Optimum Crown Temperatures for Maximum Alfalfa Growth1

Abstract

AbstractReported effects of soil or root zone temperatures on alfalfa growth have not separated the temperature effects on roots and crowns. The optimum crown temperature for maximum top, crown, and root growth was determined in this investigation. Alfalfa growth was measured at various crown temperatures while root and shoot temperatures were held constant.Two similar growth chamber experiments were conducted on ‘Vernal’ alfalfa. In the first experiment, crown temperatures of 25, 28, 34, and 36 C were used. Maximum predicted top growth occurred at a 32 C crown temperature. Average shoot length and number of trifoliate leaves per plant were the major variables that correlated with topgrowth.Top and root growth were influenced in an opposite manner (r = —0.51) by crown temperatures of 23, 31, 36, and 40 C in the second experiment. Crown weights were not significantly influenced by these temperatures. Therefore, total plant weights were evaluated. The maximum predicted‐ and actual‐total‐plant weight was at 36 C. The most topgrowth and least root growth occurred at 40 C. However, topgrowth was abnormal in appearance, and cortical cells had collapsed hi the roots. Excluding results at 40 C, the maximum top growth occurred at 31C.Optimum crown temperature is much higher than the reported‐optimum‐root temperatures for maximum alfalfa growth.