A method and a device for assessing the level of microbial activity of a substrate (9), preferably agricultural soil, biomass and other contexts, where there is enzymatic activity. The method includes: preparing one or more biodegradable threads (8); tensioning the one or more biodegradable threads with a pre-defined tension; introducing the one or more tensioned biodegradable threads partially in the substrate; leaving the one or more biodegradable threads in the substrate; measuring the time elapsed from the introduction of the one or more biodegradable threads in the substrate to the breakage of the one or more threads. The device includes one or more biodegradable threads (8) with a first fixing element (12) suited to fix one end of the biodegradable thread and a second fixing element (20) suited to fix the other end of the biodegradable thread, between which each biodegradable thread can be independently tightened with a pre-defined tension.
