Water potential and hydraulic conductivity of peat growth media in containers during drying.
The matric potential and unsaturated hydraulic conductivity of peat-based growth media in containers was measured continuously as a function of drying. The particle size distribution and the water retention characteristics of the media were determined from parallel samples. The growth media used were a light, coarse graded Sphagnum peat, a medium graded Sphagnum peat and a mixture of a perlite and the medium graded Sphagnum peat. Containers of two types were packed with the media and allowed to evaporate from saturation. Matric potential was measured automatically using tensiometers during drying.
In both container types, the matric potential of the media was similar down to 10 kPa at each of the three levels measured during drying. Further drying resulted in a large matric potential gradient between the upper and the middle levels. During drying, there was also clear shrinkage of the media. When the matric potential at the upper level reached ca. -80 kPa, the decrease in height of the media was 5–23 %. The estimated hydraulic conductivity of the media during drying was rather similar. The hydraulic conductivity of the peat-perlite mixture was, however, slightly lower than that of the pure peat media. The hydraulic conductivity decreased linearly on a log-log-scale from ca. 10-5 to less than 10-10 m/s as the matric potential decreased from -3 to -60 kPa. The hydraulic conductivity of the media was comparable to coarse sand at matric potentials below -10 kPa. The decrease in hydraulic conductivity during drying and the possible weakening of soil-root contact due to shrinkage may considerably affect the availability of water to plants.
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Published in 1993