Soil microbes exist in highly diverse communities in which thousands of bacterial species are estimated to coexist in a single gram of soil. Competitive, antagonistic, and cooperative interactions among coexisting microbial species are crucial to maintaining microbial diversity, and significantly impact the dynamics, metabolic activities, and evolution of microbial populations. These complex networks of interaction also mediate microbial community functions, such as the suppression of plant pathogens via antibiotic production. However, we have limited insight into the structure of microbial interactions within soil communities, or the implications of network structure for the ecology, evolution, and functional characteristics of soil communities. We analyzed networks of antagonistic (antibiotic inhibition), nutrient competition, and signaling interactions among sympatric populations of soil Streptomyces. We characterized variation in the structure of networks among populations from diverse soil locations; identified differences in network structure between coevolved (sympatric) and random (allopatric) collections of Streptomyces; and explored the potential for network analyses to quantify the roles of antibiotic arms race vs. niche differentiating coevolutionary dynamics in soil communities. Our results suggest that interaction network analyses offer substantial potential for providing novel insights into the factors that generate and maintain microbial functional capacities in soil communities.