Row spacings influence crop competition

Image of Dr Bhagirath Chauhan

Dr Bhagirath Chauhan monitors a mungbean crop.


Queensland research has shown that narrower row spacings, particularly in pulse crops such as mungbeans, soybeans and chickpeas, can be an effective non-chemical weed control.

Dr Bhagirath Chauhan, principal research fellow with the Queensland Alliance for Agriculture and Food Innovation (QAAFI), a partnership between the University of Queensland and the Queensland Government, has found that these crops are able to outcompete weeds for moisture and nutrients when row spacing is reduced.

Dr Chauhan found 60 to 70 per cent fewer weeds emerging three weeks after mungbean planting in 25 to 50-centimetre rows, compared to conventional 75cm rows. In the weed-free situation, as well as in low to moderate levels of weed infestation, the grain yield of mungbeans was lower when grown on 75cm rows.

“The current practice is to plant mungbeans on 75cm to 1m row spacing,” Dr Chauhan says. “Because these crops are often grown in dryland conditions, there is a concern that the crops may run out of moisture if they are planted on narrower rows. However, in other row-spacing trials, data has shown higher yields on narrow row spacing.”

Image of feathertop Rhodes grass seeds

Seeds of feathertop Rhodes grass, a major weed in the northern region of Australia.


Dr Chauhan says there may be other reasons why crops are not planted in very narrow rows – such as an increased incidence of fungal disease due to humidity in the closed crop canopy – and says, ultimately, recommendations will need to provide a compromise between weed competition, disease and moisture.

In addition to his work in non-chemical weed management, Dr Chauhan has secured GRDC funding for a further four weed-management projects in collaboration with a range of agencies, including the Queensland Department of Agriculture and Fisheries (DAF), the NSW Department of Primary Industries (DPI), the University of Western Australia and the University of Adelaide.

The first of these is a national project that is evaluating existing herbicides for use on weeds and crops on which they are not currently used. This could potentially open up new chemistries for areas where herbicide resistance is emerging, and prolong the life of existing chemistries within crop rotations in these regions.

The second project, which Dr Chauhan is leading in the north, is examining the biology of emerging weed species.

“In the northern region, we are looking at 10 weed species: three winter weeds and seven summer weeds. We want to understand their seedbank persistence and their competitive ability in different crops,” he says.

“We collected seeds from two regions: a high-rainfall zone around Toowoomba and Dalby; and a low-rainfall zone in St George. This is a five-year project and we are running a range of experiments to better understand the biology of these weeds.”

Dr Chauhan’s remaining two projects include trialling the feasibility of harvest weed-seed control – already widely practised in the western grains region but relatively new to the north – and targeted tillage, which involves cultivating a patch or patches of weeds, rather than a whole field.

The technology will first be trialled in fallow paddocks, but the ultimate goal is to apply the technology in-crop.

Dr Chauhan says the projects will deliver valuable knowledge to the discipline of integrated weed management.

“In the next four or five years, we will see problems with resistance increasing, and we may lose some of our effective herbicides. We will definitely need these kinds of non-chemical approaches,” he says.

More information:

Dr Bhagirath Chauhan,
0427 923 272,


Resistant silver grass sneaks through


Is GM technology being superseded?

GRDC Project Code UQ00080, UA00156, UWA00171

Region North, South