Suo - Abstracts of Vol. 49, 1998

The bulk density, organic matter content and soil water-retention characteristics of twenty-one afforested former agricultural peat soils were studied. Soil samples were collected from 5-10 cm, 15-20 cm, 25-30 cm and 35-40 cm soil layers. The studied soils' physical properties differed from those of undrained peatlands and peatlands drained for forestry mainly due to the mixing of mineral soil with the peat during cultivation. In the case of thick peat soils (peat layer >30 cm), the bulk density was at a maximum (0.37 g cm^-3) and the organic matter content at a minimum (54%) in the uppermost soil layer. In the case of shallow peat soils (peat layer <30 cm), bulk density increased and organic matter content decreased with increasing soil depth. In thick peat soils, total porosity and water retention at selected matric potentials were at their highest in the lowermost soil layer while in shallow peat soils, the uppermost soil layer possessed the highest total porosity and water retention. Most of the water was retained within the range -100 to -1500 kPa in both soil types. This indicated that small pores were predominant. Air-filled porosity at -10 kPa matric potential (about field capacity) was, on average, 16% in thick peat soils and 17% in shallow peat soils in the uppermost soil layer and decreased with increasing soil depth. The results suggest that the physical properties were generally rather unfavourable for adequate soil aeration and water availability as needed for satisfactory tree growth.

Key words: bulk density, organic matter, peat fields, soil aeration, water retention

The impact of precipitation on the water table level of different complexes on an ombrotrophic raised bog during a year (long-term effect) and a rain shower (short-term effect) was investigated on the basis of the data collected in the Männikjärve raised bog, Central Estonia, over the period of 1956-1991. The regression analysis showed that the effect of precipitation on the mean annual level of the water table depended on the bog complex and time-span considered. In the long-term scale the mean annual water table level depended strongly on the water table level of the previous year. The yearly amount of precipitation affected the water table level of the current year less. These effects were greater in the central pool-ridge complex than in the marginal pine bog forest. On the short-term scale, prerainfall water level affected the water level rise less than the amount of rainfall. The water level rise depended on the prerainfall water level in the central part of the bog (R2 = 0.22), but not in the marginal pine bog forest (R2 = 0.04). The effect of rainfall was of greater importance, explaining as much as 67-75% of the variation in the water level rise.

Key words: precipitation, raised bog, water table level

The effects of pellets made of wood ash and of ash mixed with other wastes (composted mink dung, composted municipal sewage sludge, dung from stomachs of slaughtered animals) on the growth and nutrition of silver birch (Betula pendula Roth.) seedlings was studied in a greenhouse experiment. Seedlings were grown in peat soil originating from a drained dwarf-shrub pine bog, peat soil from an afforested field, and in mineral soil. The pellets were applied in varying doses (0, 6, 12, 24, 48 t ha^-1). When applied at the rate of 24 t ha^-1, also the effect of pelletizing was studied. The pellets promoted the growth of the seedlings depending on the waste used, growing medium, and  the application amount. The pellets containing the highest amounts of nitrogen had the effect of increasing growth most of all. As compared with the unpelletized-waste treatment, the use of pelletized waste material decreased seedling growth.  This was probably due to the reduced solubility of the nutrients contained by the waste material when presented in pelletized form. Pellets increased the foliar nutrient concentrations of many elements depending on the waste used, the growing medium, and  the application amount.

key words: Fertilization, pelletized wastes, wood ash, mink dung, municipal sewage sludge, silver birch

The paper presents the results of a study to assess the profitability of ditch-network maintenance on some oligotrophic pine mires. The alternative ditch-network maintenance methods compared were: ditch cleaning, complementary ditching, and ditch cleaning and complementrary ditching combined. Nine drained pine-dominated mires were chosen for investigation. Only the ditch-network maintenance costs were included in the calculations. Profitability was calculated for two cases: 1) the forest owner pays all the costs and 2) he obtains the maximum state grant. Without the state grant ditch-network maintenance provided a net present value of 870 FIM ha^-1 with a 3 % rate of interest, of 220 FIM ha^-1 with the 5 % rate of interest, and on internal rate of return of 5 %. With the state grant the results were: 1620 FIM ha^-1, 970 FIM ha^-1 and 10%, respectively. The conclusions were that in most cases ditch-network maintenance is profitable even without state grant. By using 3 % and 5 % interest rates, the complementary ditching and combination provided similar profitability, specially when the state grants were provided. Using the IRR criterion, the complementary ditching provided the best profit.

key words: forest drainage, internal rate of return, net present value, Scots pine

Factors affecting the need for ditch network maintenance in northern Finland were studied. In addition, the effect of ditch network maintenance on stand growth was estimated. A dataset containing ditch, tree stand, site type and climate variables was built up on the basis of the permanent sample plots (SINKA) on peatlands. Regression analysis as well as discriminant analysis were used to identify factors and criteria that could be used to identify sites that would respond to ditch network maintenance. Instead of the ditch condition class, ditch age and depth proved to be the variables reflecting the need for ditch network maintenance. The volume of the tree stand was influenced the most by the temperature sum and age of ditching. Stand volume growth was influenced the most by the volume of the tree stand. The site type index or the volume of the tree stand did not give useful information for the planning of ditch network maintenance. When ditch age was 10-40 years, complementary ditching increased annual stand growth of pine mires by 0.6-1.0 and 1.5-1.9 m³ ha^-1 a^-1 on spruce-birch swamps.

key words: forest drainage, ditch cleaning, complementary drainage, tree stand, stand growth, decision making

The nutrient concentrations of the water percolating through fertilised peat cores were investigated in a greenhouse experiment. The nutrient concentrations in the peat cores were also determined before and after the experiment. The fertiliser treatments were 500 kg ha^-1 of PK peatland fertiliser, 5 000 and 25 000 kg ha^-1 of birch ash, and an unfertilised control. The cores were watered on three occasions after application of the fertilisers. The percolation water collected from the fertilised cores contained significantly more nutrients than the control. The total amounts of leached nutrients were equivalent to 0.01 - 20.1 % of the nutrients in the peat cores, K clearly being leached the most. The susceptibility of the nutrients to leaching followed the order K > Mg > Ca > Mn > P. The fertiliser treatments also increased the leaching of nitrate and ammonium. The amount of leached nutrients was relatively the highest from the PK treatment, but in absolute terms the highest from the largest dose of wood ash. According to the peat analyses, the concentrations of most of the nutrients had increased only in the surface layer of the peat (0 - 5 cm). In contrast, the K concentrations had increased throughout the whole profile (0 - 20 cm). The application of large amounts of ash fertiliser should be avoided in order to minimise nutrient leaching losses. Although the fertilisers used in this experiment have been or are being replaced by new types of fertiliser, the results of this study can be used to facilitate the interpretation of the results of field experiments in which these fertilisers have been used..

key words: peat core, percolation water, nutrient loss, phosphorus, potassium

Before large-scale drainage, the outflowing water from forests was naturally filtered through peatlands. The even topography, dense moss cover and the favourable physical, chemical and biological properties of surface peat facilitate versatile buffering functions in these systems. In addition to retaining suspended solids, peatlands may act as traps for nutrients or harmful metals.
Major part of these buffering systems have been lost as a result of forestry drainage. Restoring drained peatlands, being potentially well suited to act as a buffer zone between forestry land and a watercourse, is the major reason for rewetting outside nature reserves. Potentially each drainage area should include a restored part through which waters both from the drainage area itself and from the surrounding upland forest catchment would be filtered.
Preliminary results from three experimental catchments show that buffer zones restored from drained peatlands may be succesfully used in decreasing the detrimental impacts forestry operations may have on adjacent water courses. Long-term monitoring is, however, required for the quantitative assessment of the buffer efficiency.

key words: nutrient load, peatland drainage, restoration, water pollution