Evaluating flotation and sieving for removing Nassella neesiana seeds from gravel harvested from infested riverbeds in New Zealand
Nassella neesiana (Chilean needle grass) reduces farm profitability through its sharp seeds that damage wool, skins, hides and carcasses. It poses a biosecurity risk in New Zealand’s Hawke’s Bay region due to its seed dispersal via gravel and crushed aggregate from braided rivers. This study evaluated flotation and sieving to remove both dry and imbibed panicle seeds. We measured their length, width, mass, flotation, and passage through sieves with and without the awn (a hygroscopic, bristle-like structure). The dry awned seeds were, on average, 70.12 mm long and 1.13 mm wide, increasing to 74.07 mm long and 1.21 mm wide when imbibed. With imbibition, their mass with awn, increased from 9.41 to 14.06 mg, and from 3.96 to 5.04 mg with awn detached. Flotation was highest for the dry awned seeds (50%) and lowest for imbibed awned seeds (3%). The awn and imbibition restricted the seeds’ passage through sieves while sand and a crushed aggregate (GAP 20 metal) facilitated their passage. The results indicate that flotation would be ineffective for removing N. neesiana seeds from river gravel but that an 8 mm aperture sieve could effectively remove them along with fine aggregate particles
Funding
Hawke’s Bay Regional Council, Engineering section (contract HBRC-21-565)
History
Rights statement
© 2025 The Royal Society of New ZealandPublication date
2025-01-16Project number
- PRJ0122908
Language
- English
Does this contain Māori information or data?
- No