Over recent years maize has been successfully grown in north Queensland for grain and silage.
Maize has a number of features that make it well suited to north Queensland, including:
- high rainfall requirement
- cheap weed control options
- few pest and disease problems
- can tolerate rain at harvest
- a growing market in the north with the expansion of feedlots
Maize is not an ideal break crop for sugarcane because both crops belong to the grass family, which hosts root lesion nematodes. However, while high numbers of nematodes are found in the soil after maize crops, the following planted sugarcane crops have been surprisingly good. In southern regions, some growers harvest sugarcane early, plant maize in the winter and then plant a legume over the summer before returning to sugarcane.
Marketing
Maize is grown mainly for the domestic market, either as grain for feed mixes or silage in areas close to dairies and feedlots. Markets need to be close to the area of production as transport costs can be prohibitive. Growers also need to consider the availability of harvesters in their area for both grain and silage.
Identifying a market for the grain or silage prior to growing the crop is essential so appropriate management decisions can be made regarding variety, planting and harvesting times. Most grain buyers insist on pre-delivery contracts with a pre-determined price. Crops have yielded around 5 t/ha of grain but there is potential to yield to be as high as 8 t/ha. Prices vary, around $240 - $300/t, depending on the supply at different times of the year. Sourcing a harvester with a front suited to your row spacing prior to planting is a sensible precaution.
Selling maize for silage is less common but prices vary from $30 - $35/t fresh weight, at 60 - 70% moisture. Yields of silage chop range from 30 - 60 t/ha. To estimate silage yield, use this rule as a guide:
- tonnes of silage chop/ha = estimated grain yield (t/ha) x 6.
Varieties
Summer maize crops
There are many varieties of maize but only a few are suited to tropical conditions. In 2004, the varieties QX6, QX8 and 31H50 were all grown successfully. The QX varieties have been superseded by AT1 and AT2 and there are even better hybrids in the pipeline. Varieties with good tight husk cover will help prevent grain damage, such as sprouting and rots, if there is rainy weather leading up to harvest. Check with your local supplier for suitable tropical varieties.
Winter maize crops
More temperate varieties can be grown during the winter in the tropics. In 2008 nine varieties were planted in replicated trials at Silkwood, near Innisfail. One block was planted in mid-June and another in mid-August, the second having irrigation. At the time of writing, the crops are looking good and yield data will be published after harvest in November-December.
Paddock selection and land preparation
Maize will not tolerate waterlogged or saline soils. For summer cropping, avoid low-lying areas and soils that have poor drainage. Clay soils with good levels of stored moisture are best for rain-fed winter crops.
Being large seeded, maize does not need a fine seedbed. However, large clods will reduce the effectiveness of pre-emergent residual herbicides. Maize can be zero-tilled into cane trash, avoiding cultivation prior to the wet season.
The row spacing needs to match the harvester front and it may be necessary to remove compaction with a ripper where a maize row coincides with an old sugarcane inter-row.
Planting time
Summer
Summer Maize
The traditional time to plant summer maize is December, but experience has shown that December-planted crops on the coast mature in the wet season and are susceptible to weather damage such as sprouting and rotting.
Crops planted in January are less susceptible to weather damage because the cobs are still immature during the wetter months. However, cultivation in January is unwise as it leaves the soil prone to erosion, so zero-tillage techniques are recommended. Planting a summer crop fits in well with the sugarcane system as the crop will be harvested around June in time for planting cane again.
Winter
A winter crop of maize can be planted as soon as the wet season has finished if the paddock has been fallowed over the summer (ideally with a legume). A May-planted crop will be harvested around October which is considered late for sugarcane planting. It is possible to cut the fallow paddock in the first round, plant maize in June and harvest the maize in November. A legume crop can then be planted through the summer.
Planting depth and row spacing
Maize is planted with a row crop planter into moisture at a depth of 5 - 8 cm.
Row spacing depends on the spacing on the harvester front. Most harvesters on the Atherton Tablelands are on 900 mm spacing but there are 750 mm spaced fronts available.
Planting rate
Aim to get 50,000 - 60,000 plants established per ha. The planting rate needs to take into account the seed size, germination rate and expected field emergence. A summer crop could have a slightly higher plant population due to good moisture, while a lower population is recommended for the drier winter period.
Use the following formula to calculate planting rate:
- Planting rate (kg/ha) = 50,000 / 3,000 seeds/kg / 0.85 (germ rate %) / 0.90 (emergence %) = 21.7 kg seed/ha
Crop nutrition
Good nutrition is important for good yields of high quality grain. Big crops need large quantities of nitrogen, phosphorus and potassium. A soil test is recommended to help in calculating the fertiliser rate.
- Acidity: maize grows best in soils with a pH of 5.6 - 7.5. If the pH is less than 5, apply lime.
- Nitrogen: as a rule 130 - 180 kg N/ha. If a winter crop is planted after a summer legume the nitrogen rate can be reduced.
- Phosphorus: as a rule 0 - 35 kg/ha. Many sugarcane soils are high in phosphorus and may not need any to be applied.
- Potassium: sugarcane soils are commonly low in exchangeable potassium. If the soil test is low, an application of 50 kg potassium/ha is recommended.
- Trace elements: if the soil test shows deficiencies, these should be rectified.
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