In a sagebrush steppe community in SE Idaho, long term data and modeling have shown that coexistence among the four dominant plant species is stable, and maintained by strong stabilizing niche differences. In addition, these niche differences occur early in the plant’s life cycle, during germination and establishment. In collaboration with Peter Adler at USU, I set up a large plant-soil feedback experiment in the field to determine whether plant-soil feedbacks (PSFs) are the key stabilizing mechanism that maintains coexistence in this community. The goal is to use these experimental results in a multispecies population model to determine the relative contribution of PSFs and other niche mechanisms towards coexistence among focal species. Seedlings (Artemesia tripartita here) were transplanted into the field to experience conspecific or heterospecific neighbors. Three microbial treatments ensured that experimental seedlings experienced minimal biotic interactions, soil biota effects, or soil biota and root competitive effects. We also repeated the PSF experiment in the greenhouse as 1) an insurance policy, and 2) a way to compare our results directly with values in the published literature mostly derived from greenhouse experiments.