Most of the native grasslands in this country grow to the Zoysia-type of vegetation when continuously grazed by animals for years. Seasonal changes in dry matter production and efficiency of solar energy conversion of the Zoysia-type grassland were determined from the spring of 1972 to that of 1974. The grassland examined lies at the hillside of Mt. Nanashigure located near to Morioka city, Iwate Prefecture. Dry matter in both above- and under-ground organs of Zoysia plant and surface litter were harvested monthly from May to October in terms of growth analysis during one-year protection from grazing. Results are as follows. 1. Total dry weight of both the above- and the under-ground organs of Zoysia sward was high in the lower area of a slope of the grassland mostly in every season, but the seasonal trends were nearly the same among the stands of three places examined of higher, middle and lower areas of the slope. The dry weight of surface litter also showed nearly the same pattern as that of standing crop in changes with season and with the place of a slope (Fig.1). 2. The highest value of total dry matter (V_1〜V_5) of the Zoysia sward was seen in October (Table1), while that of the rate of growth (V_1〜V_5) in the period from June 10 to August 9 (Table 3). Among plant parts of Zoysia, the growth rate of erect stalks (V_2) first attained the highest value in the year during June and July following the decrease in dry weight of stolon (mostly growing below ground level as like as rhizome, V_3), that of leaves (V_1) did second during July and August and that of stolon (V_3) increased mostly from August to September. The rate of root increase (V_4) was not so much but it was rather high in spring. That of surface litter (V_6) decreased month by month excepting the period from early July to early August just after rainy season (Table 3). Most of the seasonal variation in the total dry weight was due to those in the leaves and erect stalks. Less variation was observed in those of stolon and root than in those of leaves and stalks but over the 60 percent of the total dry matter weight of Zoysia plant was composed of stolon and root in every season (Table 4). 3. Efficiencies of solar energy utilization (E_u) against total radiant energy (0.3〜4.0μ), calculated on monthly average from the growth rate data (Table 3) and the heat of combustion per unit dry weight (Table 5), ranged from 0.22% in spring to 0.62% in midsummer and decreased in autumn. The efficiency calculated for the herbage available only (E_u in HA) ranged from 0.24% in spring to 0.49% in midsummer (Table 6). The heat of combustion of Zoysia plant per unit dry weight was a little higher than those of temperate grasses measured by Okubo et al. (1969). The annual average efficiency in living whole plant growth was 0.10%, that for the growing period 0.23%. 4. From the seasonal variations in the total dry matter weight and in the fall of standing dead estimated from surface litter balance in terms of litter bag method, the annual net production was calculated by use of the equation in Table 9 (notes). The annual net production of the Zoysia-type grassland examined here was estimated as 531g/m^2/year. This value of net production was approximately corresponding to 1.5〜1.6 times as large as that of standing crop above-ground (Amax, that is, leaves and erect stalks) without standing dead. The annual conversion efficiency was 0.24% when the fall of standing dead was taken into account for the net production of the grassland.
