Nodulation and nitrogen-fixing data at the mungbean trial sites has reaffirmed the value of mungbean in low-soil-nitrogen situations. All mungbean varieties accumulated more nitrogen when planted in narrower rows, except Satin 2, which appears to compensate for the wider rows.
PHOTO: Queensland DAF
With two seasons of field trial data now analysed, Queensland Department of Agriculture and Fisheries (DAF) agronomist Kerry McKenzie says with some confidence that planting mungbean crops on narrower row-spacings supports higher yields, even if plant populations remain the same.
Mr McKenzie says the GRDC-funded pulse agronomy project led by the Queensland Alliance for Agriculture and Food Innovation (QAAFI), in partnership with Queensland DAF, at four trial sites in Queensland has demonstrated how agronomic decisions at planting influence crop yield and nitrogen fixation.
“A 10 per cent yield increase is worth about $75 per hectare based on long-term mungbean pricing, which is $3 million more in growers’ pockets if it were achieved across the sown area.”
Although seasonal conditions will continue to be the main determinant of crop performance, with yields twice as high in 2014-15 compared with 2013-14, the right row spacing, plant population and soil nitrogen can all improve the likely outcome regardless of the season.
“There were Queensland trials at Dalby and Warra for the past two mungbean seasons and at Billa Billa and Miles for the 2014-15 season only, providing crop data from a wide range of soil types and environmental conditions,” Mr McKenzie says.
“There appears to be little difference in variety performance at each row spacing, with all varieties performing as well or better at 0.5 or 0.25-metre spacings rather than the traditional summer crop spacing of 1m.
“Growers are likely to see a benefit if they plant mungbean at 0.5m or less; however, that doesn’t mean they need to spend more on seed,” he says. “Plant population per square metre did not greatly influence yield, so the standard 20 to 30 plants/m2 remains the recommendation.”
Mr McKenzie says the data indicates that the improved yield from a narrower row is most likely due to improved water use efficiency, with the plant roots able to reach the stored moisture between the rows and the larger crop canopy intercepting more light energy.
“Knowing that the population density of 20 to 30 plants/m2 is adequate for maximum yield, growers will need to consider replanting if less than 10 plants/m2 are established,” he says.
Another benefit of growing robust, high-biomass crops is the increase in atmospheric nitrogen fixed. Queensland DAF senior soil microbiologist Dr Nikki Seymour has collected nodulation and nitrogen-fixing data at the mungbean trial sites and reaffirms the value of the crop in low-soil-nitrogen situations.
“Well inoculated and nodulated mungbean crops can improve the nitrogen efficiency of the rotation provided there is not a high level of nitrogen already in the soil, such as residual fertiliser from a previous crop or mineralisation after a long fallow,” she says.
“In high-nitrogen situations it is usually better to plant a non-legume crop to make the best use of the available nitrogen.”
All mungbean varieties accumulated more nitrogen when planted in narrower rows except Satin 2, which appears to compensate for wider rows.
In a separate project, Dr Seymour is screening new mungbean germplasm in the plant-breeding program to assess their genetic ability to fix nitrogen and their affinity with current rhizobia strains. She says that mungbean generally do not leave behind high levels of nitrogen compared with other legumes so the screening of germplasm in the breeding program will help plant breeders when they are selecting for a variety of desirable traits, including increased nitrogen fixation.
The market outlook for Australian mungbean continues to be positive and interest is growing for spring planting in late September and early October.
Damien White, vice-president of the Australian Mungbean Association, says mungbean is the fastest maturing of the summer crop options, with very high water use efficiency: “In a dry year this could make mungbeans the crop to offer the lowest risk and highest potential return to growers.”
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