Centre for Plant & Water Science - Central Queensland University

Centre for Plant & Water Science 2008 Annual Report
EXPLORING THE RESPONSE OF SOME VEGETABLE SPECIES TO
OXYGATION
SUMMARY
Various trials, with and without plants, evaluated a number of aspects of oxygation. Four
species including pak choy, beetroot, shallot, and dwarf bean were studied in a pot
experiment to examine their response to oxygation. The results showed that except for
shallot, the other vegetables did not show significant increase in yield or yield components
due to oxygation. The effect of pipe size, water cross sectional area, the geometry of joiners,
and non-ionic surfactant at various concentrations on air flow rate distribution along a
20 m lateral line was also studied to understand uniformity of supply within a field situation.
The response of pak choy, beetroot, shallot, and dwarf bean grown in 26 L pots to oxygation
was studied. For each species, the experiment was laid out as a Completely Randomized
Block Design (CRBD), replicated four times with two treatments, irrigation with aerated
water by means of air injector venturi or control. In addition to the crop yield, soil oxygen
concentration, soil respiration rate, leaf chlorophyll concentration, photosynthetically active
radiation, transpiration rate, stomatal conductance and photosynthesis rate for aerated and
non-aerated treatments were measured during the growing season. Aerated shallots in
contrast to control ones showed significant higher performance in terms of leaf chlorophyll
concentration, soil respiration rate, leaf length, leaf count and leaf weight per unit area at 5%
level of confidence. The other vegetable species did not show significant response to
oxygation. Production of aerenchyma and/or shallow roots might be responsible for lack of
response in the other species.
Three pipe sizes of 13 mm, 19 mm, and 25 mm and two types of pot emitters of 0.52 mm 2
(1.2 L h -1 ) and 1.25 mm 2 (4 L h -1 ) water cross sectional area along with symmetric and
asymmetric joiners spaced at 50 cm intervals on 20 m long recirculating pipes were tested.
Generally, distribution of air flow rates in all trials was non-uniform. The closer the emitter
to the venturi, the higher the air flow rate. The result of paired t-test performed on the air
flow rates for a 19 mm pipe with asymmetric joiners indicated that the cross sectional area
of the emitters had no significant effect on the air flow rate distribution at 5% level of
confidence. By means of the same test, it was revealed that asymmetric joiners in contrast to
symmetric ones cause significantly higher air flow rates along the pipe line regardless of the
pipe size. Furthermore, with symmetric joiners, the smaller the pipe size, the higher will be
the average of the air flow rate along the pipe; this trend was reversed if asymmetric joiners
are used in the line. Application of a non-ionic surfactant (BS 1000) at 20, 35, 50, 65, 80,
and 100 ppm concentrations in a non-recirculating partially open-end 20 m pipe of 19 mm
ID with asymmetric joiners and 4 L h -1 pot drippers resulted in enhanced air flow rate
uniformity, where the minimum surfactant concentration for yielding the highest air flow
rate uniformity (CUC=80%) was 65 ppm.
PROJECT STAFF Principal Investigator: Manouchehr Torabi
Co-Principal Investigator: Prof David Midmore
Others:
Dr Surya Bhattarai & Dr Xinming Chen
FUNDING Cotton CRC, CQUniversity
INCOME $4,497
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