Response of Soil Microbial Biomass and Enzyme Activities to an Experimental Cow-Calf Management System Incorporating Rotation onto Novel Endophyte Infected Tall Fescue.

Tall fescue (Festuca arundinacea) is grown on over 14 million ha in the U.S. and is naturally infected with the fungal endophyte Neotyphodium coenophialum (E+). While the endophyte benefits tall fescue, toxic ergot alkaloids cause fescue toxicosis in grazing animals. A non-alkaloid-producing novel endophyte (NE) has been incorporated into tall fescue and maintains benefits, such as stress tolerance, for the grass. The objective of this study was to determine how microbial biomass and enzyme activities respond in soil growing toxic or novel endophyte infected tall fescue managed with an experimental grazing system. The experimental grazing system combines a fall or spring calving season with continuous grazing or rotation onto NE fescue in the spring and fall when toxin production is expected to be highest. Soil samples were collected twice in the spring and twice in the fall 2007. Preliminary analysis shows that NE as compared to E+ infection increased soil moisture, dissolved organic C, microbial biomass C, N, and C:N ratios, and dehydrogenase activities. β-glucosaminidase and β-glucosidase activities were not affected by endophyte status, although β-glucosidase activities were not measured in the spring. The experimental grazing system impacted soil moisture, dissolved N, microbial biomass N, and dehydrogenase, β-glucosaminidase, and β-glucosidase activities, often with increased values with fall calving as compared to spring calving. The experimental grazing system did not affect dissolved organic C.  While the study is ongoing, both the presence of novel versus toxic endophyte and grazing system appear to impact soil quality, specifically properties involved in C and N cycling.