Current issue: 55(4)
Under compilation: 55(5)
The aims of the present study were to determine physical and physio-chemical properties of some Finnish forest tree nursery soils, and to examine relationships between these properties and the amount of organic matter in the soil.
The following soil tillage layer properties of 33 fields belonging to 8 forest tree nurseries were determined: soil particle size distribution, organic matter content, bulk density and density of solids, total pore space, soil water volume at potentials pF 2.0 and 4.2, available water content and air space at potential pF 2.0, active acidity, electrical conductivity index and cation exchange capacities at pH 4.5 and 8.0. The soil texture class of the tillage layer parent material was sand, only in a few cases did higher percentage of silt and clay indicate a morainic nature of parent material. The amount of organic material in the soils varied within wide limits, reflecting differences in amelioration policy between the single nurseries.
Relationships between the physical properties of the soil parent material and those related to fertility were in most cases strongly influenced by the amount of soil organic matter. Soil density values decreased as the organic matter content increased from 2 to 25%, giving rise to the increase in the total pore space. However, the amount of water held at potential pF 2.0 and the available water content did not increase with increasing organic matter content. This was due to the absence of the particle fraction in the sand. Nursery soil amelioration, involving in most cases a mixture of Sphagnum peat with sand, thus gives rise to an increase in the content of drainable water.
Cation exchange capacities were positively correlated with the organic matter content. However, the absolute number of exchange sites expressed as equivalents in the tillage layer did not increase in accordance with the increase in organic matter content due to the influence of the organic matter content upon the ratio of solids in the voids.
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The paper is a part of a larger study of the basic hydrologic properties of peat. This part of the study deals with the hydraulic conductivity and water retention capacity of peat and with their dependence on some of its structural properties. The data of the study was collected in Central Finland (61°50'N; 24°20'E) from drained peatlands. The limits of the quantitative range of variation in the hydraulic conductivity of peat can be put at 2.0 x 10-6 and 1.1 x 1O-2 cm/sec. The variation occurring in the hydraulic conductivity of peat is extremely large. At saturation peat contains 82–95 volume per cent of water. The bulk density of peat seemed to be the factor best able to explain its water retention capacity. The quantity of water which can be removed from a site by draining decreases with increasing bulk density in such a way that it, in the case of well decomposed peat (bulk density 0.20 g/cm3) is slightly less than one third of that for slightly decomposed peat (bulk density 0.05 g/cm3). Also, the possibilities to estimate the quantities of water superfluous, available and unavailable to the plant cover is discussed.
The PDF includes a summary in Finnish.