Combined Effect of Hill Arrangement, Wind Direction and Wind Speed on Bending Angles of Culms and Lodging Levels in Rice Plant

[摘要] This experiment started from the observation that the cross section of a rice hill was ellipse in shape. When two rice plants cv. Koshihikari were transplanted in a 1/2000 are Wagner pot, the rice hill were arranged in four combinations, considering major and minor axes of a rice hill. The bending angles of each main culm at windward and leeward were measured to wind directions and wind speeds. Moreover, lodging levels in small rice communities grown in concrete pots were observed under natural conditions. The results are summarized as follows: 1) Plant length was about 80 cm at heading, and the number of culms was about 30 per hill just before maturation. 2) Bending angles of main culms in the hill positioned at windward can be divided largely into two groups, that is those of arrangements c and b in Fig. 1 were large and those of arrangements a and d were small. Those in the hill positioned at leeward tended to be large in arrangement a and small in c. The bending angles of arrangement b tended to be large at windward and leeward. 3) Estimating the relative values of plant height and the spreading of culms under natural conditions as 100, the value of plant height reduced with increased wind speed dropping to about 75% of the initial value at 12.5 m/s. Differences among four treatments was not found in relation to plant height. Whereas in case of the spreading of culms, three different results were obtained according to the different treatments: in arrangements a and d it was narrow, widened at first then narrowed in b, and in c the culms kept on spreading widely. 4) The lodging level was the largest when the major axis of hills was parallel to the main wind direction in small rice communities under natural conditions.

[学科分类] 农业科学（综合）

[关键词] Bending angle;稲株の長軸;Lodging level;稲株の拡がり;Major axis of a rice hill;傾斜角度;Rice hill;倒伏程度;Wind direction;風向;Wind speed;風速