Soil microbial communities are of very large importance for ecological systems and they are in the focus of searching for microorganisms producing unknown antibiotics. The composition and development of these communities is strongly dependent on the specific soil composition as well as nutrient limitations, mutual stimulation and inhibitors. It is nearly impossible to study the complex effects of the behavior of such microbial systems by conventional cultivation methods using flask incubation or Petri dishes. One key issue is to gain statistical data about the evolution of colonies under defined conditions. Previous investigations have shown that microfluidic techniques can be used for the cultivation of soil bacteria. Here, we present a new device which allows the formation, storage and observation of micro droplets of about 4.5 nl volume which are trapped in an chip array of 2592 cavities. The evolution of appropriate microbial colonies in the individual droplet can be monitored by optical means. Long-term cultivation of large sets of well-separated compartments allows the statistical analysis of the growth behavior under different media conditions.