Histological Analysis of Lignification in Birdsfoot Trefoil (Lotus corniculatus) Stems and Implications for Management.

The forage legume Lotus corniculatus, commonly known as birdsfoot trefoil (BFT), is well suited to pasture-based ruminant production systems. Understanding the progression of lignification in stems of maturing plants can inform management that seeks to optimize long-term animal gain per ha by balancing forage yield, quality and stand persistence. The 6^th internode from the base of growing stems of BFT, located approximately 7.5 cm from the soil surface, was selected for study because it is found at the recommended grazing height for this species. The lignification of this internode was studied during regrowth from elongation to maturation. The 6^th internode of alfalfa (Medicago sativa) was used as a control. Internodes were sampled during 15 weeks of summer regrowth, hand sectioned, viewed under UV light and stained with phloroglucinol/HCl and toluidine blue O to observe lignin. Patterns of lignification were similar in BFT and alfalfa, which was previously studied by Jung and Engels. The most extensive lignification in both species occurred in the secondary xylem. After 4 to 5 weeks a lignified xylary ring formed in 6^th stem internodes and grew to maximum thickness by approximately 7 weeks, which coincided with flowering. Because lignification decreases forage quality and thickening of the xylary ring reduces the ability of cattle to harvest BFT at or below the 6^th internode, our findings provide an anatomical basis for the recommendation to harvest BFT at approximately 6 weeks of regrowth.