A diverse crop sequence can cost-effectively help reduce the annual ryegrass population.

CSIRO Agriculture and Food chief research scientist Dr John Kirkegaard says research at Temora, NSW (with GRDC co-investment), from 2014–17 compared the effects of three farming systems on the weed seedbank.

The trial site had an initial annual ryegrass population of 1864 plants per square metre. System 1 comprised a conservative (‘business as usual’) crop sequence of canola (triazine tolerant)/wheat/wheat. Managing annual ryegrass involved sowing at a low density, applying trifluralin (Treflan™) or diuron incorporated by sowing, and adding 20 kilograms per hectare of upfront nitrogen.

System 2 used an aggressive (‘buy my way out of trouble’) crop sequence of canola (Roundup Ready® herbicide with PLANTSHIELD®)/wheat/wheat. Managing annual ryegrass involved sowing at a high plant density, applying pyroxasulfone (Sakura® 850 WG herbicide) or prosulfocarb + s-metolachlor (Boxer Gold® herbicide), and applying 40kg/ha of nitrogen upfront.

System 3 comprised a diverse (‘manage my way out of trouble’) approach using a vetch hay/canola (TT)/wheat/barley sequence. Managing annual ryegrass involved using a low plant density at sowing, pyroxasulfone (Sakura® 850 WG herbicide) and 20kg/ha of nitrogen upfront.

“At the crop level (Table 1), barley in the diverse vetch/canola/wheat/barley system yielded 4.8t/ha, outperforming the wheat in the same system at 3.8t/ha, wheat in the aggressive canola/wheat/wheat system (3.6t/ha) and the conservative canola/wheat/wheat system (3.1t/ha),” Dr Kirkegaard says.

“At the systems level (Table 2), the diverse vetch/canola/wheat/barley system produced a $484/ha gross margin, slightly higher but not statistically different to the aggressive canola/wheat/wheat system.

“Notably, the vetch/canola/wheat/barley sequence reduced annual ryegrass from 1864 plants per square metre to 204 plants/m². This was significantly lower than the aggressive and conservative farming sequences.”

Dr Kirkegaard says this experiment shows that barley fits into a diverse farming system.

“Barley can suppress weeds better than wheat because it is more competitive against weeds,” he says. “It also performs well in dry seasonal conditions and when there is a tight finish.”

More information: John Kirkegaard, john.kirkegaard@csiro.au

Further reading: Diverse systems and strategies to cost-effectively manage herbicide-resistant annual ryegrass (Lolium rigidum) in no-till wheat (Triticum aestivum)-based cropping sequences in south-eastern Australia.

Read also: GroundCover stories – Hardy barley proves its worth in rotation trials and Farming systems trials go paddock-scale.