Use of microorganisms in peat-free and peat-reduced substrates.

Conventional horticultural practices often rely on the use of peat as a primary component in growing media. However, due to the environmental repercussions associated with peat extraction and its limited availability, a critical need has been prompted to explore sustainable alternatives. This study, a part of the ToPGa research project "Development and evaluation of peat-reduced production systems in horticulture", focuses on addressing challenges related to nitrogen (N) immobilization, substrate compaction and optimizing plant growth in cultivation systems that minimize or eliminate peat usage by using microorganisms. A comprehensive understanding of microorganisms and their influence on substrate quality could transform horticultural practices, presenting a more environmentally conscious approach while concurrently improving plant health and productivity. First, the impact of various substrates on plant growth was examined. Eight distinct substrate mixtures, comprising peat, green compost, wood fiber, nettle fiber, digestate, loess/loam, and perlite were used. Both sterile and unsterile treatments were applied to all substrates. Petunia hybrida cv. 'Mitchell' and Ocimum basilicum were chosen as the plant species. The plants' phenotypic characteristics were observed, and the substrates were analyzed for their chemical properties at the experiment's commencement and conclusion. After six weeks, both plant species exhibited superior growth in a sterile, peat-free substrate composed of 50% green compost and 35% wood fiber, as well as in a substrate mixture of 50% peat, 25% green compost, and 25% digestate, irrespective of sterility. In the subsequent phase, diverse microorganisms will be introduced to different substrate mixtures to augment substrate quality and assess their effects on plant growth development. Various plant growth-promoting rhizobacteria (PGPR), Schizophyllum commune, arbuscular mycorrhizal fungi (AMF) and Dark Septate Endophytes (DSEs) will be employed, leveraging their unique qualities for counteracting N-immobilization and substrate compaction. This aims to establish and enhance microbial consortia designs for future studies.