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Maize - Nutrition and irrigation
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Nutrition
Maize yield and quality is influenced by crop nutrition. Maize is responsive to fertiliser, especially nitrogen, phosphorus and potassium. High yielding maize crops require large quantities of soil nutrients. In a healthy maize crop, all the upper plant leaves and most of the lower leaves remain green until the crop is nearly mature. To ensure optimal use of fertilisers, it is recommended that a soil test be taken prior to planting.
pH
Maize grows best in soils with pH in the range of 5.6 - 7.5. Should the pH be less than 5, lime should be applied. Apply 3-6 months before planting. An alternative is to apply dolomite, which has a similar neutralising value to lime and applies magnesium.
Fertilisers
Nitrogen (N)
A rule of thumb for nitrogen application (kg/ha N) is:
| Dryland | Irrigated | |
|---|---|---|
| Atherton Tablelands | 0 - 80 | - |
| Wet tropical coast | 130 - 180 | |
| Central Queensland | 0 - 40 | 80 - 200 |
| Darling Downs* | 0 - 180 | 150 - 300 |
| Moreton | - | 100 - 200 |
| South Burnett | 0 - 50 | 80 - 200 |
* Maximum rate for growers aiming for a 7t/ha dryland crop or 10 t/ha irrigated crop from ground which has been cultivated for more than 25 years and has a history of summer crops (sorghum, maize, millet, sunflower, cotton) or double cropped with winter cereals.
Symptoms of nitrogen deficiency:
- the lower leaves are light green or yellowish, often V-shaped yellow area at tips of leaves
- there may be premature drying along the midrib and the leaf tips
- plants may be stunted and slow to flower
- ears are short and often poorly filled.
Phosphorus (P)
A rule of thumb for phosphorus application (kg/ha P) is:
| Dryland | Irrigated | |
|---|---|---|
| Atherton Tablelands | 0 - 35 | - |
| Wet tropical coast | 0 - 35 | |
| Central Queensland | 0 - 20 | 0 - 20 |
| Darling Downs | 9 - 15 | 0 - 15 |
| Moreton | - | 0 - 15 |
| South Burnett | 0 - 20 | 0 - 40 |
Symptoms of phosphorus deficiency:
- leaves have a purplish colour
- plants have stunted growth
- flowering is delayed
- root systems are poorly developed
- kernel size and number is reduced.
Potassium (K)
Soil testing and strip trials are recommended to help in the early detection of potassium deficiency. A rule of thumb for potassium application (kg/ha K) is:
| Dryland | Irrigated | |
|---|---|---|
| Atherton Tablelands | 0 - 50 | 0 - 50 |
| Wet tropical coast | 0 - 50 | |
| Central Queensland | 0 - 25 | 0 - 50 |
| Darling Downs | 0 - 50 | 0 - 50 |
| Moreton | - | 0 - 50 |
| South Burnett | 0 - 30 | 0 - 50 |
Symptoms of potassium deficiency:
- young plants have a scorched appearance on their outer leaf edges
- lower leaves show yellow to brown discolouration
- the crop has a greater tendency to lodge
- the crop has small ears that fail to fill at the tip.
Zinc (Zn)
Maize is susceptible to zinc deficiency. Zinc may be applied to soil or as foliar fertiliser.
- Soil application - Apply 30 kg/ha of zinc sulphate monohydrate or zinc oxide into the soil at least three months before planting. This may correct the deficiency for up to eight years.
- Foliar application - Apply 2-4 weeks after emergence. A second application may be required 2 weeks later. Apply 1-1.5 kg of zinc sulphate heptahydrate + an equal amount of urea in 100 L of water. Apply at a rate of 100 L/ha.
If the water is hard (i.e. with high carbonate levels - the water will turn cloudy as insoluble zinc carbonate is produced). Trickle sulphuric acid (e.g. battery acid) as the tank is filling. The rate is 50 mL/100 L. This will make the zinc available to plants.
Zinc heptahydrate is not compatible with all herbicides. Read zinc products and herbicide labels to ensure compatibility.
Other zinc-based products are available. If these are used follow the label directions.
Symptoms of zinc deficiency:
- light streaking followed by a broad whitish band, starting slightly in from the leaf edge and extending to the midrib
- leaf edges, midrib and tip remain green
- plants are stunted with short internodes
- new leaves are sometimes nearly whiteLeaf edges and stalks may have a purplish colour.
Sulphur (S)
Some soils on the Darling Downs (intensively farmed for more than 20 years), may show responses to sulphur. Usually, 8 - 10 kg/ha is adequate. Gypsum at a rate of 200-400 kg/ha every three years is the most economical form of sulphur.
Symptoms of sulphur deficiency:
- young plants are pale green or yellow with only limited stunting
- in older plants, the upper leaves are pale green-yellow with the lower leaves remaining green (this is the opposite to what occurs with nitrogen deficiency).
Molybdenum (Mo)
Seed normally has sufficient molybdenum, although occasionally deficiencies can occur in acid soils, especially those which are highly leached. Molybdenum deficiency can be treated with a foliar spray of 300g/ha sodium molybdate. This is applied when there is sufficient leaf area (e.g. 30 days after planting).
Symptoms of molybdenum deficiency:
- Shortly after plant emergence, the tips of the lower leaves turn yellow, brown off and die.
- In a crop, many plants will die completely and others will be short and stunted.
Deficiencies can be corrected by application of molybdenum mixed with other fertilisers. This may correct the deficiency for up to five years.
Nutrient application
Maize does not tolerate high levels of fertiliser coming in contact with the seed and care should be taken to avoid this at planting. A starter fertiliser (small percentage of nutrient requirement) may be placed with the seed if there is likelihood of low soil temperatures or of cool waterlogged soils after planting. This provides the seed with a ready nutrient source. The starting fertiliser should not exceed 5 kg/ha N and 10 kg/ha P when sown on 90 cm rows. Application of a compound fertiliser (NPK) drilled some 5 cm to the side of the seed is a preferable.
Irrigation
Maize requires 4-8 mL/ha of irrigation, depending upon location, seasonal rainfall temperature conditions and irrigation efficiency. It is recommended that moisture use and availability be monitored, using any of a number of soil moisture monitoring tools. Consult local crop consultants and irrigation suppliers for availability of such tools.Dryland corn should ideally be planted on a full profile of soil moisture. If this moisture is marginal, consider planting sorghum instead.
For irrigated corn, it is recommended that the land be pre-irrigated and then planted
Mild water deficits during the vegetative growth stages decrease leaf area. Severe moisture deficits will reduce leaf number. Both reduce the plants photosynthetic ability and will have consequences on grain yield. Flowering is the critical stage for determining final crop yield, and irrigated crops should be well watered during flowering and through to physiological maturity. It may be necessary to irrigate every week in hot, dry weather with flood irrigation or more often with an overhead sprinkler system.
For growers who monitor irrigation in maize crops, it is useful to know that the effective rooting depth of maize is 100 cm. Even mild water deficits during vegetative growth stages will decrease leaf area. More severe moisture deficits will reduce leaf number. Both will reduce the plant's photosynthetic ability and have severe consequences on grain yield. Even if early soil moisture at planting has been adequate to produce maximum leaf area, moisture stress later will cause leaf senescence and therefore yield depression.
Author: Michael Hughes
Page maintained by Judy Shepherd
Last reviewed 30 November 2006