Soil Chemical and Biological Properties in Novel and Toxic Endophyte Infected Tall Fescue Cattle Production Systems.

Replacing toxic endophyte Neotyphodium coenophialum Glenn, Bacon, and Hanlin infected tall fescue (Lolium arundinaceum (Schreb.) S.J. Darbysh., E+) with a non-toxic endophyte infected fescue (NE+) improves cattle performance.  Previous studies investigating soil properties in fescue pastures with high and low E+ infection rates have found increased microbial biomass with low E+ infection.  Similarly, greater biomass C was found in soils incubated with endophyte-free fescue leaf material compared to E+.  Our objective was to assess differences in dissolved C and N pools, microbial biomass, and enzyme activities in the soil surface 0 to 5 cm among pastures in northern Arkansas with spring (S) and fall-calving (F) cows grazing either E+ or NE+ at different percentages of the total pasture area.  Gelbvieh × Angus crossbred cows (n=178) were stratified by weight and age within calving season and allocated randomly to one of 14 groups representing five treatments: 1) F on 100% E+ (F100); 2) S on 100% E+ (S100); 3) F on 75% E+ (F75); 4) S on 75% E+ (S75); and 5) S on 100% NE (NE100; 2 replications).  Sampling occurred prior to and following rotation of the F75 and S75 herds onto NE+ (25% NE+) pastures in the spring and fall of 2007 and 2008.  Treatment × time interaction was observed (P<0.05) from microbial biomass C and dehydrogenase activities.  Sampling time was significant for all C and N parameters measured.  Dissolved organic C and microbial biomass N were greater (P<0.05) in NE100 vs. E+ treatments, while inorganic N and β-D-glucosaminidase and glucosidase activities were not significantly different.  Therefore, while there were few differences in available N pools, soil microorganisms may be benefiting in the NE100 pastures. This project was supported by the National Research Initiative of the Cooperative State Research, Education and Extension Service, USDA, grant # 2006-55618-17114.