The relation of supplementary light and soil fertility to heading in the greenhouse of several perennial forage grasses

Experiments were conducted at State College, Pa., to determine the effects of several environmental factors on heading in the greenhouse of perennial ryegrass, orchard grass, timothy, meadow fescue, bromegrass, Canada bluegrass, and Kentucky bluegrass. The effects of various durations of supplementary light in addition to the normal winter day length were determined on all of the above species. The effects on heading of various intensities of supplementary light and of low temperature pretreatments were determined on perennial ryegrass, orchard grass, and timothy. Heading responses of orchard grass grown under favorable day lengths and with two levels of soil fertility were determined. None of the clones used of these perennial species headed under a normal winter day length of 10 hours. A few clones of the various species headed under a 12-hour day. The best heading was obtained under a 16-hour day, and almost equivalent heading occurred when the plants grown under 10 hours of daylight received 1 or 2 hours of supplementary light during the middle of the night. The dry weight of top growth of orchard grass, Canada bluegrass, Kentucky bluegrass, and a F1 hybrid of these latter two species was increased under a 16-hour day and also when the plants were grown under a 10-hour day with 1 or 2 hours of light during the night. It would appear from the results of these experiments that the length of the dark period rather than the length of the light period is a determining factor in the photoperiodic responses of these long-day species. Increasing the intensity of the supplementary light from 75 foot-candles to 150 and 300 foot-candles had little, if any, effect on increasing the number of clones of perennial ryegrass, orchard grass, or timothy that flowered. Low-temperature pretreatments of the established plants of these species before placing them under a long day did not generally increase the number of clones flowering or shorten the time required. With orchard grass, there was an indication that a longer growing period under short-day conditions aided in the initiation of heads when the plants were shifted to long days. Adequate fertility for the growth of orchard grass plants was an important factor in inducing heading. Pot-bound plants of this grass produced no heads under long days, whereas similar plants which had received a liberal top-dressing of fertilizer or had been transplanted to larger pots of new soil headed.