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Six years of field experiments have shown lint yield was higher when cotton was planted close together in narrow rows less than 40 centimetres apart.

The research – completed by Rose Roche at Narrabri as part of her PhD with The University of Queensland and CSIRO Plant Industry – is unravelling the complexity of ‘ultra-narrow row’ (UNR) cotton’s growth and development.

“Previous experiments across Australia and the USA have been inconclusive about the yield and maturity benefits of UNR, so we wanted to once and for all pin down the facts,” Ms Roche says.

“Across all our experiments the average lint yield in UNR plantings was 15.9 per cent higher than in conventionally spaced cotton, which is planted one metre apart.

“However, yield differences were not consistent, ranging from 4 bales per hectare higher to no difference at all.

“While UNR looks like a promising option for higher yields for growers, further research and evaluation of agronomic requirements and economic benefits are needed to understand under what circumstances growing UNR would be a consistently better option than one metre spaced cottons,” she says.

Data from the experiments revealed that boll size in UNR plantings was reduced by nine per cent, but this was more than compensated for with a 21 per cent increase in boll numbers in UNR plantings.

“We also found no difference in the time it took for the crops to mature, a previously reported benefit associated with UNR,” Ms Roche says.

A key finding of this research is that competition between plants occurs very early and is much higher than expected in UNR plantings – as a result plants don’t grow as quickly or as big.

Ms Roche is now working as a Post Doctoral Fellow with CSIRO Plant Industry investigating if early competition can be overcome by increasing inputs to the crop early in growth.

“We are comparing row spacings of 38 and 25 centimetres with different plant populations to identify the critical factors driving competition – such as early season water, nitrogen and light use – that may slow early growth in UNR plantings,” she says.

“We aim to be able to make some specific recommendations on row spacings and associated management so farmers can choose the most suitable option for their situation.”