Beatriz Omil, Federico Sanchez-Rodriguez, and Agustin Merino

Abstract The aim of this study was to evaluate the effectiveness of multiple applications of biomass ash to acid soils. The study was carried out in two stands of Pinus radiata D. Don, aged 13 and 15 years, in the province of Lugo (northwest Spain). The soils in the stands were developed on lutites and migmatites. Experi­mental plots (each 1,225 m2) were established, and the experimental treatments were as follows: control (untreated), ash (addition of 4.5 Mg dry matter ha-1 year-1 in 2003, 2004, and 2005) and ash plus P (addition of ash plus phosphate fertilizer in 2003).

The ash was generated in a moving grate furnace, and had the following characteristics: pH 8.9 -13.5, high concentrations of K, Ca, Mg, and P, and low N content and low concentration of heavy metals.

The responses of the forest stands, evaluated as the effects on forest nutrition and tree growth, were measured in 2005, 3 years after the initial treatment. The results showed that continuous fertilization with ash improved the nutritional status and growth of Pinus radiata D. Don stands, and resulted in increased contents of the main macronutrients in needles and soil.

6.1 Introduction

The Galician timber industry makes an important contribution to the regional economy. Forest land covers more than 60% of the total area, and the annual timber harvest is approximately 7,000,000 m3. The wood is used in sawmills and to prod­uce paper, particle board, and fiberboard. Lignocellulosic by-products generated in the latter industries are used in biomass incineration plants to meet increasing energy

B. Omil (H), F. Sanchez-Rodriguez, and A. Merino

Forestry Faculty, Escuela Politecnica Superior, University of Santiago de Compostela, 27002 Lugo, Spain

e-mail: beatriz. omil@usc. es

H. Insam and B. A. Knapp (eds.), Recycling of Biomass Ashes,

DOI 10.1007/978-3-642-19354-5_6, © Springer-Verlag Berlin Heidelberg 2011 needs and to reduce waste production. The by-products mainly consist of bark (from pine, eucalyptus, and a small amount of birch, depending on the type of manufacturing) and to a lesser extent sand, dust, and panel fragments. The volume of these by-products created annually is approximately 900,000 m3 and that of other by-products is approximately 40,000 m3.

This source of energy is considered neutral from an environmental point of view, as it releases the same amount of CO2 to the atmosphere as trees have removed. Combustion does not affect global warming or the greenhouse effect and has several advantages, such as a reduction in the use of fossil waste and the reuse of waste that has no value other than being a source of energy.

Biomass ash is produced as a result of this process (on average, combustion of wood produces 6-10% ash; Gaskin and Risse 2002). Ash is considered a non­hazardous waste (ERL codes 100101 and 100103, bottom ash and fly ash, respectively) and is therefore stocked at dumping sites. However, to reduce these stocks, alternative uses of the waste are being investigated, e. g., for production of enamel and glass (Xirokostas et al. 2001), as a building material for tracks or rural paths, for amation of coal mine (Gil-Bueno and Monterroso 1998; Seoane and Leiros 2001), as an absorbent for the removal of dichlorodi — phenyldichloroethane (DDD) and dichlorodiphenyldichloroethylene (DDE) ori­ginating from pesticides (Gupta and Ali 2001), and as an additive in cement production (Van Der Sloot and Cnubben 2000). The latter use is not recom­mended because of the high level of C in the ashes. In this case, wood ash is usually used as a pozzolan (a siliceous and aluminous material). Despite not having binding properties, pozzolan reacts with finely divided calcium hydroxide in the presence of water to form compounds with cementing properties at room temperature (ASTM 1994).

Nevertheless, wood ash contains nutrients such as P, K, Ca, and Mg, which are present in relatively soluble forms (the NPK content is typically 0-1-5). Apart from these macronutrients, the waste contains oxides, hydroxides, and carbonates. The waste is therefore highly alkaline and contains low amounts of heavy metals (Erich and Ohno 1992; Korpilahti et al. 1998; Demeyer et al. 2001; Miller et al. 2002; Solla-GullcSn et al. 2006). For all these reasons, application of wood ash to forest soils may be of interest as regards the environmental management of such waste, improvement of the nutritional status of forest plantations, and completing the CO2 cycle (Torre-Minguela and Giraldo 2006). Fertilizer is added in an attempt to replenish the nutrients exported as a consequence of the extraction of biomass after final harvesting.

However, despite the high productivity of Galician forests, most Pinus radiata D. Don plantations are deficient in nutrients such as P, Mg, and Ca (Sanchez — Rodnguez et al. 2001; Zas 2003), which can be attributed to the strongly acidic soils and to the extraction of nutrients as a result of the management of the plantation in medium rotations (less than 40 years). Fertilization with wood ash would also contribute to the sustainability of the stands, intensive exploitation of which results in large losses of nutrients.