Ashby's Medium (AHM) is a specialized microbiological culture medium designed for the isolation and cultivation of nitrogen-fixing bacteria, such as Azotobacter species, from soil and environmental samples. It features a nitrogen-free formulation with mannitol as the primary carbon source, along with essential minerals like potassium phosphate, magnesium sulfate, sodium chloride, and calcium carbonate to buffer pH and support aerobic growth. This medium is particularly valuable in soil microbiology, agricultural research, and studies on microbial ecology and nitrogen fixation processes. It enables clear observation of colony morphology and is used in laboratory settings to assess microbial populations in natural substrates.