A Purdue University researcher's motto, "No plant left behind," sums up his research on achieving increased grain yield for corn at higher plant densities.

"The only way to pursue and achieve higher grain yields on a per-acre basis at high plant densities is to make sure that every single plant has the opportunity to compete with its neighbor in the row," says agronomy professor Tony Vyn. "The only way to achieve this competition ability is to have the genetic resources, in terms of a hybrid's ability to compete and gain access to nutrients and water."

The results of a 3-year study, which looked at approximately 4,000 individual plants each of the 3 years, are published in the online version of Agronomy Journal.

Each year, from the time that seedlings first emerged from the soil, the plants were barcoded. Vyn's team grew to understand how individual plants compete with neighbors at three different plant densities and three different nitrogen rates.

"This study is perhaps the most comprehensive study that's ever been done to look at the multiple stress effects on individual corn-plant performance during its growth stages, as well as on the final result in terms of grain yield per plant," Vyn says.

One misconception the industry has is that barren plants or ears with only a few kernels at the end of the growing season are a result of when the plant first emerged from the soil back in the very beginning, Vyn says.

"It actually has a lot more to do with how that plant was able to compete with its neighbor in terms of capturing sunlight, producing a big leaf area, trying to silk and have the pollen shed at the same time, and retain green leaves well into the grain-fill period," he says. "Essentially, there is a season-long, but management-dependent, intense competition that occurs among adjacent plants.

"Competition is enhanced at high plant densities, especially when nitrogen is limiting. Nitrogen is an example of a nutrient that becomes more essential at high plant densities. This will avoid the keen establishment of hierarchies where there are many dominated plants and then a few very dominant plants, which have the ability to marshal more resources into their growth so that they have a high yield."

Vyn found that the anthesis-to-silking interval is crucial to the final grain yield.

"Basically, if you have plants that have been dominated by their neighbors, they will tend to shed pollen on time, but they will have a very delayed emergence of the silk," he says. "So the main reason for barrenness in corn plants has to do with the long time interval between pollen shed on the tassel and silk development of the ear."

From an industry standpoint, Vyn says that as the future of corn yield improvement is considered, seed companies must study the response of their hybrids and germplasms to higher plant densities in the context of nitrogen-use efficiency.

"As we've tried to push yield barriers beyond 300 and 350 bushels per acre, it's extremely important that we think about the ability of the plant to tolerate not just a single stress like high plant density, but also be able to tolerate lower nitrogen availability on a per-plant basis," Vyn says. "Our results suggest that on the plant breeding side of the equation, more attention should be focused on the joint ability of new corn hybrids to tolerate combined stresses of both high plant density and limited nitrogen.

"If the new hybrids can better tolerate both, then it will be possible for those high-density, low-nitrogen situations to achieve an overall improvement in uniformity of grain yield on a per-plant basis."