Innovative Spent Coffee Ground-Based Biofertilizer: Effects on Soil Microbiome and Crop Health

Aim: Crop health is strictly related to soil biodiversity. The transition from chemical fertilizers to biofertilizers may represent a sustainable way to restore soil biodiversity, improve crop health and productivity. Spent coffee ground (SCG) is a waste material with a high potential for the development of innovative biofertilizers. However, previous research showed that the use of SCG as fertilizer inhibits plants growth, mainly due to the presence of phytotoxic compounds. On the contrary, SCG-treated plants showed high nutritional values with an increased content in antioxidants and mineral elements. The aim of this research was to test the effects of an innovative SCG-based biofertilizer (BF) on salad crops (Lactuca sativa), and on their rhizosphere microbial communities. And thus, to evaluate its potential in mitigating SCG’s negative effects. Method: A randomized block design experiment was carried to compare the effects of BF and SCG at 3 different concentrations, each with 5 replicates. Plants functional traits and nutritional values were evaluated. 16S rRNA gene metabarcoding was used to assess the effects on rhizosphere communities. Results: BF-treated plants showed a higher polyphenols level and less stress signs compared to the SCG-treated and control ones. At the highest concentrations, BF modify bacterial communities with an increase of plant growth-promoting rhizobacteria (e.g., Azospirillium, Arachidicoccus) and other beneficial bacterial taxa, such as those involved in disease suppression, aromatic compounds degradation, nutrients cycling. Conclusions: BF resulted capable of reducing SCG negative effects on plant health, promoting the growth of plants beneficial microbial taxa and, therefore, favouring a healthier growth of crops.