When a researcher from a state that annually plants 13 million acres of corn speaks, farmers generally listen. Researcher Emerson Nafziger, professor of crop sciences at the University of Illinois, had plenty of attentive ears, if you will, when he discussed corn planting for information-hungry producers attending the Conservation Tillage Cotton and Rice Conference in Tunica, Miss.

Nafziger said seed placement, both horizontally and vertically, into a soil environment that provides good seed-soil contact, a good rooting medium and adequate plant nutrients and water are vitally important in producing top corn yields.

This is even more important as Illinois has moved to more and more acres of corn. “Our biggest problem is that we have such a small window for planting corn. In central and southern Illinois, we start in early April, and a few producers are pushing it into late March. In northern Illinois, the best time to plant is somewhere between April 15 and April 25. The problem is that we get about 4 inches of rain on average in April. Our soils are typically cold going into April.

“That's the real risk and the reason farmers have been expanding their capacity to plant very fast. Most producers in Illinois can plant their entire acreage in four to five days. They've increased the size and number of planters because of that need for speed.”

According to Nafziger, many of those producers believe they can add acreage without adding equipment, which makes it a lot easier to pay bills. On the other hand, “competition for this acreage has been very aggressive, and that's why land rents are going up so fast.

“As farm prices have gone up, farmers are finding that the cost of producing the crop tends to rise, too. Economists will tell you that's what a commodity is — over the long run, the price of producing it is going to get closer to the price that it sells for.”

Because producers in the state have moved from equal acreages of corn and soybeans to a much higher percentage of corn, “we're moving to the point where half our corn acres are going to have to follow corn.”

Planting seed into corn stubble is more problematic under those circumstances, which makes the planting operation crucial to profitability.

Nafziger noted that plant population has been moving higher for Illinois producers, and today averages about 28,000 plants per acre, up about 10 percent from 2002. “Many producers have increased their targeted plant populations in corn in recent years, yet still wonder after a good year with good yields, if they should have set the planter for even higher populations.”

Nafziger said Illinois studies indicate that corn yield continues to rise as plant population approaches 40,000 plants per acre under very good conditions, but yield tops out and sometimes drops off at plant populations of around 35,000 plants per acre under occasionally dry conditions. “There seems to be little risk, and some reward, in raising plant populations to around 35,000 plants per acre in productive soils.”

Nafziger says the uniformity of size and condition of plants is probably a more important factor for yield than non-uniformity in plant spacing.

He cited a study by farmers in field-scale strips in Illinois where researchers found that faster planting speeds increased plant spacing variability slightly, but had no effect on yield.

In a more recent study, Nafziger found that spending money to try to improve on a stand that is less than perfect in plant spacing, but within an acceptable range, probably will not increase profits much if any.

“Uniformity of size is a factor I think we should pay more attention to. When your plants are ankle high, you want them very uniform. If they're not it will cost you yield.”

According to Nafziger, yield loss from uneven emergence probably occurs when late-developing plants undergo more intense competition from adjoining, larger plants, and so they lose more yield than the earlier-emerging, larger plants can compensate.

Planting depth is one factor that affects uniformity of emergence, Nafziger says. “The ideal depth may vary some depending on soil conditions, but in most cases planting 1.5 inches to 1.75 inches deep is likely to provide the best results. Both deeper and shallower planting tends to place seed in less-uniform conditions, which can contribute to unevenness in emergence time or stand loss.

“If planting under reasonably good conditions, emergence in a field should normally take place over a period of less than 48 hours. In a study using a seed coating designed to delay emergence, yield decreased when the time to emergence was delayed and the number of days between first and last emergence was increased.

“The cardinal rule of planting, regardless of tillage, is to plant the seed into soil that is in a condition to provide the seed its best chance of germinating and emerging as fast as temperatures allow, and as uniformly down the row as possible.

“We also need to keep in mind how the roots of the plant will grow, and we need to manage soil conditions so that established plants have the best chance to grow a root system that will both anchor the plant well and help it to tap soil, water and nutrients.

“The first step is to make sure that seed is planted into soil that is loose enough to provide good seed-soil contact, and that seed is covered with enough soil to allow normal development. These are critically important regardless of tillage system, but there is a tendency in tilled soils to bury seed too deep and to press soil too firmly around the seed, while in no-till the failure to cover seed adequately is a common problem.

“It is important to prevent sidewall compaction and other planter issues that can prevent full establishment of the nodal root system — the root system the plant comes to depend on.

“Even after plants are established, with the nodal root system growing out into the bulk soil, zones of soil compaction can negatively affect root system size and shape. If the weather turns dry, this can become a critical limitation to the ability of the plant to take up enough water.”