Soil physical, chemical, and microbial community responses to two years of perennial Intermediate Wheatgrass versus annual maize/soybean management systems

Abstract

Intermediate Wheatgrass (IWG, Thinopyrum intermedium (Host) Barkworth & D.R. Dewey; IWG) is a perennial grain crop with a dense root system which has the potential to facilitate improvements in soil physical structure, fertility, and potentially soil carbon storage. An experiment was established in Rosemount, MN, USA to assess changes in soil physical, chemical, and microbial community responses to IWG system vs. annual corn/soy system management after two growing seasons. This experiment aims to 1) assess soil quality under four systems representing a gradient of perenniality, cropping system diversity and soil disturbance intervals and, 2) investigate relationships between soil microbial community characteristics and desired soil chemical and physical quality outcomes to better understand the mechanisms behind desired outcomes. In the first chapter of this study, we report the agronomic outcomes of the first two years of the experiment and examine how IWG vs. annual crop management affect soil chemical and physical properties over the course of two growing seasons. After two years, we find that the proportion of large water stable soil aggregates at 15-30 cm soil depth increased significantly in IWG but not IWG-alf intercropped systems compared to annual systems. We also find evidence of increased water use deep in the soil profile by IWG systems under drought conditions. In the second chapter, we investigate the responses of soil microbial community composition and potential function to two years of IWG vs. annual management. We find that after two years, fungal community composition varied significantly by cropping system and IWG systems are associated with increased arbuscular mycorrhizal fungi biomass and AMF indicator species. We also find evidence of greater extracellular enzyme activity in IWG systems and an annual system with cover cropping.