Effects of weed abundance and frequency of hand weeding on the establishment of transplanted Imperata cylindrica

Imperata cylindrica is an important component of grasslands in several Asian countries. Its vigorous rhizome elongation enables the plant to quickly cover bare ground, making it a candidate for revegetation projects. In these projects, initial and subsequent management practices often differ. Initial management strategies are important for encouraging rapid cover by the target species. We tested the effects of initial hand weeding on I. cylindrica cover and weed growth over 2 years. Two types of soil (A and B) were scattered on a recently constructed river embankment at a depth of 10 cm. Both soils A and B are nutrient-poor and high (> 7.0) pH. Plots were hand-weeded once or twice a year (W₁ and W₂ treatments, respectively), or mowed but not weeded (M treatment) with four replications. Plug plants of I. cylindrica were introduced. I. cylindrica became dominant in soil A with the W₂ treatment, with 50% cover in year 2. Conversely, I. cylindrica failed to establish in soil B regardless of treatment, due to dominance of the weed Sorghum halepense. Soil B included creeping rhizomes of S. halepense, and vigorous growth from rhizomes is likely a major reason for its predominance. S. halepense seedlings germinated in both soils, but were successfully eradicated when weeded at less than 1 month of age. Thus, for successful revegetation, land managers should use soil that does not contain creeping rhizomes of S. halepense. If rhizomes are not present, hand weeding twice a year for 2 years is sufficient for establishment of I. cylindrica.