Planting times
In southern Queensland, mid-September to mid-October is the premium time. December provides another suitable opportunity, especially for dryland crops. In Moreton, maize is often successfully planted as early as mid- August. Latest plantings in these areas would occur in early to mid-January, due to likelihood of disease development in late summer/autumn.
A minimum soil temperature of 12° C is needed at seed depth before attempting sowing in mid-September. Cold conditions after establishment will slow the growth of seedling maize, often causing it´s foliage to turn purple. This is probably due to reduced phosphorus availability at lower soil temperatures. However, once temperatures begin to rise again, the crop continues to grow normally. Planting at this time will avoid flowering in mid- summer heat.
December plantings flower after mid-summer heat but may be more susceptible to diseases such as rust, leaf blights and wallaby ear, and perhaps fusarium kernel rots.
Hot, dry weather can kill pollen as it is shed from the tassel, or induce uneven flowering. For example, silk emergence from the cob may be delayed and occur when pollen is no longer being shed from the tassel, resulting in poor seed set on the tip of the ear.
In central Queensland, some waxy and grit maize is planted in mid-August to early September, especially under irrigation. However, the main crop is planted late January to first week in March, to avoid heat stress which can reduce pollen viability at flowering time.
In far north Queensland, irrigated maize is planted in late July to August. Later plantings occur in late November to late January, with the optimum time being mid-December. Successful plantings have been made in late February, but these are the exception, and this time is not recommended.
- Optimal planting time
- Preferred planting time
- d - Higher disease risk
- r - Suitable for raingrown (dryland) crops
- i - Satisfactory under irrigation
- * - Late planting not recommended
- h - High risk of heat stress during flowering
Planting preparation
Soil type
Maize will grow on a wide range of soil types, providing they are well drained. A pH range of 5 - 8 can be tolerated but best growth is achieved in the range of pH 5.6 - 7.5.
Maize does not grow well in saline soils. Yield reductions of 10 - 20+ percent can be experienced if soil extracts contain 2.0 - 4.0 dS/m respectively. Yield decline is likely if irrigation water has a reading of more than 1.5 dS/m. Seedling and flower growth is most sensitive to salinity.
Soil temperature
Soil temperature at planting depth (5-7.5 cm) at 9:00 am should be 12°C or higher, and have been on an upward trend for three or more days.
While seed will germinate at 12°C, growth is often slow and foliage develops a purple colour. Temperatures of 15°C + are safer and result in better growth.
Planting moisture requirement
Dryland maize should be planted on a full soil moisture profile. Irrigated crops should be irrigated pre-plant and then if using flood irrigation not watered until 6 weeks old (pre-tasselling). If conditions are hot and dry, a quick flush 2 - 3 weeks after emergence may be required.
Maize is not tolerant of waterlogging especially during seedling and flowering stages.
Seed details
Seed has both size and shape gradings. Size varies from 4400 seed/kg (small) to 2500 seed/kg (large).
Seed shape consists of rounds or flats. Flat seed is generally best in plate seeders, while round seed is preferred by air seeders. There is no difference between the crops produced by these seed shapes.
Information on the germination percentage and the date the test was conducted should also be with the bag.
Planting time
There is some variation in planting times throughout Queensland.
Plant populations
Recommended plant populations vary between regions.
Region
’000 plants/ha
Note: This table is a guide only. The recommended population for a specific variety should be obtained from the respective seed company. If growing for silage, use the higher population ranges.
Approximate number seeds/kg
Seed size varies from 4,400 (small) to 2,500 (large). Seed is separated into round and flat grades. Refer to bag for an exact seed count.
Planting rate
The following table shows planting rates (kg/ha) for various seed sizes when using 90 cm row spacing. Average seeding rates based on 85% germination rate and 100% emergence rate.
Should different spacing be used between rows, the following calculation can be used:
Planting rate = desired population divided by (seeds/kg x germination% x emergence%)
- Planting rate = seed planted (kg/ha)
- Desired population = number of plants per hectare (e.g. 40 000)
- Seeds/kg = indicated on the seed pack (e.g. 3000)
- Germination % = indicated on the seed pack (expressed as a decimal e.g. 85% is 0.85)
- Emergence % = e.g. 90%
Working example:
Planting rate (kg/ha) = 40 000 / 3000 x 0.85 x 0.90
Planting rate = 17 kg seeds/ha
A ready-reckoner to obtain emergence percentage (%)
- Precision planters 60 - 90%
- Other planters with press wheels 50 - 70%
- Other planters with no press wheels 30 - 50%
- Or use a figure from your own experience.
Calculating seed spacing along the row
This calculation is used to calibrate the seed drill to sow at the required rate:
Distance between seeds in the row (m) = 10 000 / planting rate (kg/ha) x seeds/kg x row width (m)
Working example:
Distance between seeds in the row (m) = 10 000 / 17 x 3 000 x 0.9
Distance between seeds in the row = 0.21 m (or 21 cm)
Row spacing
Row spacing may vary with machinery used, but 75 - 91cm is usually acceptable. The rows should match the harvester width.
Seed placement depth
50 to 75 mm into moisture. Plant deep enough to allow roots to develop in moist soil and grow down into subsoil moisture ahead of the drying front.
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Evenness of establishment
Precision planters give more even plant spacing in the row. It is important to avoid seed bounce in seed tubes and in seed furrows to avoid gaps and thick patches in a row. Uneven plant establishment and uneven plant spacing both effect grain size and yield severely. This is more critical for gritting corn than for feed corn.
Further information
Growing maize in the coastal Wet Tropics
