Growth of the invasive Navua sedge (Cyperus aromaticus) under competitive interaction with pasture species and simulated grazing conditions: Implication for management

Abstract

Navua sedge (Cyperus aromaticus), a perennial monocot plant native to tropical Africa, is a major weed in pasture and cropping areas in the wet tropical regions of Australia and South Pacific countries. In grazing pasture lands, rapid growth and reproduction of unpalatable Navua sedge leads to displacement of co-occurring pasture species and depletion of livestock carrying capacity and production. Understanding the interspecific competitive ability of Navua sedge with co-occurring desirable grasses and in response to varying ecological scenarios (e.g., grazing and plant density) is critical for the management of the weed in pasture situations. In a glasshouse setting, two cooccurring pasture species-humidicola (Urochloa humidicola) and Rhodes grass (Chloris gayana) were grown with Navua sedge, in pots using a replacement series model. For each Navua sedge weed-pasture species pair, the experimental setup comprised of four ratios in two densities under simulated grazing and nongrazing conditions of the pasture grasses. Navua sedge growth and reproduction was highest when it grew as a monoculture or when cooccurring pastures were exposed to simulated grazing as this action, reduced the competitiveness of the pasture grasses. Overall and using biomass gained, tiller production and relative yield as indices of growth dynamics, Rhodes grass was more competitive against Navua sedge than humidicola in both grazed and nongrazed conditions especially under high plant density. These results suggest the potential to include competitive pastures in integrated management strategies for Navua sedge, but species selection and grazing practices may influence the effectiveness of this approach.

Utilization of the Neighborhood Design to Evaluate Suitable Pasture Crops and Their Density for Navua Sedge (Cyperus aromaticus) Management

“…This means that having faster canopy development due to its leaf shape and biomass gives lablab a competitive advantage compared to other broadleaf species and may explain the poor performance seen by stylo. Previous studies have found that Rhodes grass was more competitive than humidicola against Navua sedge [15,24], and similar results were observed in our study. This suggests that the difference in growth characteristics, such as the rate of development amongst grass pasture species, may substantially impact their competitive intensity.…”

“…There was a total of 15 Four to five seeds of Navua sedge were planted (October 2021) in the center of a 24 cm diameter pot and thinned to one plant after emergence. The pasture species were planted simultaneously surrounding the Navua sedge at a distance of 11 cm and a density of four plants per pot (88 plants/m 2 ).…”

“…Limited information is available on the effect of pasture competition on Navua sedge. One study evaluated crop competition responses in Navua sedge with only two pastures [15]. Rhodes grass (Chloris gayana) was found to be more competitive against Navua sedge than humidicola, especially at a high plant density.…”

“…Therefore, future studies should encompass a larger number of species. The study was conducted in a glasshouse [15]. Trials under controlled glasshouse conditions have shown differences in plant growth compared to trials conducted in an open environment, indicating that glasshouse and field conditions may impact plant growth differently [17,18].…”