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One of the main barriers for the successful utilization of new biomass feedstocks in commercial pellet boilers is the lack of knowledge about the combustion behavior of such fuels, particularly in terms of ash slagging, which can potentially damage the boiler and limit combustion efficiency. The VI Framework European project Domoheat studied the combustion of 15 Mediterranean woody and herbaceous biomass fuels in commercial 60 kW domestic pellet boilers. The performance of several methods for the prediction of measured boiler slagging was tested, including ash composition-based slagging indices, standard ash initial deformation temperature (IDT), and a new slagging laboratory method, the BioSlag test, based on the sieving of the ash and slag obtained in the combustion of 250 g of fuel in a furnace at controlled temperature conditions. IDT values allowed us to identify slagging in fuels with high silica (e.g., rye straw pellet) or alkali contents (e.g., almond shell) but failed to discriminate medium slagging of fuels such as contaminated poplar chip. Slagging indices based on silica and alkali content of the ashes showed success for predicting boiler-observed slagging. The BioSlag test predicted observed slagging percentage in the boiler with R 2 = 0.87. This test could discriminate both high slagging of fuels with high Si content (e.g., rye straw pellet, pinecone seed shell) and the medium slagging tendency caused by alkali elements (e.g., almond shell, olive stone) and by moderate Si contents (e.g., contaminated poplar chip).

Simple, operational tools are required for forest managers to quantify the effects of soil fertility on tree growth and ecosystem sustainability leading to precise, sustainable forest management. The simplified process-based 3-PG model (Landsberg, J.J., and Waring, R.H., For. Ecol. Manage. 95: 209–228, 1997) provides a useful framework for operational prediction of forest growth. However, no simple objective method for relating the effects of available soil nutrients to the model fertility parameter fertility rating (FR) is yet available. The present study aimed to compare several general modeling approaches for the estimation of FR values from soil relative nutrient contents (RNCs) to maximum nonlimiting values, measured in the whole soil profile, at continuous inventory plots of Eucalyptus globulus Labill. in several locations under different parent materials in northwestern Spain. The modeling approaches tested provided good predictions of FR values from RNCs. In particular, using the minimum value of the most significant RNCs showed considerable potential for modeling FR values and plantation growth responses to them. This modeling approach showed promise to be further tested as a generally applicable strategy for estimating the effect of soil nutrients on forest plantations growth.

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