Characterization of composts made in a lab-scale pilot system

Current challenges of agro-food systems call for the use of Hi-Techs to improve food productivity while reducing external inputs and preserving the soil quality and the environment. The SusMedHouse project (https://susmedhouse.eu/), funded by the European PRIMA programme, aims to develop an eco-sustainable greenhouse that improves efficiency, productivity and minimizes the consumption of water, energy, and non-renewable resources. The innovations concerning conventional, aquaponic, hydroponic and agro-photovoltaic methods will be tested in a 2000 m2 greenhouse realized at Ar&Tecs, Ankara, Turkey. CNR-ISAFOM, SusMedHouse partner, produced different composts from selected agro-food remains. The main goal is to replace the use of peat in substrates with high-quality compost to attain a standardized agronomic quality. Ingredients included readily available organic waste in the Mediterranean area. Up to 16 by-products, previously characterized for their main chemical features, have been selected, mainly focusing on residues from tomato and pepper crops, target of the project. 5 different organic mixtures, with appropriate carbon to nitrogen ratios, have been composted using a self-made equipment (COMPOSTER [1]). It includes two adiabatic and aerated 30L- bioreactors able to simulate an "industrial-like" composting and control the process which shows the typical sequence of mesophilic-thermophilic-mesophilic phases. It releases excellent mature and stable compost in a very short time. After production, all composts have been characterized for chemical-physical, molecular, and microbiological features. Metagenomic analysis was performed in order to discover microbial biomarkers associated with differential chemical composition characterizing composts. Moreover, the compost suppressiveness was evaluated using the model patho-system Fusarium oxysporum f.sp. lycopersici (FOL) - tomato. Optimized lab-scale composting determined a strong reduction in the carbon to nitrogen ratios (C/N) as results of the C-labile fraction loss, with values at the end comparable each other's; this demonstrates deep modifications and rearrangement of the molecular structure of the original matter with a minimum nitrogen loss. Lab-scale composting returned 50-60% of mature end-product (as volatile solids), in line with yields reported in literature [2, 3]. Compost #1 and #2, mostly including ligno-cellulosic ingredients, showed the higher yields due to a lower biodegradation occurred, associated with less CO2 emission (Table). Table. Characterization of the SusMedHouse composts SusMedHouse composts#1#2#3#4#5 C/Ninitial34,031,220,119,618,5 final14,413,111,913,113,8 *Carbon loss%22,024,731,834,336,1 pH6,866,776,357,509,25 Electrical conductivitydS m-11,411,671,844,354,06 Germination index (GI)%90,2100,599,781,224,8 Nitrogen% dm2,82,94,12,73,1 Potassium1,71,61,53,04,2 Phosphorus0,80,90,40,60,6 *after 32 days of thermal composting; dm = dry matter The characterization performed by solid state NMR and off-line thermochemolysis GC-MS highlighted the molecular modification usually found within real scale composting facilities. Both techniques revealed the decomposition of bioavailable polar fraction, such as polysaccharides and peptidic moieties, and the selective preservation of aliphatic and aromatic recalcitrant compounds. The structural index derived from the relative amounts of carbohydrates, lipid and lignin derivatives biomass transformation associated with a potential optimum humification process. All composts showed no phytotoxicity (GI >60%), except Compost #5 including mostly pepper crop residues which also confirmed a severe phytotoxicity in the FOL - tomato suppressiveness test. All the other compost revealed a significant reduction of FOL disease sev