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• Spring plantings
• Late plantings
• Plant population
• Calculating planting rate
• Seed quality/varietal purity
• Germination
• Row spacing and planter configuration
• Controlled traffic systems
• Seed placement depth
• Inoculum - Group I (Cowpea and Mungbean)

Mungbean varieties should be clearly separated at planting. Varietal mixtures are unacceptable in the markets for cooking and sprouting grade beans, and will usually attract substantial discounts. Unless harvest equipment and storage facilities can be thoroughly cleaned, restrict planting to one variety. The importance of achieving an even strike and even maturity cannot be over-emphasised for mungbean. Taking extra care at planting can produce more uniform flowering, making insect management and harvesting more straightforward.

To achieve a better quality sample and higher returns growers should:

• avoid paddocks with major changes in soil types which can result in uneven maturity
• avoid sowing wheel tracks which could result in staggered germination
• avoid paddocks with a rough seedbed or stones
• employ rolling or 'prickle chaining' on non-crusting soils as it helps level the surface and promotes more even emergence and maturity
• ensure an even planting depth right across the machine, particularly with air seeders
• avoid sowing mungbean if soil moisture levels are marginal, and likely to result in a patchy strike or staggered germination
• avoid seed lines with high levels of hard seed (dormant seed), which can result in an uneven, staggered germination.

Varietal selection is particularly important when planting outside the preferred planting window.

Spring plantings

Spring planted mungbeans can produce reasonable yields provided that specific attention is paid to:

• stored soil moisture levels at planting (at least 90 cm wet soil)
• management of thrips on seedling plants
• control of mirids at flowering
• desiccation prior to harvest
• increased weed pressure in spring plant situations.

The most consistent results with spring plantings in southern Queensland have been achieved with late September/early October plantings in situations with at least 90 cm of stored soil water.

Late October/November plantings are considered a riskier proposition because of the increased risk of experiencing dry, heatwave conditions on the emerging seedlings and on plants at flowering.

Crystal is suited to early plantings in spring because it is less susceptible to weather damage at harvest, and matures more evenly than other varieties. 

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Late plantings

Crystal and Satin II are preferred for late plantings because they have a degree of resistance to powdery mildew.

Late planting usually results in lower yields, as the crop often flowers around 35 days after planting, and the small plants fail to achieve canopy closure. If planting on narrower rows, increase the seeding rate by 5 kg/ha for plantings made after mid January. This helps compensate for smaller plant size.

Plant population

Dryland 200,000-300,000 plants/ha.
Irrigated 300,000-400,000 plants/ha.

Target population of 20-30 plants per square metre should be planned for when setting up your planter. Lodging can be a problem when plant populations exceed 40 plants/square metre, especially on wider row spacings.

If the emerged plant population is less than 10 plants per square metre, consider resowing.

Thin crops are short, yield poorly, mature unevenly, and can be extremely difficult to pick up at harvest.

Target populations on one metre wide rows are ideally 20-30 plants per square metre. Higher populations than this will increase the risk of lodging, especially under irrigation.

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Calculating planting rate

For example

Seed quality/varietal purity

Varietal purity is essential, as mixtures are unacceptable in both the sprouting and cooking trade. Mixed seed lines will often attract heavy discounts purely on their visual appearance. This particularly applies to contamination with varieties like Satin II, with its dull seed coat giving the appearance of weather damage in the sample. Mixtures can also create problems by germinating unevenly (consideration for sprouting beans).

The quality of seed retained on-farm can deteriorate over two to three years due to genetic drift. These seed samples often look uneven and may have a large proportion of dull blue-green seeds mixed with shiny seeds.

Replace planting seed every two to three years. Grower-kept and older seed stocks have poorer emergence than seed from the AMA Approved Seed Scheme.

See Figure 1 - AMA Accredited mungbean seed produced highest levels of emergence in comparative trials

Only purchase seed that is clearly labelled and has been inspected for disease, such as Australian Mungbean Association (AMA) Approved Seed. Resellers of this seed are available from the AMA website.

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Germination

All seed offered for sale in Queensland must clearly state the germination percentage and purity of that seed line. Seed with a high germination of around 80-90% is preferred. Growers need to be aware that hard seed levels (dormant seed) may be included in the germination percentage stated on the label.

Crystal has low levels of hard seed however Emerald and Green Diamond can contain hard seed levels as high as 70%. High levels of hard seed can result in uneven germination and establishment. This will complicate insect and harvest management decisions, and can dramatically reduce the financial return. Hard seeds planted into marginal moisture may not germinate until the next in-crop rainfall event after planting.

Hard seeded lines should also be avoided for the same reason  on lighter soils in western areas. The seed zone can dry out rapidly at planting time, with hard seed failing to germinate until there is follow-up rain.

The hard seed level of Emerald and Green Diamond should aways be checked before planting. The level of hard seeds (by test) should be kept to a minimum. Above 20% hard seed is not advisable for use as planting seed. It is important to remember that hard seed levels may change over time, so any formal seed test should be carried out as close as practical to planting time.

Seed retained on-farm for planting purposes should be heavily graded to remove small seeds, and any cracked or broken grain. Seed from the AMA Approved Seed Scheme generates higher plant populations than ungraded, grower-kept seed.

Row spacing and planter configuration

Mungbeans have been successfully grown using a wide range of planting equipment and row spacings ranging from 18 cm to 1 metre.

The available planting equipment at the time and farm layout will largely influence the final decision on the row spacing and planting configuration.

The recent trend is toward an increasingly higher percentage of the mungbean crop being grown in wider rows of 50-100 cm.

This is mainly due to the greater number of row crop planters now available, controlled traffic and the adoption of shielded and band spraying. Band spraying enables major input costs such as insecticides to be kept to a minimum. Wider row spacings also allows for the greater use of ground rigs for pesticide application and gives the grower greater control of when insecticides are being applied to their crop. High temperature application (above 28° C) is now widely recognised as one of the major causes of insecticide spray failures in summer crops.

Before growers make the final decision, they need to carefully weigh up the relative advantages of both wide and narrow row production systems.

Wide rows (50-100 cm)

• Greater ability to plant into heavy stubble cover (zero-till situations).
• Row-crop planters often provide more accurate seed placement, resulting in better establishment and more even plant stands. This can often result in more even crop maturity.
• Harvestibility - plants grow taller with a higher pod set as a result of 'within row' plant competition.
• In low yield situations, crops planted on wide rows often feed in better over the knife section due to the concentration of growth within the row.
• Input costs can by reduced by band-spraying insecticides and defoliants.
• Ability to control weeds relatively cheaply using glyphosate through shielded spraying equipment.
• Easier access for ground-spraying pesticides and desiccants.
• Under severe moisture stress conditions, the combination of wide rows and heavy stubble cover have often been observed to yield better than narrow rows.
• Easier access when checking for insects (beat cloth).

Narrow rows (15-40 cm)

• Potential yield benefit as yields increase above 1 t/ha.
• Yield margin gradually increases to 10-15% in favour of the narrow rows as yield potential approaches 2 t/ha.
• Quicker ground cover provides better suppression of weeds.
• Nitrogen fixation rates can be 15-30% higher on narrow rows.

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Seed placement depth

Plant into moisture at a depth of 30-50 mm. Do not use presswheels that exert heavy pressure directly over the row. Ideally use wide, zero-pressure wheels.

Rolling can be useful as it helps level the entire surface, and can significantly help the harvesting operation.

Inoculum - Group I (Cowpea and Mungbean)

Inoculation is essential if nodulation problems are to be avoided. Poor nodulation is a common problem in mungbeans and can result in a significant yield reduction (up to 50%) in situations where residual nitrogen levels in the soil profile are already low (i.e. double crop situations). Growers are urged to pay greater attention to inoculation practices if these problems are to be avoided.

Mungbeans are an introduced species and require the correct strain of nitrogen fixing bacteria in order to effectively fix nitrogen (the commercially available strain is CB1015).

A survey of commercial mungbean crops conducted by DEEDI in 2004-05 indicated that only 50% of crops nodulated with the applied strain and that effectiveness of this nodule occupancy was highly variable (from 0-85%). Mungbeans will nodulate with a range of native soil bacteria but the effectiveness of nitrogen fixation under these circumstances is not yet known. The most effective method of ensuring nodulation with the applied strain of inoculum is to deliver the highest possible concentration of live cultures on to the seed and sow as quickly as possible.

DEEDI field trials have found water injection to be the most effective means of delivering inoculum, producing higher levels of nodule occupancy than slurry methods and uninoculated controls. However water injection will likely require modification to planting equipment and water volumes may be unsuitable for larger areas.

• See Figure 2 - Water injection produced the highest levels of nodule occupancy by the applied rhizobium strain

The most common means of inoculating mungbeans is to coat the seed with a slurry of peat-based inoculum immediately prior to planting. New developments in inoculum delivery have resulted in products that offer easier handling and more convenient application methods.

Only inoculate seed that you can plant that day. Seed should ideally be planted into moisture immediately after inoculation to maximise nodulation. Avoid exposing recently inoculated seed to hot, drying winds, or direct sunlight as this rapidly kills the bacteria.