Research by the Graham Centre for Agricultural Innovation is adding weight to the theory that pasture legumes in the rice crop rotation can help suppress barnyard grass, a weed that can significantly reduce yields.
The research by Charles Sturt University PhD student Jhoana Opena is focused on growing pasture legumes in the lead-up to a rice crop to reduce the weed seed-bank.
“Barnyard grass is an annual summer terrestrial grass that’s considered a problem weed in 61 countries,” Ms Opena said.
“It’s been reported to reduce rice yields by 30 to 100 per cent and can also contaminate the rice seed at harvest.
“Direct sowing of rice is one strategy being implemented by growers to increase water use efficiency but delaying the introduction of permanent water can lead to the proliferation of weeds like barnyard grass.
“Another issue is the evolution of herbicide resistance in barnyard grass, highlighting the importance of developing non-chemical weed control.”
Ms Opena’s research has involved a 2018 glasshouse pot trial and field study to examine the impact of legumes and selected winter crops on barnyard grass seed mortality, emergence and growth.
She presented the results at the 19th Australian Agronomy Conference in Wagga Wagga on Tuesday 27 August.
“The study found a 97 to 98 percent reduction in emergence and a 99 to 100 percent reduction in growth of barnyard grass in pots sown with pasture legumes compared with control pots,” Ms Opena said.
“The reduced emergence and growth of barnyard grass observed may be due to competition for light, space, nutrients, and water, inhibitory chemical compounds exuded by the plants, or some combination.”
More trials are now underway assessing the impact of winter pasture legume species and its duration (one compared to two years) on barnyard grass seed mortality, the residues of winter pasture legume species on barnyard grass and rice emergence and growth. The research will also assess the allelopathic potential of different cultivars of pasture legumes on barnyard grass germination and growth.
It’s hoped the results will provide rice growers options to manage problem weeds such as barnyard grass in drill sown rice and delayed permanent water to achieve productivity using these water saving strategies.
The research has been funded by AgriFutures Australia.