Abstract
An experiment was conducted to investigate the response of warm-season grasses to the different duration of light competitive condition with preceding cool-season grasses into which the former species were undersown. Four warm-season grasses, i.e. green panic (Panicum maximum var. trichoglume cv. Petrie, abbr. as P), setaria (Setaria anceps cv. Kazungula, abbr. as S), rhodesgrass (Chloris gayana cv. Pioneer, abbr. as R), and dallisgrass (Paspalum dilatatum, abbr. as D), were sown in 12 cm diameter pots with four replications on Sep. 1, 1975. It consisted of five treatments regarding number of days under shade (29% daylight, abbr. as shade or s), i.e. 0s, 12s, 21s, 27s, and 34s from sowing, and then moved into light (87% daylight, abbr. as light), shown in Fig. 1. 1) Total plant dry weight showed the highest in R under continuous light (0s), but under continuous shade (34s) P was the highest, and S, R, and D decreased in order (Table 1). 2) The reduction of RGR owing to the shading was heavier in D, comparing other species. Two modes of adaptation to compensate the lowering of RGR under shade were observed, i.e., by means of a) the increased LAR in accordance with the higher SLA such as P, or the higher value of SLA and LWR such as D, and b) the least decline of NAR such as S and R (Table 2 and 4). 3) The increase of RGR after the transference from shade into light was observed in all the species. But after 27 days of shading, P showed less recovery comparing to D (Table 3). 4) The relationships between the log value of the total relative radiation (ΣR) and RGR were as follows (Fig. 2), a) In sptite of the highest RGR under light, R decreased rapidly in accordance with the shading. b) The smallest RGR was observed under both light and shade in D. c) The reduction of RGR with that of ΣR was not severe in P and S, comparing to R and D. 5) The difference in the shape of leaf blade among those developed under shade and light was observed especially in D (Table 5). 6) These results show that P, S and R may be suitable for undersowing practice in respect of higher dry matter production up to about 20 days of 30% daylight. But D is characterized in the highest recovery of RGR after transference into light.
