Current issue: 55(3)
Under compilation: 55(4)
The water retention characteristics and their variation in tree nurseries and related physical properties were determined for commercially produced growth media made of light slightly humified Sphagnum peat. A total of 100 samples of peat media were collected from filled seedling trays in the greenhouses of four Finnish nurseries in 1990. In addition, the physical properties were determined for two growth media made of compressed peat sheets and chips. The variation in water retention characteristics in nurseries was described using linear models with fixed and random effects. The sources of variation in the mixed linear models were producer, grade, batch (greenhouse) and sample (tray).
The water retention of the peat media at different matric potentials was comparable to that given in the literature. The media shrank an average of 0–16% during desorption. The peat grades were finer than the Nordic quality standards for peat growth media. Particles < 1 mm increased and particles 1–5 mm decreased the water retention characteristics measured. The greatest total variation in water retention was at -1 kPa. The water retention of the peat media differed least at -5 and -10 kPa. The water retention characteristics of media from different producers usually differed significantly. The grades, on the other hand, did not differ from each other in their water retention characteristics nor were there significant interactions between producer and grade. The batch effect was marked but was lower than the effect within batches, where the sample (tray) effect was greater than the effect due to random measurement error. At -10 kPa, the measurement error was, however, clearly greater than the sample effect. The random measurement error was comparable to the batch effect. Aeration of the growth media is dependent on the water content retained between saturation and -1 kPa. The water availability to seedlings at the nursery phase is affected mainly by water retention between -1 and -10 kPa.
The PDF includes an abstract in Finnish.
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.