MSc

The research work on 'Modeling crop water stress index (CWSl) in tree
seedlings' was taken up at Department of Tree Physiology and Breeding, College of
Forestry during April 2010 to March 2011.
The objective of the study was to detect water stress in seedlings of teak and
mahogany with the help of infrared thermometry by developing CWSI. Six month old
seedlings were provided with four different irrigation treatments- irrigation at
lW/ET=l, 0.6 and 0.3 on weekly interval and a control treatment was maintained
with no irrigation (IWIET=O). Plant canopy temperature was recorded on daily basis
from each treatment using a hand held infrared therinometer (HTC lR-8811). The
non-water-stressed baseline (NWSB), obtained from canopy air temperature deficit
and vapour pressure deficit (VPD) in the well watered treatment (irrigation at 1.0
lW/ET) and water stressed baseline obtained from non irrigated lW/ET=O. For teak
the lower baseline was determined as CATD = -1.01VPD+2.8 and the upper baseline
equation was CATD = -O.OSVPD+S.1. For mahogany, lower baseline equation was
CATD = -0.2SVPD-2.9 and the upper baseline equation was CATD = -0.01 VPD+6.1.
CWSl was calculated for each treatment using these baseline equations. The CWSl
responded to irrigation events along the whole season, and clearly detected mild
water stress, suggesting extreme sensitivity to variations in plant water status. Non
irrigated lW IET=O showed a greater value for CWSl for all the time followed by
treatment provided with irrigation at lW IET=O.3 while the treatments with higher
irrigation levels (IWIET= 1 and 0.6) had lower CWSl values. It indicates that there is
an increase in CWSl with time as available water in the soil decreased. It has been
observed during the study that teak seedlings are more susceptible to water stress than
mahogany. Observation on canopy air temperature deficit showed that, teak seedlings
from all treatments maintained a constant canopy air temperature deficit all over the
week. In mahogany, lWIET=l and lWIET=O maintained a constant canopy air
temperature deficit, whereas, lW/ET=0.6 and lW/ET=0.3 showed a slow increase

prior to the next irrigation. This reveals a relatively higher water use of teak seedlings
when compared to mahogany.
Well watered mahogany seedlings showed higher crude protein content
compared to other treatments indicating a significant reduction in photosynthesis
occurred during water stress. But for teak seedlings no difference was observed
among different treatments. Chlorophyll content was found to be decreasing due to
water stress in both species. Teak seedlings showed significant reduction in total
height, collar diameter, number of leaves, shoot weight, root weight, shoot root length
ratio and relative growth rate on the course of stress treatment whereas root length
was increasing. Shoot root biomass ratio was found to be least affected due to
different levels of irrigation treatment. In the case of mahogany, collar diameter,
shoot root length ratio and relative growth rate were found to be decreasing due to
water stress. Root length was found to be increasing due to water stress. Plants were
able to maintain total height, total leaf number, shoot weight, root weight and shoot
root biomass ratio unaffected even under irrigation at IWIET=O.3 also. Comparison
on growth characteristics and physiological parameters of two species- teak and
mahogany by providing different levels of irrigation revealed that mahogany uses
water more efficiently than teak seedlings. The present series of investigations
indicate the scope of CWSI in early detection of crop water stress. As is easy to find
out and less time consuming, CWSI has got an immense potential in irrigation
scheduling as well as water management.