| dc.description.abstract | Effects of runoff harvesting and supplemental irrigation
(using fresh and brackish water) on growth and gas exchange
parameters of two morphological types of a desert leguminous
tree, Acacia saligna, under arid conditions of Turkana
district were studied. The experiments were laid out as
completely randomised design (CRD) with three replicates.
Water harvesting was done by channeling the runoff water into
a 'Liman' situated adjacent to an established runoff path. The
brackish and fresh water used for the supplemental irrigation
treatments was obtained from different boreholes. The liman
was divided into 18 plots each measuring 10 m x 40 m. Trees of
the two morphotypes (broad-leaved .and narrow-leaved) which
were of similar size preselected (tagged) in each plot for
data collection. Four sets of data were taken on these trees
i.e, during i) the very dry period, ii) runoff period, iii)
irrigation episodes and iv) the drying phase between ii) and
iv). Supplemetal irrigation was done by applying 200 litres of
water fortnightly into micro-limans constructed round
previously identified trees. Diurnal trends of gas exchange
parameters and leaf water potential for the two morphotypes
were studied during the four distinct periods. Diurnal
measurements of stomatal conductance, transpiration rates,
leaf and ambient temperatures and determination of vapour
pressure deficit (VPD) were done using a porometer (at
intervals of two hours) twice every week, while that for leaf
water potenial was done using a pressure chamber. In each case
three leaves were sampled per plant. Plant growth was
moni tored throughout the experimental period by taking
measurements on leaf extension, shoot elongation and girth
increaments.
Plants which received supplemental irrigation with fresh
or brackish water showed significantly higher rates (P = 0.05)
of leaf elongation (of upto 3.7 cm/week), girth increaments
and physiological parameters such as stomatal conductance (
2.8 cms-l compared to 1.4 cms-l) and transpiration rates)
than those which received runoff water only. Use of brackish
water resulted in decreased levels of these parameters but the
effects were small and non-significant when compared to the
fresh water treatments. Significantly higher magnitudes were
shown by the broad leaved morphotypes than the narrow leaved.
Based on these findings use of runoff water and supplemental
irrigation under arid conditions enhances biomass production. | en |
