Mungbeans: Why 75mm of soil moisture matters
GROWERS considering planting mungbeans this summer are being urged to test soil moisture levels to ensure they have a minimum of 75mm of Plant Available Water (PAW).
Queensland Department of Agriculture and Fisheries senior extension agronomist Kerry McKenzie said ensuring paddocks had adequate stored soil water before planting was critical to mungbeans.
“The other critical agronomy consideration for growers planting mungbeans this summer is to opt for row spacings of 50cm or below to best utilise water and potentially maximise yields,” Mr McKenzie said.
“Getting the basics right for paddock selection and general agronomy is key to successful outcomes with this pulse crop.”
Mr McKenzie said the implementation of minimum row spacings had produced higher yields in both below average and above average seasons.
“This could be due to the larger crop canopy on narrow row spacings intercepting more light energy and reducing soil evaporation. We also suspect that narrow rows allows for greater soil exploration by roots and more efficient stored water extraction,” he said.
“Research has shown that reduced row spacings may also increase the amount of nitrogen fixation due to the increase in crop biomass production.
“Plant population has less influence on yield than row spacing, recommended plant populations for dryland are 25-30plants/m2, however if establishment is poor, a replant is recommended if there are less than an evenly spaced 10 plants/m2 ,” he said.
“But both row spacing and population are important and their effect on maximising yields in varied climates, along with improved varieties, is leading to greater grower confidence in mungbeans.
“However paddocks with less than 75mm of PAW will often produce unreliable or unprofitable crops. What we have found is most profitable crops are grown on blocks with high stored moisture from long fallow or early season rains.”
Ideally he said growers should have stored soil moisture available down to 75-80cm and selected paddocks should present no restrictions to rooting depth due to salt, sodicity, compaction or high bulk density.
He said mungbeans were extremely sensitive to salinity and sodicity, leading to poor root development, water extraction and reduced, variable yields.
Avoid soils with high exchangeable sodium percentages (above 14) in the top 10cm. Sodicity at depth has less of an impact on yield, but may restrict root development and water extraction. Saline soils with EC levels above 2 dS/m will cause yield reductions.
“Planting in paddocks with these soil constraints can also lead to uneven crop development and maturity which in turn can result in difficulties with desiccation and harvest,” he said.
Mr McKenzie also warned growers choosing mungbeans this summer to be wary of herbicide residues, and be confident any residual chemicals have had the appropriate time and rainfall to dissipate by the next mungbean plant back.
“The other consideration for northern pulse growers is to select a paddock with low soil nitrates to get the maximum amount of nitrogen fixation by the plant,” he said.
“If mungbeans are planted with high levels of soil nitrate, there will be a greater reliance by the plant on this soil nitrate and less nitrogen will be required to be fixed by rhizobia. This can actually lead to soil nitrate levels being depleted by the mungbean crop.”
Mr McKenzie said growers in Queensland and northern NSW were increasingly viewing mungbeans as a viable cropping option in farming systems, rather than a break crop for cereal dominated enterprises.
“As mungbean agronomy becomes better understood and growers are offered more robust varieties, we are seeing an increase in the number of growers planting this pulse,” he said.
Mungbean research is an initiative of the GRDC, Queensland Alliance for Agriculture and Food Innovation and DAF.