Responses of herbage and cattle tail switch hair δ15N value to long-term stocking rates on a rough fescue grassland

Abstract

The purpose of this study was to investigate the response of δ15N in herbage and cattle tail switch hair to long-term grazing pressure on a rough fescue grassland (Festuca campestris Rydb.) near Stavely, Alberta, Canada. Cattle have grazed the paddocks from 15 May to 15 November annually since 1949. Stocking rates were 0, 2.4 and 4.8 animal unit months ha−1 for non-grazing (Control), moderate grazing (MG) and heavy grazing (HG), respectively. Green standing crop (GSC) was sampled monthly throughout the grazing season in 2007. The GSC was fractioned into neutral detergent fiber (NDF), acid detergent fiber (ADF), and their total nitrogen (TN) concentration and δ15N values in NDF, ADF and GSC were determined. Tail switch hair samples from cows (>2 years old) and calves (<1 year) were collected at the end of the grazing season in 2007 and 2008 and analysed for δ15N values. The TN concentrations in NDF and δ15N values in herbage NDF and ADF fractions were higher (P < 0.05) in MG and HG than the Control, and decreased over the grazing season. The δ15N values in tail hair also decreased (P < 0.05) over the grazing season but were not affected by grazing intensity. However, as expected, δ15N values in tail hair increased with herbage δ15N values. The δ15N values in tail hair were enriched by +5.2‰ compared to herbage δ15N values in 2007. Changes in δ15N value in GSC and cattle hair reflect the influence of grazing practices on N cycles through the animal/plant/soil system on this rough fescue grassland.