Ecological Studies of Rice Variety : The problem of the temperature and its efficiency during the generative growth period

Abstract

1) Growth process in rice plant is closely connected with the temperature during its cultural period. Especially, with the recent spread of early-planting cultural method, the temperature environment have developed with multiple phases. The authors studied, therefore the ecological responses of rice plant to temperature during its generative growth period. 2) Increasing of the efficiency of rice grain production requires high temperature on and after the stage of young panicle formation. Namely, rice plant requires temperature higher than 20°C during that period, ideally, but the critical temperature for the stage of young panicle differentiation may be about 18°C, we presume. 3) Rice plant requires 750°C of integrated temperature from the stage of young panicle differentiation to the heading time. The stage of boot leaf emergence (the time when the tip of boot leaf protrudes from the sheath of the leaf just beneath it) lies at the middle of the period and makes a turning point on which the stage of young panicle formation changes into the booting stage. Therefore it is an indication of internal growth but it inclines before the middle point in case of late-planting rice culture. 4) In the process of the generative growth, we found that the critical temperature for the stage of young panicle formation (growth) was not equal to that for the stage of heading (elongation of internodes) and that the latter requires to be higher than the former. 5) Though late-maturing varieties are most effective in early-planting rice culture, in case of using any variety for early-planting rice culture anyhow, we must consider to adjust the generative growth period to high temperature period by integral temperature in calendar day. And when we make use of cultural period fully, with on exact knowledge of the regional adaptability of the variety, early-planting rice culture will be possible and the adjustment will effectuate the rice culture. 6) Judging from the above mentioned point of view, at Morioka, limiting times for transplanting and for ripening are the first part of May(about 10th of May) and from the end of September to the first part of October, respectively. So it may safely be said that rice variety "Sasashigure" is the most effective one in this region