Planting rates key to higher maize yields

Maize crop plant populations will continue to increase as part of the ongoing drive to lift maize yields

Professor Fred Below, with FAR senior maize researcher David Densley and communications manager Anna Heslop

Visiting US maize expert, Professor Fred Below, who was keynote speaker at the Foundation for Arable Research’s Premier Maize Event in Hamilton, says this will trigger other management changes including a shift to narrower row spacings. 

While average maize yields in the US go up and down depending on the weather, overall these lift about one tonne every seven to eight years because of improved genetics and better management.

Associated with this is a linear increase in the number of plants. In the US, plant populations go up about 900 plants per hectare per year and are currently almost 79,000 plants/ha.

"This will continue to increase, despite the high seed cost," says Professor Below, of the Crop Physiology Laboratory, University of Illinois. 

Yield is based on three key components, the number of plants per hectare, kernels in each plant and the weight of each kernel.

"To increase maize yield, you have to increase at least one of these. Which one do you have the most control over? Its plants per hectare," Below says.

Professor Below calculates that the maximum plant population in the US at a 76cm row spacing is 93,000 plants/ha. "Over that, you are at risk of competition, shading and lodging."

FAR senior maize researcher David Densley says New Zealand conditions mean that the upper limit for plant populations will be higher than in the US before the need to switch to narrower rows.   

"Our cooler nights and even cooler days and fewer extreme temperatures allows more plants to be grown, but there will still be a tipping point."   

Professor Below’s research team have made a major investment in trial work to compare 76cm and 51cm rows. "One huge advantage of narrow rows is that they can intercept more light and manage a higher population of plants."

A planting rate of 109,000 plants/ha in a 76cm row resulted in a plant-to-plant spacing of 12.2cm, which is too close for grain production, but may be manageable for silage. "You don’t want to sit too close to someone at the dinner table, you want some elbow room. Maize plants are the same."

In contrast, in 51cm rows, the plant-to-plant spacing is 18cm. "Going from 76cm to 51cm row spacings is worth anything from an extra half a tonne to 1.5 tonnes for grain."

However, as the plant population is increased, the size of each plant’s root system gets smaller. For every 1000 more plants per hectare there is a 1 per cent decrease in the root mass per plant. This is reversed when the row spacing is narrowed.

To ensure adequate plant nutrition for high yield as plant populations increase, Professor Below advocates better source, rate, time and placement of fertiliser.

Better placement of fertilisers is important as the horizontal spread of a maize plant’s root system is only 15cm to 20cm. "Maize roots do not cross the row."

He believed future practice would be the banding of fertiliser placed 10cm to 15cm deep, directly below the future crop row. In strip till this can be put in the strip.

"The first time we did that, in 2009, I couldn’t believe it. This was the biggest effect on yield I had seen in my career. I know this is hard and it is slow but this has to be the future of maize production."

Growers also need to do a better job of placing side dress fertiliser applications. In the US, a technique called Y drop is used which places fertiliser, usually in liquid form, on the surface along the plant row. 

Another innovation in the US is short stature maize, with a height of 2.1 metres compared with conventional hybrids at 2.7m to 3.6m. Maize is the last major grain plant to be dwarfed. Short stature maize has a number of environmental, management and physiological advantages compared to conventional tall maize hybrids, Professor Below says.

Plants have a thicker lower stem and are better able to withstand wind. They are also different in how they partition energy, with short stature maize putting 26% of its energy into its stalk, compared with 36% for tall maize. This allows more energy to go the plant’s leaves, ear and root.

The lower height also makes it a lot easier to ground spray and apply side dressings, even at more mature stages.

"Maybe it is not so good for maize silage, but be ready for the advantages of short stature maize when growing it for grain in wind."

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