Growth rates of plants are regulated by the photosynthetic ability and a multitude of environmental factors. Grasses are classified into C3 species and C4 species based on their unique photosynthetic pathway. It is important to note the anatomical differences in leaf and bundle sheath cells that occur between C3 and C4 grasses. Typically, the optimum light intensity for C4 species is ca. 50,000-60,000 lux and is twice that for C3 species (15,000-30,000 lux). The highest photosynthetic efficiency of the C4 species generally reaches at high temperature and high light intensity which is characteristics of tropical regions. The C4 species, however, cannot maintain their high photosynthetic efficiency under low light intensity and low temperature. Table2.7.1 shows that napiergrass recorded a yield of 85 t/ha/year and the yield of sugarcane is 64 t/ha/year, with a mean of 232 kg/ha/day, and 176 t/ha/day, respectively. The yield of sugarcane and guineagrass in subtropical regions is 50 t/ha (140 kg/ha/day) and that of some tropical grasses is 25-30 t/ha (50-80 kg/ha/day). Since forage grasses generally exhibit rapid regrowth and persistency, they are utilized for low-input and sustainable biomass production. As one example, “Natsuyutaka” guineagrass has attained 40 t/ha (all are dry matter weight in the report) on a seven-year average in subtropical Ishigaki Island, Okinawa. In temperate regions, winter-hardy tropical grasses such as bermudagrass and bahiagrass produce 20-30 t/ha/year (50-80 kg/ha/day) but go dormant in winter. On the other hand, temperate grasses produces 15-26 t/ha/year (40-70 kg/ha/day) but go dormant in summer. A primary advantage in utilizing perennial C3 or C4 grasses for biomass production is that less maintenance is required and stands can persist for 5-10 years producing stable amount of biomass following stand establishment.

In the annual C4 species, such as maize, exhibiting superior seedling vigor following germination can produce a rangeing, respectively from 13-34 t/ha to 132-260 kg/ha/day in 5 months. These yields are comparable to that of perennial napiergrass. These data suggest that the highest yield in tropical regions is achieved in the summer of temperate regions by using these C4 crops. Although rice is C3 plants, it can compete with C4 species and produce high amount of biomass in temperate regions. However, winter cereals, such as wheat, annual forages, can produce lower yields per day, but can be cultivated during the winter month.