Responses of annual range to gibberellic acid.

During the past several years scientists have devoted considerable study to the effect on plants of the recently available plant growth substance, gibberellic acid. Among the numerous responses reported are some appearing to have possible application to forage production on range, although these responses usually have not been studied using range species. Increased dry weight and stimulated growth at low temperatures are reported behaviors of this type. Freitas, McClung, and Quinn (1957) reported significant fresh and dry weight increases in the Brazilian pasture grass, Panicum maximum, during winter months following foliar sprays with gibberellic acid. Leben and Barton (1957) obtained significant dry weight increases in Kentucky bluegrass in Indiana when harvested November 10, having been sprayed 15 days earlier with this chemical. Wittwer and Bukovac (1957a) found that winter dormant Kentucky bluegrass resumed vigorous growth in Michigan within a few days after being sprayed in March. These investigators (1957b) also noted that adequate fertility, particularly nitrogen, aided in stimulating growth following the hormone spray, and that the effect of spraying might persist for 2 to 6 months. Other work provides less promise that beneficial uses may be found for range. Marth, Audia, and Mitchell (1956) surveyed the response of many plants to the hormone and found that behavior differed pronouncedly among species with some being little affected by treatment. Youngner (1958) reported that although dry weight of clippings was increasedin Zoysia grasses, treatment with gibberellic acid did not improve the rate of turf establishment. Field applications have been made in England by Morgan and Mees (1956) who found that although the dry weight of forage cut after gibberellic acid application was increased at the first cut, it decreased at the second cut resulting in no significant increased yield from the sward. Both the stimulation of growth at seasons when low temperatures normally retard growth and the increases in dry weight of forage frequently reported following treatment with gibberellic acid, appear to be features warranting additional study on range species growing under range conditions. The present study was undertaken with these objectives in mind.