## 1 Introduction
Digestate can stimulate soil bacterial growth as well as increase the development of arbuscular mycorrhizal hyphae [8; 24]. The rhizosphere bacterial community responds to digestate by showing phylum-level shifts, influenced by nutrient dynamics [8]. Biochar, resistant to microbial consumption, may indirectly alter soil microbial communities [25]. Significant increases in soil microbial biomass and growth rates were observed after biochar application, attributed to enhanced soil moisture [26; 27]. Conversely, other findings revealed minimal effects on microbial abundances [28; 29]. Recent research described shifts in soil microbial community structure towards bacterial dominance and higher fungal-to-bacterial ratios in biochar amended soils [25; 30]. Furthermore, when applied to the soil, digestate can raise concerns related to potential hygienic issues, such as the presence of pathogens [16; 31], and environmental hazards, including antibiotics, pollutants, and metals [1; 16; 32]. Farmers currently express apprehensions about the use of digestate in cultivating forage crops, in particular for downstream processes such as cheese manufacturing [33]. Digestate may harbor the presence of _Clostridium_ spp., like _Clostridium_tyrobutyricum_, _Clostridium_butyricum_, and _Clostridium_sporogenes_. These bacteria are known for their ability to produce metabolites, some of which can detrimentally affect the quality of forage crops and cheese during the aging phase. The distribution of digestate in fields raises concerns about the potential spread of these spore forming bacteria from one farm to another, leading to soil and crop contamination [33]. Additionally, there is a need to determine the appropriate doses of digestate that will achieve the desired fertilization effects while ensuring the safety of agroecosystems. In this regard, the evaluation of phytotoxicity also needs to be conducted, serving as a valuable parameter for assessing the actual impact of digestate spreading on crops and functioning as an indicator of its overall ecotoxicological effects [6]. The Germination Index (GI) assay is commonly used as an indirect test to assess the impact of external organic matter (EOM) on seed germination and plant growth, due to its simplicity, short time requirement, and sensitivity [6; 34]. This assay employed water-extracts of the EOM, and its results are strongly dependent on the assumed solid-to-liquid ratio [6]. [PERSON] et al. [35] documented residual phytotoxicity in digestate making it unsuitable for agricultural use, attributed to high organic N and C concentrations. [PERSON] et al. [36] revealed that highly concentrated digestate water extracts inhibited seed germination, while concentrations below <50% showed phyto-stimulation. Hence, application of digestate should follow appropriate rates and timings to prevent direct contact with seeds, as also noted by [PERSON] et al. [20]. Despite these concerns, there is a lack of comprehensive understanding regarding the impact of digestate and/or biochar on soil organic matter formation/decomposition, soil microbial community activity, and crop yield. Limited information is available on the combined applications of digestate and biochar, particularly concerning the microorganisms involved in the N transformations [4]. Our research was designed to better define the potential benefits and risks associated with the land spreading of digestate and biochar in agriculture. It aligns with the principles of sustainability and circular bioconomy by exploring environmentally friendly practices aimed at minimizing waste and enhancing resource efficiency. The novelty lies in its focus on investigating digestate from two pilot AD reactors and biochar, specifically examining the soil microbial functional potential and phytotoxicity with macrophytes, filling a gap existing literature regarding the effects of their applications on soil health.