WP 6 - Deliverable D6.3 Analysis of Chemical-physical and Biological Properties of the Final Growing Media

Innovative peat-free-growth media for a more sustainable greenhouse cultivation have been realized by mixing selected HQ compost with proper natural inorganic components (zeolites) which are alluminosilicatic minerals occurring in specific volcanic rocks called "zeolites". It is known that zeolites exhibit remarkable soil amending properties, because of their high cation exchange capacity (CEC ranging from 1.8 to 4.5 mEq/g) combined with the presence of plant nutrient elements inside the zeolitic crystal structures. These plant macronutrients occur in their cationic form (e.g. K+, NH4+) and are called "extra framework cations" as they are free to migrate through the voids of the zeolitic crystal structure and can be, thus, released in soils via cation exchange. Moreover, zeolites can improve the water use efficiency of soils as these minerals can easily adsorb and retain water within their crystal structure, slowly releasing it under prolonged drought conditions. CEC, the types of elements occurring in the crystal structure as extra framework cations and the water absorption capacity of zeolites are strictly dependent on the type of zeolitic mineral and its crystallochemical-structural properties. Different volcanic rocks containing various types of natural zeolites were investigated, in order to select those that are more suitable to be used as growing media in combination with HQ compost. To this purpose, the main mineralogical, physical and chemical properties of zeolites were determined by means of X Ray Powder Diffraction (XRPD), Scanning Electron Microscopy (SEM), Thermogravimetric Analyses (TGA-DTA-DTG), Cation Exchange Capacity determinations (CEC AMAS) and 19Si 27Al MAS Solid State NMR. Based on the results obtained, the zeolitic rocks showing the more promising characteristics will be selected for the subsequent experimentation. The zeolites selected should exhibit high performing features with respect of the average performances recorded on this type of materials. This means that they should present high zeolite contents (at least 50% w/w), good water adsorption values (Cads > 6% w/w at RH>90%), high CEC (>3 mEq/g) and a dominance of zeolite types featuring plant macronutrients as extra framework cations. New growth media consisting in blends of selected zeolites and HQ compost were, then, developed. The mixtures were fine-tuned by measuring their main chemical-physical parameters (such as cation exchange capacity, water holding capacity, pH and EC of the water extract) and by consequently varying the proportions of the components of the mixtures in order to optimize their features and phyto-nutrients contents. The most promising blends were ultimately selected and additionally characterized by means of 13C 19Si 27Al MAS Solid State NMR in order to obtain their chemical-physical fingerprints that can be used as a reference for the future further production and quality control of these growth media.