Good General Management Guidelines for Irrigated Maize

The climate and environmental conditions influence the development and yield of maize. With production under irrigation we can manipulate some of the environmental and managerial variables to optimise production. This information is provided to emphasise the critical production practices including efficiency and timing needed for optimum growth to achieve higher yields and profits.

Cultivation:

• An even soil surface is advantageous in establishing an optimum plant population.
• Excessive runoff can be a problem and is often due to a compaction layer.
• If the soils are prone to runoff, perform a "wet-rip" before the V5 growth stage.
• It increases water infiltration and aeration - irrigate soon after the operation as plants can rapidly go into moisture stress.
• If a system of minimum tillage is used, a strip-till cultivation considerably improves soil temperatures in the strip, optimising conditions for better germination.

Weed Control:

Good weed control is critically important in the plant’s early development stages. The obvious reasons are that weeds use the water and plant nutrients intended for the maize plant. The other very important reason is that the young maize plant receives 40% of its ultraviolet light needs from light reflection from the ground. Therefore, if the sun's rays hit any chlorophyll (read green growing weeds), the light is lost to the maize plant. Keep the soil surface free of growing weeds. Dead material does not absorb light. No-till cultivation practices and other cultivation practices where plant residues remain on the surface of the land are therefore in order.

Plant Population:

• The goal is to achieve even emergence and minimum interplant competition.
• This is determined by the proper and efficient functioning of your planter.
• Ensure that it is set up and calibrated correctly before planting and monitor performance regularly throughout the planting process. Uniformity is enhanced by:
• An even soil seedbed, meticulous plant spacing, planting depth, good contact with the soil, fertiliser placement and consistent soil moisture.
• Good contact between the seed, soil and moisture is a function of planting depth and the adjustment of the press wheel for optimal compaction.
• Optimal germination will take place between 18-30°C. In no-till systems, a strip-till can provide a warmer seedbed in the rows. The row should be exposed and clean of any residual stover to allow the strip to warm up.
• Formation of a crust and clods are unfavourable.

Row spacing:
Popular row widths are 0.45, 0.76 and 0.91 meters.

Twin rows:
Main rows 0.76 m centre to centre and twin rows at least 15 to 20 cm apart.
The aim is to place the seeds in zig zag pattern.

Intra-row spacing:
13-15 cm (not less than 12 cm between plants).

Plant population:
80 000 – 100 000/ha for ultra early hybrids.

Planting depth:
5-8 cm.

Planter:

• Optimum plant population is one of the keys to success.
• Calibrate and test the plantability of the seed.
• Regularly check the calibration of each planter unit.
• A low planting speed of ±5.5 km/hour is essential to ensure uniformity.
• Avoid planting in wet soil as it may cause a smear action, resulting in a compaction layer.
• Management is very important.
• Regularly open rows and check spacing and depth of the seed.
• Be aware of crusting after heavy rainfall. Cultivate with a rotary hoe to break up crusts.

Plant Health:

• For best yield, keep plants green for as long as possible.
• Fungicides contribute to a healthy plant and roots.
• It is important to adhere to the directions on chemical labels and avoid additional surfactants and mixtures.
• Be aware of the plant's critical development stages.
• Avoid spraying during the V10-V16 growth stage (risk of Arrested Ear Development) and during the flowering period (risk of problems with pollination).

Fertilisation:

General:
Check fertiliser application regularly.
Fertigation is effective.
Always avoid nutrient deficiencies.
Beware of a high salt index and fertiliser burn when band placing fertiliser. Pay particular attention to the nitrogen and potassium fertiliser levels which have a high salt index. For band placement in 0.76 m and 0.91 m rows, a maximum nitrogen plus potassium per hectare of 90 kg/ha and 70 kg/ha respectively is recommended.
Band placement improves early vigour.

Nitrogen:
The nitrogen recommendations are determined by the yield target and clay content of the soil. The abbreviated Fertasa nitrogen recommendations are as follow:

However, these guidelines need to be considered in the context of the other nutrients and, very importantly, water scheduling. Good soil health and management practices are also required to realise the yield target for the amount of nitrogen applied. Please consult your fertiliser agent for more in-depth fertiliser recommendations.

The norm is to broadcast a portion of the nitrogen beforehand and apply a portion in the row during the planting process. The balance is applied as top dressings. The reason for broadcasting a portion before planting is to limit the amount that is later applied as top dressing so that it will not burn the plants. If stubble is incorporated, it can cause a nitrogen negative period. This can be avoided by pre-spreading approximately 15 kg N/ha for each ton of material incorporated before planting the seed.

Under irrigation, the norm is to apply the balance of the nitrogen (about 60% of the total nitrogen) from about two weeks after emergence to the soft dough stage. It has been observed at successful clients that the amount of nitrogen top dressed is directly associated with increased yield. The balance of nitrogen can be applied in up to six top dressings, depending on the soil type. The amount can be progressively increased as plants become more mature. Keep in mind that the fertiliser takes about ten days to convert into a plant absorbable form.

As an example, the top-dressings can be applied through the pivot at the following growth stages. In many cases farmers include potassium top-dressings from about the ten-leaf growth stage until just before tasselling takes place:

1 After emergence, at about the three-leaf stage
2 Five to six leaf stage
3 Ten to twelve leaf stage
4 Eighteen leaf stage
5 Just before the tassels emerge (a general practice is to include a dressing of potassium nitrate at this stage)
6 Just after flowering (max. 25 kg N/ha)

Critical Growth Stages:

5 Leaf stage:
The yield potential is established, and the growing point is close to the soil surface.
A new leaf appears approximately every three to four days (dependant on the number of Heat Units).
The theoretical yield potential is determined.
Damage by hail, wind and leaf feeding insects can reduce the number of rows on the cob.
100% damage may occur when plants are frosted.
53% damage may occur when all the leaves are destroyed by hail.

12 Leaf stage:
The number of kernels in the rows of the ear is determined. The number of potential kernels and size of the cobs is determined. The theoretical yield potential is determined.
A new leaf appears about every two days.
No water and nutrient shortages should occur.

14 Leaf to flowering stage:
Rapid vegetative growth and development of the cobs takes place.
Avoid any water stress.

Tassel appearance to the end of grain filling:
It is critically important to maintain optimum growing conditions.
Irrigate until 80% of the husk leaves have turned brown and the moisture content of the kernels reaches 35% or less.

Water Scheduling:

Uniform application:
Check uniformity and physical delivery of the sprinkler package.
Nozzles have a limited lifespan. It is advisable to test the water delivery thoroughly at least every five years and replace nozzles if necessary. Make sure the sprinkler package can supply enough water during the critical development periods. The most critical time to ensure optimum soil moisture availability is one week before pollination and up to the completion of grain filling period.
Ensure that the correct amount of water and nutrients are available at the right time and at right amount per growth stage.
The water application is a function of soil type, climate and root development.
Check uniform application or wetting of the field. Use measuring instruments to monitor soil moisture content.

Corrective Management Practices:

• Apply corrective measures if necessary, under the following circumstances:
• Heavy rainfall after planting and before emergence.
• Large variation between day and night temperatures.
• Low night temperatures.
• Crusting.
• Leaching of fertiliser.

Apply quality control regularly without exception.

It’s the little things that make the big things possible. Only close attention to the fine details of any operation makes the operation first class.
~John Willard Marriott