Seasonal and diurnal changes in aucubin, catalpol and acteoside concentration of plantain herbage grown at high and low N fertiliser inputs

This experiment aimed to characterise the concentration of secondary compounds aucubin, catalpol and acteoside in plantain ( Plantago lanceolata ) herbage and determine if harvesting at different times or nitrogen (N) fertiliser inputs alter concentrations. Herbage of plantain was harvested each season over two years from plots fertilised at 180 or 450 kg N/ha/yr. At each harvest date, samples were taken in at 0700 h and 1600 h. The concentration of secondary compounds in plantain herbage was greatest for acteoside (range 1.77‐36.0 mg/g DM), intermediate for aucubin (range 0.566–5.85 mg/g DM) and lowest for catalpol (<0.390 mg/g DM). Compound concentrations were unaffected by N fertiliser and showed limited diurnal fluctuation. There was a strong seasonal effect on all secondary compounds with peaks in concentration occurring in spring for aucubin and acteoside. This experiment suggests environmental factors other than soil N fertility and diurnal patterns influence the concentration of secondary compounds in plantain. Abbreviations: DR: digestibility‐reducing; DM: dry matter; HPLC: High performance liquid chromatography; N: nitrogen; NH 3 : ammonia