Soil biological activity in semi-arid drylands may be greatly restricted due to lack of moisture, aboveground diversity, continuous cropping, and/or low soil organic matter content.  Soil biological activity improves nutrient cycling and soil physical structure (i.e. aggregation) which may increase aboveground production by increasing water infiltration and water holding-capacity and directly linking plant roots to nutrients made available via enzymatic production primarily by bacteria and fungi. Arbuscular mycorrhizal fungi (AMF) are a key component to this system since they can access microsites in soil and absorb water and nutrients which are funneled into AMF colonized roots. Multiple plants may be linked to each other through hyphal conduits which transfer nutrients and water between plants, including nitrogen fixed by rhizobium in legume roots ending up in nearby non-legume plants. Northern U.S. Great Plains research is studying how multi-species cover crop mixtures both in-season or as season-long green manures may enhance precipitation use efficiency in subsequent crops. This research is also measuring glomalin, a glycoprotein produced by AMF, and its impact on aggregate stability as one mechanism of enhancing the biological, chemical, and physical parameters to alleviate water and nutrient stress in semi-arid cropping systems. Data from Central and Southern Plains looking at other microbial communities and enzymatic production is being used to develop further studies linking above- and below-ground communities in improving nutrient and water use efficiencies.