Soil Seed Bank Dynamics of Pastures Invaded by Navua Sedge (Cyperus aromaticus) in Tropical North Queensland

Abstract

Navua sedge (Cyperus aromaticus) is threatening crops, pasture species and natural ecosystems in Pacific Island countries and northern Queensland, Australia. To aid future management efforts of this exotic invasive weed, research was conducted to understand the soil seed bank dynamics of pastures invaded by Navua sedge. Six grazing properties were chosen across two landscapes, coastal and inland/upland, with areas that had Navua sedge infestations in Queensland, Australia. At each site, soil was collected from two soil depths, 0-5 and 5-10 cm, and from plots with high and low infestation levels of Navua sedge. It was observed that the soil seed bank dynamics varied significantly between these study sites. Navua sedge was the dominant species in the soil seed bank at all the sites contributing between 62% to 95% of the total seed bank, while pasture seeds occupied only 3% to 24%. Broadleaf seeds were even lower in abundance, showing between 2% to 13% of the total seed count. The abundance of Navua sedge seed present in the soil was significantly correlated with the aboveground biomass of Navua sedge (r=0.53, p=0.006), but no correlation was found with the infestation age of Navua sedge. Based on this work, it is clear that the seed bank of Navua sedge is very large and concentrated within the top 0-5 cm of the soil, with, 83% of total Navua sedge seeds being in this layer. It was also noted that, although, high infestation plots had significantly higher number of seeds than low infestation plots, more than 18,000 Navua sedge seeds/m2 were still found in the 0-5 cm soil layer of plots regarded as low infestation. We suggest that insights achieved from our soil seed bank study may be used to devise management strategies to minimise the impact of Navua sedge weed in critical grazing and agricultural areas.

Preliminary study on the effect of certain weeds control strategies on the seed bank of the soil

“…After preparation of soil seed bed for sowing maize crop, the experimental area was divided into eight longitudinal slice sections of 30 m long and 4 m width as shown in photo. (1). Each slice section (Column) was divided into ve plots (Rows) plus 10 m were left as a border in the two sides of maize experiment, and the total area of each plot was 14 m² (3.5 m long x 4 m wide).…”

“…From each plot, forty samples were chosen in a shaped of X English alphabetic, of which, twenty samples were chosen as shown in Photo. (1), and taken at depth of 5 cm, and twenty were taken at depth 15 cm to form a sample unit that represent each plot at 5 and 15cm depths, then samples were mixed and homogenate, then split to a subsample of one kg and 100 g each. Finally, the soil weed seed bank was determined for four times during the two seasons (before and after application of weed control treatments), using following methods.…”

“…The shifting from conventional to conservation agricultures has led to shifting of dynamic change in weed species, and their population and diversity, (Haring and Flessner, 2018). In no tillage system, weed seed banks were found to be accumulated in the top soil layer 0-5 cm, while in plowing system, most weed seeds were displaced to deeper layers of 5-10 and of 10-20 cm and their seed banks found to be three times less than those in no tillage system, Szewczyk, et al, 2020, also the seed bank dynamics were varied signi cantly between soil layers and among plots with high and low infestation levels, Chadha et al, 2022. Zhang et al, 2021, found that total weed seed bank and their population dynamics were reduced by 51%, and the dominant grassy weed population density was reduced by 53% compared to those determined at the start as a result of applying weed management program for 6 years. They also stated that integrated weed management method could reduce the number of herbicide applications by half and reduce costs and labor by 30%.…”

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

“…However, mechanical weed control is unsustainable, being less effective, necessitating regular repetition, and promoting seed spread to surrounding areas [2,6]. Tillage has been considered effective in burying seeds deeper into the soil [4], as the Navua sedge seed bank is primarily concentrated within the top 0 to 5 cm layer of soil, and Navua sedge seeds require exposure to light for germination [5,8]. However, this practice may prolong infestation by extending seed longevity in the soil seed bank and reducing seed losses [3].…”

Assessing Seed Longevity of the Invasive Weed Navua Sedge (Cyperus aromaticus), by Artificial Ageing

“…Management efforts are often focused to reduce the above-ground cover of weeds while efforts to manage their seedbank are not given comparable importance. However, recent study has shown the presence of more than 35,000 viable Navua sedge seeds/m 2 in the soil seedbank in grazing pastures of tropical north Queensland [7] which is clearly of concern. This high density of seeds in the soil seedbank will contribute to the maintenance of future Navua sedge populations, but it is noted that these seeds have a finite lifespan and variable periods over which their seedbank remains viable.…”