Restoring Arbuscular Mycorrhizal Fungi in Agroecosystems: Oats (Avena sativa) Shows Promise As a Cover Crop.

Fall-planted cover crops provide a plant host during otherwise fallow periods and thus may increase arbuscular mycorrhizal fungi (AMF) numbers and diversity in agroecosystems.   Increased AMF numbers and diversity should increase mycorrhizal colonization of the subsequent cash crops, which has been linked to more efficient utilization of soil nutrients.  Sustainable farming systems that use less chemical inputs per crop produced have been shown to have elevated levels of AMF.  We have conducted replicated field trials at two locations (a research farm and a cooperating producer) in eastern South Dakota that evaluated cover crop treatments for their ability to boost soil AMF propagule numbers.  At both locations, oats and cover crop mixtures containing oats significantly (p<0.05) increased the number of soil AMF propagules.  At the research farm location, we established a rotation that had oats planted as a cash crop preceding corn to a rotation with winter wheat preceding corn.  The corn following oats was more extensively colonized by AMF than corn following wheat.   A replicated greenhouse study was conducted where four candidate cover crop species were compared for their ability to retain a diversity of AMF present in an inoculum.  Using rRNA gene sequence analysis, we found that oats retained the largest amount of AMF diversity compared to the other three cover crops (spring wheat, vetch, crimson clover).  Cover crop mixtures that include oats (or restoration efforts that include oats) can increase AMF numbers and diversity, perhaps to a point where ecosystems services are significant.