Molecular characteristics of water-extractable organic matter from different composted biomasses and their effects on seed germination and early growth of maize

Four water extractable organic matter (WEOM) were obtained from composts made out of residues of: 1. artichoke (C-CYN), 2. artichoke/fennel (C-CYNF), 3. tomato/woodchips (C-TOM), 4. Municipal solid waste (C-MSW), and their bioactivity was tested for maize seed germination and maize seedling growth. The molecular properties of both original composts and their WEOM were characterized by spectroscopic (13C-CPMAS- and 1H NMR, FTIR-ATR), thermochemolysis-GC/MS, and thermal methods (TGA, DSC). While all WEOM had significant effects on plant growth, CYN-WEOM was the only material that concomitantly increased germination rate and primary and lateral root length of maize seedlings. The lignin-rich WEOM from green composts were generally more effective than those obtained from equally hydrophobic, but mainly alkyl-rich municipal organic wastes. A flexible conformational structure, due to the balanced content of aromatic compounds and carbohydrates, appeared to facilitate the release of bioactive molecules from WEOM suprastructures and stimulate plant growth. [Display omitted] •WEOMs from composted green residues may be useful as biostimulants for plant growth.•Little information on the relationship between WEOM chemical composition and its bioactivity•WEOMs tested have different significant effects on maize growth.•The effects on plant are related to the intrinsic molecular composition of materials.