CONTENTS

KUMAR et al
I 7
and I 8
irrigation treatments (Table 1).However, the
crop in I 2
used 93.6 mm and 65.4 mm less water in
comparison to I 3
and I 6
,respectively.Further the crop
in I 2
treatment on an average registered 104.6%,
33.5%, 37.1%, 30.7% and 49.2% more yield over I 1
,
I 4
, I 5
, I 7
and I 8
, respectively. Among all the treatments
lowest castor bean yield was observed in I 1
(daily
drip irrigation at 0.4Epan throughout the crop lifewith
a seasonal ETcof 239.3 mm) treatment. Bean yield
under surface check basin irrigation at 0.8 IW/CPE
ratio throughout the crop life (I 8
) with a seasonal water
requirement of 445.9 mm produced significantly lower
bean yield in comparison to drip irrigation treatments
(I 2
to I 7
) except I 1
. These trends were traced to
favourable soil water balance as evident from crop
evapotranspiration (ETc) : reference crop
evapotranspiration (ETo) ratio (> 1.0 at flowering and
capsule development stage) an indicator of soil water
deficit (Nair et al., 2013) under drip irrigated I 2
,I 3
and
I 6
irrigation treatments. Further the regression of bean
yield on seasonal ET c
revealed a significant
correlation with an explained total variation of 99%
in bean yield as evident from the following equation.
Y = – 9535 + 68.603ETc – 0.0895
ETc 2 (R 2 = 0.99 F-value = 35.7 * )
This favourable soil water balance under I 6
,
I 3
and I 2
treatments aided the crop plants to put forth
improved performance over other treatments, since
water plays a vital role in the carbohydrate
metabolism, protein synthesis, cell wall synthesis
and cell enlargement (Chaveset al., 2002). Therefore,
crop plants in I 6
, I 3
and I 2
treatments had more plant
height, which in turn helped the plants to put forth
more canopy i.e., LAI (Table 1) and dry matter. It is
well documented that cell enlargement is very
sensitive to water deficits and the consequence is a
marked reduction in leaf area (Pettigrew, 2004).
Sudhakar and Rao (1996) opined that the LAI was
the growth characteristic which limited the rate of
dry matter accumulation of castor under soil water
deficits. This improved growth performance in the
form of plant height, LAI and dry matter by the crop
in I 6
, I 3
and I 2
treatments in turn may have contributed
more number of spikes plant -1 with longer spike
length, more number of capsules plant -1 , seeds
capsule -1 and test weight (Table 1). The dependence
of bean yield on growth and yield components was
apparent from the positive and significant (P=0.01)
correlation it had with plant height (r = 0.95), LAI (r =
0.69), dry matter (r= 0.82), spikes plant -1 (r= 0.94),
spike length (r= 0.64), capsules plant -1 (r = 0.90),
seeds capsule -1 (r= 0.84) and test weight (r= 0.91).
The cumulative effect of all these increased growth
and yield traits was well marked on bean yield of drip
irrigated crop in I 2
, I 3
and I 6
treatments.
On the other hand, irrigations at lower
evaporation replenishment factor in I 1
, I 4
, I 5
and I 7
drip irrigated treatments during individual growth subperiods
of vegetative, flowering and capsule
development induced soil water deficits in the crop
root zone. This caused ET c
to fall below in I 1
, I 4
, I 5
and I 7
drip irrigated treatments relative to ET c
under
I 2
, I 3
and I 6
treatments. This unfavourable soil
moisture environment not only reduced the plant
height, LAI, and dry matter but also brought
significant reduction in yield contributing characters
like number of spikes plant -1 , spike length, capsules
plant -1 and test weight (Table 1).The greater sensitivity
of flowering and capsule development period to ET c
deficits in I 1
, I 4
, I 5
and I 7
treatments could be partly
related to the fact that crop reached its peak ET c
requirement (3.97mm day -1 ) during this period.
Additionally, this is the period in which the potential
spike size and capsule number is determined. Thus,
water deficits at flowering period might have caused
abortion of flowers as is evident from the number of
spikes, spike length and capsules plant -1 in I 1
, I 4
, I 5
and I 7
treatments, which limited the total number of
seeds per plant and possibly non-availability of
assimilates to capsules might have reduced the bean
weight(Sudhakar and Rao,1996). All these effects
finally reduced the bean yield in I 1
, I 4
, I 5
and I 7
treatments and the effect of water deficits is well
marked (Table 1).
Whereas, under conventional check basin
irrigation method (I 8
treatment) due to longer irrigation
interval (8 – 12 days)the fluctuations in soil matric
potentials are relatively large as compared to high
frequency (1 – 2 days interval) drip irrigation (Rao,
2011) and this might have affected the crop growth
and yield contributing characters resulting in reduced
crop yields.
Thus, it could be concluded that for higher
bean yield of castor crop grown during winter season
daily drip irrigationat 0.6Epan throughout the crop life
with a seasonal ETcof 334.5 mm is recommended.
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