Sorghum halepense is an aggressive invasive species in the arid and semi-arid regions throughout the world including India. We quantified the species richness in the Sorghum halepense-invaded communities and communities not yet invaded by the weed. Sorghum soil and no-sorghum soil were analysed for total phenolics, microbial activity, available nitrogen and organic carbon. Manipulative experiments were designed to understand the allelopathic potential of S. halepense. Soil was amended with root or shoot leachate of S. halepense, and its impact on plant growth and soil properties was studied. Sorghum halepense did not impact species richness in natural settings. S. halepense-invaded soil had higher levels of total phenolics and lower levels of available nitrogen. Root leachate had greater inhibitory effects on the root growth of two common species, Brassica juncea or Bidens pilosa, than did shoot leachate of the weed. Shoot leachate-amended soil had higher levels of total phenolics and available nitrogen than root leachate-amended soils. Sorghum halepense allelopathic potential is argued due to lower levels of available nitrogen. Higher inhibition in the root dry weight of assay species in root leachate-amended soil compared to shoot leachate-amended soil can be due to lower levels of nitrogen in root-amended soil. Relative allelopathic potential of root versus shoot leachates in bioassays for allelopathy should be examined to distinguish the role of chemicals versus nutrient availability.