Kids who grow up in large families learn early that coming late to a meal often results in meager helpings. Quantity of food is rarely the issue. It's a distribution problem.
Now apply the same analogy to corn. For four years, Purdue University agronomist Tony Vyn has been working to understand how plant density impacts high-yielding corn hybrids.
"What we learned is that the only way to pursue and achieve higher grain yields on a per-acre basis at high plant densities is to make sure every single plant has an equal opportunity to compete with the neighboring plant in the row,” Vyn says.
He refers to it as the "no plant left behind” concept. "For the plant to achieve this competitive ability, it must have the right genetic resources to allow each plant in the hybrid to gain access to sufficient nutrients and water so that shoot growth rate is consistent for all plants.”
Vyn looked at 4,000 individual plants of two hybrids in each of the four years. The plants were bar-coded soon after seedling emergence and tracked to see how each plant competed at three planting densities and three nitrogen rates.
"It was a comprehensive look at the multiple stress effects on individual corn plant performance during its growth stages, as well as the final result in terms of grain yield per plant,” Vyn says.
Earless plants. Ever notice a barren plant or a stalk with only a few kernels on the ear at the end of the growing season? Vyn says growers and scientists have traditionally assumed these nonproductive stalks were the result of late emergence or variable plant spacing.
"Turns out it has a lot more to do with how the plant was able to compete in terms of capturing sunlight, producing a big leaf area and trying to silk and have pollen shed at the same time. The ability to retain green leaves into the grain-fill period also contributed,” Vyn explains. "Essentially, there is a season-long, management-dependent, intense competition that occurs among adjacent plants.”
Are you too dense? Vyn notes that competition gets tougher at high plant densities, especially when nitrogen is limited. "Plants can become dominant and bully their way to gain more nutrients if adequate nutrients aren't provided for all,” he notes.
Vyn also found that the anthesis-to-silking interval is crucial to the final yield. "If you have plants that have been dominated by their neighbors, they tend to shed pollen on time, but they have a delayed emergence of the silk,” he explains.
"The main reason for barrenness in corn plants has to do with too slow a growth rate near the pollination period. Slow growth is most evident in the long time interval between pollen shed on the tassel and silk development of the ear.”
Vyn says the studies indicate that today's high-yielding hybrids don't always benefit from higher density planting. "We didn't see a lot of yield differences between 22,000 and 42,000 final population in the long-season hybrids examined that routinely yield in the 240-bu. range,” he reports. "The genetic capability for achieving high yields at high density needs to be there, but you also need to have the environment that allows each plant to produce about the same size ear. It is plant-to-plant variability that limits yield.”
Seed breeders and seed companies need to consider these interactions as we push yield barriers beyond 300 bu. and 350 bu. per acre, Vyn says. "It's extremely important that we think not just about the ability of the plant to tolerate a single stress like high plant density, but also its ability to tolerate lower nitrogen availability on a per-plant basis,” he says.
You can e-mail Pam Smith at firstname.lastname@example.org.