177The Tsim values obtained from the PNUTGRO model are greater than Tsla values.
The greater Tsim values can be attributed to the greater amounts of biomass pre-
dicted by crop model under these conditions. The TE values are lower compared
to those obtained by Wright et al. (1996). This could be due to the high VPD of
1.82–2.26 under field conditions. These values are comparable to those obtained
by Hubick et al. ( 1986 ) when groundnut studies were conducted in glasshouse at a
VPD of 2.2. Similar to those reported here were obtained by Azam ali et al. ( 1989 )
at VPD of 2.1 kPa in drying soil; Mathews et al. ( 1988 ) at 1.9 kPa in dry season with
occasional irrigation.
The results from this field study clearly show that both temperature and water
stress decrease pod yields in groundnut, but the cultivars used in this study differed
in their responses to temperature and water stress. Temperature moderately reduced
total biomass or vegetative weight (leaf + stem). In contrast, a severe decrease
in pod yield was recorded due to high temperature. However, under water stress
conditions, a greater decrease in biomass and vegetative yield occurred along with
a decrease in pod yield. This provides evidence to suggest that crop plants react
differently to environmental stresses and adopt different strategies to overcome the
stress events occurring at a particular location.
Pod yield decrease under water stress conditions can be attributed to a decreased
source (vegetative weight), and in one cultivar to a slight decrease in partitioning.
Such decrease in vegetative weight has been recorded in many experiments (Wright
et al. 1991 ; Sarma and Sivakumar 1989 , 1990 ). There exists evidence in literature
for this decrease in pod yield under water stress conditions (Nageswara Rao et al.
1988 ; Ravindra et al. 1990 ; Williams et al. 1986 ). Thus, under water stress condi-
tions, pod yield is source limited. Decrease in partitioning was also recorded in
earlier studies by Greenberg et al. ( 1992 ).
Fig. 8.8 Amount of water
received by the crop ( ETC)
and cumulative transpira-
tion values derived using
SLA ( Tsla) and simulated by
PNUTGRo model ( Tsim) in
irrigated (100 % ETC) and
water stress (40 % of ETC)
treatments in sowing 1 and
sowing 2 from flowering to
harvest
8 Effect of High Temperature and Water Stress on Groundnuts ...