As a general guide, use the maturity group ratings to choose a variety suitable for a summer planting in your region:
- north Queensland - groups 8 and 9
- central Queensland - groups 7 and 8
- southern Queensland - groups 5, 6 and 7
Recommendations for inland regions
In the inland regions of Queensland, soybeans are generally grown for grain. They are also a valuable forage crop. December is the preferred planting time in southern Queensland.
In some situations the planting period may extend from mid-November to mid-January. For central Queensland, mid to slow-maturing types are the most suitable. Crops planted in mid-December mature from 115-125 days.
Because most soybeans flower in response to shortening day length, early plantings will take longer to flower whereas late sowings will mature faster as the day length shortens. To avoid problems with excessive vegetative growth from early plantings, earlier maturity varieties such as Soya 791 are the best choice. Conversely, late maturing varieties such as Stuart are a better option for late plantings because they will help extend the length of the vegetative phase which has a strong correlation with potential yield.
Avoid planting any variety after the third week in January otherwise growth, stature and crop yield are likely to be restricted. Leichhardt is the latest sowing option and will extend a couple of weeks longer in warmer situations but is not a preferred option in inland production areas.
Forage crops
Soybean crops are suitable for both green-chop and hay production. The best forage yields can be expected from early planted, long-season varieties, cut around the mid pod-fill stage. The preferred varieties for southern Queensland districts appear to be Warrigal, Jabiru and Oakey.
Soybean Seed, which come from the soybean pod.
Silage yields (at around 35% dry matter, cut at the milky-dough/pod-fill stage) expected from dryland soybeans range up to 25 t/ha. This equates to around 8 t/ha dry matter yield.
Remember that two-thirds of the fixed nitrogen is removed from the field if you cut the crop for hay or silage production.
Recommendations for coastal Queensland
In the coastal sugarcane regions of Queensland soybeans are grown for grain and as green manure crops. It is difficult to grow soybeans for grain successfully in the wet tropics due to the restrictions of the wet season on harvest.
In the wet tropics soybeans are grown specifically for green manure and to protect fallow paddocks from erosion. In coastal areas for the Burdekin to Beenleigh, farmers have the option of growing soybeans for both grain and green manure.
The slow-maturing Leichhardt and Stuart varieties are specially adapted to the tropical coastal areas from Mackay to Far North Queensland and are well suited to rotation with sugarcane. In coastal areas prone to waterlogging and hard-setting soils it is advantageous to plant into hills or beds. This practice promotes better seedling emergence and establishment.
Irrigation
Soybean crops will achieve maximum yield potential if they are free from moisture-stress throughout the season. Moisture is critical during crop establishment as hot, dry soil kills rhizobia and root nodules. Very hot conditions can also kill emerging seedlings. Experience has shown that many crops, particularly in the Burdekin, have failed to nodulate sufficiently (and thus grow to potential) because they did not receive sufficient irrigation when small.
Once the soybean plant is established it can tolerate minor moisture-stress without significant yield loss in the vegetative stages. However, to maximise yield potential, the crop should be maintained in relatively well-watered conditions. Yield potential in excess of 5 t/ha is common in crops with good plant populations that are maintained on a 60 mm or lower irrigation deficit. It is important to maintain irrigation into the grain-fill period to ensure seed size and to maximise yield.
For fully irrigated crops on heavier soils, schedule irrigations so that soil moisture deficient does not exceed 70 - 90 mm, usually two to three irrigations. Yields of 2.5 - 3.5 t/ha are normally realised with irrigated soybeans. In recent years, good crop husbandry practices under favourable seasonal conditions have seen some varieties return in excess of 5 - 6 t/ha.
Where sowing late or choosing varieties with a tendency to produce less vegetative growth, there may be some yield advantage in adopting narrower row spacing of 50 - 70 cm. In coastal soybean crops, many canefarmers irrigate in the same cycle as their cane and achieve good results as the peak moisture demand for cane in South East Queensland coincides with the peak demand for soybeans.
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