Growth Analysis of Rice and Echinochloa oryzicola Vasing. in Mixed Stands

• Published in: Journal of Weed Science and Technology Vol. 42; no. 4; pp. 365 - 372
• Main Authors: Yamasue, Y., Murayama, H., Inoue, H., Matsui, T., Kusanagi, T.
• Format: Journal Article
• Language: Japanese
• Published: The Weed Science Society of Japan 1998
• Subjects: crop-weed competition; Echinochloa oryzicola Vasing; growth analysis; weed plasticity
• ISSN: 0372-798X; 1882-4757
• DOI: 10.3719/weed.42.365

Growth of rice (Oryza sativa L.) and Echinochloa oryzicola Vasing. was studied in mixed stands with a substitutive design to identify characters of the weed that confer aggressiveness in competition. Both rice above-ground dry weight and grain yield per plant in the mixed stands were heavily reduced to 55 and 49%, respectively, compared with those of the pure stands. Mathematical growth analysis showed that crop growth rate (CGR) of the crop and weed changed in parallel to the change of leaf area index (LAI) in the two stand types. However, these two growth parameters of the weed were far larger than those of the crop throughout their growing seasons. The weed CGR and LAI in the mixed stands were 29g/m2/day and 3.0, respectively, whereas those of rice were 9g/m2/day and 1.9 on 60 days after transplanting. The variation in CGR could be largely accounted by the variation in positively correlated net assimilation rate (NAR) in both of the two species of the mixed stands during the late growth season, but the crop CGR tended to correlate negatively with its LAI and the weed CGR did positively with LAI. It was likely that upper expanding leaves of the weed greatly contributed to its large dry matter production. In contrast, the markedly small rice CGR appeared to be resulted from the light interception by the weed upper leaves. The weed showed a plastic response of plant height. The pure stand weed became taller than the weed mixed with its shorter rice neighbor. When grown with three neighboring plant species with different heights the weed always grew a little taller than the neighboring plants. However, the plant height of rice was the same in the pure and mixed stands and had a far larger dry weight allocation to the panicles by its nature of a crop. We therefore concluded that the plasticity of E. oryzicola in plant height was one among the characters conferring its competitive aggressiveness in flooded rice.