Theoretical analysis of the tillering capacity for the lower density of seedling establishment in direct seeding cultivation of rice (Oryza sativa L.)

The effects of an irregular density of seedling establishments in direct seeding cultivation of rice (Oryza saliva L.) on growth and grain yield and their relations were investigated in a paddy field (1.0 ha). The population density of established seedlings varied from 56 to 336 plants m(-2), averaging 159 plants m(-2), and its coefficient of variation was 38%. The coefficient of variation of the maximum number of stems per m(2) decreased up to 23%, and that of the grain yield was only 17%. The maximum number of tillers per plant was negatively correlated with the population density. Consequently, lower population density did not affect the grain yield. Furthermore, to analyze the tillering capacity for a lower density of seedling establishments, the nodal position of the most recent primary tiller to appear and the maximum order of tiller were examined in rice plants grown under different densities of seedling establishments. There was a tendency for the nodal position of the most recent primary tiller to appear and for the maximum order of tiller to be larger as the population density decreased. Therefore the potential number of tillers per plant, which could be calculated by using these data, increased as the population density decreased. To produce 500 panicles m(-2), if the percentage of fruitful culms was 65%, the minimum number of plants was calculated to be 24-46 m(-2).