Development of corn hybrids that better tolerate stress has allowed corn growers in the Southeast to increase plant populations by 25-35 percent over the past decade — the result is potentially higher yields.

With so many growers returning to corn or growing it for the first time in 2007, it is important to recognize changes in corn planting and the impact this has on nutrient management.

With fertilizer costs, particularly nitrogen, doubling over the past few years, it becomes even more critical for growers to find the optimum nutrient use rate for their high value corn.

“We have planted corn this year at 4-inch plant spacing and over 130,000 plants per year. Ten years ago, if you planted available varieties at such narrow plant spacings there would be bare stalks up and down the rows. Though we don't recommend plant populations nearly that high, these new hybrids do make double and triple the normal number of plants possible,” says Ronnie Heiniger, North Carolina State corn specialist.

“In tests in a grower field near Shawboro, N.C., we measured ears in some of the 4-inch plant spacings and narrow row spacings that produced enough ears and kernels to produce more than 300 bushels per acre. The ears weren't very large, but they should produce a big yield,” the North Carolina corn specialist says.

New, improved corn hybrids have allowed growers to dramatically increase plant populations to 35,000-40,000 plants per acre and increase yield potential. The increased yield potential comes at a price. Heiniger says plants at close spacings have more needs and the grower has to manage the corn plant differently than corn planted at much lower plant spacings.

He says that by the V6 stage of plant development, the number of rows on the ear has been determined. Nothing a grower can do will cause that plant to set more rows. However, at this growth stage, many growers are putting out lay-by fertilizer or herbicide, yet the corn ear's production potential has already been set.

By growth stage V14, the length of the ear of the corn has been set. To manage that corn plant for best growth potential, the grower needs to do whatever he can to set the maximum number of ears by growth stage V6 and to finish that plant's growth potential by growth stage V14.

The first step in good nutrition management in corn at both narrow row and narrow plant spacings, Heiniger says, is to get enough starter fertilizer to the plant before the V6 stage to get good ears on every corn plant in the field.

Speaking at the recent annual Northeast Ag Expo in Shawboro, N.C., Heiniger held up root systems from corn plants with 10-27-0 fertilizer plus Avail at 10 gallons per acre compared to check plots with no starter fertilizer. The root system from the check plot was only half the size of the root system with starter fertilizer plus Avail.

Avail, Heiniger explains keeps phosphorous in the 10-27-0 mixture from being tied up by the clay soils in the area into a form that is unavailable to the plant.

In tests in 2006, Heiniger says a 19-19-0 fertilizer was used as a starter. “In every case we say yields increase with the starter fertilizer. The yield increase is directly related to increased plant populations,” he explains.

The 10 gallon per acre rate of 19-19-0 formulation, plus some potassium applied as a dry fertilizer banded over the row at planting has been the basic starter fertilizer used by many North Carolina corn growers. Back to 2004, this basic starter fertilizer performed well, leading Heiniger and other researchers in the Southeast to wonder whether this formula can be tweaked a little bit and improved even more for narrow row and narrow plant spacings.

By simply upping the rate of 19-19-0 from 10 gallons to 40 gallons per acre clearly made a difference in ear length. Whether the additional fertilizer is economically beneficial remains to be seen (when the test plots are harvested), he says.

In the test plots, without exception, corn ears did not completely fill out to the tip. The period of growth most impacted was V6-V14 — when the corn plant sets rows. Starter fertilizer, by comparison, expanded the root system, giving the plant the ability to uptake water and put it where it needs to be.

Clearly applying some of the total nitrogen application in a starter formulation is beneficial to corn in narrow row, narrow plant spacings. How use of 17-17-0 or 19-19-0 or other one to one formulations affects total nitrogen use over the season is another factor Heiniger hopes to determine from the grower tests in Shawboro.

Heiniger showed the crowd results from 30, 60, and all the way up to 210 pounds of total nitrogen use on corn. The 30 pound rate produced plants obviously stressed from lack of nitrogen. The yellowing typical of nitrogen stress extended to the ear leaves in these plants.

In the 60 pound nitrogen plots, the tale-tale yellowing was significantly less. “These plants don't look too bad. They are not all filling to the tip of the ear, which means we are not getting everything we need from this treatment,” Heiniger says.

The 90 pound per acre plots showed little difference from the 210 pounds per acre of nitrogen. “It looks like in this field in this year, the optimum nitrogen use will work out to be somewhere between 60 and 90 pounds of total nitrogen per acre,” Heiniger concludes.

The North Carolina researchers also applied Nutrisphere to the various nitrogen rates to determine the effects of this slow release mechanism on total nitrogen use in the crop.

Normally, when urea comes into contact with urease in the soil, urease works to break down urea into a state can volatize some to all of the applied nitrogen. NutriSphere-N creates a shield that stabilizes nitrogen in the soil by preventing urease volitization.