Artikkelit kirjoittajalta Marjut Karsisto

Activity during the first phase of this SUOSILMU subproject was mainly focused on the development of methods for the fractionation of peat into its organic components and for the determination of microbial bio-mass. It is now possible to characterise peat using some fifty organic compounds. Using these methods, the effects of drainage intensity and fertilization on the organic character of the peat have been investigated. From the preliminary results, it appears that these methods can be used to determine more exactly the effects of such amelioration practices on the decomposition of peat. During the next phase of the project (1993— 1995), the production and decomposition rates of different organic compounds will be determined in long-term incubation experiments. Keywords: Decomposition, microbiological analysis, organic compounds, peatland

• Karsisto, The Finnish Forest Research Institute, Department of Forest Ecology, P.O. Box 18, FIN-0I30I Vantaa, Finland Sähköposti: ei.tietoa@nn.oo

The results obtained from old ash fertilization experiments established in Finland in the 1930's have shown that wood ash is ideally suited for forest fertilization. The aim of this study is to determine the changes which have taken place in the microbial population and decomposition of organic-matter in the peat of old ash fertilization plots. The area of Tohmajärvi, where the ash fertilization experiment was established in 1939, completely lacked tree cover at the time of fertilization. The total production of the tree stand which has developed since fertilization is about 300 m3/ha. The oldest ash fertilization experiment in the Nordic countries is located in Sweden. The total production of the tree stand growing in the Norra Hällmyren area (fertilized 1926) was about 200 m3/ha until the year 1973 (Holmen 1979). The annual growth of the tree stand on the corresponding unfertilized areas is below 1 m3/ha. The results of chemical analyses carried out on the peat from Tohmajärvi are shown in Table 1. The ash fertilization has decreased the acidity by such a small amount only that this alone could not account for the good growth rate of the trees. The total amount of nitrogen has decreased in the surface layer of the peat in the plots which have got ash fertilization. This indicates that ash fertilization has brought about the conversion of nitrogenous compounds in the peat into a form that can be utilized by the plants. Organic matter decomposition at Tohmajärvi has been studied by observing the decomposition of cellulose strips placed at different depths in the peat (Fig. 2). Decomposition was more effective at a depth of 40—50 cm on the fertilized plots than at a depth of 5—10 cm on the unfertilized plot. Bacterial determinations were carried out on peat samples taken from Tohmajärvi on the 9th August 1977. The results are shown in Fig. 4. The numbers of different types of bacteria at all depths studied were many times greater on the plot given ash fertilization than at corresponding depths in the unfertilized plot. Ash fertilization has had the clearest effect on the number of bacteria in the 10—20 cm deep peat layer. Bacterial determinations were carried out on samples taken from the Hällmyren ash fertilization plots on the 23rd August 1979. The results are presented in Fig. 5. Ash fertilization has had an increasing effect on the number of bacteria only in the 0—10 cm surface layer. The numbers of different types of bacteria decrease very steeply on passing deeper down into the peat. Ash fertilization has increased the pH in the Hällmyren peat by one pH unit, but only in the 0—10 cm surface layer. Both tree growth in Tohmajärvi and Hällmyren areas and the microbiological analyses which were carried out show that ash fertilization brings about a permanent ameliorative effect. In the study areas where ash fertilization is already over 30 and 40 years-old, tree growth is still good and the numbers of different types of bacteria higher than in the unfertilized plots. However, the tree growth in the Hällmyren area is not as good as that at Tohmajärvi. This may be due to the fact that the natural nutrient status at Hällmyren is not as good as at Tohmajärvi and drainage is clearly less effective. It should be born in mind that if ash is to be used for forest fertilization, then efficient drainage is also neccessary.

• Karsisto, Sähköposti: ei.tietoa@nn.oo

The aime of the study is to determine whether the decomposition of organic matter and the activity of different groups of micro-organisms has changed in peat-lands where the ground-water table has been maintained at different depths for a considerable length of time. The study has been carried out in sample plots situated on Scots pine and Norway spruce swamps where the groundwater table has been maintained at depths of 10, 30 and 70 cm since 1960. The annual growth of the trees has been followed since the time when the experiment was established. It has thus been possible to examine the connection between tree growth and the numbers of different types of bacteria and the rate of decomposition of the organic matter. Experiments with NPK fertilizer were established in 1961—1962 on plots where corresponding ground-water table regulation had been carried out. The plots in North Finland were refertilized in 1965, and those further to the south in 1967—1969. Intensification of drainage on the sample plots established on spruce swamps has produced a considerable increase in stand growth (Fig. 1). Decomposition of cellulose in the peat has also increased (Fig. 2). Cellulose decomposition on the plots which have been efficiently drained is effective down to a depth of at least 50 cm. Fertilization increased stand growth most on those plots on the spruce swamp where the ground-water table had been maintained at a depth of 10 cm from the surface. Cellulose decomposition also became more effective on these plots. The nutrient reserves in peat which has been efficiently drained, have possibly been sufficient without any fertilizer addition. Fertilization has had a strong effect on stand growth on the pine swamps, the best results being obtained with a drainage depth of 30 cm. Fertilization has also had the strongest effect on cellulose decomposition in the plots on pine swamps where the ground-water table has been maintained at a depth of 30 cm. The numbers of aerobic, ammonification and proteolytic bacteria in the surface layer of the unfertilized peat have been the greater, the deeper the ground-water table (Fig. 5). Intensifying drainage has had the strongest effect on the number of ammonification bacteria. Fertilization, similarly, had the strongest effect on the number of ammonification bacteria. In other words, the activity of both the trees and the bacteria has been limited by a lack of nutrients, which fertilization has alleviated. Although drainage makes the conditions in the peat more aerobic, the number of anaerobic, bacteria has not decreased as the efficiency of drainage increased. Generally speaking, the higher the level of bacterial activity, the better the tree growth. Following changes in the number of different types of bacteria provides information about the decomposition of organic matter in the peat. However, this is not sufficient and chemical analyses are also required.

• Karsisto, Sähköposti: ei.tietoa@nn.oo