Trial results from the Mallee Farming Systems site at Karoonda have consistently shown increased surface soil moisture, crop establishment, crop biomass and brome competition achieved through edge-row sowing, could reduce brome grass seed set.
After four years of trials on non-wetting sands – water-repellent soils – stronger crop competition had been shown to have an immense impact on brome seed production.
In a difficult environment where crop establishment is often patchy, researchers have demonstrated that water and nutrient harvesting within the crop furrow could result in better establishment when crops are sown on or near last year’s row.
CSIRO research group leader Rick Llewellyn said brome grass was the most costly weed for SA and Vic Mallee farmers to manage, even though herbicide resistance in brome grass was quite low in the region.
“A series of trials have investigated the effect of different herbicide use, particularly pre-emergence herbicides, and row placement on crop yield and brome grass seed production,” he said.
“To successfully manage brome grass it is necessary to keep weed seed numbers low and avoid blow-out situations. Our aim was to find the best options for reducing seed set.”
The trial’s key message was if a crop could make use of the resources from the previous season’s furrow, there was more reliable crop germination and it could allow earlier sowing in years with marginal rainfall.
On non-wetting sands, the practice of edge-row sowing has led to reductions in brome seed set of at least 55 per cent – and as high as 75pc in the past four seasons.
“Using edge-row seeding to achieve stronger establishment and crop competition on the difficult but widespread sands has resulted in a large and relatively reliable impact on brome grass seed production,” Dr Llewellyn said.
“Growers will need to weigh this benefit against any potential disease risk and any stubble management issues in parts of a paddock that are not non-wetting sands, before changing their seeding set-up for edge-row sowing.”
He said an important observation was also the extent of brome grass germination in the crop row at the time of applying the pre-seeding knockdown.
It was found seven times more brome grass seedlings emerged on the row, so a knockdown herbicide was important and allowed the pre-emergent herbicide the best chance of success.
Pre-emergent herbicides have the potential to achieve up to 75pc control of brome grass.
Dr Llewellyn said reduced seed production was the most important component of effective weed management.