Everything you need to learn about maize cultivation in Australia:- 1. Introduction to Maize 2. Botany of Maize 3. Soil 4. Climate 5. Harvesting 6. Varieties 7. Management 8. Marketing.
Introduction to Maize:
Wild maize was first gathered and sown by the ancient Inca tribes of Peru. From there it was taken to Central America where the Aztecs cultivated it. Indian tribes later spread the plant over North America and the islands of the Caribbean Sea, where it was first seen by Europeans. Maize is now one of the chief food plants of the world, and is grown in many parts of Europe, Asia, and the Americas.
Although maize is grown on 5000 New South Wales farms, and many in Victoria and Queensland, it is only the tenth most important Australian crop. The grain is either fed to sheep or pigs, or is used in the manufacture of breakfast foods.
Some maize is grown for silage. Most maize grown is of the dent kind, the grains shrinking in at the top when dry. Sweet corn has grains with no hard layer on the outside, and the drying grain shrinks and wrinkles. Popcorn has small cobs with small pointed grains.
Botany of Maize:
Maize is a giant grass and belongs to the family Gramineae. It is an annual and has separate male and female flowers. The stalks or culms are almost straight and possess joints or nodes separated by long internodes. Look at Figure 26.1 and notice how the nodes are far apart in the middle of the stalk, but are closer together at the top.
Lower down the internodes are grooved on alternate sides, and a bud is found where a groove meets a node. The buds on the centre part of the stalk may develop into ear or cob shoots, while the stem buds below ground may develop into tillers. The stalks should stand erect, for if they lean over or lodge, machinery harvesting may be difficult.
A lean of 30 degrees is counted as lodging, but the stalks of hybrid varieties are stronger than those of the old open-pollinated varieties. Green stalks may contain 8 per cent sugar, but as the grain forms the sugar disappears.
Maize leaves have a lamina or blade, a sheath wrapping around the stem, and at the junction of the blade and sheath the ligules and auricles are found. The upper surface of the lamina is hairy and has few stomates, but the lower surface is smooth with many stomates.
The number of leaves is constant for any variety and indicates the length of the growing season. Fast-growing varieties have few leaves. Leaf numbers vary from 8 to 48, but most varieties have leaf numbers of 10 to 27. The average maize grown in New South Wales has 18 leaves.
Maize roots are of three kinds – Seminal or seed roots arise from the germinating grain. Crown roots arise from the first 7 or 8 stem nodes below the ground level, and are the chief feeding roots of the plant. Brace, prop, or stilt roots arise from the first few nodes above ground, and serve to hold up the stalks. The roots usually spread sideways 1 to 2 m from the base of the plant, and this lateral spread occurs early in the life of the plant.
The last cultivations between the rows should therefore be shallow so that these roots are not pruned off. Later root growth is in depth, and roots often go down 2 to 3 m in alluvial soils. The size of the root system keeps pace with the tops, so that stunted top growth means poorly developed roots and less ability to withstand drought.
The number of primary lateral roots developed on the main fibrous roots depends on the amount of water in the soil. In dry soils there may be as many as 9 primary laterals per cm of root length, whereas in irrigated soils the number may be as low as 4 per centimetre.
1. The tassel consists of the male flowers growing at the top of the stalk. Each group of flowers is called a spikelet, and the spikelets are in pairs, one sessile and the other stalked. Each spikelet contains two florets, and each floret encloses three stamens. The average tassel makes 4 500 000 pollen grains which are so light that they are carried by the wind to the silks of the cob on another plant. Maize is usually highly cross-pollinated.
2. The ear or cob is produced by one of the buds on the centre portion of the stalk. This bud grows into a short side branch with the nodes very much compressed. From the lower nodes of this branch arise leaf-like structures which are called the husk, and they grow up around the cob. The end of this side branch forms the core of the cob, on which 500-1000 ovaries grow. Each ovary has a long silk attached to it, and the silk grows and protrudes from the open end of the husk.
Hot dry weather hastens the ripening and shedding of pollen, but cold weather retards it. On the other hand, hot dry weather delays the growth of the silks from the husks. Pollen shedding usually begins first but overlaps silk development. Now the silks from the middle and lower third of the cob are the first to emerge and be pollinated, those from the tip emerging last.
Therefore a spell of hot dry weather may speed up pollen shedding and so delay silk growth that there is no living pollen left to fertilise the silks from the tip of the cob. Poorly filled cobs will be the result. This is why maize growers say that the two most important periods for rain are after sowing (for germination and early growth) and tasselling (for a good set of grain).
When a pollen grain lodges on a silk, it germinates and makes a pollen tube in less than a quarter of an hour. This tube then enters the central core of the silk. It takes from 15 to 36 hours for the pollen tube to grow right down the silk, reach the ovary, and fertilise it.
The grain stops growing 45 days after fertilisation, but it continues to change as follows:
1. The sugar in the endosperm changes into starch. This change is very rapid in hot weather, and farmers growing sweet corn must have the crop ripening at intervals. They must harvest quickly or the grains will lose their sweetness.
2. The grain dries out and shrinks in at the dent.
3. Proteins are stored under the skin.
Soil Required for Maize Cultivation:
Soil water and soil nitrogen are two chief soil needs for high maize production. Therefore unless a soil is naturally rich, water and nitrogen must be conserved in it by good management. The growing of legumes is the best way of building up soil nitrogen, and in every case of high maize yields it will be found that a legume rotation has been used, and perhaps fertilisers added as well.
Weeds are the chief enemy of maize, so they must be removed either by good cultivation or by the use of weed-killing chemical sprays.
Deep alluvial soils of the tablelands and slopes are ideal for maize. Alluvial soils of the coast may be leached of nutrients, and may need care to bring them to a high state of fertility. In cold districts light sandy soils may be best for maize because they heat up quickly in spring.
Climate Required for Growing Maize:
Maize likes a summer climate which has bright sunshine, short days, and long warm nights. We must first consider the effect of temperature. When maize is a few cm high it will stand a light frost, but once it grows up frost will kill it. A week of temperatures below 7°C but above freezing point will often kill maize. It will not germinate or grow below a temperature of 10°C.
Most American maize is grown where the average summer temperature is between 21°C and 27°C, and the average night temperature is 14°C. In places where the average night temperature is 13°C—that is, only 1°C below 14°C—not much maize is grown.
This shows how very important a high night temperature is to maize. In parts of the highlands of Victoria and New South Wales, the night temperatures are often too low, and for this reason, maize should not be planted in cold deep valleys in those districts.
Maize needs a lot of water for its growth, and most American maize is grown in areas receiving more than 660 mm per annum. More rain is needed in hotter and lower areas than in colder higher areas.
Rain is especially needed in spring and at tasselling time. Lack of water is the chief factor which limits the growth of maize in Australia, and production could be greatly increased with the use of irrigation.
The length of the summer days influences the growth of maize. If the days are short, maize will set seed more quickly than if the days are long. If a maize variety from Queensland where summer days are short is taken to Tasmania and grown there, it will make bigger stalk and leaf growth, but will take longer to mature. This means that early-maturing varieties will do better in southern areas, and later-maturing varieties better in northern areas of Australia.
Harvesting of Maize:
Maize grain must be properly dry before being harvested, or it will not keep. In wet autumns, cobs often take a long time to dry out especially if the husk covering is tight. They are often left in the field and not harvested until winter.
The danger in this practice is that frosts may kill the seed embryos, but this is not important unless the grain is to be used as seed. In the days of the open-pollinated varieties, maize was harvested by hand pulling, but most high-producing crops of hybrid maize are now harvested by corn pickers owned by harvesting contractors.
Varieties of Maize:
There were once more than 1000 varieties of open-pollinated maize. So few of these older varieties are grown now that it is difficult to collect samples of them. Maize is commonly cross-fertilised, the pollen from the tassel of one plant drifting in the air and falling on the silks of another plant. If the pollen from one plant is made to fertilise the silks on that same plant, the maize is said to be self-fertilised or inbred.
Early in the century, Shull and East in America found that when maize was inbred year after year, the plants showed less vigour and produced many different strains. These inbred strains became pure and bred true to type. They then found that if two of these inbreeds were crossed, a very vigorous plant or hybrid was produced. However this seed could not be used by farmers because too little of it was produced.
Then in 1917, Jones, an American agronomist, showed that seed could be multiplied by starting from four inbreeds instead of two, and by making a second or double cross. At present, hybrid maize seed is produced at Grafton Research Station, at Gatton Agricultural College, and by some private companies. Late-maturing hybrids are made at Grafton.
The advantages of maize hybrids are a higher yield and a more even growth of plants. The stalks are also stronger.
On the coast, late-maturing hybrids are grown to take advantage of the long frost-free season. GH 128 is the most popular of the late-maturing hybrids. It has a tight husk that resists weevils but makes the grain slow to dry.
The grain is deep and a dark yellow colour. GH 390 is a hybrid similar to GH 128. It is tall and the ears are set high on the stalks. It has good resistance to disease, including maize dwarf mosaic disease.
PX 48 is one of the popular early-maturing hybrids grown on the tablelands. The ears are set high on the stalks and it has an open husk. Some of the hybrids produced by the De Kalb-Shand Seed Company are very popular. The hybrid XL 81 is very uniform in growth. The De Kalb hybrids XL 45, XL 66 and XL 361 are also very popular and mature in about five months.
Hybrid varieties of popcorn, sweet corn, and white dent corn have also been produced. Sweet corn is very early in maturing and does not grow very high. The cobs must be harvested while the sugar content of the grain is still high.
Popcorn varieties are also very early in maturing, but the yield is low because of the small size of the cobs. Popcorn must be properly dry before being harvested.
General Management of Maize Cultivation:
Successful maize growing requires careful planning. The first step in the plan is to build up soil nitrogen by growing a legume crop. On the table-lands one of the clovers might be used since they can also be grazed off, but on the coast the choice might be cowpeas. The second part of the plan is the conserving of soil water.
The high rainfall in coastal areas means that enough water can be taken into the soil in a short time. On the tablelands the soil must be left in a rough open condition to allow as much winter rain as possible to enter the soil. Along the inland streams where maize is irrigated, the need for conserving rainfall is not so important.
The choice of implements used in preparing a seed bed will vary with the soil and climate. However it is never a good idea to work the soil down to too fine a state, as this only makes it easier for weed seeds to germinate.
Maize has a large grain and it will germinate quite well in a rough seed bed. The time to sow is when the danger of spring frosts has passed. On the coast sowing may be done in August, but on the tablelands it is unwise to sow before the third week in October.
Seed is usually sown with a two-row drill in a direction at right angles to the last cultivation. It is important for many reasons that the rows be kept straight, latitude of only 5 to 7 cm being allowed. Otherwise it is too hard to cultivate between rows to kill weeds.
The two halves of the drill wheels press the seed furrows together and close them after sowing. The seed is sown at 5 to 10 cm depth and germinates in 5 to 7 days.
The rate of sowing varies with the soil fertility and how much water has been saved in the soil. On poor dry soils each plant must be given more room. On rich soils which have enough water, a population of 29 000 plants per hectare is the aim. This means sowing the rows 106 cm apart, and the seeds 25 to 30 cm apart in the rows.
When these plants grow up, their leaves will shade the ground between the rows and so help to keep the weed growth down. Weeds are hard to control if the checkerboard system of sowing is used. If chemical weedicides have not been used there will be a greater need for weed control by cultivation.
The first cultivation should be done when the plants are 30 cm high, and tines with wide weed-cutting points are used. The second cultivation is done either when the plants are 70 cm high, or after storm rains.
This time penetrating tines are used along the centre of the rows only. If the plants are 90 cm high at the second cultivation, the work is not commenced until after 10 a.m. when the stalks are suppler. Special steps may have to be taken if boil smut disease is a problem in the district.
Maize is a greedy feeder, and takes more nitrogen and phosphorus out of soil than winter cereals. It is usual to apply superphosphate at the rate of 250 kg per hectare on the coast, and 125 to 188 kg per hectare on the tablelands. Ammonium sulphate added as a side dressing during growth increases yields, but it is not used much because it is costly.
Marketing of Maize:
Harvested cobs must be shelled, and the grain bagged before being marketed. The price of shelled corn varies from season to season, and over the last five years has varied from about $90 to $125 per tonne.
Since the price of hybrid seed is usually around $35 per 25 kg bag and the costs of cultivation are high, growing maize for grain is not profitable unless the price is high enough. In 1979 a price of $80 per tonne was necessary.