On 19th of April 2018, Ginevra Fabiani successfully defended her master thesis entitled “Application of biomass ash from FPBO production to grassland: effects on chemical and microbiological properties” within the framework of our Residue2Heat project. The master work performed under the supervision of Prof. Heribert Insam, Dr. Marina Fernández-Delgado Juárez (University of Innsbruck) and Prof. Giacomo Pietramellara (University of Florence), presents the outcome data from a traineeship performed at the University of Innsbruck. She received the grade of 110/110 cum laude at the Institute of Science and Technology of Forestry Systems, curriculum Forestry Management at the University of Florence. Dr. Marina Fernández-Delgado Juárez joined the defensio via Skype.
In last decades various technologies for enhancing the use of biomass as energy source have come into the limelight. One of them is the Fast Pyrolysis Bio-Oil (FPBO) which allows the production of a liquid biofuel from woody biomass. A by-product is biomass fly ash (FA). Due to its properties, FA could be used as soil ameliorant, and thus enhance soil fertility and productivity. A greenhouse trial was conducted to investigate the impact of fly ashes on soil physico-chemical and microbiological properties. Fly ashes were added to an acidic grassland soil at a rate of 2% with Trifolium pratense (L.) (red clover) used as test plant. After an incubation period of 138 days soil and plants were collected. Biomass fly ashes affected soil physical properties: water holding capacity, pH and electrical conductivity increased. The improved soil nutritional status stimulated soil organic matter turnover. The soil P pool increased (specifically total, inorganic, and plant available P, as well as microbial P), while the ALP gene (phoD) abundance was decreased. However, no differences in plant yields were observed in ash-treated soils compared to the control. Microbial activity, assessed by basal respiration and microbial biomass carbon, was enhanced by ash application; nevertheless, a higher metabolic quotient in ash-amended soils might indicate a less efficient use of C–sources by the soil microbial community. No changes in N mineralization were observed, but different abundances of ammonia oxidising archaea (AOA) and bacteria (AOB) were found in untreated and treated soils. The low nitrogen content of fly ashes can be a constraint for its agricultural application. Eventually, the combined use of those ashes and N sources derived from other waste streams, such as manures or digestates, can constitute an efficient and safe way for the disposal and recycling of both products.