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Wheat Information
Service
Number 72: 46-50 (1991)
Scheduling
irrigation in wheat through leaf water
potential
Alok Kumar* and R. P. Tripathi
Department of Soil Science, G. B. Pant University of Agriculture
& Technology, Pantnagar, Nainital, India- 263145
Introduction
Observations indicate that crop growth and yield are determined
directly by the plant water stress and only indirectly and partially
by the soil water status (Kramer 1969). Therefore, warning stress for
irrigation should come from the crops themselves. Leaf water
potential (LWP) represents the integrated effect of soil water
deficit, atmospheric evaporative demand, rooting pattern and crop
susceptibility characteristics (Cary and Wright 1971; Clark and Hiler
1973; Hiler and Clark 1971; Hiler et al 1974; Teare et al 1974). The
concept of stress day index (Hiler and Clark 1971) was suggested to
detect crop water stress for optimizing irrigation timings. It is
numerically expressed as the product of the crop susceptibility
factor (CS) and the stress day factor (SD). CS indicates the plant's
susceptibility to a given water deficit at different growth stages
and depends on the crop species and growth stages of the given crop.
Stress day factor is a measure of the degree and duration of plant
water deficit and can be characterised from the measurement of leaf
water potential. The objective of this investigation was to evaluate
the effectiveness of stress day criteria using LWP for scheduling
irrigation to wheat (Triticum aestivum L.) crop.
Materials and Methods
The experiment was conducted in Haldi Loam soil series at the
Crop Research Centre, Pantnagar, India. The soils are moderately well
drained and water table fluctuated from 1.8 to 2.3m during the wheat
season. The ground water was slowly flowing and free from hazardious
chemicals (EC<0.4ds/m). The crop susceptibility (CS) factor for
wheat (RR-21) was determined experimentally as fractional reduction
in grain yield resulting from not irrigating the crop at a particular
growth stage and irrigating at all other stages during the wheat
growing seasons of 1980-81 and 1981-82 under field conditions in the
above mentioned soil series. CS for growth stage i was expressed as
(Hiler and Clark 1971).
CSi = (X-Xi)/X
Where X is the grain yield from the treatment irrigated at all growth
stages and Xi is the yield in the treatment subjected to water
deficit only in the growth stage i. Crop susceptibility (CS) as
determined from the two years experiment was averaged for each growth
stage (Table1).
For getting a range of irrigation schedules five values of morning
leaf water potential (SD1) were chosen as 4, 6, 8, 10 and
12 bars ranging from those prevailing at Crown root initiation (CRI)
to milk stages (as per previous observation). At these chosen values
of SD1 and experimentally determined values of CS, stress
day factor (SD) at irrigation was determined (Hiler et al 1974).
Irrigation schedules thus prepared (Table
2) were executed.
The experiment was laid out in 6 x
5m plots with six
treatments with four replicates in 1982-83. In next year (1983-84)
most promising treatment of 1982-83 was taken along with three
treatments (Table
2) based on
existing growth stage concept to compare and confirm the previous
years' findings.
These four treatments with four replication were also laid out in 6 x
5m plots. The SDI treatment amounted to avariable leaf water
potential (LWP) characterized from the measurement of morning LWP (30
minutes after sunrise) by a pressure chamber (Scholander et al 1965).
Irrigations were applied when the absolute value of morning LWP (SD)
approached the specified value for that growth stage. Each irrigation
amounted to 6 cm, measured with a parshall flume. Final grain yield
and the total amount of water received by each treatment was
determined during both the years.
*Present address: Department
of Agronomy N. D. Univ. of Agri. & Tech., Kumarganj, Faizabad,
India-224229.
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