Factors influencing maize yield

Yield potential refers to the maximum yield that a farmer can obtain from a crop in a given environment and is largely determined by a specific combination of factors. Magda du Toit spoke to industry experts about the basic principles that determine yield and profit in maize farming, and how a farmer can improve results.

Factors influencing maize yield
Kobus van Huyssteen of the South African National Seed Organization cautions farmers to buy good-quality, certified, tested seed to help ensure a good crop.
Photo: Magda du Toit
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Many economic and agronomic factors influence the productivity, profitability and long-term success of farming.

A number of these are within a producer’s control, as successful maize production depends to a large extent on the farmer’s choices and correct application of production inputs, says Hendrik van Staden, Syngenta Seed’s business unit head for sub-Saharan Africa.

“Although farmers have no control over environmental stress conditions such as rain or drought, certain practices can minimise these risks. Farmers can manipulate the environment in which they produce maize through hybrid choice, cultivation practices, soil conditioning and fertilisation, crop rotation, irrigation, and pest and disease control,” he explains.

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Andries Wessels, seed product development manager at Syngenta, points out that the first 40 days of a maize plant’s development are critical.

“Management practices during this period can have a substantial influence on yield potential. When planting, the goal is to establish a land comprising uniformly spaced and sized plants at a density that will result in the best economic return on your seed investment.”

According to Grant Pringle, product agronomist at Pannar, soil environmental conditions needed for germination include suitable temperatures, adequate water supply, oxygen, and proper seed placement.

Soil temperature at planting is a critical environmental factor that has an influence on the even germination and emergence of maize seed. Germination occurs most rapidly and is generally most successful at the optimal temperature.

If a minimum air temperature of 10°C to 15°C is maintained for seven successive days, germination should proceed normally. Virtually no germination or growth takes place below 10°C.

Pringle warns that planting should not be carried out if the average daily soil temperature is below 14°C, as this will not only delay emergence, but also expose the seed to additional risk.

“No-till maize farmers should also make sure they measure soil temperatures at the intended planting depth underneath plant residue,” he adds.

The average daily soil temperature can be calculated by adding the temperatures at the planned planting depth at 6am and 6pm on the same day and dividing by two.

“Sudden temperature change from hot to cold will have a shock effect that may either kill the young plants or cause damage that will last for the entire season. Also avoid planting in dry soil, which heats up faster and to a higher temperature than moist soil, and in particular avoid irrigating the seeds with cold water soon after planting,” says Pringle.

He adds that the growth point and the entire stem of the plant are 25mm to 40mm below the soil surface during seed germination. Under warm, moist conditions, seedlings emerge after six to 10 days, but under cool or dry conditions this may take two weeks or longer.

The optimal temperature range for germination is between 20°C and 30°C, while the moisture content of the soil should be approximately 60% of its capacity.

According to Wessels, seed should be planted at a soil depth that provides adequate moisture and allows for soil coverage, but not so deep that the energy storage capacity of the seed is depleted before the seedling emerges. If planted too deep, the mesocotyl may open below the soil surface and the seedling will die.

Maize planting should be scheduled so that the growth stages most sensitive to water shortage and heat (for example, the flowering stage) don’t coincide with midsummer droughts.

The exposed leaves of a newly emerged plant are highly susceptible to wind erosion, and hail and frost damage, but damage to the growth point should be negligible as it is still below the soil surface.

“But waterlogging at this stage may be harmful to the seedling and cause permanent damage. Also avoid tilling close to the seedlings, as this may harm the roots, which will negatively affect yield,” Wessels warns.

He elaborates on the potential problems caused by suboptimal conditions at each growth stage:

  • During growth stage 2 of a maize plant’s development (with eight leaves completely unfolded), the growth point is between 5cm and 7,5cm above the soil surface. During this stage, hail may cause a yield loss of 10% to 20%, while nutrient deficiencies will restrict leaf growth.
  • During growth stage 3 (with 12 leaves completely unfolded), the tassel begins to develop in the growth point, and stress as a result of water or nutrient deficiencies will affect the ultimate size of ears, and consequently yield.
  • During growth stage 4 (16 leaves completely unfolded), water and nutrient deficiencies may detrimentally affect silk development and therefore the number of kernels per ear.
  • At growth stage 5, during which the silk appears and pollen is shed, water supply is important, as wilting of plants due to water stress early in the morning can affect pollination.

Crop nutrition and soil health
Wessels points out that maize is grown in a wide variety of soil types, and soil health and condition will determine fertiliser requirements.

“The first important action should be to bring the soil in balance. Regular soil analysis is needed to find the exact nutrient composition of the soil and the pH. The wrong application of nutrients can result in an imbalance in the soil and eventually affect the environment and even contaminate the water.

“If the levels of some elements are too high, this could have a detrimental effect on soil biology. Soil biology, in turn, has a direct effect on soil structure and chemistry and is key to enabling the accessibility of vital nutrients for soil organisms and plants.”

Pringle explains that certain prime nutrients have crucial roles to play:

  • Nitrogen fuels crop growth and development and must be readily available.
  • Phosphorus aids strong root development and good crop establishment.
  • Potassium helps to mitigate the effects of frost damage and reduces lodging.
  • Magnesium, sulphur, iron and zinc boost photosynthesis.
  • Calcium ensures plant strength.
  • Boron is required for pollen tube growth and consequently helps with good grain set.

Seed quality
Kobus van Huyssteen, acting technical manager at the South African National Seed Organization (Sansor), says: “Over the years, countless farmers have fallen into the trap of buying cheap, uncertified, untested seed, sometimes packaged in unlabelled bags.

“In addition to the risk of poor germination and inferior yields, these seed containers could also contain unwanted weed seeds, consequently contaminating an entire field, farm or even district.”

He adds that by buying good-quality seed, farmers may eliminate a potential source of crop failure and increase the likelihood of reaping a profitable harvest. He urges producers to buy seed from reputable seed companies such as Sansor members or distributors.

“Pay attention to the label on the seed bag or container. Understanding the label will allow for proper decision-making when it comes to seed purchases and planting.”

Planting density
Wessels explains that the seeding rate is the number of seeds planted per unit area (unit or row). “Plant population on the land is determined by the seeding rate and the number of seeds that emerge together. Some seedling mortality occurs during emergence.”

He adds that seeding rate recommendations are based on yield potential, hybrid and purpose.

“Maize planted for grain has a different seeding rate to maize planted for silage. Other factors that influence the rate are annual precipitation, length of the growing season, soil type, soil fertility, planting date, and hybrid maturity.”

Drought and heat stress
Wessels points out that drought and heat stress often occur simultaneously, exacerbating the effect. Under drought stress, stomata in the leaves of maize plants close to reduce transpiration, which can have a negative effect on flowering, pollination and grain fill.

“Moisture stress during critical development stages can easily reduce maize yield by up to 50%. The extent of damage caused to maize plants depends on the duration of the drought stress and the crop’s stage of development.

“An air temperature higher than 36°C reduces the viability of pollen and hence pollination rate, grain fill and yield. High air temperature and solar radiation also damage maize leaves, reducing the area of chlorophyll production needed for growth and grain fill.
“It’s estimated that maize needs 450mm to 600mm of water per season.”

Disease management
Plant diseases are caused by fungi, bacteria and viruses, and affect different parts of the maize plant at various stages of its development, potentially causing major yield losses.
Early identification of disease reduces the risk of widespread damage and allows the best treatment programme, says Pringle. “A combination of preventative and corrective sprays should be used. The key is regular scouting.”

Wessels adds that low soil temperature and poor drainage create favourable conditions for the development of plant diseases.

“Root diseases are caused by a variety of soil pathogens that include species of Pythium, Fusarium and Rhizoctonia, as well as nematodes. Stressed plants, due to extreme temperatures, excess moisture, herbicide damage, and physical damage due to insects, strong winds or machinery, are more prone to infection.”

He cautions that diseases occurring in one season are likely to be carried over to the next.

“Knowledge of the exact disease, its prevalence and severity is pivotal for making sound management decisions for the next season’s crop.”
He adds that crop rotation can be used to manage crop diseases.

Weed management
Wessels stresses the importance of starting each season with a land free of weeds to help the seedlings develop unhindered.

“Weed control, especially in the first 10 weeks of crop emergence, is essential, and will reduce the competition from weeds for available light, water and nutrients.”

Weed control can have a major impact on maize yield. Worldwide, weeds cause yield losses of up to 12,8% on lands where weed control is practised, and 29,2% in the case of no weed control.

“If there are many weeds on a land at harvest time, the entire process can be slowed down. In addition, grain polluted with weed seeds can end up with a lower grading. To remove weed seeds also adds extra cost.”

An integrated weed management programme, in which cultural, mechanical and chemical methods are combined, is always a wise practice to follow.

“Management practices such as higher planting densities and crop rotation can be used in the weed control programme,” he says.

Pringle points out that lodging has a financial implication for the farmer, as the planned yield might not be realised because it is not economical to pick up the ears that lie on the soil.

Email Grant Pringle at [email protected], or Andries Wessels at [email protected].

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Magda du Toit is a freelance communication consultant and journalist. She has worked in the agriculture sector for more than 35 years. She obtained a BA in Communication (Hons), and also completed a Post-Graduate Diploma in Marketing Management. Throughout her career she has received recognition and various awards for individual and team contributions. She was also the chairperson of the northern branch of Agricultural Writers SA and still serves on both its executive bodies. Magda is also the South African representative at the International Federation of Agricultural Journalists, where she chairs one of the committees.