The Effects of Temperature and Day Length on Seedling Emergence and Early Growth of Several Pasture Species

T effects of weather are probably more critical during the period of germination and the early seedling stage than during any subsequent period of the plant's life. 'Probably greater losses in effort and substance are sustained through a failure "to get a stand" of the seeded grass or legume than through any subsequent step in a forage crop program. Thus, it seemed advisable to determine, under conditions which could be controlled, the effects of several of the environmental factors which may be encountered in obtaining a satisfactory stand of several of the forage species seeded. The environmental conditions considered in the study here reported include air temperature, soil temperature and the length of day. Although it is impractical to create by artificial means optimum conditions for germination and the early growth of seedlings in the field, it is possible to choose dates of seeding following which such optimum conditions are most likely to occur. Information on the effects of temperature and other environmental factors on seedling emergence and early seedling growth of forage species is limited. In laboratory tests using blotters Toole and Hollowell (n) have shown that numerous winter annual legumes of the genus Trifolium have limited germination at temperatures above 30° to 35° C but that at temperatures of 20° C or below germination was not inhibited. Gassner (4), Kearns and Toole (6), Morinaga (8), Sprague (9), and Toole (10) also using laboratory methods have shown that low temperatures favor germination of both dormant and nondormant seed of several of the forage grasses. Moore (7) obtained under field conditions increased seedling emergence from grasses and legumes seeded on mulched areas as compared with those seeded on bare soil. While these data were not intended to indicate the effects of temperature on seedling emergence, it is interesting to note that mulching reduced the soil temperature in the surface inch as much as 6° to 14° F at temperatures which might have been critical. Furthermore, several of the greater increases in seedling emergence due to mulching were obtained with orchard grass and timothy which are shown in the study here being reported to be sensitive to such high temperatures as existed in the bare soil. Most of the investigations on the effect of temperature on plant growth have been conducted with established plants. Brown ( i ) , using established plants of Kentucky bluegrass which were transferred from the greenhouse to controlled conditions for testing, reported greatest herbage production at 80° and 90° F and greatest root and rhizome production at 60° F. It is probable that -the increased herbage obtained at the higher temperatures was produced from reserve foods stored in the plants during the establishment period and also at the expense of markedly decreased root and rhizome growth during the test period. The total increase in dry matter during the 8-week test period was almost the same at 60°, 70°, and 80° F but decreased at 90° F. With orchard grass, the greatest production of herbage and roots occurred at 70°, but this was only slightly greater than the growth at 60° F. While there was a still further decrease in growth at 50° F, this was of lesser magnitude than that .which occurred at 80° F. Darrow (3) obtained slightly more top growth of Kentucky bluegrass supplied with nitrogen in sand cultures at 59° than at 77° F but obtained slightly more root growth at 77° F. Harrison (5) reported the greatest initial herbage production from established Kentucky bluegrass sods at 80° F, but after the reserves in the plants were depleted the rate of growth declined sharply and plants grown at 60° F far outyielded those at 80° F. Under field conditions, Brown (2) found that Kentucky bluegrass swards made little growth in the spring until soil temperatures reached 50° F. Maximum growth occurred in May when the average soil temperatures ranged from 60° to 64° F. Minimum herbage production was obtained during July when average soil temperatures ranged from 80° to 82° F even though the plots were irrigated.