Artikkelit jotka sisältää sanan 'water content'
Kasvualustana käytetyn heikosti maatuneen rahkataturpeen lämmönjohtavuus.
English title: Thermal conductivity of low-decomposed Sphagnum peat used as growth medium.
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The thermal conductivity of low-decomposed Sphagnum peat, used as a growth medium for container seedling production in tree nurseries, and of a sandy mineral soil was studied using the single thermal probe method in the laboratory. The thermal conductivity of the peat was low and decreased from 0.5 to 0.05 W m-1K-1 when the water content decreased from near saturation to air-dry. In comparison, the thermal conductivity of the sandy soil was much higher, decreasing steeply from 1.5 to 0.5 W m-1K-1 with decreasing water content. Results are in accordance with those reported earlier for similar media. The results suggest markedly weaker and more delayed temperature fluctuations in pure peat media compared with media containing mineral soil, which is in agreement with observations made in tree nurseries.
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Heiskanen,
Finnish Forest Research Institute, Juntintie 40. FIN-77600 Suonenjoki, Finland
Sähköposti:
ei.tietoa@nn.oo
TDR-mittausten kalibrointi viljeltyjen turvemaiden kosteuden mittaamiseen.
English title: Calibration of time domain reflectometry (TDR) for soil moisture measurements in cultivated peat soils.
Avainsanat:
water content;
dielectric number
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Time domain reflectometry (TDR) is a relatively new technique for measuring soil water content. It is based on measuring the apparent dielectric number (Ka) of the soil from the propagation velocity of an electromagnetic pulse travelling in the soil. Soil water content is then calculated from the apparent dielectric number. In this study, an empirical relationship between the apparent dielectric number and the volumetric water content was established for cultivated peat soils in the laboratory. A third-degree polynomial described the relationship with a coefficient of determination of 0.980 and a standard deviation of 0.027 m3m-3. The relationship can be used to measure water content in typical cultivated Sphagnum and Carex peat soils in the range usually prevailing in the field, i.e. 0.3-0.8 m3m-3.
Key words: dielectric number, water content
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Myllys,
Agricultural Research Centre of Finland, Institute of Crop and Soil Science, FIN-31600 Jokioinen, Finland
Sähköposti:
ei.tietoa@nn.oo
- Simojoki, Sähköposti: ei.tietoa@nn.oo
Näytelieriön täyttötavan vaikutus kasvuturpeen vedenpidätyskykyyn.
English title: The effect of sample handling on the water retention of growth peat substrate.
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The water retention of Sphagnum peat substrate as used in the production of containerized forest tree seedlings was determined at increasing matric potentials from saturation. Samples of commercially available peat substrate were taken and compressed to correspond to a wet bulk density of 0.2 g cm-3 — the value of the substrate used in practice in the nursery. The samples were saturated (-0.1 kPa) and the water content determined after applying successive matric potentials of -1, -10 and -100 kPa by means of a pressure plate apparatus. The effect of loosening the substrate was investigated, as was also the effect of applying the higher potentials directly to saturated samples. The volumetric water retention varied between 88-93% at -0.1 kPa, 72-85% at -1 kPa, 29-30% at -10 kPa and 18-25% at -100 kPa. Loosening the substrate between applying successively higher potentials to the same samples and, in the case of the higher potentials, determining retention directly from saturated samples gave the lower retention values. It was concluded that the most natural and practical way to determine water retention is to use the same samples, successively applying higher potentials without loosening between applications. Such a procedure includes the effect of increasing compaction and changes in pore size distribution of the substrate upon drying.
Keywords: Compaction, matric potential, shrinkage, water content
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Heiskanen,
The Finnish Forest Research Institute, Suonenjoki Research Station, SF-77600 Suonenjoki, Finland
Sähköposti:
ei.tietoa@nn.oo
Havaintoja rahkasammallajeista ja niiden suhteista kasvillisuuteen ja ympäristötekijöihin Bromarvin Östanberg Stormossenilla.
English title: Observations on Sphagnum species and their relation to vegetation and ecological factors in Östanberg Stormossen, southern Finland.
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The relations between Sphagnum species, vegetation, and the macrotopographical and microtopographical environmental gradients of a plateau bog located on the southern coast of Finland were studied. A profile was levelled from the mire margin to the mire centre and 16 sample plots were located along the profile. The vegetation of each sample plot was described using coverage percentages. The mire water level, pH, and specific conductivity were measured for each plot. Samples of the capitula of different species of Sphagnum were taken and they were measured for water content. Hummock surfaces were predominant in the mire centre. The hollows were relatively dry ombrotrophic small sedge bogs. The mire margin fen was mostly mesotrophic. In the northern part of the mire there was also a eutrophic flark fen. In the mire centre the pH was 4 or less and the specific conductivity ranged from 10 to 25 µS/cm. In the mire margin fen the pH ranged from 4.7 to 5.7 and the specific conductivity was c. 50 µS/cm. The water content of the capitula of the Sphagna was in general high, ranging from 300 to 3000 %. In the hollows of the mire centre the water content of Sphagnum tenellum was as low as 15 %.
Key words: mire vegetation, ecology, plateau bog, water content, Sphagnum.
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Heikkilä,
Department of Geography, University of Helsinki, Hallituskatu 11, SF-00100 Helsinki, Finland
Sähköposti:
ei.tietoa@nn.oo
- Löytönen, Sähköposti: ei.tietoa@nn.oo
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