ISHS Acta Horticulturae 644: International Symposium on Growing Media and Hydroponics
ESTIMATION OF AVAILABLE WATER AND EVAPOTRANSPIRATION OF POTTED PLANTS WITH A FREQUENCY-DOMAIN SENSOR |
| Authors: | R. Baas, A. Bulle, C. Vonk Noordegraaf |
| Keywords: | Chamaecyparis, Chrysanthemum, dielectric constant, moisture content, keeping quality, permittivity, Spathiphyllum, Viburnum |
| Abstract:
The relation between volume fraction water (  ) of different peat-based growing media and permittivity (or dielectric constant,  ) was determined using a frequency-domain (FD) sensor.
After calibration in two organic mixes, could be estimated in rooted mixes in pot volumes ranging from 0.5 to 4 liter.
Marketable plants had a within the range 0.5-0.65 after a subirrigation period of 10 minutes ( at capacity). Wilting point was at 0.12-0.20 for the potted ornamental plants Spathiphyllum, Chrysanthemum, Chamaecyparis and Viburnum. With the use of FD measurements, evapotranspiration of potted plants was determined under different transport and consumer conditions.
Evapotranspiration varied between 7 and 91 g pot-1 day-1 for the crops.
By dividing the amount of available water (derived from pot volume and difference between at capacity and at wilting point) with evapotranspiration data, potential transport time of potted plants was estimated to be at least 8 days.
Both increased relative humidity (70 versus 40%) and decreased temperature (5 versus 15°C) decreased evapotranspiration during transport simulation up to 50%. Given the standard deviation in of 0.03-0.06 and desired accuracy (e.g. 0.05) it was calculated that 7-23 pots had to be measured in order to obtain a reliable sample estimation of water content.
Application of the FD-sensor include quality control in the grower-retailer-consumer chain and on-line feed-back irrigation control.
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