Keep maize plant population up

This is being fuelled by seed companies – with limited data to support their low population ideas – trying to make quick seed sales.

Pioneer's trialling programme includes population trials which evaluate new hybrids in a range of growing environments. This is done to establish the optimum plant population for each hybrid. The optimum seeding rate is not the one that produces the highest yield, but instead the one that produces the most profit after factoring in seed and seed treatment costs.

During the past five decades, New Zealand maize silage hybrids have been increasing at 166kgDM/ha/year. On a per plant basis there is not much yield difference between older and newer hybrids. The big yield gains have been made in the newer hybrids' ability to perform well under stress conditions. Improved leaf angles, better root and stalk strength and higher drought tolerance means newer hybrids can perform better at higher plant densities than older genetics. This is where the yield increase has mainly come from.

NZ research has shown that today's hybrids (irrespective of brand), perform best when planted at seeding rates which will give higher, rather than lower, established plant populations.

While crops which have lower established plant populations are often more visually appealing (larger plants and bigger cobs), this does not normally translate to higher drymatter yields. That's because the higher plant population crops have smaller plants, with smaller cobs, but there are more of them!

Published NZ research1 shows that established plant population has very little impact on maize silage quality. A summary of 12 maize hybrids grown at 13 locations over two seasons showed there was no statistical difference in starch, soluble sugar, ADF, NDF or in vitro digestibility of maize silage from crops with established populations of 85,000-145,000 plants/ha. As plant population increased, maize silage crude protein dropped slightly.

Two factors which impact the optimum established population for a maize silage hybrid are the expected crop yield level and the hybrid maturity.

High yield environments including high fertility dairy farm paddocks with good soil types will deliver the most profit at a higher optimum established plant population than lower fertility, repeat cropping paddocks or crops planted on drought-prone soils. Recommended NZ planting populations are often higher than US planting populations because we typically have better growing conditions with less moisture and/or heat stress during the growing season.

Shorter maturity hybrids are smaller in stature and require higher established plant populations to achieve optimum yield than longer maturity hybrids. For this reason South Island recommended planting populations are typically higher than those in the North Island.

The Pioneerbrand maize for silage catalogue outlines ideal established populations for hybrids planted in high, medium and challenging yield environments. They assume good seed establishment conditions. If you are planting very early into a less-than-ideal seed bed or where insect pressure may be high, seeding rate will need to be increased to compensate for early seedling mortality.

Don't be tempted to cut costs by reducing planting population this season. What you lose in drymatter yield is likely to cost you a lot more than you save in seed cost.

1Densley R.J.; Brenton-Rule, R. J.; Austin, G.M.; Densley, D.W.; Tsimba, R. 2003. The effect of increasing plant population on maize silage yield and quality. Proceedings of the New Zealand Grassland Association 65: 117-121.

• Ian Williams is a Pioneer forage specialist. Contact him at This email address is being protected from spambots. You need JavaScript enabled to view it.