Artikkelit jotka sisältää sanan 'shrinkage'

Ryszard Oleszczuk, Jan Szatylowicz, Tomasz Brandyk, Tomasz Gnatowski. An analysis of the influence of shrinkage on water retention characteristics of fen peat-moorsh soil.
Avainsanat: shrinkage; moisture retention characteristic; fen peat
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The paper presents the results of laboratory-and field-measured soil moisture retention characteristics for different layers in peat-moorsh soil developed from a fen.Field de termination was based on the measurements of the moisture content and pressure head values performed on undisturbed soil columns during a drying process.Laboratory measurements were performed with sand table and pressure chambers.In order to ob tain moisture retention characteristics related to actual volumetric moisture content, the shrinkage characteristics were measured for different soil layers.The comparison of the laboratory and field measured moisture retention characteristics showed that the results of field measurements were very close to those of laboratory measurements, expressed in terms of fictitious volumetric moisture content.This expression of water content based on initial soil volume provides a better estimation of differential water capacity.
  • Oleszczuk, Department of Environmental Development and Land Improvement, Warsaw Agricultural University, ul. Nowoursynowska 166, 02-787 Warsaw, Poland Sähköposti: ei.tietoa@nn.oo (sähköposti)
  • Szatylowicz, Sähköposti: ei.tietoa@nn.oo
  • Brandyk, Sähköposti: ei.tietoa@nn.oo
  • Gnatowski, Sähköposti: ei.tietoa@nn.oo
Juha Heiskanen. Turvepohjaisten kasvualustojen tiivistyminen yksivuotisessa paakkutaimikasvatuksessa.
English title: Compaction of growth media based on Sphagnum peat during one-year culturing of container seedlings.
Avainsanat: shrinkage; nursery management; soil physical properties; substrate; water retention
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Changes in bulk density and water retention during one-year culturing of container seedlings were studied in pure, low-humified Sphagnum peat and in peat-based two-component growth media. In all growth media, the bulk density increased slightly with time. The corresponding decrease in total porosity was negligible (< 1 %-unit for pure peat). At matric potentials < -1 kPa, water retention of growth media tended to increase somewhat with time. On the other hand, shrinkage at desorption decreased during seedling culturing. The results suggest that, from the standpoint of seedling growth, the structure of growth media based on Sphagnum peat does not markedly change or deteriorate during one-year culturing of seedlings. However, in seedling culturing peat growth media containing hydrogel may possess restricted aeration due to excess water retention, while addition of coarse textured materials, such as perlite, to peat can increase aeration. Key words: nursery management, soil physical properties, shrinkage, substrate, water retention
  • Heiskanen, The Finnish Forest Research Institute, Suonenjoki Research Station, FIN-77600 Suonenjoki, Finland Sähköposti: ei.tietoa@nn.oo (sähköposti)
Juha Heiskanen. Näytelieriön täyttötavan vaikutus kasvuturpeen vedenpidätyskykyyn.
English title: The effect of sample handling on the water retention of growth peat substrate.
Avainsanat: water content; Compaction; matric potential; shrinkage
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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
  • Heiskanen, The Finnish Forest Research Institute, Suonenjoki Research Station, SF-77600 Suonenjoki, Finland Sähköposti: ei.tietoa@nn.oo (sähköposti)

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