165The calculated vapour pressure deficit (VPD) values were 1.82 and 2.26 kPa in T1
and T3, respectively. It was not possible to record RH in the T2 heat tunnel due to
lack of instruments and therefore VPD could not be estimated in T2. The RH level
in T4 during the 20-day period of high temperature averaged to 57 % (SE ± 1.12),
slightly above that of the ambient T3 treatment. VPD was therefore slightly lower
in T4, 2.06 kPa than in T3 (2.26 kPa).
Due to lower ambient temperature in T1 (sowing 1), heat tunnels for T2 were
kept closed during the greater part of the day to achieve the target temperature
of > 40 °C. This led to a buildup of humidity in the heat tunnel near to saturation,
which must have reduced the VPD. A better control of humidity was achieved in
the T4 heat tunnel treatment (sowing 2), keeping the heat tunnel open to reduce the
maximum temperature which at times was > 48 °C. These very high temperatures
were achieved because ambient temperatures were much higher at the second sow-
ing (> 38 °C).
Fig. 8.3 Daily maximum and minimum air temperatures recorded under ambient- and high-tem-
perature conditions and relative humidity in a early and b late sown groundnut crop
8 Effect of High Temperature and Water Stress on Groundnuts ...