Horticultural and Floricultural Applications of Urban Wastes Originated Fertilizers

Different origin composts and a digestate from a biogas plant and their respective alkali soluble (SBO) and insoluble (IOR) fractions have been tested as organic fertilizers in growth media. The materials have been characterized by determination of pH, salinity, C, N, P. and K content. A preliminary evaluation of the possible phytoxicity has been performed by determination of the germination indexes of cress (Lepidium sativum), white mustard (Sinapsis alba) and radish (Raphanus sativus). Most of the materials did not promote the germination of the seeds. Notwithstanding these negative results, the materials were also used as partial peat substitute in a commercial substrate to test the growth of marigold (Tagetes patula), radish (Raphanus sativus), and spinach (Spinacia oleracea). The dimension and dry weight of the plants grown on the substrate mixed with the composts, the digestate or the SBOs were similar to those observed on the substrate. Moreover, most of the SOBs provoked the increase of the dry weight of the roots of the radishes, therefore an increase of the quality. The insoluble fractions (IOR) from the composts allowed a growth of the plants similar to that obtained with a commercial substrate. In contrast, the IOR obtained from the digestate was phytotoxic.