Plant close to maximise yield
WHEN ALL OTHER FACTORS are equal, planting mungbeans on narrow rows (50 cm or less) has been shown to have a large influence on yield, putting up to $900/ha extra in growers’ pockets.
This sort of return on a relatively cheap and easy to implement agronomic practice must be taken seriously, according to Kerry McKenzie, former DAF researcher and now principal at PulseAG Consulting.
Mr McKenzie, who oversaw most of the southern Queensland sites in the recently-completed Northern Pulse Agronomy Initiative, funded by the GRDC, QAAFI and Queensland DAF, said that peak yields always occurred in field plots where the narrowest of row spacings was applied.
“At the southern Queensland sites, 25 cm row spacing gave the best yield at most of the individual trial sites, however when all sites were statistically analysed together there was no yield difference between the 25 cm and 50 cm row spacing, but yields dropped dramatically if planted any wider,” he said.
“The results were consistent, regardless of the seasonal yield potential. We had sites that averaged less than 0.5 t/ha and others that averaged 2.2 t/ ha, and 25 cm rows were the winner each time.”
When the yields of plots sown on 25 cm row spacing were compared to those planted on 100 cm row spacing, the yield benefit of the narrower configuration was anywhere between 13% and 45%.
“For example, at the highest yielding replicated site at Warra in the 2014/15 season, Jade-AU yielded 1.6 t/ha when planted at 100 cm, but 2.5 t/ ha at 25 cm. When mungbeans are worth almost $1000/t that represents a potential benefit of $900/ha just from planting on narrower rows,” said Mr McKenzie. “Even at the lowest yielding site the benefit of narrower rows was worth $50/ ha.”
Trials were also conducted in the Emerald area by Doug Sands (DAF) and the effect of row spacing on yield was less consistent. Yield benefits of narrow rows were observed but the yield potential of the crop needed to be over 1 t/ha for the difference to be statistically relevant.
The reasons why the narrow rows yielded more centred around better light interception and better access to stored soil moisture.
“By measuring sunlight interception we could see that plants grown on 25 cm rows had more energy to grow more biomass. These plants were also able explore more of the soil and extract more stored soil moisture – worth up to an additional 30 mm of stored moisture,” said Mr McKenzie.
“Mungbeans produce about 8 kg of grain per mm of moisture per hectare, so extracting an additional 30 mm can support the production of 0.25 t/ha more grain,” he said. “This goes against the idea that wider rows allow for soil moisture to be saved for later in the season, if this was the case the wider rows would yield better in the low potential years, but this theory doesn’t seem to hold true for pulse crops.”
In addition to the yield benefit, crops on narrower rows can fix more atmospheric nitrogen, potentially leaving more soil nitrogen for following crops, and the stronger crop competition reduces weed biomass and the number of weed seeds set.
More information: www.mungbean.org.au
Mungbeans planted at 25 cm row spacing can yield 13 and 45% more than mungbeans planted in rows 1 m apart. Photo: Kerry McKenzie