Marjut Karsisto

Maanparannustoimenpiteiden vaikutuksista orgaanista ainetta hajottavien mikrobien aktiivisuuteen suometsissä. Osa II. Tuhkalannoituksen vaikutus

Karsisto M. Maanparannustoimenpiteiden vaikutuksista orgaanista ainetta hajottavien mikrobien aktiivisuuteen suometsissä. Osa II. Tuhkalannoituksen vaikutus.

Tiivistelmä

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.

Vastaanotettu 31.10.2017 Julkaistu 1.1.1979

Katselukerrat 1156

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