Resumen
Soluble bio-based substances (SBS) may be isolated from the anaerobic digestate of the organic humid fraction of urban waste; from the whole vegetable compost made from gardening residues and from the compost obtained after aerobic digestion of a mixture of urban waste digestate, gardening residues and sewage sludge. These SBS can be used as sustainable and efficient plant biostimulants in alternatives to the commercial products based on fossil sources such as the Leonardite. The present review summarizes the main findings obtained from recent studies accomplished with the SBS applied on several ornamental (Euphorbia; Lantana; Murraya; Hibiscus) and vegetable species (tomato; red pepper; spinach; maize; bean; wheat; tobacco; oilseed rape) with the aim to evaluate their effect on plant growth; fruit and ornamental quality. The main results from these studies show that the non-commercial SBS are more efficient than commercial fossil-based products; at equal applied doses; in enhancing plant growth; leaf chlorophylls; photosynthetic activity; fruit ripening and yield and aesthetic effect; improving flower and fruit quality and optimizing water use efficiency. Depending upon the plant species, increases of the plant performance indicators ranging from zero to 1750% are reported for the plants cultivated in the presence of SBS, relatively to the control plants cultivated in absence of SBS added to the cultivation substrate. The review suggests that biowaste recycling is a sustainable and environmentally friendly source of plant biostimulants, as an alternative to existing fossil sourced agrochemicals.