Metla Project 3264

Maintainance of sustainable nutrient status in peatland stands

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Duration: 1999-2003   Keywords: drainage, fertilization response, foliar nutrients, nutrient deficiencies, peatlands, phosphorus leaching, soil nutrients, tree stand
Research Programme: Ecologically and economically sustainable forestry on drained peatlands


Topics for research

1: The assessment of the nutritive status of the tree stand

The aim is to develop reliable, predictive or preventive measures to determine the nutrient status of Scots pine (Pinus silvestris), pubescent birch (Betula pubescens) and Norway spruce (Pices abies) growing on peatland sites. It should be possible to use some of the measures during the growth period as well. The measures should comply with the requirements of practical forestry, and it should be possible to apply them in the field of forest planning. Another aim is to make the estimates of the extent of nutrient deficiency on peatland sites more precise by nature.

Some nutrient deficiencies are to be seen in the tree stands as clear deficiency symptoms. Well-known deficiencies of this kind are changes in needle colour, abnormalities in growth or decreases in needle age classes. The relationship between the onset of these symptoms and the nutritional status of the stand has not, as yet, been fully studied. The object of study in this project is the relationship of certain deficiency symptoms to the nutritional state employing resolution analysis and logistic models. The data comprises tests and practical forest sites with clear deficiency symptoms (such as changes in foliage colour, number of needle age classes etc.). Needle and leaf samples are taken, their nutrient content and the content of polyamines and putrescine being analysed. Background data is also collected on growth sites, tree stands and their developmental history in order to determine the nutritional limits of the substratum and tree stand. Efforts more precise than to date will be made to ascertain the reasons for annual and monthly changes in the nutritional status.

Experimental forest stands are being established in the near vicinity of the Metla test stations in various parts of the country, where the nutrient content is analysed every year. In addition to temporal changes, the study follows the changes occurring in the nutrient content of the trees and the various parts of the tree, as well as the variations within the different trees and parts of trees as well as between the various annual sets of needles. The data from the reference forest stands is used to adjust interpretations.

A data base is compiled of the results of all the needle analyses to date, this being continually updated. The data base is used, among other things, in compiling sequences of the nutritional state index , as well as in seeking answers for clients.

2: Fertilization and soil amelioration methods in peatland stands

With the help of background data from field work and of new intensive testing, a data base is formed for the development of a fertilization growth model suited to the prevailing terrain. Further, estimates are made of the total increase in timber production resulting from the fertilization of the marshes, as well as of the effect of the fertilization on the growth and external quality of the stand, on the regeneration of the forest and on the biodiversity of the stand.

An abundance of fertilization tests have been carried out in research areas all over Finland during the period 1960-90 with the aim of the strength and duration of the effect on the trees of basic and further fertilization. Attention was focused especially on the effects on the earth and the tree stands of slowly-dissolving fertilizers such as apatite, biotite and wood ash. As a working hypothesis we would suggest that slow solubility prolongs the length of the influence of the fertilization, thus decreasing the washing of nutrients into the environment.

One aim of the on-going project is to publish a fertilization guide as a guide to fertilization in practice. The guide presents methods for determining the nutritive level of the drainage area stand, describes nutrition deficiencies as well as the effect on the stands and gives hints regarding the correct fertiliser combination. The guide will also aim to give advice regarding further fertilization. Methods are defined in the guide for determining the nutritional status of the stand in the area being drained. Nutritional deficiencies and effects on the stand produced by fertilization are described, with advice being given on the choice of a correct combination of fertilizer.

The new experiments will concentrate only on the sub-areas where, to date, the current experimental material has not come up with any answers. Topics of research include changes in the afforestation propensity of the substrate upon the addition of nutrients, the effect of the fertilization on the microbe population, mycorhizae, berries and mushrooms.

3. Prevention of phosphorus leaching from fertilized peatlands

The purpose of the project is to look into the criteria for evaluating the leaching risks of fertilizer phosphorus. The effects of aluminium and iron on the leaching of fertilizer phosphorus and on the growth reactions in the tree stand are studied. The project is embarking on the development of a new type of phosphorus fertilizer with aluminium or iron added to prevent phosphorus leaching.

In addition to fertilizers containing growth-inhibiting nutrients (N, P, K, B), phosphorus-binding aluminium and iron compounds are added in the greenhouse to seedlings growing in Sphagnum peat. The aim of the test is to determine the best possible combination of aluminium or iron compound and the correct amounts to be applied, on the one hand to prevent phosphorus leaching, and on the other, to ensure the good growth of the seedlings. The influence of the new fertiliser from the point of view of the growth of the stand and of the quality of the runoff waters will be monitored in a field experiment based on a calibration period/control site method.

In addition to this research the effects of wood ash fertilisation on the elemental and heavy metal concentrations of berries, mushrooms and food of game animals are studied in a joint project 7092.


The research project was part of the SUO (Ecologically and economically sustainable forestry on drained peatlands) research program, which ran from 1999 to 2003. The program looked into the present state of Finland’s peatland forests, evaluating the need for management measures; stand amount, quality and growth; improvements in the use of peatlands; the possibilities for improving stand growth, and development forecasts for peatlands. The aim of this project was to 1) develop reliable predictive or preventive methods for determining the nutrient statuses of various tree species, 2) develop a fertilisation growth model and assess the growth increase gained with basic and advanced fertilisation on various types of sites (and various tree species) around Finland, and 3) determine the criteria suitable for evaluating the risks of phosphorus leaching.

The project was a joint effort of Metla (Muhos, Parkano, Kannus, Joensuu and Vantaa units), Metsähallitus (Forest and Park Service), Ministry of Agriculture and Forestry, and Kemira GrowHow. The research data was gathered from Metla’s peatland fertilisation and soil amelioration experiments, and peatland drainage sites, of varying age. The data included stand measurements, results from polyamine, nutrient and colour analyses of the fertilisers, needles and peat, site descriptions, as well as some visual observations from the sites.

The results suggest that the nutrient status of a coniferous tree can be determined accurately with needle samples collected in winter, or even early autumn. Also the nutrient status during the growing period could be inferred with polyamine, amino acid and nutrient analyses. Peat analysis proved to be a relatively good indicator of nutrient status in peatland stands on drainage areas, as well as on former peat fields and cut-away peatland areas. The most important indicators are acidity, peat species, its level of decomposition and nitrogen content. The ammonium nitrogen content in surface peat, as well as the total nitrogen content and the C/N ratio were good indicators of stand nitrogen nutrition status. The results give support to the existing idea of using peat total nitrogen content as an indicator when assessing a site’s potential productivity. The need for nitrogen fertilisation can also be estimated with the level of decomposition: the more there is nitrogen in peat, the more decomposed it is. Evaluating the level of decomposition is also possible by visual observation at the site.

The biochemistry of a tree is much quicker in responding to stress than are its nutrient concentrations. By analysing polyamines, amino acids and nutrients it was possible to infer the nutrient status during the growing period.

The growth and nutrient regime of peatland stands was improved with PKB fertilisation. It was observed that the fertilisation had a longer-lasting effect than was previously assumed. The most noticeable increases in growth are to be gained in thick-peated nitrogen-rich mires, where the growth response was observed as late as 30 years from the application. PK fertilisation proved to be quite profitable in nutrient deficient pine bogs (internal rate of return 10–12 % during 18 years), provided that the nitrogen status of trees was adequate.

On nitrogen-poor drained areas the effects were clearly less intense and less profitable. As regards species, the response of pine was more pronounced than that of spruce, and spruce responded more favourably than downy birch. Usually there are no economic grounds for fertilising birch.

The project studied the properties and the effects of low soluble compounds — apatite as a source of phosphorus and biotite as a source of potassium. Biotite turned out to be a longer-lasting K fertiliser than soluble potassium salts. It is also possible to increase growth in peatland stands with mineral soil addition, peat ash, and especially wood ash.

On areas with a thin peat layer (less than 30 cm), the trees were able to make use of the growth medium’s mineral nutrients to such an extent that there were no occasions of serious nutrient imbalances. What is essential to secure a successful practical fertilisation in aged drainage areas, where the vegetation has undergone change, is the proper identification of nitrogen availability (rich or poor) and the mire’s original type (bog or fen).

The results show that the effect of refertilisation, after 10–20 years, on stand growth was clearly lesser than that of the first fertilisation. The stand responded more slowly as well. The effects of refertilisation were largely bound to the stand’s potassium status: on sites with limited potassium availability the added potassium increased stand growth substantially. Productively, however, it is probably enough to refertilise once at the most during the rotation period.

The leaching of phosphorus from fertilisers has been considered to be a problem for the environment. Aluminium and iron compounds, in the fertiliser or in peat, prevent phosphorus leaching. If the growth medium lacks these compounds, phosphorus will eventually leach from the contemporary fertilisers’ phosphorus source, apatite, as well. The sites most liable to phosphorus leaching are oligotrophic bogs. The results suggest that iron, when added to the fertiliser, prevents phosphorus leaching very efficiently, but at the same time, slows down the response to fertilisation. Wood ash proved to be an ‘environmental-friendly’ fertiliser in peatlands: only a small portion of its phosphorus was leached.

Project leader: Moilanen, Mikko
The Finnish Forest Research Institute, Oulu Unit, PL 413, FI-90014 Oulun yliopisto, FINLAND
Phone: +358 29 532 3743

Other researchers: Hartman, Markus, VA (1999-2003), Hytönen, Jyrki, KA (1999-2003), Hökkä, Hannu, RO (2002-03), Kaunisto, Seppo (2000-02), Kojola, Soili, VA (2002), Koskela, Merja-Leena, ES (2001), Nieminen, Mika, VA (2000-04), Nokso-Koivisto, Antti (2000), Pietiläinen, Pekka, MU (1999-2003), Piiroinen, Marja-Leena, MU (2001-03), Rautjärvi, Heli (2002-03), Reinikainen, Antti (2002), Saarinen, Markku, PA (2004), Sarjala, Tytti, PA (1999-2001), Silfverberg, Klaus, VA (1999-2003), Tolonen, Timo (2001-02), Veijalainen, Heikki (1999-2001)

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Updated 12.06.2012