Forage Quality in Stratified Canopies of Alfalfa, Birdsfoot Trefoil, and Red Clover1

Abstract

Forage quality usually is evaluated on a total‐herbage basis although in vitro digestible dry matter (IVDDM) and crude protein (CP) concentrations can vary greatly among plant parts. This study was conducted to compare IVDDM and CP concentrations of leaf blades (leaves) and remaining plant parts (stems) and the relative amount of these plant parts present within plant‐canopy segments of alfalfa (Medicago sativa L.), birdsfoot trefoil (Lotus corniculatus L.), and red clover (Trifolium pratense L.). Unseparated herbage of white clover (Trifolium repens L.) was included for comparison. Plants were sampled three or four times during two 6‐week growth periods, starting when plants were in the prebud stage. At each harvest, alfalfa and birdsfoot trefoil stems were separated above 6th and 12th nodes (from cut stem base), and leaf blades were removed. Red clover was divided above the 3rd and 6th nodes, and leaf blades also were removed. The IVDDM concentration in total herbage was greatest in white clover and frequently least in alfalfa. The IVDDM concentration of alfalfa and birdsfoot trefoil stems decreased about twice as rapidly as total herbage plant IVDDM concentration during advancing maturity. Stem bases had less IVDDM concentration than stem tops with a rate of change among stem segments of about 20 g kg‐1 dry matter (DM) node‐1. Red clover stems had greater IVDDM concentration than did leaves until flowering. The rate of change among red clover stem segments was less than 8 g kg‐1 DM node‐1. In contrast to IVDDM, range in CP concentration among the plant parts was nearly as large at the beginning as at the end of each period because of a nearly parallel rate of CP decline in the plants. Leaf mass decreased and stem mass increased in the basal segment during each period, which decreased the leaf‐to‐stem mass ratio of basal segments to 0.06 or less for alfalfa, 0.16 for birdsfoot trefoil, and 0.23 or less for red clover by the end of the two periods. We conclude that attempts to improve forage quality of alfalfa and birdsfoot trefoil should be directed toward the lower portion of the plant canopy.