Abstract
Effects of soil temperature on establishment of oversown grasses in a serial non-tilled sowing were investigated by pot and field experiments with special reference to competitions between preceding and succeeding warm-or cool-season grasses. 1. Bahiagrass (Paspalum notatum, abbr. as Ba) was oversown into Italian ryegrass (Lolium multiflorum, abbr. as Ir) swards at 4 levels of soil temperature (18, 23, 28, 33℃). The better growth and establishment of Ba was found at the higher soil temperature (above 28℃). The poorer establishment of Ba at lower soil temperature (below 23℃) was supposed to be mainly due to severer competition for light and nutrients between Ba and Ir. When Ir was oversown into Ba swards at 4 levels of soil temperature (15, 20, 25, 30℃), the early growth and establishment of Ir were much better at lower soil temperature (below 20℃). 2. Both the TTC (2, 3, 5-Triphenyl tetrazolium chloride)-reduction and respiration rate of roots of the grasses grown in nutrient solution at 4 levels of solution temperature (18, 23, 28, 33℃) were higher at higher temperature (above 28℃) in Ba and at lower temperature (below 23℃) in Ir. Remarkable effects of solution temperature on root-activity of Ba and Ir indicate that soil temperature affected the nutrient absorption and thus the growth competition between these grasses. 3. In three seeding time (May 20, June 5 and June 20), each of Ba, Rhodes grass (Chloris gayana, abbr. as Ro) and Dallis grass (Paspalum dilatatum, abbr. as Da) was oversown into Ir swards in fields. The best establishment of these warm-season grasses was obtained in the seeding time when the soil temperature became above 25℃. Among the grasses, Ro showed more rapid early growth and higher root-activity than Ba and Da. On the other hand, the establishment of Ir swards could be obtained without any difficulties in the preceding Ro, Ba or Da swards, if Ir oversown at the lower soil temperature (below 20℃).
