by Deborah Jeanne Sergeant

Bigger is better for corn yields, especially during periods when corn experiences price spikes. Producers need to make the most of their possibilities for profits and maximize their yield. Tony J. Vyn, from Purdue University’s Agronomy Department, presented “Tricky Keys to Big Corn: Bigger Plants, More Kernels or Bigger Kernels?” as part of Cornell’s recent virtual Corn Congress.

“The biggest news is corn is getting the very rapid increase in price we’ve received,” Vyn said. “It’s a very unusual event to receive an increase during harvest and early storage period. That, of course, is prompting more discussion and thoughtfulness about how to take advantage of the higher prices than we’ve seen for several years. The approach might be having bigger plants, more kernels or bigger kernels.”

Vyn said that modern hybrids have been developed to offer greater stress tolerance so they can better manage drought.

He said some hybrids do not offer progressively bigger plants – and some even dare reducing the plant height. Better tolerance of plant density is also a feature that can help farmers increase their harvest.

“There’s no question modern corn hybrids are bred in a way that achieves higher plant density tolerance,” Vyn said.

Vyn said growers have returned to relying upon nitrogen application much higher than 60 lbs./acre to boost plant density.

“There’s quite a wide range,” he said. “The average might be 70 bushels per acre response. They acknowledge the fact that we get a higher response to nitrogen with a higher plant density.”

He suggested that if farmers choose hybrids based on nitrogen response, they should look at how that affects their nitrogen management.

“That is one of the tricky situations,” Vyn said. “It’s fundamental when you look at results from commercial companies suggesting a nitrogen responsive hybrid versus a nonresponsive hybrid.” A responsive hybrid would require the expense of using more nitrogen. Farmers must evaluate if the higher yield validates the additional expense.

“Yes, hybrids are going to result in variation in the amount of nitrogen required to get to an optimum yield, yet at the same time, I want to push us in the direction to changing our nitrogen timing to synchronize with plant uptake to limit the negative environmental impact of applying too much nitrogen fertilizer,” Vyn said. Since modern hybrids increase uptake in the post-silking period, it’s important to time application right.

He reviewed the principles of higher yield: establishment and season-long maintenance of high leaf area with good functional photosynthesis capability; low stress at flowering to achieve synchrony in silk emergence and pollen shed and limited kernel abortion; cooler temperatures that extend grain filling period duration; and strong ear sink demand so that 55% to 60% of total plan weight at maturity is in the kernels, with strong stalks to limit lodging.

Less understood is the relationship between kernel number and kernel weight for specific hybrids in each production environment.

“Getting to bigger corn is more about higher kernel weights than more and more kernels per plant or per unit area,” Vyn said. He added that it’s true that during the post-flowering period, ears could abort kernels.

“Kernel weight is a function of the reproductive period itself,” Vyn said. “For the first 15 days, they’re not gaining any weight after being pollinated. There’s rapid cell division going on but they’re not gaining weight. We call this the lag period. Then we go to the linear period. We want this period to be as steep and long as possible to get the highest individual kernel weight.”

Creating that optimal environment in the plant to get a longer grain filling period includes helping the plants remain healthy through lower disease and better nutrition.

In one recent research project, Vyn’s team grew hybrids side by side representing 70 years of hybrid improvements. They averaged 113 days in maturity and were grown at five different nitrogen managements (applied at the V3 period) and all were grown at a rate of 32,000 plants/acre. The yield was substantially higher for corn responsive to a higher nitrogen application than earlier hybrids which did not actively respond to higher levels of application and the control group that received no application.

When looking at hybrids from 1976 forward, the kernel number and kernel weight gains plateau.

“We’re pretty sure that the changes, especially in the past 20 years, in corn hybrids has been the realization you can push plant density only so far,” he said. “Otherwise, we might pay for it, especially in not realizing kernel weights we need to get to have a corn plant that has 60% or so of its weight in its grain, especially in a grain production scenario.”

Vyn also looked at the nitrogen use and recovery efficiency over time.

“The grain/nitrogen combination is declining in modern corn hybrids,” he said. “But they’re also quite good in increasing the grain/nitrogen combination when higher levels of nitrogen are applied.”

He said that it’s not just about higher yields but boosting the protein level of the grain that’s in the finished product.

“Our nutrient levels are perhaps more important during the grain filling period than the vegetative period when it comes to achieving higher yield,” Vyn said. “It takes not just adequate nutrition during the vegetative period but adequate nutrition that extends through the grain filling period. We need to be vigilant in adequate nutrition through grain filling period to achieve the higher kernel weights required in the modern hybrid systems.” That means more nitrogen can be removed from the field and more potassium can be removed through the plan itself.

Drought stress during the filling period can severely limit kernel weight gains. “You can essentially have almost no gain in kernel weights over the whole time period of hybrids from different eras,” he said. Timing nitrogen application can help keep plants healthier during the grain filling period.

His research showed that nitrogen timing in continuous corn on irrigated sandy soil showed yield increases with up to 250 pounds of nitrogen compared with no nitrogen, whether it was applied at planting or partway through its growing stages, but the biggest growth spurts were observed when nitrogen was applied at the latter stages rather than at planting.

Timing of the uptake also makes a difference. “In these trials, about 70% of the nitrogen was in the plant at the time of the R1 stage, during vegetative growth,” Vyn said. “Another 30% was added after that time period.”

He also said that other nutrients going into the corn plant benefits its growth, such as sulfur. About 42% of plants’ sulfur uptake is after the R1 stage and 55% of phosphorus and zinc.

“We’ve got a lot of nutrients going into the plants, representing new uptake during the vegetative period,” Vyn said. He added that analyzing plants at the R1 stage does not indicate how long the leaves will remain green during the grain filling period.

“It’s not predictive of what else is happening elsewhere in the canopy,” he said. “The last to die off and turn yellow are in the middle where the ear leaf is positioned.”

Vyn also said that higher plant densities make a difference in plant health. “When it comes to zinc, phosphorus and nitrogen, it is harder to get to critical concentrations when we have higher plan densities,” Vyn said.

The reason a farmer grows the crop also matters. “In dairy, you’re addressing potassium needs of your soils,” he said. “In cash crop production, potassium is too low for optimum yields.”

He’s studied when to add potassium. “We can get 20 to 30 bushels of corn per acre at 230 pounds per acre of nitrogen application when we have added potassium,” Vyn said. “If we don’t add potassium, we get a plateau of nitrogen response much sooner. Response to nitrogen may sometimes be limited by insufficient potassium in corn plants and that’s harder to achieve with higher plant density.”

Getting the optimal nutrients into the plant during the grain filling period “is tricky. It is difficult and it takes good management and higher prices to survive in corn production for yourself and the next generation of farmers that will follow you.”

Many wonder if it’s easier to achieve big corn yields with today’s hybrids. “Modern corn hybrids require less nitrogen per unit of yield, but probably need better and more balanced nutrition around flowering in the lag phase and during grain fill to attain higher kernel weights,” Vyn said.

He said it’s important to think of management as “no plant left behind.” “Make sure they’re responding uniformly within the row so competition is even. We need to be more focused on plant tissue sampling at early and later stages at the grain filling period to make sure we’re meeting the needs of farm plants.”

To help farmers better match their nutrient management to specific hybrids, he recommended acquiring as much background information on the yield responses as possible across a range of rates, application timings and plant populations.

“Nutrient balance is extremely important,” he said. “A lot of that is association between a nitrogen and potassium 1:1 ratio during the lifespan of the corn plant.”

Farmers also need to learn more about the late season ability to stay green, kernel number and kernel weight flexibility of specific hybrids that indicate a likelihood of response to later application of nutrients.

“One of the things that limits us most with late season surface supplies of nitrogen is having rainfall occur within five days of application,” Vyn said. “If it’s at the B12 stage and we don’t get rain two weeks after we applied at the surface, that isn’t going to help us. More water to some extent is good. Corn plants are pretty resilient if you have good depth of rooting and you don’t have compaction. It’s surprising how well modern corn plants can do if you don’t have a few weeks of rainfall.”