Assessing the Suitability of Biomass Ashes from Combustion in Boilers as Soil Fertilizers: Statistical Entropy Analysis and Introduction of the Potassium Utilization Potential Factor

Utilizing agricultural residues for energy and heating purposes is gaining momentum in the EU and even more in areas where biomass is a fundamental pillar of the economy like, e.g. South Tyrol in Northern Italy. In previous studies, the authors studied the combustion, in a commercial boiler of four different types of agricultural residues that were previously pelletized. This study has the scope to assess the suitability of the deriving biomass ashes as soil fertilizers. In this analysis potassium is identified as a key indicator for the nutrient content of biomass residue ashes. Therefore, this study introduces a new factor for assessing the utilization potential of biomass residues ashes, which is defined as the “potassium utilization potential factor” or KUP factor (with K representing potassium). The analysis is based on combining the initial concentration of potassium in the feedstock and the efficiency of statistical entropy. Statistical entropy analysis showed that combustion had a diverse substance concentrating efficiency of potassium for the four different types of biomass, ranging from 25 to 40%. In total, apple logs and apple pruning had the best performance in respect to their suitability as soil fertilizer since these feedstocks had the highest KUP factors.