Sneha C creator A V Santhosh Kumar(Guide) text xxu Vellanikkara Department of Tree Physiology and Breeding,College of Forestry 2011 monographic eng

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74 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. MSc 634.9 SNE/MO http://krishikosh.egranth.ac.in/handle/1/5810028921 http://krishikosh.egranth.ac.in/handle/1/5810028921 150131 20220328154440.0