Biochar and Hemp as Peat Substituents in Horticultural Substrates and Their Effects on Presence of Microbiota

Abstract: The extraction of peat has been shown to have a detrimental impact on the environment in several ways, including through emissions of greenhouse gases but also through a negative impact on fragile habitats, ecosystems, and ecosystem services. The horticultural sector is a major user of peat products and thus contributes to both emissions and habitat changes. This work explores the possibilities of reducing the use of peat in cultivation substrates as part of reducing the environmental impact of peat extraction. The aim of the study is to instead use biochar, which has previously been reported to have good effects in the agricultural sector, as well as residual products from seed hemp production, to achieve utilization of residual product streams. The physicochemical properties of the substrates were evaluated as well as the effect on growth in a greenhouse experiment of Lactuca sativa. In addition, a screening of microbial communities was conducted to gain an understanding of what properties novel substrates may have on the microbiome. The conclusions from this work are that biochar amendment with 31.25% in a peat substrate had best growth of all treatments. Hemp amendment, however, gave high numbers of colony forming units, poor performance in terms of growth, and development of plants and not satisfactory numbers in terms of water holding capacity and nutrient supply.