Corn Illustrated Results Don’t Back Seed Rate Increases

Jumping population not total answer to raising yields.

Published on: Mar 17, 2008

A farmer recently reported to Corn Illustrated that he received a mailing from two competitive seed companies in the same day. Both included information on the same topic- increasing final plant population. Both were making the push to shove those rates on up into the lower 30-thousand range. That would require seeding rates in the low-to-mid -30s range to achieve final populations in that category.

Ironically, the farmer had already decided to back of this planting rates this year from 32,000 to about 30,000 seeds per acre. He farms both typical land and drought-prone land, but he intends to make the change on both. One of the factors helping him decide that he didn't need to plant so thick was the results of the 2007 Corn Illustrated population study. The Corn Illustrated project is an exclusive of Farm Progress Companies.

In high yield tests under irrigation in '07, yields for three non-GMO-hybrids were actually higher at 32,000 seeds per acre than 41,000 seeds per acre, reports Dave Nanda, crops consultant for Corn Illustrated and a long-time plant breeder, currently president fo Bird Hybrids LLC, Tiffin, Ohio. Highest yield in the field-size plot reached 242 bushels per acre at the lower population. The plot was irrigated, but still survived approximately 40 days of 90 degree F temperatures, or higher.

While lodging did not increase significantly at 41,000 plants per acre under irrigation, ear drop dead. Nanda attributes the tendency to drop ears to increased stress caused by the higher plant population. About one dropped ear in 175 feet of a single row amounts to a bushel per acre of yield loss, according to formulas suggested for yield loss calculations by Purdue University ag engineers.

To discover if there would have been a plus side to going halfway between 32,000 and 41,000, a population study is planned for '08. A wider range of populations at 4,000 seeds per acre increments will be compared to determine trends in population. This study is planned for dryland in '08.

The Corn Illustrated projects team will also conduct another trial going for top yield again in '08. Current plans for that study under irrigation call for dropping 34,000 seeds per acre. "But the goal in this study is maximum agronomic yield, not maximum economic yield," Nanda says.

In the same study, current plans call for applying roughly 250 actual pounds of N per acre following soybeans, and an extra 30 pounds following corn. Those aren't levels that Nanda would suggest on ordinary fields this year, even with current corn prices. Nitrogen input prices are also at record high levels.