil sampling was done at 30 cm, 60 cm, 90 cm, 120 cm, and 150 cm distances
from plant stem along and in between the drip emitters and at 0-20 cm, 20-40 cm,
40-60 cm, 60-80 cm, and 80-100 cm depths once in January and subjected to analysis
for available nutrients (N, P, K, Fe, Mn, Cu and Zn). One plant basin from each repli-
cated plot (7 experimental plants per treatment) was taken for soil sampling. Available
nutrients were determined by following the standard procedures [28]. The depth wise
mean values of available nutrients in different treatments were calculated and aver-
aged for entire root zone depth (0-100 cm).
Three- to fi ve- months old leaf samples (3rd and 4th leaf from tip of nonfruiting
branches) at a height of 1.5 m from ground surface surrounding the plant canopy were
collected at end of October and analyzed for macronutrients (N, P, K) and micronutri-
ents (Fe, Mn, Cu, and Zn) following the standard methods [28].
Stem water potential measured at 12:00-13:00 PM (mid-day stem water potential,
MSP) was determined fortnightly on a cloudless day using a Pressure chamber (PMS
instrument, Oregon, USA). Two leaves per plant near the trunk or a main scaffold
branch were covered by both aluminum sheet and black polythene sheet before 2 h of
measurement and their water potential represented the MSP [23]. Moreover, the mid-
day water stress integral (S
ψ
) for each treatment was calculated using the midday stem
water potential data, according to the Eq. (3) by Gonzaalez-Altozano [12].
i
=
1
{
}
∑
(
)
S
Ψ=
Absolute value of
ψ
i i
,
+
1
−
C
n
(3)
i
=
0
where: S
ψ
is water stress integral (MPa day), ψ
i, i+1
is average midday leaf/stem water
potential for any interval i and i+1 (MPa), c is maximum leaf/stem water potential
measured during the study and n is number of days in the interval.
The net photosynthesis rate (P
n
), stomatal conductance (g
s
), and transpiration rate
(T
r
) of leaves were recorded fortnightly, in one hour interval from 9 am to 3pm on a
clear-sky day by portable infrared gas-analyzer (LI-COR-6400, Lincoln, Nebraska,
USA) during the irrigation seasons. Four mature leaves per plant (3rd or 4th leaf from
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