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Doctoral thesis, 2001

Wood ash application effects on elemental turnover in a cutover peatland and uptake in vegetation

Nilsson, Torbjörn

Abstract

Forest harvesting and removal of logging residues implies loss of essential soil nutrients and may in the long-term endanger site productivity. Compensatory fertilization is now recommended in Sweden for such sites. As wood ash contains all the mineral elements that were withdrawn from the forest ecosystem by harvest, the ash is often suitable as a compensatory fertilizer. Peat is also a fuel that is used to some extent in Sweden. After peat harvesting is terminated, the cutover peatland should be reclaimed. The most common re-use of cutover peatlands is forestry. However, as the nutrient pool in the remaining peat is usually low, especially for P and K, nutrients need to be applied to establish and maintain a sustainable biomass production. As wood ash contain the most necessary nutrients, it is a suitable fertilizer for forestry on cutover peatlands. This thesis investigates how wood ash fertilization on a cutover peatland affects i) the distribution of ash elements in the peat, ii) the leaching of these ash elements and iii) the biomass and nutrient allocation in different compartments in 3-7 year-old trees of seven different species; and how the application of different wood ash and lime products on a mineral soil affects iv) the uptake of nutrients and heavy metals in bilberry fruit.
To achieve soil nutrient conditions suitable for forest growth, wood ash (23 000 kg ha'1) was applied to a cutover peatland in west-central Sweden. Seven tree species were planted and for all of these except two Salix species, the increase in soil pH and nutrient pools seemed sufficient to maintain a sustainable biomass production. The crucial growth limiting nutrients, K and P, were applied in large quantities, 670 and 210 kg ha1 respectively. However, these two elements will probably be growth limiting in the next tree generation, as an marked increase in the output of K was observed in the stream water, and as phosphate ions could be adsorbed to the large amount of Fe compounds present in the peat.
In the short-term, the application of different wood ash products on a mineral soil did not significantly affect the content of different nutrients or heavy metals in bilberry fruit, even if high doses were applied.
​​​​​​​It can be concluded that wood ash fertilization on cutover peatlands and compensatory fertilization with wood ash on mineral soils are both suitable soil improvement measures that have relatively small effects on the environment if precautions are taken concerning the quality of the wood ash product.

Keywords

Alnus incana; Alnus glutinosa; base cations; Betula pubescens; heavy metals,leaching; Picea abies; Pinus sylvestris; Salix dasyclados; Salix viminalis; Vaccinium myrtillus

Published in

Acta Universitatis Agriculturae Sueciae. Silvestria
2001, number: 208
ISBN: 91-576-6092-1
Publisher: Department of Forest Soils, Swedish University of Agricultural Sciences

Authors' information

Swedish University of Agricultural Sciences, Department of Forest Soils

UKÄ Subject classification

Soil Science
Forest Science

URI (permanent link to this page)

https://res.slu.se/id/publ/107991