The Relationship of Photoperiod to Growth and Flowering of Melilotus Species

Sweetclover is used extensively in Iowa as a soil-improving crop and forage legume. The two species utilized are Melilotus officinalis, the yellow-flowered type, and M. alba, the white-flowered type. Although both annual and biennial forms of M. alba are available, the biennial form is grown more extensively. Only biennial forms of M. officinalis are grown. Since Garner and Allard (1920) first demonstrated that relative length of day was an important factor in the sexual reproduction of plants, numerous studies have been conducted on the effect of photoperiod on plant growth. Extensive literature reviews have been published by Murneek and Whyte (1948), Leopold (1951), and others. Few investigators, however, have reported studies concerning the effect of light and other environmental factors on the growth and flowering of sweetclover. Pieters (1925) noted that annual species exhibited longer internodes than biennial species under normal day lengths. This phenomenon was especially noticeable with seedlings grown out of doors in the late summer. Roberts and Struckmeyer (1938) obtained Melilotus dentata plants with a greater height when grown under long day conditions. Smith (1942) observed an increase in plant height of M. alba and M. officinalis when these species were subjected to long day periods. He also noted an increase in dry weight for plants grown in long days, although a greater proportion of the total weight was found in the roots of plants grown under short day conditions. The primary purpose of the present investigation was to study the effect of various day lengths on the growth rate and flowering of the commonly grown species of Melilotus