Weed suppressive potential of winter cover crops established as monocultures and mixtures in Southern Australia

Abstract

Leguminous and other cover crops provide rotational diversity resulting in reduced erosion, improved soil tilth, moisture retention, weed control and nitrogen fixation in mixed farming and cropping systems. Cover crops suppress weeds through competition for resources or through the production and release of phytotoxic metabolites exuded by living roots or decomposing plant residues. Field experiments were established in winter growing season in Wagga Wagga and Narrabri NSW, and Kingaroy QLD, to evaluate the establishment of various cover crop species and assess their competitive traits for winter weed suppression in 2018, 2019 and 2020; however, only results from
the experiments established in the 2020 growing season are presented. Crop and weed competitive traits were estimated by assessment of canopy light interception (LI), and crop and weed biomass, in both monocultures and binary species mixtures of cover crops. Overall, grazing oats and tillage radish as winter covers accumulated the greatest biomass and strongly reduced weed number and biomass in winter annual weeds. Interestingly, binary mixtures of suppressive cover crops performed similarly to individual monocultures with respect to ground cover and accumulation of weed biomass.
Experimentation to optimise the economical use of productive monocultures and mixtures in eastern Australia is underway.