Abstract
This study was undertaken to obtain some information on the relation of the pasture utilization during autumn and winter to the next spring regrowth of tropical grasses in the lowlands of southern Kyushu. Changes of plant photosynthetic ability (daily maximum rate of net CO_2 absorption on a fine day, Pa) in dallisgrass (Dg) , bahiagrass (Bg) and Rhodesgrass (Rg) grown under different intensities of defoliation from late Nov. in 1987 to next early Feb., were examined during overwintering (Expt 1). In this experiment, defoliations were done intermittently so as to keep no green leaves or to keep about a half of green unfolded leaf. In the another experiment, changes of Pa, tiller numbers (Tn) and shoot dry matter (Dw) during overwintering were compared among Dg grown under different duration of defoliation (Expt 2). In this experiment, all green leaves were removed intermittently until Jan. 23 in 1989 from Oct. 8, Nov. 1 or Dec. 20 in 1988. In Dg and Bg, Pa before late Dec. was higher in the plant with less intensity or shorter duration of defoliation, and there was a relation that the higher the Pa before late Dec., the higher was the Pa in next spring (Expt 1 and 2). This relation was not found in Rg which is less cold tolerant than the other two species (Expt 1). In Dg, the plants with a higher Pa before late Dec. had a larger Dw at this time and also had a higher rate of increase in Tn, Dw and Pa in next spring. However, the spring regrowth of the plant defoliated from Dec. 20 was nearly the same as that of the plant grown without defoliation (Expt 2). Thus, the photosynthesis before late Dec. is effective on spring regrowth and utilization of pasture in late Dec. has no deteriorative effect on the regrowth in next spring in such a species as Dg or Bg which is comparatively cold tolerant among tropical grasses.
