Novel substrates based on high-quality compost mixed to zeolites

Mediterranean intensive horticulture systems, especially greenhouse cultivation, provide high quality products all-year round with a large use of resources and hand-labor. However, productive capacity and sustainability can be sensibly improved by using agro-ecological innovation on energy, soil and water management. Challenges resulting from climate change, scarcity of resources, demographic growth, contamination, desertification, degradation of arable lands make these improvements necessary. Moreover, in the Mediterranean basin, technological updates of the sector are even strongly needed in order to face increasing competition arising from globalization of production and marketing. By exploiting self-learning artificial intelligence (AI) combined with innovative applications, the SusMedHouse project (https://susmedhouse.eu/) aims to develop an eco-sustainable greenhouse model able to improve and valorize local resources with efficient use of energy, water, nutrients and organic matter. In this context CNR-ISAFOM, SusMedHouse partner, developed peat-free growth media containing high quality composts added to selected zeolites. Starting from a wide range of organic substrates, primary composting was carried out using a laboratory pilot system (COMPOSTER, Figure-a). The evaluation of the chemical composition, molecular characteristics and suppressive properties led to the final selection of mature composts made from the residues of tomato (T) and pepper (P) crops. Mixing the selected composts (T and P) with suitable zeolites (chabazite and clinoptilolite) and using two different volumetric mixing ratios (1:1 and 3:1, compost:zeolites), 8 innovative peat-free substrates (Zeo-Compost) were designed, analyzed by solid state NMR and verified in a preliminary growth promotion assay, evaluating tomato plantlets grow up in a short-term potting trial carried out in greenhouse on an ebb-and-flow system (Figure-b). The NMR spectra of compost T and P mixed with the selected zeolites showed a different C distribution in respect to basic compost samples. The main variation relates to the relative increase of alkyl-C components in the 0-45 ppm region and the corresponding decrease of band intensity of O-Alkyl-C groups associated with polysaccharides and carbohydrates. A possible reason of observed modification is the activation of biochemical transformation promoted by the presence of active surface of inorganic colloids. The adsorption capacity of clay-type minerals towards the organic components is a well-known process that promotes the formation of clay-organic complexes in natural environments. The selective interaction with hydrophilic compounds may have thus allowed a preferential exposure of O-Alkyl molecules to the slackened but persistent enzymatic activity of microbial community of mature composts [1]. The addition of zeolites significantly reduces compost P- phytotoxicity. Moreover, also other criticalities showed by both T and P compost (i.e high EC and pH) were partially contained by mixing them with zeolites, even at lower dosage, thus revealing good potential for using Zeo-Compost as growth medium for potted crops. Treatments including compost without fertilization in the substrates showed agronomic performances comparable to those of the fertilized control (peat-based substrate), thus revealing reasonable fertilizing properties. Clinoptilolite better enhanced the agronomic properties of both composts at lower dosage. The resulting best performing Zeo-Compost will be further tested on-farm in larger agronomic trials at SusMedHouse, the innovative greenhouse built for test and demonstration at Ar&Tecs, Ankara, Turkey. Figure. (a) Pilot system for composting; (b) Short-term trial with potted Solanum lycopersicum plantlets grown on 8 innovative substrates including zeolites added to compost (Zeo-Compost) Funds SusMedHouse has received funding from the European Commission PRIMA programme under grant agreement No 1917. http://prima-med.org/