Ecological studies on weed damage of rice plants in rice cultivation. I and II. On the mechanism of competition between rice plants and weeds
Arai, Masao; Ryoichi; Kawashima
Proceedings Crop Science Society Japan 25(2): 115-119
The experiment was carried out with 3 plots, in which the kind and population of growing weeds were regulated by sowing, thinning or additional transplanting of weeds early in July after the rice seedlings were transplanted. The kind and population of growing weeds affected the growth and yield of rice plants. In plot A where few weeds grew the highest yield of rice was obtained; in plot B, with more kinds and a larger population of weeds, the rice yield was 82.2% of plot A; in plot C where weeds were numerous the yield as 57.1% of plot A. From the 2nd-10th days of July the growth of rice plants and weeds tended to be vigorous and competition was great. Nitrogen competition was greatest in plot C and moderate in plot B. Competition for light was most serious in plot C at about the full-tiller stage. The difference in the competition in the 3 plots was due to the difference in growth habits and population of weeds, which varied in height, dry weight and nutrient absorptivity. Panicum crusgalli L. was the most competitive, varying with the difference of community structure. Damage to rice plants was analyzed into 3 factors from the synecological standpoint; the total weight of community including rice plants and weeds, the ratio of rice plants to total weight of community, and the ratio of grains to weight of rice plants. At about the full-tiller stage, the ratio of rice plants to total weight of community approached the minimum value and thereafter varied slightly. Variation between plots was small in connection with the other 2 factors.