Abstract
The vegetational control of paddy levees is one of the important works to maintain the structure strength of levees. In this study, the author investigated the vegetational change on the paddy levee with annual cutting frequency during the six years from 1992 to 1997 in Okayama Prefecture Agricultural Experiment Station. The three plots of cutting frequency, 2-3, 4-5, and 6-8 times a year, were adopted here, and the dominant species grown on the levees used for the survey was bahiagrass or purple nutsedge. At the 6-8 cutting frequency, the dominance of bahiagrass increased by year, but contrary to this the purple nutsedge dominance decreased. On the other hand, at the 2-3 times cutting frequency bahiagrass become less dominant, and needlegrass became the dominant species. However, the vegetational change was not observed in the plots with the 4-5 cutting frequency. The vegetational control by cutting treatments was regarded as one of the important factors contributable to sustain or increase the physical strength of the levee structure. These results suggest that the best annual cutting frequency on levees is 4-5 times in the western districts of Japan.
