Nutritional status and growth of a young Pseudotsuga menziesii plantation in a temperate region after application of wood-bark ash

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Abstract

Application of wood-bark ash to forest soils can prevent the soil nutrient depletion that may result from intensive harvesting in forest plantations. Douglas fir plantations are of increasing importance in the temperate Atlantic region of Europe, where differences in the nutrient supply imply considerable variation in tree vigour and growth. The aim of the present study was to evaluate the effects of the application of wood-bark ash to a 5-year-old Pseudotsuga menziesii plantation growing on an acid soil with deficient levels of K, Mg and Ca, in a temperate region of southern Europe (Northern Spain). The responses in terms of soil properties, nutrient foliar concentrations and tree growth were assessed over a period of 4 years following the application of wood-bark ash at rates of 10 and 20 Mg ha−1 in a randomized experimental design.

Wood-bark ash application resulted in increases in soil pH, as well as in soil available Ca, Mg and K, and subsequently in significant increases in foliar K, Ca, N and P concentrations. The improved status of Ca and K were confirmed by the use of vector analysis. The concentrations of heavy metals were always low and remained unchanged after application of the wood-bark ash. The improved supply of nutrients led to increases in basal soil respiration, although they did not involve changes in the N mineralization rates. The better nutritional condition resulted in higher tree yield, in terms of height, diameter and biomass. The percentage increases in rate of height growth were 5.4 and 18% for the 10 and 20 Mg ha−1 treatments, respectively. There were increases in all biomass components, especially foliage and twigs, as a result of the amendment. The results suggest that wood-bark ash from the forest industry may be recycled and used to improve the nutritional status of trees growing in acid forest sites. Nevertheless, the material should be applied at rates adapted to the liming needs of the soil and also taking into account the chemical composition of the ash.

Introduction

Biomass-burning power plants attached to sawmills, chipboard and paper mills generate large amounts of wood-bark ash derived from the combustion of wood and woodwaste that cannot be used as a raw material in the industrial process. In NW Spain the annual production of such ash amounts to 40,000–50,000 Mg, most of which is disposed in landfills, although in recent years a certain amount has been used to restore mining areas (Asociación Galega Monte-Industria, personal communication). The production of biomass ash may increase in the near future as a result of the promotion of the use of wood fuel as a way of reducing CO2 inputs to the atmosphere and of diversifying energy supplies.

Wood-bark ash is strongly alkaline, contains large amounts of nutrients and low levels of heavy metals, which are suitable properties in terms of improving fertility of acid soils and the nutritional status of plants (Vance, 1996). For this reason its application has been considered as an alternative to fertilization and amendment (Campbell, 1990). Thus, notable increases in tree growth as well reductions in symptoms of nutrient disorders and dieback in different species have been reported after wood ash application (i.e. Ferm et al., 1992, Moilanen et al., 2002, Hytönen, 2003). However, most such studies have been carried out in mature forests located in cold climates, mainly in old-growth stands. The addition of ash as a way of replenishing the large amount of nutrients exported from fast growing temperate plantations has been investigated in few studies (Park et al., 2004, Solla-Gullón et al., 2004).

The increase in soil pH and the changes in the chemical properties of the soil brought about by the application of wood-bark ash usually lead to changes in the soil microbial community structure and activity, often implying enhanced decomposition rates (i.e. Zimmermann and Frey, 2002, Perkiömäki et al., 2004). However, since most of this type of research has been carried out on organic soils from boreal and central European forests, changes in microbial processes in mineral soils from warmer climates must be investigated to identify undesirable effects on nutrient cycling. Thus, decreases in the amount of soil microorganisms and microbial processes have been described as resulting from initially high concentrations of dissolved salts in the soil solution after application of wastes (Guerrero et al., 2000).

In the humid and temperate areas of southern Europe, forest plantations are established in acid soils with low reserves of available nutrients and, as a consequence, nutritional deficiencies are common in most species. Under these conditions, intensive exploitation results in high rates of nutrient export and the nutrients must be replaced through the application of fertilizers (Merino et al., 2005). Douglas fir (Pseudotsuga menziesii) is a common species in productive plantations in NW Spain (40,000 ha), covering an ever larger surface area during the last decade (Álvarez, 2004). The growth of this species, however, is strongly limited by P, Mg and Ca (Zás, 2003). Nutrient export due to intensive harvesting of these plantations may be high enough to lead to soil impoverishment if not compensated by fertilization (Ranger et al., 1995).

There is little data available on the effectiveness of wood-bark ash as a fertilizer and amendment in forest plantations in humid temperate areas. The present study was therefore undertaken to investigate the changes in soil chemistry, forest nutritional status and growth response in a 5-year-old P. menziesii plantation of poor nutritional status located in a temperate region in southern Europe. The results will help in elaborating a suitable strategy for applying wood-bark ash in the conditions of such systems.

Section snippets

Site description

The study sites were established in a 5-year-old P. menziesii plantation situated at an altitude of 395 m in Frades, A Coruña (43°03′52.1″N, 8°17′52.9″W). The climate of the area can be classified as temperate subtropic with humid winter. The average annual precipitation is approximately 2000 mm and the average minimum and maximum temperatures, 3.7 and 23.9 °C, occurring in January and June, respectively. The soil is developed on acidic schists and, according to the FAO–UNESCO system is classified

Soil chemical and biological properties

Forest soils studied were acid, with initials pH values of approximately 4.0 (Fig. 1a). Addition of wood-bark ash resulted in slight increases in soil pH. Although the initial effect diminished gradually, differences were significant up to 22 months after ash application, and could still be distinguished 4 years after addition of wood-bark ash.

The initial concentrations of soil available P were also low (<15 mg kg−1). In spite of the amount of total P applied in the ash (52–104 kg ha−1), ash

Nutritional status of the stand

The results of the present study showed the ash to have a moderate liming and fertilizing capacity, with the effect being dependent on the application rate. The responses can be attributed to the alkaline character of the material and the high contents of hydroxides and carbonates of Ca, Mg and K (Campbell, 1990). The increase in pH, however, was lower than that observed in a sandy soil from the same region where wood-bark ash was incorporated into the upper 20 cm of the soil (Solla-Gullón et

Conclusions

The results of this 4-year-long study showed that the nutrients supplied with wood-bark ash improved the nutritional status and subsequent growth of a young P. menziesii stand, initially deficient in K, Ca and Mg. The application of wood-bark ash appears to be a safe method of improving nutritional status and growth of trees in these stands. Because of the relatively high amounts of less soluble P, Ca and Mg, the use of wood-bark ash may also be suitable for maintaining soil reserves of these

Acknowledgements

Funding for this research was provided by the Ministry of Science and Technology and by the Asociación Galega Monte-Industria. We appreciate the help of Mr. José Buela and Mr. Carlos Casas, from ENCE S.A. and Mr. Javier Viñas (Asociación Galega Monte-Industria). ICP-OES analyses were carried out by Ms. Montserrat Gómez and Dr. Verónica Piñeiro from RIAIDT-Lugo (University of Santiago de Compostela). We are also grateful to Mr. Jose Santos Baamonde, Mr. Cesar Pérez-Cruzado and Mr. Miguel

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