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Enabling better global research outcomes in soil, plant & environmental monitoring.

Logging Water Potential of Cotton

PSY1 Stem Psychrometers are ideally suited to use in cotton. The large lignified stem provides long straight round internodes for ease of installation and does not exude sap or extracts from the xylem into the Stem Psychrometer chamber. The results clearly show a perfect diurnal response to the daily water use and rehydration that the plant experiences. The PSY1 can be used for extended periods throughout the growing season to generate a valuable history of management information.

PSY1 Stem Psychrometers enable a direct in-situ and continuous measurement of a plants water status. The total water potential, measured in Mega-Pascals (Mpa), is an absolute measure of the plants integrated and overall reaction or a direct plant response rather than an inferred response to all of the prevailing environmental parameters such as:

  • Ambient Air Temperature
  • Vapour Pressure Deficit (VPD)
  • Solar Radiation
  • Wind Speed
  • Soil Moisture
  • Nutrients
  • Effects of Pests & Disease

 

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Photo 1. Prof. Mike Dixon University of Guelph Canada & John Watson, Kilmarnock Boggabri NSW Australia, selecting a cotton plant for installation of a Stem Psychrometer.
 The PSY1 in-situ Stem Psychrometer is a powerful research tool for evaluating the consequences of plant-environment interaction in terms that are directly relevant to the plant’s capacity to withstand stress and to assess mechanisms of stress response and recovery. One direct application of the technique in cotton production is to improve irrigation scheduling and interpreting plant response and production to irrigation events.
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Photo 2. Preparing the stem for installation. It is important to remove all living tissues to expose the water conducting xylem. The area must be rinsed with deionised water and rubbed dry prior to installation of the psychrometer.
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Photo 3. Stem Psychrometer installed on the stem. Use a silicon vacuum grease to seal around the edge of the psychrometer and any exposed xylem to prevent localised drying of the plant tissues which would cause artificially high water potential readings.
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Photo 4. Installing foam around the Stem Psychrometer for thermal insulation from rapid ambient fluctuations. An additional layer of aluminium foil wrapped around the foam is also required to reflect direct radiation which would also generate an elevated and variable thermal gradient within the psychrometer chamber.
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Photo 5. The integrated stand alone logger of the PSY1 attached to the cotton stem. The PSY1 supplies power from an internal battery, controls the Peltier cooling pulse, logging interval and data collection of the psychrometer. All data, both raw measurements and processed water potentials is saved on an internal 2GB MicroSD memory card.

 

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Photo 6. Completed PSY1 Stem Psychrometer installation including; reflective radiation insulation around Psychrometer chamber with stand alone logger attached to a neighbouring plant stem.

Results:

The PSY1 Stem Psychrometer took approx 90 minutes to equilibrate after installation at 3:30 pm. The water potential was then monitored and increased (became less stressed) from late afternoon to early evening until a rehydrated equilibrium was reached approx by 11:30 pm. A rainfall event of approx 16 mm occurred overnight and it would appear to have commenced at approx 3:00 am due to the noticeable increase in water potential at this time. The following day the plant was destructively sampled by uprooting the whole plant with Stem Psychrometer intact. Monitoring of the plant continued revealing stomatal closure at approximately –1.88 MPa and subsequent cavitation and desiccation of the plant caused by the removal of its water source.

Figure 1. Non-destructive, continuous diurnal plant water potential measured at 30 minute temporal resolution.

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Conclusion:

PSY1 Stem Psychrometers are ideally suited to use in cotton. The large lignified stem provides long straight round internodes for ease of installation and does not exude sap or extracts from the xylem into the Stem Psychrometer chamber. The results clearly show a perfect diurnal response to the daily water use and rehydration that the plant experiences. The PSY1 can be used for extended periods throughout the growing season to generate a valuable history of management information. Additional field trials and research projects are being conducted with a range of species to evaluate crop specific questions such as longevity of installation. With cotton it is expected that installations may easily last two weeks up to several months before re-installation is required.