Soil biological response to multi-species cover crops in the Northern Great Plains

Farmers in semi-arid regions are experimenting with cover crop mixtures as partial summer fallow replacement, the goal of increasing soil biological activity. We compared extracellular enzyme activity, microbial biomass, potentially mineralizable nitrogen (PMN) and mycorrhizal colonization levels after growing crops comprised one or four functional groups. asked whether can alter those processes components relative to during cash season, a mixture (CCM) will have greater impact than single-species legume green manure (LGM) two rotations wheat. Cover were planted at sites Montana April 2012 May 2014, additional 2013, 2015, terminated each site approximately 60 days seeding. Wheat was for following season. treatments included control, sole pea LGM, FULL mix consisting eight species, species Four single groups second rotation crops. The geometric mean activity increased (1.1–1.3 fold) first rotation, by 1.1–1.4 fold three sites. At fourth site, LGM 1.4 1.5 fold. response individual enzymes less consistent. Microbial biomass PMN and/or site-years, 1.2–1.7 1.6–2.1 PMN. Mycorrhizal wheat least treatment six decreased site. There no differences traits measured among single-functional-group treatments. Soil parameters correlated 7 16 comparisons rotation. After rotations, 5 8 correlations remaining Precipitation declined 30–50 % from Positive effects on systems may be measurable only when environmental conditions do not limit growth.